|
|
|
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
First published online 14 March 2007
doi: 10.1242/dev.000836
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 Division of Mammalian Development, National Institute of Genetics, Yata 1111,
Mishima 411-8540, Japan.
2 SOKENDAI, Yata 1111, Mishima 411-8540, Japan.
3 Cellular and Molecular Toxicology Division, National Institute of Health
Sciences, 1-18-1 Kamiyoga, Setagayaku, Tokyo 158-8501, Japan.
Author for correspondence (e-mail:
ysaga{at}lab.nig.ac.jp)
Accepted 14 February 2007
 |
SUMMARY |
|---|
TOP
SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES |
|---|
Key words: Somitogenesis, Notch signaling, Presomitic mesoderm, Segmentation
|
INTRODUCTION |
|---|
|
TOP
SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES |
|---|
;
Pourquie, 2003;
Saga and Takeda, 2001). The
somites provide the basic axial structures that underlie the segmental
architecture of not only the vertebra, ribs and muscles, which are all somite
derivatives, but also of the vascular and nervous systems
(Borycki and Emerson, 2000;
Brand-Saberi and Christ, 2000;
Monsoro-Burq and Le Douarin,
2000). Periodicity is generated by Notch signal oscillations
linked to the segmentation clock (Bessho et
al., 2001; Huppert et al.,
2005; Morimoto et al.,
2005; Rida et al.,
2004). The temporal information that results from this is
translated into spatial patterns in the anterior PSM, which is defined by the
so-called determination front (Dubrulle
and Pourquie, 2004).
The Mesp2 transcription factor plays important roles during somitogenesis
(Saga et al., 1997), and its
expression is periodically activated by cyclic Notch signaling and Tbx6 at the
anterior PSM in the determination front
(Yasuhiko et al., 2006). Mesp2
demarcates the next segmental boundary and defines the rostro-caudal identity
of somites (Takahashi et al.,
2000). It has been shown that Mesp2-null embryos fail to
segment and that the resulting non-segmented somites show caudalized
properties (Saga et al.,
1997). Previously, we have shown that Mesp2 suppresses Notch
activity via the activation of Lfng, which might function as a
negative regulator of Notch signaling
(Morimoto et al., 2005). In
addition, Mesp2 acts as the transcriptional activator of Epha4 in the
anterior PSM (Nakajima et al.,
2006). Mesp2 is also known to be a strong suppressor of genes such
as Dll1 and Uncx4.1 that confer caudal properties upon the
somitic cells via Notch signaling
(Takahashi et al., 2000).
However, the manner in which the caudal genes are suppressed is currently
unknown. In our current study, which aimed to elucidate the molecular
mechanisms underlying the regulation of somitogenesis by Mesp2, we have
compared the gene expression patterns of Mesp2+/- and
Mesp2-/- embryos, and found that several genes are
affected by the Mesp2 knockout. Among the downregulated genes that we
identified in the Mesp2-null embryo, we focused on a putative
transcriptional repressor. This gene turned out to be Ripply2, which
was recently reported as a mouse homolog of zebrafish ripply1
(Kawamura et al., 2005).
Morpholino-mediated knockdown analysis revealed that ripply1 is
required for the proper transition from the PSM to somites. We generated a
Ripply2-knockout mouse and now show that Ripply2 is
activated by Mesp2, but also functions negatively toward Mesp2 to regulate the
levels of Notch signaling in the anterior PSM. This negative regulation is
required for the periodic generation of the rostro-caudal patterning within a
somite.
|
MATERIALS AND METHODS |
|---|
|
TOP
SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES |
|---|
). All of these data are also now available online at the
National Institute of Health Sciences
(http://www.nihs.go.jp/tox/TtgSubmitted.htm).
|
Luciferase assay
For luciferase reporter analysis under the control of the 1.5 kb
Ripply2 anterior-PSM enhancer (EcoRI-BamHI)
fragment (20 ng), reporter constructs were co-transfected with the expression
vectors 3xFLAG-Mesp2 (0, 30, 100 ng) and 3xFLAG-E47 (0, 50 ng) into NIH3T3
cells (0.25x105 cells per well in 24-multiwell plates) using
Lipofectamine Plus (Invitrogen), following the manufacturer's instructions.
