Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 11529
*Author for correspondence (e-mail: ctchien{at}ccvax.sinica.edu.tw)
Accepted April 23, 2001
![]() |
SUMMARY |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: phyllopod, SOP, Cell fate, Notch, seven in absentia, tramtrack, Drosophila melanogaster
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
An adult es organ (bristle) consists of four different daughter cells (neuron, sheath cell, hair cell and socket cell) that are generated through asymmetric division of a SOP cell (Gho and Schweisguth, 1998; Gho et al., 1999; Reddy and Rodrigues, 1999). After the first asymmetric division, the SOP cell produces two secondary precursors, IIa and IIb (see schematic drawing in Fig. 7A). The IIb cell again divides asymmetrically to generate a precursor IIIb and a glial cell that migrates away soon after, and the IIa cell divides to generate a hair cell and a socket cell (the two outer support cells). Finally, the IIIb precursor divides to produce a neuron and a sheath cell. Proteins encoded by numb and N play a key role in the binary fate determination. Numb, a membrane-associated protein, localizes to a crescent during mitosis and segregates preferentially to one daughter cell after cell division (Rhyu et al., 1994; Knoblich et al., 1995). In numb loss-of-function mutants, cell fate transformation from IIb cells to IIa cells, hair cells to socket cells, and neurons to sheath cells occur (Uemura et al., 1989; Rhyu et al., 1994; Wang et al., 1997). By contrast, misexpression of numb results in cell fate transformation that is opposite to the phenotype observed in numb mutants (Rhyu et al., 1994). Biochemical and genetic analyses suggest that numb controls cell fate at least in part by antagonizing N activity (Guo et al., 1996). The asymmetrically segregated Numb protein prevents N activation in the daughter cell that inherits the Numb protein. Activation of N in the other daughter cell leads to activation of downstream signaling events that specify a cell fate distinct from that of its sibling. The zinc-finger protein Tramtrack (Ttk) is one of the nuclear targets to receive such N signaling (Guo et al., 1995; Guo et al., 1996). The ttk gene encodes two alternatively spliced forms of protein, Ttk69 and Ttk88 (Read and Manley, 1992), and both forms act as transcriptional repressors (Read et al., 1992; Xiong and Montell, 1993). The roles of ttk in cell fate determination have been closely examined in the developing eye and peripheral nervous system (PNS). In the eye, loss of ttk88 function results in formation of supernumerary R7 cells (Xiong and Montell, 1993; Li et al., 1997). In es organ development, ttk is expressed in the outer support cells and sheath cells, and loss of ttk function results in transformation from IIa to IIb cells and from sheath cells to neurons (Guo et al., 1995). Misexpression of ttk causes a phenotype opposite to that of ttk mutants in the es organ lineage (Guo et al., 1995), indicating that ttk acts as a binary cell fate switch in these asymmetric cell divisions. Genetic analyses show that ttk functions downstream of numb and N, and that Ttk protein levels are positively regulated by N (Guo et al., 1996)
|
In this report, we describe the roles of phyl in cell fate specification of SOP and SOP daughter cells in es organ development. We present our characterization of phyl loss-of-function and phyl misexpression phenotypes in both embryonic and adult es organ development. Also, we show that phyl interacts genetically with sina, and promotes es organ development by antagonizing ttk activity. phyl acts epistatically to N in cell fate specification of both SOP and its daughter cells. phyl is expressed in cells with neural potential (neuroblast, SOP and IIb cells), and its expression is negatively regulated by N signaling.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
To produce phyl mutant clones, yw hs-FLP; FRT42d phyl2245/FRT42d y+, FRT42d pwn phyl2/FRT42d; hs-FLP Sb/+ and yw UAS-FLP; sca-GAL4 FRT42d phyl2245/FRT42d y+ flies were generated. To generate phyl mutant clones in Nts flies, females of Nts ombp1/+; FRT42d p[conD]/+ were crossed with males of FRT42d pwn phyl2; hs-FLP Sb/SM5-TM6B. Larvae at 24-48 hours after egg laying were heat treated at 37°C for 15 minutes twice to induce the mutant clones. Supernumerary microchaetes were induced by incubating the Nts pupae (0-6 hours after puparium formation; APF) at 30°C for 6 hours.
For misexpression of phyl, five independent UAS-phyl transgenic lines were generated. All lines gave similar phenotypes. UAS-phyl 1b and 2a gave stronger phenotypes and were used for further experiments. UAS-NACT (Doherty et al., 1996) and UAS-ttk69 (Lai and Li, 1999) were also used in this study.
For heat shock treatment of Nts embryos, embryos collected between 10-15 hours at 17°C were incubated at 32°C for another 5 hours to eliminate the N activity, and were then placed at 25°C for another 2.5 hours prior to fixation.
