Department of Molecular and Cellular Biology, and The Arizona Cancer Center, Salmon Building, Rm 0975, 1515 N. Campbell Avenue, University of Arizona, Tucson, AZ 85724, USA
*Author for correspondence (e-mail: selleck{at}u.arizona.edu)
Accepted October 4, 2001
![]() |
SUMMARY |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Reductions in cyclin A but not cyclin B or string expression, suppress dally cell division defects in the optic lobe. cycA mutations also dominantly rescue many dally adult morphological defects including lethality, phenotypes that are unaffected by reducing cycB function. dally mutants show abnormal Cyclin A expression in the dividing cells affected, with appreciable levels of Cyclin A remaining in late prophase and metaphase, stages where Cyclin A is normally absent. Given that Dally is known to regulate the activity of secreted growth factors our findings suggest that extracellular cues influence the degradation of Cyclin A in a manner that controls cell cycle progression and ultimately, cell division patterning.
Key words: Glypican, dally, Cell division, Cyclin A
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We have taken advantage of the highly ordered divisions required for normal assembly of the Drosophila visual system to identity genes required for cell division patterning during development. Previously, we described a gene required for ordered division in the eye and larval brain, division abnormally delayed (dally) (Nakato et al., 1995). dally mutants show defects in progression through G2-M for specific sets of dividing cells. dally mutations are pleiotropic, also affecting the morphogenesis of several adult tissues, including the eye, antenna, wing and genitalia.
dally encodes a member of the glypican family of integral membrane proteoglycans (Nakato et al., 1995). Glypicans bear one or more chains of the glycosaminoglycan heparan sulfate, and are attached to the cell surface via a glycosylphosphatidylinositol (GPI) linkage (Lander et al., 1996). Like the vertebrate glypicans, Dally is GPI-linked and heparan sulfate modified (Tsuda et al., 1999). Recently, a number of studies have demonstrated that Dally serves as a regulator of growth factor signaling during development, affecting the activity of both Wingless (Wg), and Decapentaplegic (Dpp) (Jackson et al., 1997; Lin and Perrimon, 1999; Tsuda et al., 1999) in a tissue-specific manner. These findings are consistent with Dally serving as a molecule that promotes the assembly of discrete signaling complexes on the cell surface.
In recent years a myriad of genetic studies have established the importance of proteoglycans and their glycosaminoglycan modifications in patterning and growth factor signaling during development (Selleck, 2000). Both the core proteins and the biosynthetic machinery required for their glycosaminoglycan modifications are critical. For example, mutations affecting a human core protein, Glypican-3 (GPC3), cause pre- and postnatal overgrowth and a number of morphological abnormalities including kidney dysplasia (Pilia et al., 1996). Mutations affecting glycosaminoglycan biosynthesis have profound effects on signaling during Drosophila development, compromising Wg, FGF, Hh and Dpp-mediated patterning (Baeg and Perrimon, 2000). Specific modifications of glycosaminoglycans are also critical for discrete patterning events, and indeed the signaling of specific growth factors (Bellaiche et al., 1998; Kamimura et al., 2001; The et al., 1999). Loss of heparan sulfate 2-O sulfotransferase, an enzyme required for a specific heparan sulfate modification, produces renal aplasia in the mouse (Bullock et al., 1998), and heparan sulfate 6-O sulfotransferase is required for the branching morphogenesis mediated by the FGFR-related protein breathless in Drosophila (Kamimura et al., 2001). While proteoglycans are known to affect both cell division and patterning during development, the molecular basis of their effects on cell cycle are not understood. We therefore examined the cell division abnormalities produced by mutations in a Drosophila glypican, Dally.
Earlier characterization of dally mutants identified two sets of morphologically similar sets of dividing cells in the eye and optic lobe that are affected by this cell surface proteoglycan. Lamina precursor cells (LPCs) are derived from the outer proliferative center of the optic lobe and go through two cell division cycles before producing lamina neurons, the synaptic targets of photoreceptors R1-6 (Selleck and Steller, 1991). The second of these divisions is triggered by photoreceptor axons arriving in the brain, while the first proceeds normally in the absence of photoreceptor ingrowth (Selleck et al., 1992). Each of these division cycles is disrupted in dally mutant third instar larvae (Nakato et al., 1995). The first division cycle is delayed, with cells failing to enter M phase on schedule. The second division does not occur, presumably because the abnormal timing of the first division disrupts the ability of photoreceptor axons to trigger the second division cycle. In the developing retina there are likewise two coordinated division cycles and the first of these shows the same G2-M progression delay in dally mutants. However, unlike the dally phenotype in LPCs, the second division cycle in the retina does occur.
