1 The Howard Hughes Medical Institute, The Johns Hopkins University School of
Medicine, 725 North Wolfe Street, PCTB 818, Baltimore, MD 21205, USA
2 Department of Molecular Biology and Genetics, The Johns Hopkins University
School of Medicine, 725 North Wolfe Street, PCTB 818, Baltimore, MD 21205,
USA
3 Department of Neuroscience, The Johns Hopkins University School of Medicine,
725 North Wolfe Street, PCTB 818, Baltimore, MD 21205, USA
4 The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
* Author for correspondence (e-mail: rreed{at}jhmi.edu)
Accepted 25 November 2003
![]() |
SUMMARY |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: Olfactory, Axon targeting, Transcription factor
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Analysis of the promoter regions of several ORN enriched genes revealed a
conserved sequence, the Olf1 sites, that bound a factor present in olfactory
nuclear extracts (Kudrycki et al.,
1993; Wang et al.,
1993
). Studies in transgenic animals suggested that this site
contributes to specific expression of an olfactory-specific gene in vivo
(Kudrycki et al., 1998
;
Walters et al., 1996
). A
family of related factors (Olf1/EBF or O/E proteins; Ebf1 - Mouse Genome
Informatics) encoding a novel repeated helix-loop-helix (rHLH) domain that
bound to the Olf1 site was identified by the yeast 1-hybrid screen and
subsequent homology screens (Wang and
Reed, 1993
; Wang et al.,
2002
; Wang et al.,
1997
). In vitro analysis of O/E1, O/E2, O/E3 and O/E4 revealed
that they activate transcription of a reporter gene and bind the Olf1 site as
dimers consisting of any two O/E subunits. Although the O/E1 mRNA is
expressed in several adult tissues examined, expression of O/E2, O/E3
and O/E4 are more restricted with highest levels of expression of
each member detected in olfactory epithelium
(Wang et al., 2002
;
Wang et al., 1997
).
O/E proteins are present in the central and peripheral nervous system
during development. In the CNS, O/E messages were detected as early as
embryonic day nine (E9) in post-mitotic cells in distinct but overlapping
patterns (Davis and Reed,
1996; Garel et al.,
1997
; Wang et al.,
1997
). In the spinal cord, O/E messages were present in
post-mitotic cells of the subventricular mantle layer. As these cells migrate
away from the ventricular zone, they first cease O/E3 expression, and after
terminal differentiation, the neurons cease expression of O/E1 and O/E2. The
O/E mRNAs are also observed in sensory structures including the olfactory
epithelium, vomeronasal organ (VNO), retina, dorsal root ganglia (DRG) and
some cranial nerve ganglia. Expression in most regions is transient and only
detected during embryonic development, implying a role in neuronal
differentiation. The olfactory epithelium and VNO continue to express O/E
proteins into adulthood, consistent with the continual neuronal
differentiation in these tissues and an independent role for the O/E proteins
in regulating mature ORN gene expression.
Homologs of the O/E genes have been characterized in C. elegans,
Drosophila and Xenopus
(Bally-Cuif et al., 1998;
Crozatier et al., 1996
;
Dubois et al., 1998
;
Gisler et al., 2000
;
Pozzoli et al., 2001
;
Prasad et al., 1998
). The
overexpression of Xenopus Xcoe2 (orthologous to mouse O/E3) promoted
ectopic neuronal differentiation whereas expression of a dominant-negative
allele showed that it was required for neuronal development. Additional
experiments suggested a role for Xcoe2 in Notch-Delta signaling and placed
Xcoe2 between neurogenin 1 (Ngn1) and NeuroD in a transcriptional regulation
cascade. Studies of Xenopus Xebf3 (orthologous to mouse O/E2) showed
that this protein promoted neuronal differentiation and functions downstream
of NeuroD. The Drosophila O/E-like protein, Collier, may
mediate Notch and Hedgehog signaling
(Crozatier and Vincent, 1999
;
Vervoort et al., 1999
).
Mutations in the C. elegans O/E homolog, UNC-3, leads to aberrant
cell fate in the motoneuron lineage and an uncoordinated phenotype.
Additionally, unc-3 worms display specific defects in ASI
chemosensory neurons.
The O/E1 protein also contributes to gene regulation outside of the nervous
system. Mice lacking functional O/E1 protein, independently identified and
cloned as EBF (early B-cell factor), exhibit a profound defect in B-cell
development (Hagman et al.,
1993; Lin and Grosschedl,
1995
; Travis et al.,
1993
). However, disruption of the Ebf (O/E1)
gene did not alter tissue morphology or gene expression in the olfactory
epithelium, presumably owing to redundancy and functional rescue by other
O/E family members (Wang et al.,
1997
). Interestingly, in the striatum and cranial nerve nuclei
where only O/E1 is expressed, absence of the O/E1 protein leads to atrophy and
abnormal cellular migration, axonal fasciculation and projection
(Garel et al., 2000
;
Garel et al., 1999
;
Garel et al., 2002
). The
apparent functional redundancy of the multiple O/E proteins expressed in
olfactory epithelium might obscure efforts to elucidate the function of single
family members by gene disruption.