Immunohistology
Embryos were fixed and stained as described previously (Chien et al., 1998). The primary antibodies used were mouse anti-Elav antibody (1:200), rabbit anti-Prospero antibody (1:1000) (Vaessin et al., 1991), rat anti-Cut antibody (1:2000) (Blochlinger et al., 1990), rat anti-Su(H) antibody (1:1000) (Gho et al., 1996), and mouse and rabbit anti-ß-galactosidase antibodies (1:250 and 1:1000, respectively). For antibody staining of pupal nota, nota were dissected in 1x PBS and fixed in 4% paraformaldehyde. After washing with 1x PBS, nota were then incubated with primary antibodies: mouse anti-Elav antibody (1:50), rabbit anti-Prospero antibody (1:200) and rat anti-Cut antibody (1:1000), followed by Cy3, Cy5, Alexa-488, or FITC-conjugated secondary antibodies.
X-gal staining
Imaginal disks and pupal nota were dissected in 1x PBS, and fixed in 0.3% glutaraldehyde solution (in 1x PBS) for 10 minutes. Disks and nota were washed in PBS for 15-30 minutes before staining in 0.3% X-gal in Fe/NaP solution.
In situ RNA hybridization
The procedure used for in situ hybridization has been described by Tautz and Pfeifle (Tautz and Pfeifle, 1989). Digoxigenin-labelled RNA probes of phyl and lacZ were prepared as described previously (Lehmann and Tautz, 1994).
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
Closer examination of phyl mutants indicated that at 14-18 hours APF, ac-lacZ expression remained in clusters of cells (Fig. 1F, inset), while in the wild type animal at the same stage, lacZ expression was restricted to single cells (Fig. 1E, inset). This observation suggests that phyl may function at a later stage than proneural genes to promote SOP formation. We tested this possibility by examining the SOP markers. The enhancer trap line A101 drives lacZ expression in SOP cells and is an early marker for SOP cell fate (Huang et al., 1991) (Fig. 1G). In phyl mutants, most of the A101 expression was eliminated (Fig. 1H). We also examined the expression of another SOP marker, asense-lacZ (ase-lacZ). asense encodes a bHLH protein that is specifically expressed in SOP cells (Brand et al., 1993), and the ase-lacZ transgene was detected at a later stage than A101 (see Fig. 1I and Figure legends). In phyl mutants, most of the X-gal staining was absent (Fig. 1J). We observed similar results for macrochaetal SOP cells in the wing disks in which staining for A101 disappeared in phyl mutants (data not shown). Anti-Cut antibody can recognize all daughter cells of the es organ (Blochlinger et al., 1990). Consistently, only a few Cut-positive clusters were seen in pupal nota of phyl mutants (data not shown). These results indicate that phyl is essential for the fate specification of SOP cells.
phyl is required for binary cell fate specification in the es organ lineage
In phyl mutants, some SOP cells formed and developed into bristles with abnormal compositions (Fig. 1B,D; Table 1), which was likely due to fate transformation of the sibling cells within the es organ lineage. To determine whether phyl is required for the binary cell fate decisions in the es organ lineage, we examined the composition of es organs in phyl mutants during embryonic development. In phyl mutant embryos, the numbers of the sensory neurons and the sheath cells, recognized by anti-Elav and anti-Prospero antibodies, respectively, were significantly reduced (compare Fig. 2B with Fig. 2A). In strong phyl mutants (phyl1/phyl2), 75% of the neurons and 50% of the sheath cells were missing. We focused subsequent studies on two es organs in the dorsal-most (dm) region of abdominal hemisegments (Fig. 2C,E) since they are well separated from the rest of the sensory organs, thus making it easier to identify their constituent cells. In strong loss-of-function phyl2245/phyl2245 and phyl1/phyl2 mutant embryos, more than 80% of the neurons and sheath cells in the dm region were missing (Fig. 2D). However, anti-Cut antibody staining revealed that only 12% of the es organs at the dm region were absent (Cut-negative) (Fig. 2F), which might have resulted from failure in SOP formation. These results suggest that in phyl mutant embryos, most of the SOP cells of the dm es organs form and divide to produce four Cut-positive cells, and that the large number of missing neurons and sheath cells is not due to failure of SOP formation.
|
In phyl mutant adults, most SOP cells of notal bristles were missing, while in phyl mutant embryos, the majority of SOP cells formed in the dm es organs. One likely reason for this difference is the masking of the embryonic SOP phenotype by maternally deposited phyl transcripts. When both maternal and zygotic phyl mRNA were removed, however, the defects were similar to the zygotic mutant phenotypes; 75% of the neurons and 60% of the sheath cells in the abdominal hemisegments, and 10% of the dm es organs were missing (data not shown). Furthermore, in phyl1/phyl2 mutants, the staining pattern with anti-Cut antibody showed that, in addition to the dm es organs, most es organs of the embryonic PNS formed (data not shown). These results suggest that phyl is partly required for the fate specification of SOP cells in embryonic es organ development.