dally phenotypes are the result, at least in part, of compromised Dpp signaling. In the eye, for example, dally phenotypes are dominantly enhanced by dpp mutations, and dally eye abnormalities can be rescued by increasing dpp+ expression. It is also evident that the cell cycle abnormalities found in dally mutant eye disks can be phenocopied by loss of Dpp signaling components. For example, dally mutants show a delay in the loss of Cyclin B in the first coordinated division cycle in the eye disk and mutant clones for either saxophone, schnurri or thickvein produce the same defect (Penton et al., 1997).
We have investigated the molecular basis of the cell cycle abnormalities in dally mutants by evaluating changes in the expression and function of known cell cycle regulators. We find that dally cell division phenotypes are selectively rescued by reduction in cycA function. Consistent with this genetic finding, Cyclin A protein is not lost at the appropriate step in M phase in dally mutants, suggesting that the cell cycle delay is the result of a failure to degrade Cyclin A on schedule.
![]() |
Materials and Methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The effect of cycA mutations on dally adult phenotypes was tested using the following cross, dallyP2TM3 Sb x dallyP2 cycA3/TM2 Ubx and comparing the phenotypes observed in dallyP2, cycA3/dally progeny with dallyP2/dallyP2 flies from control crosses reared under identical conditions (food, temperature, number of parents/vial). A similar cross with dallyP2 cycA5/TM3 Sb tested the interaction between dallyP2 and cycA5. Adults were examined and scored for the following phenotypes: rough eye, reduced antenna, incomplete wing vein V and reduced genitalia.
For the analysis of cycA effects on cell division in the larval brain, third instar larvae were obtained from the cross: dallyP2/TM6B Tb X dallyP2 cycA3 (or cycA5)/TM6B Tb. Tb is a dominant larval marker that allows the identification of dally cycA/dally larvae. The larval brains were dissected and stained with either anti-Cyclin B or anti-Cyclin A antibodies (Whitfield et al., 1990), as well as the fluorescent DNA stain, propidium iodide, according to previously published methods (Nakato et al., 1995). Each larval brain was serially sectioned by confocal microscopy in order to assess existence of two discrete domains of expression of Cyclin A or Cyclin B. Confocal analysis of these preparations was conducted using a Biorad MRC600 or Nikon confocal scanning microscope.
The analysis of genetic interactions between dally and cycB was performed by comparing cycBDf(2R)59AB/+; dally/dally with Sco/+; dally/dally progeny from the following crosses: +/+; dally/TM3 Sb (virgin females) x cycBDf(2R)59AB/Sco; dally/Sb (males). Two dally alleles were tested using this type of cross, dallyP2 and dallyP305.
Scanning electron microscopy of adult heads was performed on an ISI DS-130 scanning electron microscope. All flies were reared on medium consisting of a mixture of instant fly food, agar and oatmeal with added yeast at 25°C as previously described (Condie and Brower, 1989; Manseau et al., 1997).
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We began by determining whether removing one functional copy of cycA or cycB influenced the adult phenotypes of animals homozygous for partial loss-of-function dally mutations. Reducing the level of cycA function had a dramatic effect on the lethality and morphological defects of dally mutants (Table 1). Flies heterozygous for either of two independently derived null alleles of cycA showed reduced lethality and reductions in the penetrance (% of animals affected) of defects in the eye, antenna, and wing (Table 1; Table 2). A more detailed analysis of eye defects in a separate experiment showed that cycA mutations reduced both the penetrance and severity of dally eye phenotypes, where cycA dally/dally mutants showed threefold fewer animals with severe defects than dally homozygotes (Fig. 1). Decreasing cycA function does not affect all dally-associated phenotypes; however, the penetrance of genitalia defects is unaltered by the level of cycA function (data not shown).