The vector containing the Renilla luciferase gene under the control
of the thymidine kinase promoter (1 ng) was co-transfected as an internal
standard to normalize for transfection efficiency, and the amount of total
plasmid was adjusted with pcDNA3.1. After 36 hours, luciferase activities were
measured using a Dual Luciferase Assay Kit (Promega).
Electrophoretic mobility shift assay (EMSA)
A 3xFLAG-Mesp2 protein was produced using the FreeStyle 293 Expression
System (Invitrogen) and then collected via a nuclear extraction method.
Double-stranded DNA oligonucleotide probes were end-labeled with DIG and
protein-DNA complexes were detected using a DIG Gel Shift Kit (Roche). Binding
reactions were carried out for 30 minutes on ice, and protein-DNA complexes
were analyzed on 6% native polyacrylamide gels.
Ripply2 gene targeting strategy
The mouse Ripply2 gene consists of four exons, the first of which
harbors two putative in-frame translational initiation codons. We generated a
targeting vector with a floxed neo cassette to remove a portion of
exon 1, which would introduce a termination codon just after the second
initiation codon and produce a null allele. The resulting linearized vector
(25 µg) was then electroporated into TT2 ES cells
(Yagi et al., 1993).
G418-resistant cell clones were further selected by PCR. Correct homologous
recombination was confirmed by Southern blotting, and targeted cell clones
were aggregated with ICR 8-cells and then transferred to pseudopregnant female
recipients. The resulting chimeric mice were bred with ICR females. Germline
transmission of the targeted allele was confirmed by PCR. The floxed neomycin
cassette was later removed by breeding with a CAG-Cre transgenic mouse
(Sakai and Miyazaki,
1997).
Gene expression and histochemical analysis
Methods for gene expression analysis by in situ hybridization of
whole-mount samples and by skeletal staining have been described previously
(Takahashi et al., 2000). The
probes used in this study have been described previously
(Takahashi et al., 2000;
Takahashi et al., 2003;
Nomura-Kitabayashi et al.,
2002). For the Ripply2 RNA probe, we used a full-length
cDNA clone containing intron 1. Section in situ hybridization and
immunohistochemical detection of proteins were performed as previously
described (Morimoto et al.,
2005). For whole-mount detection of Mesp2-venus, embryos were
fixed with 4% paraformaldehyde in PBS overnight at 4°C, incubated with
rabbit anti-GFP (MBL; 1:1000), followed by Alexa-488-conjugated goat
anti-rabbit IgG (Molecular Probes; 1:400) and observed using a fluorescent
microscope (Olympus BX61).
|
|
|
|
RESULTS |
|---|
|
TOP
SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES |
|---|
; Nakajima et al.,
2006). Moreover, expression of the Dll1 and
Uncx4.1 genes, which are expressed in the caudal half of the somite
(Bettenhausen et al., 1995;
Leitges et al., 2000), is
increased in the Mesp2-null mouse, indicating that Mesp2 is required
for their suppression (Takahashi et al.,
2000). However, the molecular mechanisms underlying this are
unknown. To identify novel genes that operate downstream of Mesp2, we
performed GeneChip analysis using RNAs prepared from both wild-type and
Mesp2-null embryos. Among the genes that showed a reduction in
expression in the Mesp2-null embryos (see Table S1 in the
supplementary material), we selected a cDNA clone (corresponding to RIKEN cDNA
C030002E08) that showed an identical expression pattern to that of
Mesp2 by in situ screening of 11.5 dpc embryos. This cDNA was
subsequently revealed to be the mouse Ripply2 gene recently reported
by Kawamura et al. (Kawamura et al.,
2005). The initial expression of Mesp2 was found to be
restricted to the nascent mesoderm at E7.0, but Ripply2 expression
appeared to be absent or very weak prior to somitogenesis
(Fig. 1A). However, its
expression became evident in the anterior PSM as a pair of bands by 8.0 dpc,
similar to Mesp2 (Fig.