Misexpression of phyl promotes ectopic SOP formation and transforms outer support cells to neurons and sheath cells
In phyl mutant adults, the phenotype of missing bristles is due to failure in SOP formation. To test whether misexpression of phyl can promote SOP formation, we used Eq-GAL4 to drive phyl expression in the notum. Eq-GAL4 was expressed in the anterior of the presumptive notum in the wing disk (Fig. 3A), and of the pupal notum (6-8 hours APF) with stronger expression in the anterior midline region (indicated by arrows). When the phyl expression was driven by Eq-GAL4, we observed ectopic bristles in the notum (Fig. 3D). In general, there was a 30%-70% increase in the number of notal microchaetes, with a highest density in the midline region (Fig. 3F). When dpp-GAL4 was used to misexpress phyl, ectopic bristles were also observed on the scutellum (Fig. 3H) and the third wing vein (data not shown). These ectopic bristles were derived from ectopic SOP cells, as was evident from the appearance of ectopic ß-gal-positive cells in the A101 scutellum (Fig. 3J, arrows). These data indicate that misexpression of phyl can promote ectopic SOP formation.
|
A similar phenotype of cell fate transformation was also observed in adult bristles. As shown in Fig. 3O, the outer hair and socket structures of microchaetes were all missing when phyl was misexpressed by GAL4109-68. Pupal nota stained with anti-Elav and anti-Prospero antibodies showed clusters of two neurons and two sheath cells (Fig. 3Q), in contrast to wild-type es organs with clusters of one neuron and one sheath cell (Fig. 3P). Clusters of 3-4 neurons with 0-2 sheath cells were occasionally observed (data not shown). Therefore, misexpression of phyl in both embryonic and pupal es organ lineages most often resulted in transformation of outer support cells (hair cells and socket cells) to internal cells (neurons and sheath cells). Together with the phyl loss-of-function mutant phenotypes, these data indicate that phyl functions as a binary cell fate determinant in the formation of IIa and IIb cells in es organ development.
sina is involved in es organ development
During R7 photoreceptor differentiation, Sina forms a complex with Phyl to promote R7 cell fate by targeting the transcriptional repressor Ttk for degradation (Li et al., 1997; Tang et al., 1997). We found that sina is also involved in es organ development. Similar to phyl mutants, two distinct bristle phenotypes were observed in sina loss-of-function mutants (Fig. 4B,H and Table 1). In sina2/sina3 adults, 41% of the notal and 62% of the abdominal microchaetes were missing. Also, some of the remaining microchaetes showed abnormal phenotypes such as duplicated bristles (17% in the notum and 65% in the abdomen). To determine whether formation of SOP cells is affected in sina mutants, we examined the expression pattern of A101 and ase-lacZ in sina2/sina3 pupae. Compared to wild-type pattern (see Fig. 1G), in sina2/sina3 mutants, some A101-positive cells were missing near the anterior midline region (arrows in Fig. 4M) where the microchaetes were affected most in mutant adults (Fig. 4B). This result demonstrates that sina is required for the formation of some microchaetal SOP cells. To our surprise, ase-lacZ expression in sina mutants was mostly eliminated (Fig. 4N), despite the fact that only a fraction of bristles in sina2/sina3 adults are missing. Since ase is not essential for bristle formation (Jarman et al., 1993), the missing ase expression does not necessarily correlate with the missing bristles. Nevertheless, these data indicate that sina is important for ase expression in most SOP cells.
|
phyl, sina and ttk interact genetically in es organ development
Because phyl and sina mutations cause similar phenotypes, and ttk is also essential for the binary cell fate decision of SOP progeny, we explored the possibility that phyl, sina and ttk function in the same genetic pathway in es organ development. We first examined their genetic interactions in adult bristle development. When one copy of phyl2245 or phyl2 alleles was introduced into the sina2/sina3 mutants, the number of microchaetes was reduced on both nota and abdomens. Also, the percentage of abnormal notal microchaetes was increased more than twofold (Fig. 4C,I; Table 1), indicating that phyl mutations dominantly enhanced the sina mutant phenotypes. We then tested whether ttk mutations suppress sina and phyl mutant phenotypes. We used two ttk mutant alleles: ttklell, a null allele (Xiong and Montell, 1993), and ttkosn, in which the 69 kDa protein expression is absent and the level of the 88 kDa Ttk protein is reduced (Guo et al., 1995). When one copy of ttklell or ttkosn was introduced into phyl2/phyl4 mutants, the numbers of both notal and abdominal bristles were significantly increased, and the percentage of abnormal notal bristles was largely reduced (Fig. 4F,L; Table 1). A similar suppression effect was also observed when one copy of the ttkosn allele was introduced into sina2/sina3 mutants (Fig. 4D,J; Table 1). Therefore, our genetic analyses are most consistent with the notion that phyl, sina and ttk function in the same genetic pathway, and phyl and sina promote bristle development by antagonizing ttk activity. One exception is that removing one copy of ttk enhanced the abnormal bristle phenotype in phyl mutant abdomen (Fig. 4L and Table 1).