|
|
|
Rescue of cell division abnormalities of dally mutants with reductions in cycA but not cycB or stg
dally function affects the normal cell cycle progression of a specific set of dividing cells in the larval brain, lamina precursor cells (LPCs). LPCs complete two division cycles from their origin in the outer proliferative center (OPC) before differentiating into lamina neurons, the synaptic target cells for photoreceptors R1-6 (Selleck et al., 1992). As LPCs progress through their two division cycles, they occupy more posterior positions with time, eventually differentiating into lamina neurons that are added to the anterior face of the developing lamina (Selleck et al., 1992; Selleck and Steller, 1991). The overall organization of the LPC divisions is very similar to the coordinated cell cycles observed across the morphogenetic furrow of the eye (Dong et al., 1997; Thomas et al., 1994), and indeed dally mutations affect cell cycle progression in the eye as well. The second LPC division cycle is triggered by photoreceptor axon ingrowth as processes contact LPCs and promote entry into S phase from G1 (Selleck et al., 1992).
dally mutants show defects in both division cycles, with a delay in progression through the G2-M segment of the first division cycle, and the complete absence of the second division. Cyclin B protein expression peaks in late G2 and early M, and is rapidly degraded at the metaphase-anaphase transition (Whitfield et al., 1990). Cyclin B therefore provides a cell cycle-specific marker for the two LPC division cycles and readily shows the absence of the second division cycle found in dally mutant larval brains.
We assessed the ability of cycA mutations to suppress LPC division defects by determining whether the second division cycle is restored in cycA, dally/dally double mutants. Reducing the level of cycA function had a dramatic effect on LPC division, restoring in large measure the ability of LPCs able to enter the second division cycle (Fig. 2A). To evaluate the ability of cycA mutations to rescue LPC division defects in detail we stained dally/+, dally/dally and dally cycA/dally third instar larval brains with anti-Cyclin B antibody and examined these preparations by serial section confocal microscopy. Each larval brain was scored in a double-blind fashion for the percentage of LPCs that showed the second domain of Cyclin B expression. Reducing cycA function dramatically suppressed LPC division defects, reflected in the percentage of LPCs that can proceed into the second division cycle (Fig. 2B). Detailed analysis of the serial sections for each larval brain revealed that the restoration of Cyclin B expression in the second LPC division of dally cycA/dally animals occurred in a spatially and temporally precise manner. These findings document that reductions in cycA restore the normal patterning of LPC divisions in dally mutants. A second independently derived cycA allele, cycA5, showed a similar effect on LPC divisions in dally mutants (data not shown).
|
For the analysis of stg dally/dally mutants, we used an anti-cyclin A antibody. Cyclin A expression in LPCs, such as that of Cyclin B, reflects the two consecutive division cycles normally present (Fig. 3). The normal pattern of Cyclin A expression is observed in dally heterozygotes, but larvae homozygous for dally show only the first domain of Cyclin A expression, indicative of the failure of the second division cycle (Fig. 3). In contrast to the effects of cycA mutations on LPC division, reductions of stg function did not rescue the second division cycle (Fig. 3). In fact, the domain of Cyclin A expression in the first LPC division is expanded, suggesting that a reduction of stg expression prolongs the already abnormal G2-M segment of the first LPC division.
|
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We found that the adult phenotypes in the eye, wing and antenna, as well as the lethality of dally mutants, are all rescued selectively by reducing the expression of cycA. This rather surprising finding suggests that either the primary cause of morphological abnormalities in dally mutants is a defect in cell cycle regulation, or cycA plays a role in events outside of cell cycle control. There is circumstantial evidence that cyclins and Cdks function in non-dividing cells. Both G1 and mitotic cyclins are expressed in differentiated cells and proposed functions for cyclins outside of the cell cycle include stabilizing the differentiated state, coordinating metabolism of differentiated cells with extracellular cues, and providing components of an apoptotic pathway that can be activated in post-mitotic cells (Gao and Zalenka, 1997).
We do have evidence that dally participates in differentiation processes during imaginal disc development. dally serves as a component of the Dpp signaling apparatus in some tissues, and dally mutants show reduced activation of Dpp target genes, spalt and optomotorblind in imaginal discs (Jackson et al., 1997). It is surprising that the morphological defects in adult tissues, such as the eye and antenna where dally clearly participates in Dpp signaling events, are rescued by reducing cycA function. Perhaps there is a wider role for cell division regulation in controlling differentiation than is readily apparent. The normal assembly of the wing margin is certainly one example of where Wg and Notch affect cell cycle progression as part of the morphogenesis program (Johnston and Edgar, 1998). Inhibition of cell division is critical for normal gastrulation and is mediated by tribbles, an inhibitor of stg function (Grosshans and Wieschaus, 2000; Mata et al., 2000; Seher and Leptin, 2000). In addition, known regulators of cell division and growth can affect patterning (Blaumueller and Mlodzik, 2000; Boedigheimer et al., 1997; McCartney et al., 2000). Altering the length of the cell cycle can have dramatic effects on gene expression and morphogenesis in the chick limb (Ohsugi et al., 1997). In contrast to these findings, there is evidence from the analysis of animals mosaic for cdc2 that overall patterning is unaffected in the Drosophila wing disc when cell division does not take place (Weigmann et al., 1997). The role of cell division cycle control in differentiation remains poorly understood but it is intriguing that dally, a gene with clear cell cycle effects and a role in growth factor signaling, influences morphogenesis via a Cyclin A-mediated process.