1A). The expression of Ripply2 then continued until 12.5
dpc, during the somite-forming period (Fig.
1A and data not shown). The expression domains of Mesp2
and Ripply2 were next compared by double in situ hybridization of
embryonic tail sections. Two typical patterns are shown in
Fig. 1B. One shows single bands
that are completely merged, whereas the other is of a single Mesp2
band and two Ripply2 bands in which the caudal band is merged with a
distinct Mesp2 band. This observation indicates that Mesp2
expression precedes that of Ripply2, but that Ripply2
persists for longer. In addition, Ripply2 expression was lost in the
Mesp2-null embryo (Fig.
1C), as predicted from our GeneChip analysis. These data thus
indicated that Ripply2 might be a target of Mesp2.
|
;
Nakajima et al., 2006). We
next employed a luciferase reporter assay system to ascertain whether the
enhancer activity was dependant upon Mesp2. Two reporter constructs were
generated - one containing the 1.5 kb genomic fragment and the other harboring
six repeats of the 171 bp consensus sequence. Both constructs were activated
by the addition of Mesp2, but not in conjunction with E47 (also known as
Tcfe2a - Mouse Genome Informatics) (Fig.
2E). This result was different from the findings of our previous
study of the Epha4 enhancer
(Nakajima et al., 2006), in
which Mesp2 was observed to bind and transactivate the reporter activity only
in the presence of E47, a possible heterodimeric partner. Since Mesp2 belongs
to the bHLH-type transcription factor family, which is known to bind either to
E-box or N-box motifs, we screened the 171 bp Ripply2 gene consensus
sequence for E-boxes, or for an N-box which is capable of binding to Mesp2
with or without E47. We identified a DNA fragment containing a highly
conserved E-box CATCTG sequence, and confirmed that this binds to Mesp2,
whereas a mutated form did not (Fig.
2F,G). E47 was also found to bind to this E-box, but this might
not be functional binding as no associated activity was detectable by
luciferase reporter assay. Furthermore, the binding of Mesp2 was weakened by
the addition of E47. These results are consistent with the idea that Mesp2
binds to this E-box in the enhancer of the Ripply2 gene, and that
this enhancer does not require E47 for subsequent transactivation.
The Ripply2-knockout mouse exhibits a rostralized phenotype
Because Mesp2 confers rostral properties to the somites and is involved in
the formation of the somite boundary, we speculated whether Ripply2 might
function in this Mesp2 pathway during somitogenesis. To elucidate this
possibility, we generated Ripply2-knockout mice using ES
cell-mediated gene targeting (Fig.
3A). Since the heterozygous mice were found to be normal, we
performed timed intercross matings to analyze the phenotypes of the
homozygotes. As expected from the expression patterns, the
Ripply2-/- embryos failed to proceed through normal
somitogenesis and the embryos displayed no clear segmental borders
(Fig. 4A-D). These homozygous
mice also died soon after birth. The morphology of the 17.5-dpc fetus was
found to be similar to that of the Mesp2-null embryo, with a short
trunk and tail (Fig. 3B)
(Saga et al., 1997). However,
the vertebral phenotype of the Ripply2-/- embryos, as
revealed by skeletal staining, differed from that of Mesp2-null
embryos as it features extensive fusion of the pedicles in the neural arches
owing to the caudalized characteristics of the somitic mesoderm
(Saga et al., 1997).
|
). The findings of our gene expression studies using both
rostral and caudal molecular markers are consistent with these skeletal
defects. In Ripply2+/- embryos, the expression of the
caudal markers Uncx4.1 and Dll1 in the segmented somites was
restricted to the caudal compartments of the somites
(Fig. 5A,C). The expression of
these genes is increased and more expansive in Mesp2-null embryos
(Takahashi et al., 2000), but
was greatly reduced in the Ripply2-null embryos,
(Fig. 5B,D). In addition, no
Dll1 stripe could be observed within the somitic region or in the
anterior PSM, although the expression in the posterior PSM was intact in the
Ripply2-/- embryo (Fig.