In embryonic PNS, phyl also showed strong genetic interaction with ttk. In phyl1/phyl2 mutant embryos, 75% of the neurons in abdominal hemisegment and all of the dm neurons were missing (see Fig. 2B). However, in phyl1/phyl2; ttkosn/+ embryos, only 10% of the PNS neurons were absent and each dm region contained at least one neuron (Fig. 4Q). This result shows that the ttk mutation strongly suppresses the phyl mutant phenotypes in embryonic PNS, and indicates that phyl promotes cell fate specification of embryonic PNS neurons by antagonizing ttk activity.
phyl acts upstream of ttk and downstream of N in es organ development
Our genetic analyses suggest that phyl and ttk function in the same genetic pathway in es organ development. In embryonic development, lack of ttk activity causes fate transformation in sensory organ lineages that leads to overproduction of sensory neurons (Fig. 5H). This phenotype is in contrast to that observed in phyl mutant embryos (see Fig. 2B). In embryos lacking both phyl and ttk activity, we observed the formation of supernumerary sensory neurons (Fig. 5I) that was indistinguishable from that of the ttk mutant embryos. This result suggests that ttk functions epistatically to phyl.
In adults, most microchaetes were missing when ttk was misexpressed by Eq-GAL4 (Fig. 5A). The lack of microchaetes was the result of failure of SOP formation as most A101-positive cells disappeared (Fig. 5C). When phyl and ttk were coexpressed by Eq-GAL4, most notal microchaetes were missing (Fig. 5B), suggesting that misexpression of ttk can suppress the ectopic bristle phenotype caused by misexpression of phyl. Therefore, these results are consistent with the model that ttk acts downstream of phyl in the formation of SOP cells.
In es organ development, N is required to single out the SOP cells and to specify the cell fate of hair cells and socket cells. In N mutants, many supernumerary SOP cells are formed and hair cells and socket cells are transformed into neurons (Hartenstein and Posakony, 1990). Since phyl mutant phenotypes are opposite to those of N mutants, and both genes acts upstream of ttk in es organ development (Fig. 5 and Guo et al., 1996), we were interested to examine their epistatic relationship. In the strong loss-of-function phyl2 mutant clones, most bristles were missing and the few remaining ones had a four-socket phenotype (Fig. 5D). In contrast, when the activity of N was eliminated during the stage of SOP emergence (6-12 hours APF) by using the Nts allele, the number of microchaetes was significantly increased (Fig. 5E). When a phyl2 mutant clone was generated in the Nts fly with N activity inactivated, most of the bristles were lost within the clone (Fig. 5F). This result shows that phyl is epistatic to N in SOP cell fate specification. We also tested whether phyl acts epistatically to N in cell fate specification of SOP progeny in embryos. In the embryos from the cross of Nts/Nts; phyl2/+ females with Nts/Y; phyl1/+ males, a quarter of them were Nts and phyl double mutants and the rest were Nts mutants. When these embryos were incubated at the permissive temperature (17°C), 24% of them (n=40) showed a strong reduction in the number of sensory neurons (<20 neurons per abdominal hemisegement; Fig. 5J). The rest of the embryos (76%, n=127) had a normal number of neurons (42 in each abdominal hemisegment). This result indicates that about one quarter of the embryos in this cross were indeed phyl mutants. To inactivate N activity during embryonic development, the embryos were incubated at the non-permissive temperature (32°C) when SOP cells and their progeny were undergoing asymmetric divisions (Guo et al., 1996). We found that 21% of the embryos (n=39) had fewer than 20 neurons in each abdominal hemisegment (Fig. 5L), and a small fraction of embryos (2.6%, n=5) exhibited an intermediate phenotype with 20-40 neurons (data not shown). Overproduction of neurons was seen in 76% of the embryos (n=143; Fig. 5K). In a control experiment, we confirmed that this phenotype of neuron overproduction was indistinguishable from that of Nts embryos at 32°C (data not shown). Therefore, this data showed that phyl acts epistatically to N in cell fate specification of SOP daughter cells in embryos.
phyl is expressed in SOP cells and IIb lineage and its expression is negatively regulated by N signaling
The distribution of phyl mRNA was examined by whole-mount in situ hybridization. Although weak, the expression of phyl in wing imaginal disks was detected in the SOP cells of wing margin bristles (Fig. 6A,B), notal macrochaetes (Fig. 6A,C), and other sensory organs (Fig. 6A). In leg disks, phyl mRNA was also detected in the precursors of the femoral chordotonal organs, as well as in external sensory SOP cells (data not shown). During embryogenesis, the maternally contributed phyl transcripts were ubiquitously present before cellularization (data not shown). During stages 9-11, phyl was expressed in neuroblasts (Fig. 6E) and the SOP cells (Fig. 6F). From stage 12 onward, phyl transcripts diminished gradually, but remained detectable in a subset of PNS cells at stages 12-14 (Fig. 6G). These cells were probably the IIb cells and their progeny (neurons and/or sheath cells), since at the same stage, phyl mRNA was no longer detected in numb mutants (Fig. 6H), in which the IIb cells were transformed to the IIa cells (Uemura et al., 1989).