dally mutations show a completely penetrant cell division defect in lamina precursor cells. All LPCs along the dorsal-ventral axis go through two synchronous cell divisions, reflected as two bands of Cyclin B expression at the surface of the larval brain. In dally mutants the first division cycle is delayed along the G2-M transition, and the second division does not take place at all, with the loss of the corresponding domain of Cyclin B. We used this patterning of Cyclin B expression to evaluate the ability of cycA to affect the cell division abnormalities in dally mutants. Larvae heterozygous for two different cycA null mutations showed a remarkable restoration of the second division cycle in independently derived dally mutants. This result shows that there is a functional link between dally and events regulated by Cyclin A in LPCs.
If the rescue of dally cell cycle defects is strictly a function of reducing signals promoting G2-M progression, we would expect that mutations in other genes known to drive cells into M phase would similarly suppress dally mutant phenotypes. This is not the case. Reducing the levels of stg, the phosphatase regulator of several mitotic cyclin-Cdk complexes, or cycB does not suppress dally cell division defects. Likewise, reductions in cycB activity had no effects on any of the adult phenotypes of dally mutants, providing further evidence that dally specifically affects Cyclin A function.
The suppression of dally-associated cell division defects by reducing cycA expression suggested that dally normally serves to reduce Cyclin A levels. We tested this by examining the pattern of Cyclin A expression in dally mutants. Indeed, the normal patterning of Cyclin A expression is disrupted, the sudden loss of the protein normally associated with entry into mitosis does not occur. dally mutants also show cells with high levels of Cyclin A beyond the phase of the cell cycle where it is normally degraded. These findings provide an explanation for the rescue of dally mutants by removing one functional cycA gene; Cyclin A is inappropriately elevated in dally mutants.
Mechanism of Cyclin A-induced cell cycle delay
Our analysis of the interaction between dally and cycA indicates that elevated levels of Cyclin A are responsible for the cell division defects found in dally mutants. This defect is characterized by prolonged expression of the mitotic cyclin, Cyclin B, and a delayed entry into M phase, indicating that an event somewhere during the G2-M segment is disrupted. However, we do not know which exact step within the G2-M segments of the cell cycle is abnormal and if this is the only defect caused by dally mutations. How then could elevated Cyclin A delay cell cycle progression? Expression of a form of Cyclin A that cannot be degraded by the cell cycle-dependent proteolytic machinery produces a delay in metaphase (Jacobs et al., 2001; Kaspar et al., 2001; Parry and OFarrell, 2001; Sigrist et al., 1995). Perhaps elevated levels of Cyclin A found in dally mutants produce a delay in exit from mitosis. It is also possible that disruption of cycA function in G2 could affect other events during G2-M progression in dally mutants.
We have now established several functional links between dally and other genes affecting cell division and morphogenesis. What is the picture that is emerging? First, in imaginal tissues, dally affects cellular responses to the TGF-ß/BMP-related growth factor, Dpp (Jackson et al., 1997). In addition, clones of cells defective for Dpp reception in the eye disc show the same cell cycle defect, in the very same division cycle that we have observed in dally mutants (Penton et al., 1997). These latter findings suggest that dally participates in the cell cycle control functions of Dpp. Now we find that the cell cycle defects of dally mutants are selectively rescued by removing one functional copy of cycA, and that dally mutants show inappropriately high levels of Cyclin A. Perhaps Dally and Dpp cooperate in signaling events that downregulate the levels of Cyclin A.