Recently, a genetic disruption of the Ebf2 (O/E3) gene has been generated
and the consequences of O/E3 loss examined in neuronal and non-neuronal
tissues (Corradi et al.,
2003). In addition to abnormalities of the neuroendocrine axis
resulting in hypogonadism, there were specific defects in peripheral motor
nerves. These neuronal phenotypes appeared to derive, at least in part, from
hypomyelination and segmental dysmyelination. The expression of additional O/E
family members in these neurons were not specifically examined.
We have used homologous recombination to generate mice in which tau-lacZ and tau-GFP reporters replaced multiple coding exons of O/E2 and O/E3 genes, respectively. The directed expression of a reporter such as ß-galactosidase (ß-gal) or GFP in O/E-expressing cells permits the analysis of the role of O/E proteins in cell fate decision and axonal projection. Neonatal lethality was observed before postnatal day 2 in O/E2lacZ/lacZ-null animals, and frequent postnatal lethality was observed in O/E3GFP/GFP-null animals, although approximately half survived into adulthood. The expression of putative O/E-target genes and the morphological appearance of the olfactory epithelium are normal in both mutant lines. However, there is a marked defect in the projection of olfactory axons to the dorsal olfactory bulb (OB) surface in O/E2lacZ/lacZ-and O/E3GFP/GFP-null animals, and a similar phenotype was observed in O/E2lacZ/+/O/E3GFP/+ double heterozygous mice. Together, our observations suggest that O/E proteins are only partially redundant in the olfactory system and make both distinct and dose-dependent contributions to ORN targeting in the OB.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Linearized replacement constructs were electroporated into R1 129 embryonic stem (ES) cells, and G418-resistant clones with homologous recombination events were identified by Southern hybridization. The genetically modified ES cells were expanded and injected into C57BL/6 blastocysts, and the resulting 129/Sv-C57BL/6 chimeric mice and their O/E heterozygous progeny were mated with cre-expressing transgenic mice to generate O/E mutant alleles that deleted the Neo selection cassette. The genotypes of subsequent generations of O/E mutant mice were determined by PCR analysis.
In situ hybridization
Digoxigenin-labeled riboprobes (Wang et
al., 1997) synthesized from plasmids containing the cDNA sequences
of OMP, CNGA2, O/E1, O/E2 and O/E3 were hybridized to paraformaldehyde or
Bouin's solution-fixed embryonic and adult olfactory tissues sections (14-20
µm). In situ hybridization was performed as previously described
(Schaeren-Wiemers and Gerfin-Moser,
1993
) with the following modification in pre-prehybridization
treatment. Tissue sections were post-fixed in Bouin's solution (Sigma, St
Louis, MO, USA) or 4% paraformaldehyde (PFA) for 10 minutes at room
temperature and washed in PBS (three times, 5 minutes each). Proteinase K
treatment (20 µg/ml) was carried out at room temperature for 10 minutes
followed by PBS wash and post-fixation in Bouin's solution or 4% PFA (10
minutes at room temperature). The tissue sections were then washed in PBS
(three times, 5 minutes each) followed by water (5 minutes) and acetylation in
triethanolamine/acetic anhydride/HCl solution. Finally, the tissue sections
were washed three times in PBS before prehybridization and probe addition.
Immunohistochemistry
Immunohistochemistry was performed on PFA-fixed embryonic and adult
olfactory tissue sections (14-20 µm). Sections were washed in Buffer T (0.1
M Tris, pH 7.5, 0.15 M NaCl, 0.1% Triton X-100, three time, 5 minutes each)
before incubation in buffer T+10% normal serum (buffer T1). Incubation with
primary antibody was diluted in buffer T1 and incubated at 4°C overnight.
Sections were washed in Buffer T three times (5 minutes each) at room
temperature and antibody binding visualized with Cy3- or HRP-(horse radish
peroxidase) conjugated secondary antibodies. A monoclonal antibody to Map2
(Sigma) was used to visualize relay neuronal dendrites. Fluorescent Nissl
stain (Neurotrace 546, Molecular Probes) was used according to manufacturer's
directions.
X-gal staining
The X-gal staining for whole-mount preparation and on sections was
performed essentially as described
(Mombaerts et al., 1996).
Fixed tissues were isolated following intracardiac perfusion of anesthetized
mice (ketamine-xylazine, RBI, Natick, MA). For cryosections, dissected tissues
were treated with 20% sucrose plus 250 mM EDTA for 24 hours at 4°C, frozen
in OCT compound (Sukura Finetek, Torrance, CA), and sections cut (10-20 µm)
in a cryostat.