|
To further confirm that N negatively regulates phyl activity by repressing its expression, we tested whether misexpression of phyl rescues the defects caused by misexpression of NACT. phyl is essential for fate specification of IIb cells in the embryonic sensory organ lineage. When UAS-phyl and UAS-NACT were coexpressed in embryos by sca-GAL4, the total numbers of PNS neurons and sheath cells (both are progeny of IIb cells) on average were double that in sca-GAL4/+; UAS-NACT/+ embryos (Fig. 6M,N). This result shows that misexpression of phyl rescues the defects caused by NACT in the embryonic sensory organ development.
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The functions and regulations of phyl in es organ development
Our genetic analyses show that phyl functions together with sina to promote SOP formation by antagonizing ttk activity. These results suggest that degradation of the Ttk protein is a major function of Phyl in the cell fate specification of SOP cells. Consistent with this idea, we found that misexpression of ttk can inhibit the formation of SOP cells and suppress the ectopic bristle phenotype caused by misexpression of phyl. Several lines of evidence also indicate that Ttk functions as a repressor to inhibit SOP cell fate. (1) Ttk is expressed ubiquitously in the pupal notum except in SOP cells (Ramaekers et al., 1997). (2) In embryos, overexpression of ttk inhibits the formation of es organs (Guo et al., 1995). (3) Injection of ttk dsRNA results in extensive increase of neurons in embryonic PNS, a phenotype observed in neurogenic mutants (Kennerdell and Carthew, 1998). All of these results suggest that ttk might play a negative role in the fate specification of SOP cells, and phyl promotes SOP fate specification by degrading Ttk.
phyl is essential for formation of pupal SOP cells, but is partly required for embryonic SOP cells. In senseless mutants, the larval SOP cells fail to form, but the embryonic SOP cells form and divide to generate daughter cells that fail to differentiate (Nolo et al., 2000). These results suggest that there are some distinctions between the SOP cell fate specification of embryos and larvae.
Our studies showed that phyl is required for IIb cell fate specification. In phyl mutants, more than half of the adult notal microchaetes and more than 80% of the embryonic dm es organs exhibited IIb to IIa cell fate transformation. Cell fate transformation from hair cells to socket cells also occurs in adult bristle (four-socket phenotype seen in phyl2 clone), but much less frequent in embryonic dm es organs (less than 5%). Transformation from neurons to sheath cells in es organs was rarely seen in phyl embryos. These results suggest that unlike numb and N, phyl is mainly required for the binary cell fate determination between IIa and IIb cells in both adult and embryonic es organs. In support of this conclusion, misexpression of phyl in both adult and embryonic sensory organ lineages most often resulted in a two-neuron/two-sheath cell phenotype.
In phyl1/phyl2 mutant embryos, most of the neurons and sheath cells in chordotonal organs were also lost (Fig. 2B, lateral and ventral region), indicating that phyl is also required for the formation of neurons and sheath cells in chordotonal organ lineage. In weaker mutant embryos (phyl2245/phyl2245), we often observed more sheath cells than neurons in the regions where chordotonal organs lch5 and vchA and B are located. Therefore, phyl may be required for cell fate determination between neurons and sheath cells in the development of chordotonal organs.
During lateral inhibition, the N pathway is essential to single out the SOP cells. Our in situ analyses indicate that phyl expression is negatively regulated by N. Also, the supernumerary bristles in N mutants were suppressed by phyl mutation. These results strongly suggest that down-regulation of phyl expression is a major function of N signaling to suppress SOP cell fate.
In the SOP lineage, N also plays an important role in the cell fate specification of SOP progeny. Several components of the N pathway, such as Delta, Serrate (Zeng et al., 1998), Su(H) (Schweisguth and Posakony, 1994), Hairless (Bang and Posakony, 1992), and proteins of the Bearded (Leviten and Posakony, 1996; Lai et al., 2000) and E(spl) (Tata and Hartley, 1995) families, have been shown to be involved in the cell fate specification of all or subsets of progeny. We found that phyl acts epistatically to N in the cell fate specification of SOP daughter cells and is expressed in IIb cells. Also, misexpression of phyl rescues the defects caused by NACT, indicating that N regulates the phyl activity in sensory organ lineage at the transcriptional level.