This model is supported by the activity of TGF-ß in vertebrate cells. TGF-ß signaling has been shown in several different cell types to decrease the levels of cyclin A mRNA, and recent studies indicate this regulation occurs at the transcriptional level (Djaborkhel et al., 2000; Satterwhite et al., 1994; Slingerland et al., 1994; Sugiyama et al., 1997; Yoshizumi et al., 1997). Recent studies of Drosophila myb provide further evidence for the conservation of molecular activities of TGF-ß and Dpp. TGF-ß, in addition to downregulating cyclin A mRNA, inhibits the levels of B-myb mRNA (Satterwhite et al., 1994). Analysis of temperature-sensitive mutations in D-myb show that, like cycA, D-myb promotes G2-M progression (Katzen et al., 1998). Thus, a conserved molecular cassette can be proposed: (1) TGF-ß/Dpp signaling is enhanced at the cell surface by integral membrane proteoglycans of the glypican family; and (2) TGF-ß/Dpp serves to affect cell cycle progression in part by downregulation of both Cyclin A and Myb expression. The difference between the fly and vertebrate systems could simply be the outcome of the TGF-ß/Dpp signaling. In Drosophila the output is to promote cell cycle progression, whereas in vertebrate cells the principal activity of TGF-ß is to arrest cells in G1. Developmentally regulated cell cycle arrest in G2 has now been documented extensively in Drosophila (Edgar and OFarrell, 1990; Johnston and Edgar, 1998; Kylsten and Saint, 1997; Milan et al., 1996) and Dpp may provide an important means of relieving this cell cycle arrest and integrating cell division with differentiation.
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Baeg, G. and Perrimon, N. (2000). Functional binding of secreted molecules to heparan sulfate proteoglycans in Drosophila. Curr. Opin. Cell Biol. 12, 575-580.[Medline]
Bellaiche, Y., The, I. and Perrimon, N. (1998). Tout-velu is a Drosophila homologue of the putative tumour suppressor EXT-1 and is needed for Hh diffusion. Nature 394, 85-88.[Medline]
Blaumueller, C. M. and Mlodzik, M. (2000). The Drosophila tumor suppressor expanded regulates growth, apoptosis, and patterning during development. Mech. Dev. 92, 251-262.[Medline]
Boedigheimer, M. J., Nguyen, K. P. and Bryant, P. J. (1997). Expanded functions in the apical cell domain to regulate the growth rate of imaginal discs. Dev. Genet. 20, 103-110.[Medline]
Bullock, S. L., Fletcher, J. M., Beddington, R. S. and Wilson, V. A. (1998). Renal agenesis in mice homozygous for a gene trap mutation in the gene encoding heparan sulfate 2-sulfotransferase. Genes Dev. 12, 1894-1906.
Condie, J. M. and Brower, D. L. (1989). Allelic interactions at the engrailed locus of Drosophila: engrailed protein expression in imaginal discs. Dev. Biol. 135, 31-42.[Medline]
Djaborkhel, R., Tvrdik, D., Eckschlager, T., Raska, I. and Muller, J. (2000). Cyclin A down-regulation in TGFbeta1-arrested follicular lymphoma cells. Exp. Cell Res. 261, 250-259.[Medline]
Dong, X., Zavitz, K. H., Thomas, B. J., Lin, M., Campbell, S. and Zipursky, S. L. (1997). Control of G1 in the developing Drosophila eye: rca1 regulates Cyclin A. Genes Dev. 11, 94-105.[Abstract]
Edgar, B. A. and Datar, S. A. (1996). Zygotic degradation of two maternal Cdc25 mRNAs terminates Drosophilas early cell cycle program. Genes Dev. 10, 1966-1977.[Abstract]
Edgar, B. A. and OFarrell, P. H. (1990). The three postblastoderm cell cycles of Drosophila embryogenesis are regulated in G2 by string. Cell 62, 469-480.[Medline]
Gao, C. and Zalenka, P. (1997). Cyclins, cyclin-dependent kinases and differentiation. BioEssays 19, 307-315.[Medline]
Grosshans, J. and Wieschaus, E. (2000). A genetic link between morphogenesis and cell division during formation of the ventral furrow in Drosophila. Cell 101, 523-531.[Medline]
Jackson, S. M., Nakato, H., Sugiura, M., Jannuzi, A., Oakes, R., Kaluza, V., Golden, C. and Selleck, S. B. (1997). dally, a Drosophila glypican, controls cellular responses to the TGF-ß-related morphogen, Dpp. Development 124, 4113-4120.