Images of whole-mount X-gal staining were acquired using a Leica ZFIII stereomicroscope and Zeiss Axiocam color digital camera. GFP fluorescent images in whole-mount tissues were obtained as flattened z-stack images collected on a Zeiss LSM510 confocal microscope.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
Phenotype of O/E2-deficient mice
Neonatal lethality was observed in O/E2 mutant animals. An
expected 1:2:1 Mendelian inheritance pattern was observed in embryonic and
newborn litters of heterozygous crosses but none survived to adulthood
(Table 1). At birth, the
O/E2lacZ/lacZ neonates were indistinguishable from
heterozygous and wild-type littermates, but most
O/E2lacZ/lacZ mutants died within 1 day, and all
homozygous mutant animals died by postnatal day 2 (P2).
|
|
The ORN axons in adult O/E3 null mice displayed a stereotyped abnormal projection in the OB. When visualized by whole-mount GFP fluorescence, the dorsal aspect of the OB in O/E3GFP/GFP mice were void of olfactory glomeruli, and this region possessed few if any axon fibers (Fig. 4A). In coronal sections of adult OB, glomeruli were clearly absent on the dorsal surface, and GFP fluorescence and OMP staining showed a reduction of fibers in this region (Fig. 4A, Fig. 5A). In contrast to P1 O/E2lacZ/lacZ mice, OMP immunoreactivity was detected on the entire surface of rostral OB sections in O/E3GFP/GFP neonates (Fig. 4B). In more caudal sections, OMP staining diminishes in intensity and extent. In all sections, the thinner external plexiform layer on the dorsal aspect of the OB in O/E3GFP/GFP mice was consistent with the eventual absence of axons and glomeruli in this region seen in the adult.
|
|
We next asked whether the dorsal OB that lacks innervation by ORNs retains cells that comprise the normal neuronal circuitry. Nissl staining of OB from O/E3GFP/GFP mice revealed the characteristic mitral cell layer and scattered neuronal cells in the external plexiform region (Fig. 5C). Additional Nissl stained cell bodies were observed where periglomerular cells normally reside, but are not organized around discrete glomeruli in the absence of ORN axons. Moreover, the dramatically reduced Map2 staining in the dorsal bulb region (Fig. 5C) suggests that there are significant perturbations in dendritic organization.
The pattern of olfactory enriched genes and guidance molecules appear normal
Semaphorin (Sema) family of guidance molecules and their receptors,
neuropilins (Npns), have been implicated in the projection of olfactory axons
and proper formation of the olfactory circuitry
(Pasterkamp et al., 1999;
Renzi et al., 2000
;
Schwarting et al., 2000
). The
levels of Npn1, Npn2, Sema3a and Sema3f message expression and their patterns
along the anterior-posterior axis were grossly normal in E16.5 O/E2-
and O/E3-null animals (data not shown). This observation suggests
that the ORN projection defect was not caused by misexpression of these
guidance molecules. In addition, the expression of CNGA2, OMP and two
olfactory receptors (M72 and M4) were not significantly altered in the
O/E2 and O/E3 mutant animals (see Fig. S2 at
http://dev.biologists.org/supplemental).
Finally, electro-olfactogram (EOG) recordings revealed normal responses to
short single-pulse odorant applications in O/E3GFP/GFP
mice (data not shown). This indicates that olfactory gene expression is
grossly normal and the odorant transduction machinery is present in the
absence of O/E2 or O/E3.
Phenotype of O/E2 / O/E3 double heterozygous animals
The mouse O/E proteins exhibit largely overlapping expression in the
olfactory epithelium during development and into adulthood, and share a
similar ability to bind DNA and activate transcription in vitro. Although
there are phenotypic differences between O/E2- and O/E3-null
animals, common ORN projection defects are shared among these animals. In
order to investigate whether the observed projection phenotype is specific to
each O/E mutation or the effect of reduced total O/E dose, we studied
the ORN projection pattern in
O/E2lacZ/+/O/E3GFP/+ double heterozygous
animals.
The O/E2/O/E3 double heterozygous animals are viable, and their gross appearance is similar to that of their O/E2 or O/E3 single heterozygous and wild-type littermates. The O/E2lacZ/+/O/E3GFP/+ double heterozygous animals exhibit an ORN projection defect that is similar to O/E3GFP/GFP littermates: failure to innervate dorsal OB. In contrast to homozygous O/E2- and O/E3-null animals, the OB of the double heterozygous animals is similar in shape and size to O/E heterozygous and wild-type animals (Fig. 6A,B). Thus, the presence of projection defects in ORNs of O/E2lacZ/+/O/E3GFP/+ double heterozygous animals but normal OB size suggests that total O/E gene dose accounts for some, but not all of the observed phenotypes.
|
The patterns of ORN projection and glomeruli formation on the OB of mice
carrying O/E3-tau-GFP and OMP-tau-lacZ alleles was dependent
on the O/E3 locus and not on the amount of tau-reporter
(Fig. 6). As expected,
O/E3GFP/GFP animals carrying one OMP-tau-lacZ
allele exhibited the same ORN projection defect seen in O/E3 mutant
animals with wild-type OMP loci
(Fig. 6E). In mice carrying one
O/E3-tau-GFP (O/E3GFP/+) and two
OMP-tau-lacZ alleles (OMPlacZ/lacZ), the patterns
of ORN projection and olfactory glomeruli appeared normal indicating that the
high level of tau-reporter present in these animals did not cause ORN
projection defects (Fig. 6C,D). Based on our results and the normal ORN projection in animals expressing
tau-reporters under OMP and OR promoters
(Belluscio et al., 1999;
Mombaerts et al., 1996
;
Strotmann et al., 2000
;
Wang et al., 1998
;
Zheng et al., 2000
), we
conclude that the observed ORN projection phenotype is caused by mutations in
the O/E genes.