Functions of sina in es organ development
Our genetic analyses of phyl, sina and ttk are mostly consistent with the model that Phyl functions together with Sina to promote es organ development by degrading Ttk. In embryos, strong defects are only detected when both maternal and zygotic sina transcripts are removed, suggesting that maternally contributed sina transcript play an essential role in the development of embryonic es organs. Consistently, no genetic interaction between zygotic sina and phyl, and between zygotic sina and ttk was detected in embryonic PNS development (data not shown). In adults, the bristle phenotypes in sina mutants are weaker than in phyl mutants. One possible reason is that the perdurance of sina gene products from maternal transcripts might supply activity for some adult bristles to develop normally. Another possibility is that phyl is able to down-regulate ttk activity in a sina-independent manner. In the Drosophila genome, a sequence (CG 13030) is located next to sina in the genome and encodes a putative protein with 50% identity and 70% similarity with Sina. It might be possible that sina functions redundantly with this gene in bristle development.
Comparison of phyl in cell fate specification of photoreceptors and es organs
Our studies of phyl/sina/ttk in es organ development and previous studies in photoreceptor differentiation indicate that the Drosophila eye and es organs depend on the same protein complex to specify their cell fate. In both cases, phyl mutations transform neural cells to non-neural cells. Both studies also show that phyl expression is tightly regulated by the upstream signaling pathways. The expression of phyl is activated by the Ras pathway in photoreceptor cells. In SOP cells, the transcription of phyl is likely activated by the proneural genes ac and sc, and is repressed by N signaling. Interestingly, it has been shown that the Egrf/Ras/Raf pathway acts antagonistically with the N pathway in SOP formation of adult macrochaetes (Culi et al., 2001) and chordotonal organs (zur Lage and Jarman, 1999). Whether these two pathways converge on phyl expression to regulate sensory organ formation remains to be examined.
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Artavanis-Tsakonas, S., Rand, M. D. and Lake, R. J. (1999). Notch signaling: cell fate control and signal integration in development. Science 284, 770-776.
Bailey, A. M. and Posakony, J. W. (1995). Suppressor of Hairless directly activates transcription of Enhancer of split complex genes in response to Notch receptor activity. Genes Dev. 9, 173-189.
Bang, A. G. and Posakony, J. W. (1992). The Drosophila gene Hairless encodes a novel basic protein that controls alternative cell fates in adult sensory organ development. Genes Dev. 6, 1752-1769.[Abstract]
Bier, E., Vaessin, H., Shepherd, S., Lee, K., McCall, L., Barbel, S., Ackerman, L., Carretto, R., Uemura, T., Grell, E., Jan, L. Y. and Jan, L. N. (1989). Searching for pattern and mutation in the Drosophila genome with a P-lacZ vector. Genes Dev. 3, 1273-1287.[Abstract]
Blochlinger, K., Bodmer, R., Jan, L. Y. and Jan, Y. N. (1990). Patterns of expression of Cut, a protein required for external sensory organ development in wild-type and cut mutant Drosophila embryos. Genes Dev. 4, 1322-1331.[Abstract]
Brand, M., Jarman, A. P., Jan, L. Y. and Jan, Y. N. (1993). asense is a Drosophila neural precursor gene and is capable of initiating sense organ formation. Development 119, 1-17.
Campuzano, S. and Modollel, J. (1992). Patterning of the Drosophila nervous system: the achaete-scute gene complex. Trends Genet. 8, 202-207.[Medline]
Carthew, R. W. and Rubin, G. M. (1990). seven in absentia, a gene reguired for specification of R7 cell fate in the Drosophila eye. Cell 63, 561-577.[Medline]
Chang, H. C., Solomon, N. M., Wassarman, D. A., Karim, F. D., Therrien, M., Rubin, G. M. and Wolff, T. (1995). phyllopod functions in the fate determination of a subset of photoreceptors in Drosophila. Cell 80, 463-472.[Medline]
Chien, C.-T., Wang, S., Rothenberg, M., Jan, L. Y. and Jan, Y. N. (1998). Numb-associated kinase interacts with the phosphotyrosine binding domain of Numb and antagonizes the function of Numb in vivo. Mol. Cell. Biol. 18, 598-607.
Culi, J., Martin-Blanco, E. and Modolell, J. (2001). The EGF receptor and N singalling pathways act antagonistically in Drosophila mesothorax bristle patterning. Development 128, 299-308.
Dickson, B. J., Dominguez, M., Straten, A. and Hafen, E. (1995). Control of Drosophila photoreceptor cell fates by Phyllopod, a novel nuclear protein acting downstream of the Raf kinase. Cell 80, 453-462.[Medline]
Doherty, D., Feger, G., Younger-Shepherd, S., Jan, L. Y. and Jan, Y. N. (1996). Delta is a ventral to dorsal signal complementary to Serrate, another Notch ligand, in Drosophila wing formation. Genes Dev. 10, 421-434.[Abstract]
Frise, E., Knoblich, J. A., Younger-Shepherd, S., Jan, L. Y. and Jan, Y. N. (1996). The Drosophila Numb protein inhibits signaling of the Notch receptor during cell-cell interaction in sensory organ lineage. Proc. Natl. Acda. Sci. USA 93, 11925-11932.