Jacobs, H. W., Keidel, E. and Lehner, C. F. (2001). A complex degradation signal in Cyclin A required for G(1) arrest, and a C-terminal region for mitosis. EMBO J. 20, 2376-2386.
Johnston, L. A. and Edgar, B. A. (1998). Wingless and Notch regulate cell-cycle arrest in the developing Drosophila wing. Nature 394, 82-84.[Medline]
Kamimura, K., Fujise, M., Villa, F., Izumi, S., Habuchi, H., Kimata, K. and Nakato, H. (2001). Drosophila heparan sulfate 6-O-sulfotransferase (dHS6ST) gene. Structure, expression, and function in the formation of the tracheal system. J. Biol. Chem. 276, 17014-17021.
Kaspar, M., Dienemann, A., Schulze, C. and Sprenger, F. (2001). Mitotic degradation of cyclin A is mediated by multiple and novel destruction signals. Curr. Biol. 11, 685-690.[Medline]
Katzen, A. L., Jackson, J., Harmon, B. P., Fung, S. M., Ramsay, G. and Bishop, J. M. (1998). Drosophila myb is required for the G2/M transition and maintenance of diploidy. Genes Dev. 12, 831-843.
Knoblich, J. A. and Lehner, C. F. (1993). Synergistic action of Drosophila cyclins A and B during the G2-M transition. EMBO J. 12, 65-74.[Abstract]
Kumagai, A. and Dunphy, W. G. (1991). The cdc25 protein controls tyrosine dephosphorylation of the cdc2 protein in a cell-free system. Cell 64, 903-914.[Medline]
Kylsten, P. and Saint, R. (1997). Imaginal tissues of Drosophila melanogaster exhibit different modes of cell proliferation control. Dev. Biol. 192, 509-522.[Medline]
Lander, A. D., Stipp, C. S. and Ivins, J. K. (1996). The glypican family of heparan sulfate proteoglycans: major cell-surface proteoglycans of the developing nervous system. Perspect. Dev. Neurobiol. 3, 347-358.[Medline]
Lehner, C. F. and OFarrell, P. H. (1989). Expression and function of Drosophila cyclin A during embryonic cell cycle progression. Cell 56, 957-968.[Medline]
Lehner, C. F. and OFarrell, P. H. (1990). The roles of Drosophila cyclins A and B in mitotic control. Cell 61, 535-547.[Medline]
Lin, X. and Perrimon, N. (1999). Dally cooperates with Drosophila Frizzled 2 to transduce Wingless signalling. Nature 400, 281-284.[Medline]
Manseau, L., Baradaran, A., Brower, D., Budhu, A., Elefant, F., Phan, H., Philp, A. V., Yang, M., Glover, D., Kaiser, K. et al. (1997). GAL4 enhancer traps expressed in the embryo, larval brain, imaginal discs, and ovary of Drosophila. Dev. Dyn. 209, 310-322.[Medline]
Mata, J., Curado, S., Ephrussi, A. and Rorth, P. (2000). Tribbles coordinates mitosis and morphogenesis in Drosophila by regulating string/CDC25 proteolysis. Cell 101, 511-522.[Medline]
McCartney, B. M., Kulikauskas, R. M., LaJeunesse, D. R. and Fehon, R. G. (2000). The neurofibromatosis-2 homologue, Merlin, and the tumor suppressor expanded function together in Drosophila to regulate cell proliferation and differentiation. Development 127, 1315-1324.
Milan, M., Campuzano, S. and Garcia-Bellido, A. (1996). Cell cycling and patterned cell proliferation in the Drosophila wing during metamorphosis. Proc. Natl. Acad. Sci. USA 93, 640-645.
Nakato, H., Futch, T. A. and Selleck, S. B. (1995). The division abnormally delayed (dally) gene: a putative integral membrane proteoglycan required for cell division patterning during postembryonic development of the nervous system in Drosophila. Development 121, 3687-3702.
Ohsugi, K., Bardiner, D. M. and Bryant, S. V. (1997). Cell cycle length affects gene expression and pattern formation in limbs. Dev. Biol. 189, 13-21.[Medline]
Parry, D. H. and OFarrell, P. H. (2001). The schedule of destruction of three mitotic cyclins can dictate the timing of events during exit from mitosis. Curr. Biol. 11, 671-683.[Medline]
Penton, A., Selleck, S. B. and Hoffmann, F. M. (1997). Regulation of cell cycle synchronization by decapentaplegic during Drosophila eye development. Science 275, 203-206.