Odorant receptor-dependent axonal convergence in O/EGFP/GFP mice
Odorant receptors (ORs) are expressed in one of the four spatial zones in
the olfactory epithelium, and cells expressing a particular OR project their
axons to spatially defined glomeruli within the OB
(Mombaerts, 1999;
Mori et al., 1999
;
Ressler et al., 1993
;
Vassar et al., 1993
). Neurons
expressing a particular OR project axons to two regions of each OB, one on the
medial surface and the other on the lateral surface
(Mombaerts et al., 1996
;
Royal and Key, 1999
;
Wang et al., 1998
). We first
examined whether OR-dependent axonal convergence occurs normally in
O/E3 null animals. Mice were generated that carried
O/E3-tau-GFP alleles and either P2-IRES-tau-lacZ
(P2lacZ) or M72-IRES-tau-lacZ
(M72lacZ) tagged odorant receptor genes. These mice
allowed us to examine the projection of both ventral and dorsal-targeting ORN
axons in an O/E3 mutant background.
The axons of P2-expressing neurons converge to characteristic locations on the medial surface of the OB in O/E3 heterozygous animals (Fig. 7A). In O/E3GFP/GFP homozygous animals, however, few fibers are visible on the medial surface, and most fibers terminate on the ventral surface in close juxtaposition to the cribriform plate (Fig. 7B). We next performed X-gal staining on coronal sections of the OB of O/E3GFP/GFP mice carrying P2lacZ alleles in order to address whether P2 axons converge to defined glomeruli and to determine the positions of the labeled glomeruli. We observed convergence of P2 ORN axons to defined glomeruli on the lateral and medial aspects of each OB, indicating that absence of the O/E3 gene product did not affect the ability of axons to converge (Fig. 7D,F). The different shape of the olfactory bulb in O/E3GFP/GFP mice make it difficult to assign specific perturbations to the projection pattern of lacZ-labeled axons. However, consistent with the patterns observed in whole-mount staining, P2 axons in O/E3GFP/GFP animals converged to more ventral positions in the medial (Fig. 7C,D) and lateral (Fig. 7E,F) aspects of the OB relative to their heterozygous littermates. The ventral shift of P2 axon projection pattern suggests that there may be an overall ventral shift of olfactory glomerular positions in O/E3 null mice, resulting in the absence of ORN fibers and olfactory glomeruli on the dorsal surface of the OB. Alternatively, the apparent shift in the position of the P2 glomerulus may simply result from changes in bulb shape and the dorsal projection defect in O/E3GFP/GFP animals derived from an independent primary defect, elimination of dorsal glomeruli.
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We describe the generation and analysis of mice carrying O/E2 and
O/E3 null mutations. Replacement of the 5' coding exons of
O/E2 and O/E3 with tau-lacZ and tau-GFP
reporter genes, respectively, allow the visualization of the neurons that
normally express these O/E genes and examination of their axonal
projections. Many CNS and PNS neurons express O/E proteins during development,
and the expression of individual O/E proteins follows distinct temporal and
spatial patterns. Defects in brain regions that express only O/E1 were
reported in O/E1 knockout animals
(Garel et al., 2000;
Garel et al., 1999
;
Garel et al., 2002
). These
studies relied on the expression of additional markers, and were limited in
their ability to trace axon projection, cellular lineage and migration.
Although we have not analyzed regions outside of the olfactory system,
O/E2- and O/E3-tagged animals could assist such studies by
providing reporters for monitoring cell lineage, cellular migration and axonal
projection.
Although our findings strengthen the notion that O/E proteins are at least
partially redundant in maintaining the expression of target genes, O/E
expression in developing neuronal systems suggest that O/E genes are
activated in distinct stages of development
(Garel et al., 1997). In
Xenopus primary neurogenesis, Ngn1, O/E3, NeuroD and
O/E2 are proposed to participate in a sequential transcriptional
cascade where Ngn1 can bypass O/E3 and regulate NeuroD expression, and a
similar transcriptional cascade may be present in the mouse olfactory system
(Cau et al., 2002
;
Dubois et al., 1998
;
Pozzoli et al., 2001
).
Therefore, the overall phenotype associated with each O/E genotype is
likely to be a combination of both O/E gene-specific and O/E dose
effects. An alternative yet complementary transcriptional cascade involving
Mash1, Ngn1 and NeuroD has been proposed for the development of ORNs
(Cau et al., 2002
;
Cau et al., 2000
;
Cau et al., 1997
). However, the
contributions of O/E2 and O/E3 proteins were not specifically addressed, and
further studies are necessary to elucidate the interactions of HLH factors
during ORN development.