5D). By contrast, the rostral markers were found to be present in
the Ripply2-/- embryo
(Fig. 5E-H). Tbx18,
which is known to be involved in the maintenance of the rostral properties of
the somites (Bussen et al.,
2004; Kraus et al.,
2001), was expressed in the rostral compartment of the segmented
somites (Fig. 5E). In
Ripply2-/- embryos, this expression was expanded
throughout the entire somite region and no clear segmental pattern was evident
(Fig. 5F). In addition,
Epha4 was expressed in the rostral compartment of S0 and S1 somites
in the Ripply2+/- embryo
(Fig. 5G), and this expression
in the Ripply2-/- embryo was increased and the expression
domain expanded as compared with the wild type
(Fig. 5H). We thus conclude
that the Ripply2-null mouse displays a rostralized phenotype.
Ripply2 is a negative regulator of Mesp2 expression
As we have previously reported, the rostro-caudal polarity of the somites
is generated by the interaction between Mesp2 and the Notch signaling pathway
in the anterior PSM (Morimoto et al.,
2005). To identify the underlying cause of the rostralized
phenotype in the Ripply2-null embryo, the Mesp2 gene
expression profile was examined. During somitogenesis in the anterior PSM,
both wild-type and Ripply2+/- embryos generally showed
either a single Mesp2 expression band of variable width or no band,
depending on the cyclic expression stage
(Fig. 5I and data not shown).
However, we observed that Mesp2 is expressed in the
Ripply2-/- embryo as either one or two bands
(Fig. 5J). In other words, an
additional band was frequently observed in the more-rostral region (four out
of six examined). In addition, we did not observe any
Ripply2-/- embryos without Mesp2 expression,
suggesting either that Mesp2 expression is prolonged or that the
Mesp2 transcripts are stabilized in a Ripply2-/-
background. To distinguish these possibilities, we performed in situ
hybridization using an intron probe. Although the signal obtained was low, we
frequently detected two bands in the Ripply2-/- embryos
(Fig. 5L; in all three
examined), but only one band in the Ripply2+/- embryos
(Fig. 5K). Hence, the
transcription of Mesp2 appears to be prolonged in the absence of
Ripply2, although the possibility that differences exist in their mRNA
stability cannot yet be excluded.
We next examined how the expression of the Mesp2 protein is influenced in
the Ripply2-/- background. As we have shown previously,
Mesp2-venus can be used to visualize functional Mesp2 proteins in vivo because
the homozygous knock-in mouse is viable and shows normal somitogenesis
(Morimoto et al., 2005). In a
typical case, a single Mesp2-venus band was detectable in the area just caudal
to the next presumptive segmental border in the Ripply2+/-
background (Fig. 5M). However,
in the Ripply2-/- embryo, two broader and interconnected
bands could be discerned (Fig.
5N). These data suggest that Mesp2 is negatively
regulated by Ripply2, and that these factors form a negative-feedback loop to
restrict the levels of Mesp2.
|
Mesp2, but not Lfng, is responsible for the Notch suppression necessary for rostro-caudal patterning
In somite-stage embryos, Notch activity oscillates in the posterior PSM and
stabilizes as a clear stripe in the anterior PSM with elevated activity
(Huppert et al., 2005;
Morimoto et al., 2005). To
further understand the molecular events operating in the anterior PSM of
Ripply2-/- embryos, we first examined the expression of
Notch1 mRNA (Fig.
6A,B) and Notch1 protein (Fig.
6C,D) in these embryos. Interestingly, these expression patterns
were found to be expanded in the anterior PSM in the
Ripply2-/- embryo (Fig.