Pilia, G., Hughes-Benzie, R. M., MacKenzie, A., Baybayan, P., Chen, E. Y., Huber, R., Neri, G., Cao, A., Forabosco, A. and Schlessinger, D. (1996). Mutations in GPC3, a glypican gene, cause the Simpson-Golabi-Behmel overgrowth syndrome. Nat. Genet. 12, 241-247.[Medline]
Satterwhite, D. J., Aakre, M. E., Gorska, A. E. and Moses, H. L. (1994). Inhibition of cell growth by TGF beta 1 is associated with inhibition of B-myb and cyclin A in both BALB/MK and Mv1Lu cells. Cell Growth Differ. 5, 789-799.[Abstract]
Seher, T. C. and Leptin, M. (2000). Tribbles, a cell-cycle brake that coordinates proliferation and morphogenesis during Drosophila gastrulation. Curr. Biol. 10, 623-629.[Medline]
Selleck, S. B. (2000). Proteoglycans and pattern formation: sugar biochemistry meets developmental genetics. Trends Genet. 16, 206-212.[Medline]
Selleck, S. B. and Steller, H. (1991). The influence of retinal innervation on neurogenesis in the first optic ganglion of Drosophila. Neuron 6, 83-99.[Medline]
Selleck, S. B., Gonzalez, C., Glover, D. M. and White, K. (1992). Regulation of the G1-S transition in post-embryonic neuronal precursors by axon ingrowth. Nature 355, 253-255.[Medline]
Sigrist, S., Jacobs, H., Stratmann, R. and Lehner, C. F. (1995). Exit from mitosis is regulated by Drosophila fizzy and the sequential destruction of cyclins A, B and B3. EMBO J. 14, 4827-4838.[Abstract]
Simon, M. A., Bowtell, D. D., Dodson, G. S., Laverty, T. R. and Rubin, G. M. (1991). Ras1 and a putative guanine nucleotide exchange factor perform crucial steps in signaling by the sevenless protein tyrosine kinase. Cell 67, 701-716.[Medline]
Slingerland, J. M., Hengst, L., Pan, C. H., Alexander, D., Stampfer, M. R. and Reed, S. I. (1994). A novel inhibitor of cyclin-Cdk activity detected in transforming growth factor beta-arrested epithelial cells. Mol. Cell. Biol. 14, 3683-3694.[Abstract]
Sugiyama, A., Nagaki, M., Shidoji, Y., Moriwaki, H. and Muto, Y. (1997). Regulation of cell cycle-related genes in rat hepatocytes by transforming growth factor beta1. Biochem. Biophys. Res. Commun. 238, 539-543.[Medline]
The, I., Bellaiche, Y. and Perrimon, N. (1999). Hedgehog movement is regulated through tout velu-dependent synthesis of a heparan sulfate proteoglycan. Mol Cell 4, 633-639.[Medline]
Thomas, B. J., Gunning, D. A., Cho, J. and Zipursky, L. (1994). Cell cycle progression in the developing Drosophila eye: roughex encodes a novel protein required for the establishment of G1. Cell 77, 1003-1014.[Medline]
Tsuda, M., Kamimura, K., Nakato, H., Archer, M., Staatz, W., Fox, B., Humphrey, M., Olson, S., Futch, T., Kaluza, V. et al. (1999). The cell-surface proteoglycan Dally regulates Wingless signalling in Drosophila. Nature 400, 276-280.[Medline]
Weigmann, K., Cohen, S. M. and Lehner, C. F. (1997). Cell cycle progression, growth and patterning in imaginal discs despite inhibition of cell division after inactivation of Drosophila Cdc2 kinase. Development 124, 3555-3563.
Whitfield, W. G., Gonzalez, C., Maldonado-Codina, G. and Glover, D. M. (1990). The A- and B-type cyclins of Drosophila are accumulated and destroyed in temporally distinct events that define separable phases of the G2-M transition. EMBO J. 9, 2563-2572.[Abstract]
Yoshizumi, M., Wang, H., Hsieh, C. M., Sibinga, N. E., Perrella, M. A. and Lee, M. E. (1997). Down-regulation of the cyclin A promoter by transforming growth factor-beta1 is associated with a reduction in phosphorylated activating transcription factor-1 and cyclic AMP-responsive element-binding protein. J. Biol. Chem. 272, 22259-22264.