Mutation in O/E genes leads to abnormalities in olfactory bulb innervation
The failure of axons to extend to the most dorsal aspects of the bulb in
O/E2- or O/E3-null mice could arise from the elimination of
target glomeruli in an intrinsic map of the bulb, from a global shift in the
underlying bulb organization, or from an intrinsic failure in axon extension
by ORNs. The glomeruli in the dorsal OB receive innervation from the most
dorsal zone (zone-I) of the four spatial zones in the epithelium
(Mori et al., 2000). If the
phenotype observed in O/E3 mutants results from elimination of
glomeruli on the dorsal surface of the OB, one would expect that specific ORs
from zone I of the olfactory epithelium would not be
expressed.(Konzelmann et al.,
1998
). ORs in zone I and zone II (M72 and M4, respectively)
(Qasba and Reed, 1998
;
Zheng et al., 2000
) were
present in their normal domains of the epithelium in adult
O/E3GFP/GFP mice (see Fig. S2 at
http://dev.biologists.org/supplemental),
demonstrating that zone I OR expression for at least one receptor is largely
normal. In addition, the observed patterns of dorsal projecting M72 axons and
ventral targeting P2 axons are consistent with a global shift in the
glomerular map in O/E3GFP/GFP mice. However, axons of M72-
and P2-expressing cells do not target to the region of the OB where glomeruli
are absent in O/E3-null mice. A specific perturbation in expression of ORs
whose axons target to the dorsal-most glomeruli may also be responsible for
the observed projection defect. This analysis must await the identification
and genetic targeting of this subset of receptors.
Primary olfactory axons play an important role in glomerular definition and
formation (Belluscio et al.,
2002; Bozza et al.,
2002
; Carr and Farbman,
1993
; Couper Leo et al.,
2000
; Fiske and Brunjes,
2001
; Schwob et al.,
1992
). The aberrant axonal projection patterns could derive from a
misreading of the gradients and cues present in the olfactory bulb. These
axons would then induce glomeruli at inappropriate locations. The stereotyped
location of glomeruli in the bulb are established by ORN axons perinatally and
are retained in position in spite of continual replacement of the neurons. An
inability of the ORN axons to extend as far on the bulb surface would lead to
a similar reorganization of glomerular position.
The defects in ORN projection to dorsal OB, although distinct, are very
similar in O/E2lacZ/lacZ and
O/E3GFP/GFP mutants. The inability of ORNs to innervate
dorsal OB in both mutants suggests that reduced O/E dose levels in these cells
may contribute to the observed phenotype. Consistent with this notion, the ORN
axons of O/E2lacZ/+/O/E3GFP/+ double
heterozygous animals also fail to innervate the dorsal bulb. These gene dose
effects, combined with high O/E expression in olfactory epithelium and absence
from the OB, suggests an alternative mechanism to account for the projection
defects. The expression of OR protein is essential to proper axon targeting
(Mombaerts et al., 1996;
Wang et al., 1998
) and
receptor expression levels could represent a crucial determinant in the length
of axon extension. The presence of O/E consensus binding sites in the minimal
promoter region for several ORs (Vassalli
et al., 2002
) (R.R.R., unpublished) further implicates in these
transcription factors in receptor expression. The overlapping expression of
each of the O/E family members in all olfactory neurons is consistent with the
total dose of O/E gene expression rather than the particular identity that
results in a failure to project all of the way to the most dorsal regions of
the bulb.
In summary, although O/E2 and O/E3 mutant animals have
distinct gross phenotypes, they share similar abnormal ORN projection
patterns. We have demonstrated that the functions of O/E genes are
not completely redundant, and the olfactory phenotype in each mutant probably
derives from O/E dose dependent and individual O/E gene-specific
effects. Although no olfactory phenotype has been reported in O/E1
knockout mice (Lin and Grosschedl,
1995), our results suggest these mice may have similar defects
that have not been detected in these untagged O/E1 mutant animals.
O/E proteins are potential regulators of ORN gene expression, and their
expression in embryos suggests a broader function in the development of the
nervous system. Detailed investigation of the brains of O/E1 mutant
mice have indicated a role for O/E1 in neurodevelopment, and similar analysis
of O/E2 and O/E3 mutant animals may reveal additional
functions for these O/E family members.
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
Footnotes |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Baker, H., Cummings, D. M., Munger, S. D., Margolis, J. W.,
Franzen, L., Reed, R. R. and Margolis, F. L. (1999). Targeted
deletion of a cyclic nucleotide-gated channel subunit (OCNC1): biochemical and
morphological consequences in adult mice. J. Neurosci.
19,9313
-9321.