Gho, M., Bellaiche, Y. and Schweisguth, F. (1999). Revisiting the Drosophila microchaete lineage: a novel intrinsically asymmetric cell division generates a glial cell. Development 126, 3573-3584.
Gho, M., Lecourtois, M., Geraud, G., Posakony, J. M. and Schweisguth, F. (1996). Subcellular localization of Suppressor of Hairless in Drosophila sense organ cells during Notch signalling. Development 122, 1673-1682.
Gho, M. and Schweisguth, F. (1998). Frizzled signalling controls orientation of asymmetric sense organ precursor cell divisions in Drosophila. Nature 393, 178-181.[Medline]
Ghysen, A. and Dambly-Chaudiere, C. (1988). From DNA to form: The achaete-scute complex. Genes Dev. 7, 723-33.[Medline]
Gomez-Skarmeta, J.L., Rodriguez, I., Mattinez, C, Culi, J., Ferres-Marco, D., Beamonte, D. and Modolell, J. (1995). Cis-regulation of achaete and scute: shared enhancer-like elements drive their coexpression in proneural clusters of the imaginal discs. Genes Dev. 9, 1869-1882.[Abstract]
Greenwald, I. (1998). LIN-12/Notch signaling: lessons from worms and flies. Genes Dev. 12, 1751-1762.
Guo, M., Bier, E., Jan, L. Y. and Jan, Y. N. (1995). tramtrack acts downstream of numb to specify distinct daughter cell fates during asymmetric cell division in the Drosophila PNS. Neuron 14, 913-925.[Medline]
Guo, M., Jan, L. Y. and Jan, Y. N. (1996). Control of daughter cell fates during asymmetric division: interaction of Numb and Notch. Neuron 17, 27-41.[Medline]
Hartenstein, V. and Posakony, J. W. (1990). A dual function of the Notch gene in Drosophila sensillum development. Dev. Biol. 142, 13-30.[Medline]
Heitzler, P., Bourouis, M., Ruel, L., Carteret, C. and Simpson, P. (1996). Genes of the Enhancer of split and achaete-scute complexes are required for a regulatory loop between Notch and Delta during lateral signaling in Drosophila. Development 122, 161-171.
Hinz, U., Biebel, B. and Campos-Ortega, J. A. (1994). The basic-helix-loop-helix domain of Drosophila lethal of scute protein is sufficient for proneural function and activates neurogenic genes. Cell 76, 77-88.[Medline]
Huang, F., Dambly-Chaudiere, C. and Ghysen, A. (1991). The emergence of sense organs in the wing discs of Drosophila. Development 111, 1087-1095.[Abstract]
Jan, Y. N. and Jan, L. Y. (1994). Genetic control of cell fate specification in Drosophila peripheral nervous system. Annu. Rev. Genet. 28, 373-393.[Medline]
Jarman, A. P., Brand, M., Jan, L. Y. and Jan, Y. N. (1993). The regulation and function of the helix-loop-helix gene, asense, in Drosophila neural precursors. Development 119, 19-29.
Kennerdell, J. R. and Carthew, R. W. (1998). Use of dsRNA-mediated genetic interference to demonstrate that frizzled and frizzled 2 act in the wingless pathway. Cell 95, 1017-1026.[Medline]
Knoblich, J. A., Jan, L. Y. and Jan, Y. N. (1995). Localisation of Numb and Prospero reveals a novle mechanism for asymmetric protein segregation during mitosis. Nature 377, 624-627.[Medline]
Lai, E. C., Bodner, R. and Posakony, J. W. (2000). The Enhancer of split Complex of Drosophila includes four Notch-regulated members of the Bearded gene family. Development 127, 3441-3455.
Lai, Z.-C. and Li, Y. (1999). Tramtrack 69 is positively and autonomously required for Drosophila photoreceptor development. Genetics 152, 299-305.
Lecourtois, M. and Schweisguth, F. (1995). The neurogenic Suppressor of Hairless DNA-binding protein mediates the transcriptional activation of the Enhancer of split complex genes triggered by Notch signaling. Genes Dev. 9, 2598-2608.[Abstract]
Lecourtois, M. and Schweisguth, F. (1998). Indirect evidence for Delta-dependent intracellular processing of Notch in Drosophila embryos. Curr. Biol. 8, 771-774.[Medline]
Lehmann, R. and Tautz, D. (1994). In situ hybridization to RNA. In Drosophila melanogaster: Practical Uses in Cell and Molecular Biology. (ed. L. S. B. Goldstein and E. A. Fyrberg), pp. 576-598. San Diego: Academic Press, Inc.