6B,D), but the Notch activity appeared to be lost as judged from
the fact that the expression of Hes5, a Notch target gene
(Ohtsuka et al., 1999), was
absent (Fig. 6E,F). To further
confirm this reduced Notch1 activity and its relationship to Mesp2 expression,
we conducted double immunostaining analysis using anti-active Notch1 and
anti-Mesp2 antibodies in both wild-type and Ripply2-/-
embryos. In the wild-type embryos, the Notch activity in the anterior PSM
exhibited a sharp boundary with Mesp2 that determines the next segmental
boundary (Fig. 6G). In
addition, the contrast between Notch activities leads to the generation of
future rostral and caudal compartments of the somites, whereby the Notch
active site becomes the future caudal compartment. In the
Ripply2-/- embryo, the Notch1 signals oscillated normally
in the posterior PSM (Fig.
6H,I). However, the elevation of Notch activity in the anterior
PSM appeared to be repressed in these null embryos, whereas the Mesp2
expression banding was found to upregulated, as shown previously
(Fig. 6H,I).
Since the expression of Lfng is under the control of Mesp2, we speculated that the suppression of Notch signaling might be the result of the prolonged activation of Lfng in the Ripply2-/- embryo. To test this possibility, we generated a Ripply2/Lfng double-knockout embryo from which we prepared skeletal specimens, and then examined the somite properties by analyzing the expression of the caudal molecular marker Uncx4.1 (Fig. 7). Intriguingly, the vertebral morphology of the Ripply2/Lfng double-knockout mouse was not recovered, and was more rostralized as compared with either the Ripply2-/- (compare Fig. 4F with Fig. 7C) or Lfng-null fetus (Fig. 7B). The expression of Uncx4.1 was also not recovered by the additional loss of Lfng (compare Fig. 5B with Fig. 7C), and was found to be completely diminished in the double-knockout embryos.
|
|
DISCUSSION |
|---|
|
TOP
SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES |
|---|
), in which
the clock genes Hes7 and Lfng are negatively regulated by
several mechanisms, including transcriptional suppression, protein degradation
and destabilization of mRNA (Bessho et al.,
2003; Chen et al.,
2005; Cole et al.,
2002; Hirata et al.,
2004; Morales et al.,
2002). In the anterior PSM, the levels of Mesp2 are strictly
regulated to achieve the periodic suppression of Notch signaling, and also to
establish the correct rostro-caudal polarity. During this activation step, the
cooperation between Tbx6 and cyclic activated Notch-signaling is crucial for
the periodic induction of Mesp2
(Yasuhiko et al., 2006)
(Fig. 8A). However, these
processes must be regulated by both activation and inhibition. Previously, we
reported that Mesp2 is regulated negatively by the proteasome pathway
(Morimoto et al., 2006). In
addition, our current study has identified Ripply2 as a potent negative
regulator of Mesp2 transcription, and as a factor that is required
for the correct establishment of rostro-caudal patterning. In the absence of
Ripply2, Mesp2 expression is maintained over a longer period and leads to the
suppression of caudal properties (Fig.
8B). It is noteworthy in this regard that Ripply2 might function
exclusively to negatively regulate Mesp2, because the phenotype of the
Ripply2-knockout mouse is almost completely reversed by the
additional loss of Mesp2. The Ripply2-null mutant exhibits not only an expansion of rostral marker genes but also a reduction in the expression of caudal markers. Immunohistochemical analysis further revealed a decrease in the activated form of Notch1 in the anterior PSM in these Ripply2-null embryos. Previously, we have shown that Mesp2 suppresses Notch signaling to establish segmental boundaries via the activation of Lfng. However, Lfng appears not to be crucial for the suppression of Notch signaling in the Ripply2-null embryo as this suppression was not rescued by the additional loss of Lfng, and, in fact, this results in a further reduction in Notch signaling activity. We speculate that this is caused by the function of Lfng during Mesp2 distribution, based upon our observations of the Mesp2-venus knock-in mouse. In the wild-type embryo, the Mesp2-venus expression pattern shows a clear gradient, being higher in the presumptive rostral compartment. However, in the absence of Lfng, such a biased gradient is not generated, and the Mesp2-venus pattern shows a diffuse distribution in this background (our unpublished data). The phenotype of the Ripply2/Lfng double-knockout mouse appears also to reflect this distribution defect. In this double-null mouse, the expression of Mesp2 is prolonged owing to the lack of Ripply2, and is distributed across a much wider area along the anterior-posterior axis because of the lack of Lfng. This in turn enhances the function of Mesp2 that suppresses Notch signaling in the anterior PSM, and results in the somites becoming completely rostralized in these double mutants.