Bally-Cuif, L., Dubois, L. and Vincent, A. (1998). Molecular cloning of Zcoe2, the zebrafish homolog of Xenopus Xcoe2 and mouse EBF-2, and its expression during primary neurogenesis. Mech. Dev. 77,85 -90.[CrossRef][Medline]
Belluscio, L., Koentges, G., Axel, R. and Dulac, C. (1999). A map of pheromone receptor activation in the mammalian brain. Cell 97,209 -220.[Medline]
Belluscio, L., Lodovichi, C., Feinstein, P., Mombaerts, P. and Katz, L. C. (2002). Odorant receptors instruct functional circuitry in the mouse olfactory bulb. Nature 419,296 -300.[CrossRef][Medline]
Bozza, T., Feinstein, P., Zheng, C. and Mombaerts, P.
(2002). Odorant receptor expression defines functional units in
the mouse olfactory system. J. Neurosci.
22,3033
-3043.
Carr, V. M. and Farbman, A. I. (1993). The dynamics of cell death in the olfactory epithelium. Exp. Neurol. 124,308 -314.[CrossRef][Medline]
Cau, E., Casarosa, S. and Guillemot, F. (2002). Mash1 and Ngn1 control distinct steps of determination and differentiation in the olfactory sensory neuron lineage. Development 129,1871 -1880.[Medline]
Cau, E., Gradwohl, G., Casarosa, S., Kageyama, R. and Guillemot,
F. (2000). Hes genes regulate sequential stages of
neurogenesis in the olfactory epithelium. Development
127,2323
-2332.
Cau, E., Gradwohl, G., Fode, C. and Guillemot, F.
(1997). Mash1 activates a cascade of bHLH regulators in olfactory
neuron progenitors. Development
124,1611
-1621.
Cho, J. Y., Min, N., Franzen, L. and Baker, H. (1996). Rapid down-regulation of tyrosine hydroxylase expression in the olfactory bulb of naris-occluded adult rats. J. Comp. Neurol. 369,264 -276.[CrossRef][Medline]
Corradi, A., Croci, L., Broccoli, V., Zecchini, S., Previtali,
S., Wurst, W., Amadio, S., Maggi, R., Quattrini, A. and Consalez, G. G.
(2003). Hypogonadotropic hypogonadism and peripheral neuropathy
in Ebf2-null mice. Development
130,401
-410.
Couper Leo, J. M., Devine, A. H. and Brunjes, P. C. (2000). Focal denervation alters cellular phenotypes and survival in the rat olfactory bulb: a developmental analysis. J. Comp. Neurol. 425,409 -421.[CrossRef][Medline]
Crozatier, M., Valle, D., Dubois, L., Ibnsouda, S. and Vincent, A. (1996). Collier, a novel regulator of Drosophila head development, is expressed in a single mitotic domain. Curr. Biol. 6,707 -718.[Medline]
Crozatier, M. and Vincent, A. (1999).
Requirement for the Drosophila COE transcription factor Collier in formation
of an embryonic muscle: transcriptional response to notch signalling.
Development 126,1495
-1504.
Davis, J. A. and Reed, R. R. (1996). Role of
Olf-1 and Pax-6 transcription factors in neurodevelopment. J.
Neurosci. 16,5082
-5094.
Dubois, L., Bally-Cuif, L., Crozatier, M., Moreau, J., Paquereau, L. and Vincent, A. (1998). XCoe2, a transcription factor of the Col/Olf-1/EBF family involved in the specification of primary neurons in Xenopus. Curr. Biol. 8, 199-209.[Medline]
Ebneth, A., Godemann, R., Stamer, K., Illenberger, S., Trinczek,
B. and Mandelkow, E. (1998). Overexpression of tau protein
inhibits kinesin-dependent trafficking of vesicles, mitochondria, and
endoplasmic reticulum: implications for Alzheimer's disease. J.
Cell Biol. 143,777
-794.
Fiske, B. K. and Brunjes, P. C. (2001). Cell death in the developing and sensory-deprived rat olfactory bulb. J. Comp. Neurol. 431,311 -319.[CrossRef][Medline]
Garcia, M. L. and Cleveland, D. W. (2001). Going new places using an old MAP: tau, microtubules and human neurodegenerative disease. Curr. Opin. Cell Biol. 13, 41-48.[CrossRef][Medline]
Garel, S., Marin, F., Grosschedl, R. and Charnay, P.
(1999). Ebf1 controls early cell differentiation in the embryonic
striatum. Development
126,5285
-5294.
Garel, S., Garcia-Dominguez, M. and Charnay, P.
(2000). Control of the migratory pathway of facial branchiomotor
neurones. Development
127,5297
-5307.
Garel, S., Marin, F., Mattei, M. G., Vesque, C., Vincent, A. and Charnay, P. (1997). Family of Ebf/Olf-1-related genes potentially involved in neuronal differentiation and regional specification in the central nervous system. Dev. Dyn. 210,191 -205.[CrossRef][Medline]
Garel, S., Yun, K., Grosschedl, R. and Rubenstein, J. L. (2002). The early topography of thalamocortical projections is shifted in Ebf1 and Dlx1/2 mutant mice. Development 129,5621 -5634.[CrossRef][Medline]
Gisler, R., Jacobsen, S. E. and Sigvardsson, M.