Leviten, M. W. and Posakony, J. W. (1996). Gain-of-function alleles of Bearded interfere with alternative cell fate decisions in Drosophila adult sensory organ development. Dev. Biol. 176
Li, S., Li, Y., Carthew, R. W. and Lai, Z.-C. (1997). Photoreceptor cell differentiation requires regulated proteolysis of the transcriptional repressor Tramtrack. Cell 90, 469-478.[Medline]
Masucci, J. D., Miltenberger, R. J. and Hoffmann, F. M. (1990). Pattern-specific expression of the Drosophila decapentaplegic gene in imaginal disks is regulated by 3' cis-regulatory elements. Genes Dev. 4, 2011-2023.[Abstract]
Nolo, R., Abbott, L. A. and Bellen, H. J. (2000). Senseless, a Zn finger transcription factor, is necessary and sufficient for sensory organ development in Drosophila. Cell 102, 349-362.[Medline]
Ramaekers, G., Usui, K., Usui-Ishihara, A., Ramaekers, A., Ledent, V., Ghysen, A. and Dambly-Chaudiere, C. (1997). Lineage and fate in Drosophila: role of the gene tramtrack in sense organ development. Dev. Genes Evol. 207, 97-106.
Read, D., Levine, M. and Manley, J. L. (1992). Ectopic expression of the Drosophila tramtrack gene results in multiple embryonic defects, including repression of even-skipped and fushi tarazu. Mech. Dev. 38, 183-196.[Medline]
Read, D. and Manley, J. L. (1992). Alternatively spliced transcripts of the Drosophila tramtrack gene encodes zinc finger proteins with distinct DNA binding specificities. EMBO J. 11, 1035-1044.[Abstract]
Reddy, G. V. and Rodrigues, V. (1999). A glial cell arises from an additional division within the mechanosensory lineage during development of the microchaete on the Drosophila notum. Development 126, 4617-4622.
Rhyu, M. S., Jan, L. Y. and Jan, Y. N. (1994). Asymmetric distribution of Numb protein during division of the sensory organ precursor cell confers distinct fates to daughter cells. Cell 76, 477-491.[Medline]
Schroeter, E. H., Kisslinger, J. A. and Kopan, R. (1998). Notcn-1 signaling requires ligand-induced proteolytic release of intracellular domain. Nature 393, 382-386.[Medline]
Schweisguth, F. and Posakony, J. W. (1994). Antagonistic activities of Suppressor of Hairless and Hairless control alternative cell fates in the Drosophila adult epidermis. Development 120, 1433-1441.
Staehling-Hampton, K., Jackson, P. D., Clark, P. D., Brand, A. H. and Hoffmann, F. M. (1994). Specificity of bone morphogenetic protein-related factors: cell fate and gene expression changes in Drosophila embryos induced by decapentaplegic but not 60A. Cell. Growth. Differ. 5, 585-593.[Abstract]
Struhl, G. and Adachi, A. (1998). Nuclear access and action of Notch in vivo. Cell 93, 649-660.[Medline]
Tang, A. H., Neufeld, T. P., kwan, E. and Rubin, M. (1997). PHYL acts to down-regulate TTK88, a transcriptional repressor of neuronal cell fates, by a SINA-dependent mechanism. Cell 90, 459-467.[Medline]
Tata, F. and Hartley, D. A. (1995). Inhibition of cell fate in Drosophila by Enhancer of split genes. Mech. Dev. 51, 305-315.[Medline]
Tautz, D. and Pfeifle, C. (1989). A nonradioactive in situ hybridization method for the localization of specific RNAs in Drosophila embryos reveals translation control of the segmentation gene hunchback. Chromosoma 98, 81-85.[Medline]
Uemura, T., Shepherd, S., Ackerman, L., Jan, L. Y. and Jan, Y. N. (1989). numb, a gene required in determination of cell fate during sensory organ formation in Drosophila embryos. Cell 58, 349-360.[Medline]
Usui, K. and Kimura, K.-i. (1993). Sequential emergence of the evenly spaced microchaetae on the notum of Drosophila. Rouxs Arch. Dev. Biol. 203, 151-158.
Vaessin, H., Grell, E., Wolff, E., Bier, E., Jan, L. Y. and Jan, Y. N. (1991). prospero is expressed in neuronal precursors and encodes a nuclear protein that is involved in the control of axonal outgrowth in Drosophila. Cell 67, 941-953.[Medline]
Wang, S., Younger-Shepherd, S., Jan, L. Y. and Jan, Y. N. (1997). Only a subset of the binary cell fate decisions mediated by Numb/Notch signaling in Drosophila sensory organ lineage required Suppressor of Hairless. Development 124, 4435-4446.
Xiong, W. C. and Montell, C. (1993). Tramtrack is a transcriptional repressor required for cell fate determination in the Drosophila. Genes Dev. 7, 1085-96.[Abstract]
Zeng, C., Younger-Shepherd, S., Jan, L. Y. and Jan, Y. N. (1998). Delta and Serrate are redundant Notch ligands required for asymmetric cell divisions within the Drosophila sensory organ lineaage. Genes Dev. 12, 1086-1091.
zur Lage, P. and Jarman, A. P. (1999). Antagonism of EGFR and notch signalling in the reiterative recuitment of Drosophila adult chodotonal sense organ precursors. Development 126, 3149-3157.