(2000). Cloning of human early B-cell factor and identification
of target genes suggest a conserved role in B-cell development in man and
mouse. Blood 96,1457
-1464.
Grant, P., Sharma, P. and Pant, H. C. (2001).
Cyclin-dependent protein kinase 5 (Cdk5) and the regulation of neurofilament
metabolism. Eur. J. Biochem.
268,1534
-1546.
Grundke-Iqbal, I. and Iqbal, K. (1999). Tau
pathology generated by overexpression of tau. Am. J.
Pathol. 155,1781
-1785.
Hagman, J., Belanger, C., Travis, A., Turck, C. W. and Grosschedl, R. (1993). Cloning and functional characterization of early B-cell factor, a regulator of lymphocyte-specific gene expression. Genes Dev. 7, 760-773.[Abstract]
Iwema, C. L. and Schwob, J. E. (2003). Odorant receptor expression as a function of neuronal maturity in the adult rodent olfactory system. J. Comp. Neurol. 459,209 -222.[CrossRef][Medline]
Konzelmann, S., Saucier, D., Strotmann, J., Breer, H. and Astic, L. (1998). Decline and recovery of olfactory receptor expression following unilateral bulbectomy. Cell Tissue Res. 294,421 -430.[CrossRef][Medline]
Kudrycki, K., Stein-Izsak, C., Behn, C., Grillo, M., Akeson, R. and Margolis, F. L. (1993). Olf-1-binding site: characterization of an olfactory neuron-specific promoter motif. Mol. Cell Biol. 13,3002 -3014.[Abstract]
Kudrycki, K. E., Buiakova, O., Tarozzo, G., Grillo, M., Walters, E. and Margolis, F. L. (1998). Effects of mutation of the Olf-1 motif on transgene expression in olfactory receptor neurons. J. Neurosci. Res. 52,159 -172.[CrossRef][Medline]
Lin, H. and Grosschedl, R. (1995). Failure of B-cell differentiation in mice lacking the transcription factor EBF. Nature 376,263 -267.[CrossRef][Medline]
Mackay-Sim, A. and Kittel, P. (1991). Cell dynamics in the adult mouse olfactory epithelium: a quantitative autoradiographic study. J. Neurosci. 11,979 -984.[Abstract]
Mombaerts, P. (1999). Molecular biology of odorant receptors in vertebrates. Annu. Rev. Neurosci. 22,487 -509.[CrossRef][Medline]
Mombaerts, P., Wang, F., Dulac, C., Chao, S. K., Nemes, A., Mendelsohn, M., Edmondson, J. and Axel, R. (1996). Visualizing an olfactory sensory map. Cell 87,675 -686.[Medline]
Mori, K., Nagao, H. and Yoshihara, Y. (1999).
The olfactory bulb: coding and processing of odor molecule information.
Science 286,711
-715.
Mori, K., von Campenhause, H. and Yoshihara, Y. (2000). Zonal organization of the mammalian main and accessory olfactory systems. Philos. Trans. R. Soc. Lond. B Biol. Sci. 355,1801 -1812.[CrossRef][Medline]
Nadi, N. S., Head, R., Grillo, M., Hempstead, J., Grannot-Reisfeld, N. and Margolis, F. L. (1981). Chemical deafferentation of the olfactory bulb: plasticity of the levels of tyrosine hydroxylase, dopamine and norepinephrine. Brain Res. 213,365 -377.[CrossRef][Medline]
Nagy, Z., Maccioni, R. B. and Cambiazo, V. (2000). Cell cycle regulatory failure in neurones: causes and consequences. Role of microtubule-associated proteins in the control of microtubule assembly. Neurobiol. Aging 21,761 -769.[CrossRef][Medline]
Paglini, G., Peris, L., Mascotti, F., Quiroga, S. and Caceres, A. (2000). Tau protein function in axonal formation. Neurochem Res. 25,37 -42.[CrossRef][Medline]
Pasterkamp, R. J., Ruitenberg, M. J. and Verhaagen, J. (1999). Semaphorins and their receptors in olfactory axon guidance. Cell. Mol. Biol. (Noisy-le-grand) 45,763 -779.
Pozzoli, O., Bosetti, A., Croci, L., Consalez, G. G. and Vetter, M. L. (2001). Xebf3 is a regulator of neuronal differentiation during primary neurogenesis in xenopus. Dev. Biol. 233,495 -512.[CrossRef][Medline]
Prasad, B. C., Ye, B., Zackhary, R., Schrader, K., Seydoux, G.
and Reed, R. R. (1998). unc-3, a gene required for axonal
guidance in Caenorhabditis elegans, encodes a member of the O/E family of
transcription factors. Development
125,1561
-1568.
Probst, A., Gotz, J., Wiederhold, K. H., Tolnay, M., Mistl, C., Jaton, A. L., Hong, M., Ishihara, T., Lee, V. M., Trojanowski, J. Q. et al. (2000). Axonopathy and amyotrophy in mice transgenic for human four-repeat tau protein. Acta Neuropathol (Berl) 99,469 -481.[CrossRef][Medline]
Qasba, P. and Reed, R. R. (1998). Tissue and
zonal-specific expression of an olfactory receptor transgene. J.
Neurosci. 18,227
-236.
Renzi, M. J., Wexler, T. L. and Raper, J. A. (2000). Olfactory sensory axons expressing a dominant-negative semaphorin receptor enter the CNS early and overshoot their target. Neuron 28,437 -447.[Medline]
Ressler, K. J., Sullivan, S. L. and Buck, L. B. (1993). A zonal organization of odorant receptor gene expression in the olfactory epithelium. Cell 73,597 -609.[Medline]
Royal, S. J. and Key, B. (1999). Development of
P2 olfactory glomeruli in P2-internal ribosome entry site-tau-lacZ transgenic
mice. J. Neurosci. 19,9856
-9864.
Schaeren-Wiemers, N. and Gerfin-Moser, A. (1993). A single protocol to detect transcripts of various types and expression levels in neural tissue and cultured cells: in situ hybridization using digoxigenin-labelled cRNA probes. Histochemistry 100,431 -440.[Medline]
Schwarting, G. A., Kostek, C., Ahmad, N., Dibble, C., Pays, L.
and Puschel, A. W. (2000). Semaphorin 3A is required for
guidance of olfactory axons in mice. J. Neurosci.
20,7691
-7697.
Schwob, J. E., Szumowski, K. E. and Stasky, A. A. (1992). Olfactory sensory neurons are trophically dependent on the olfactory bulb for their prolonged survival. J. Neurosci. 12,3896 -3919.[Abstract]
Strotmann, J., Conzelmann, S., Beck, A., Feinstein, P., Breer,
H. and Mombaerts, P. (2000). Local permutations in the
glomerular array of the mouse olfactory bulb. J.
Neurosci. 20,6927
-6938.
Travis, A., Hagman, J., Hwang, L. and Grosschedl, R. (1993). Purification of early-B-cell factor and characterization of its DNA-binding specificity. Mol. Cell. Biol. 13,3392 -3400.[Abstract]
Vassalli, A., Rothman, A., Feinstein, P., Zapotocky, M. and Mombaerts, P. (2002). Minigenes impart odorant receptor-specific axon guidance in the olfactory bulb. Neuron 35,681 -696.[Medline]
Vassar, R., Ngai, J. and Axel, R. (1993). Spatial segregation of odorant receptor expression in the mammalian olfactory epithelium. Cell 74,309 -318.[Medline]
Vervoort, M., Crozatier, M., Valle, D. and Vincent, A. (1999). The COE transcription factor Collier is a mediator of short-range Hedgehog-induced patterning of the Drosophila wing. Curr. Biol. 9,632 -639.[CrossRef][Medline]
Walters, E., Grillo, M., Tarozzo, G., Stein-Izsak, C., Corbin, J., Bocchiaro, C. and Margolis, F. L. (1996). Proximal regions of the olfactory marker protein gene promoter direct olfactory neuron-specific expression in transgenic mice. J. Neurosci. Res. 43,146 -160.[CrossRef][Medline]
Wang, F., Nemes, A., Mendelsohn, M. and Axel, R. (1998). Odorant receptors govern the formation of a precise topographic map. Cell 93, 47-60.[Medline]
Wang, M. M. and Reed, R. R. (1993). Molecular cloning of the olfactory neuronal transcription factor Olf-1 by genetic selection in yeast. Nature 364,121 -126.[CrossRef][Medline]
Wang, M. M., Tsai, R. Y., Schrader, K. A. and Reed, R. R. (1993). Genes encoding components of the olfactory signal transduction cascade contain a DNA binding site that may direct neuronal expression. Mol. Cell. Biol. 13,5805 -5813.[Abstract]
Wang, S. S., Betz, A. G. and Reed, R. R. (2002). Cloning of a Novel Olf-1/EBF-like Gene, O/E-4, by degenerate oligo-based direct selection. Mol. Cell Neurosci. 20,404 -414.[CrossRef][Medline]
Wang, S. S., Tsai, R. Y. and Reed, R. R.
(1997). The characterization of the Olf-1/EBF-like HLH
transcription factor family: implications in olfactory gene regulation and
neuronal development. J. Neurosci.
17,4149
-4158.
Weintraub, H. (1993). The MyoD family and myogenesis: redundancy, networks, and thresholds. Cell 75,1241 -1244.[Medline]
Zhao, H. and Reed, R. R. (2001). X inactivation of the OCNC1 channel gene reveals a role for activity-dependent competition in the olfactory system. Cell 104,651 -660.[Medline]
Zheng, C., Feinstein, P., Bozza, T., Rodriguez, I. and Mombaerts, P. (2000). Peripheral olfactory projections are differentially affected in mice deficient in a cyclic nucleotide-gated channel subunit. Neuron 26,81 -91.[Medline]