The mechanisms underlying the suppression of Mesp2 by Ripply2 are currently
unknown. Ripply2 appears to be required for the termination of Mesp2
expression at an appropriate time. Moreover, because Ripply2 has no apparent
DNA-binding domain, it is plausible to assume that it suppresses
Mesp2 by recruiting the Groucho homolog Tle1 and/or Tle3 via the WRPW
motif, as revealed previously by in vitro assays in both zebrafish and mouse
(Kawamura et al., 2005) (data
not shown). Tle1 and Tle3 are known to be expressed in the
PSM, but their expression patterns are not segmental
(Dehni et al., 1995) (our
unpublished data), and no loss-of-function studies have yet been reported. In
the zebrafish, ripply1 morphants also display upregulation of
mespb in their somitic regions, and this is accompanied by the
upregulation of tbx24, deltaC and deltaD. This might also
account for the upregulation of mespb
(Kawamura et al., 2005). We
have previously identified a 300 bp upstream region of the Mesp2 gene
as a promoter-enhancer sequence required for the faithful expression of
Mesp2 in the anterior PSM where T-box factor binding in combination
with Notch signaling is involved in the gene activation
(Yasuhiko et al., 2006).
However, Tbx6 expression is unchanged (data not shown) and the Dll1
expression profile is somewhat decreased in the Ripply2-null embryos.
Hence, although the impact of the loss of Ripply proteins upon Mesp gene
expression appears to be similar between mouse and zebrafish, the underlying
mechanisms might well be different.
Supplementary material
Supplementary material for this article is available at
http://dev.biologists.org/cgi/content/full/134/8/1561/DC1
|
ACKNOWLEDGMENTS |
|---|
|
Footnotes |
|---|
These authors contributed equally to this work
|
REFERENCES |
|---|
|
TOP
SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES |
|---|
Bessho, Y., Sakata, R., Komatsu, S., Shiota, K., Yamada, S. and
Kageyama, R. (2001). Dynamic expression and essential
functions of Hes7 in somite segmentation. Genes Dev.
15,2642
-2647.
Bessho, Y., Hirata, H., Masamizu, Y. and Kageyama, R.
(2003). Periodic repression by the bHLH factor Hes7 is an
essential mechanism for the somite segmentation clock. Genes
Dev. 17,1451
-1456.
Bettenhausen, B., Hrabe de Angelis, M., Simon, D., Guenet, J. L.
and Gossler, A. (1995). Transient and restricted expression
during mouse embryogenesis of Dll1, a murine gene closely related to
Drosophila Delta. Development
121,2407
-2418.[Abstract]
Borycki, A. G. and Emerson, C. P., Jr (2000).
Multiple tissue interactions and signal transduction pathways control somite
myogenesis. Curr. Top. Dev. Biol.
48,165
-224.[Medline]
Brand-Saberi, B. and Christ, B. (2000).
Evolution and development of distinct cell lineages derived from somites.
Curr. Top. Dev. Biol.
48, 1-42.[Medline]
Bussen, M., Petry, M., Schuster-Gossler, K., Leitges, M.,
Gossler, A. and Kispert, A. (2004). The T-box transcription
factor Tbx18 maintains the separation of anterior and posterior somite
compartments. Genes Dev.
18,1209
-1221.
Chen, J., Kang, L. and Zhang, N. (2005).
Negative feedback loop formed by Lunatic fringe and Hes7 controls their
oscillatory expression during somitogenesis. Genesis
43,196
-204.[CrossRef][Medline]
Cole, S. E., Levorse, J. M., Tilghman, S. M. and Vogt, T. F.
(2002). Clock regulatory elements control cyclic expression of
Lunatic fringe during somitogenesis. Dev. Cell
3, 75-84.[CrossRef][Medline]
Dehni, G., Liu, Y., Husain, J. and Stifani, S.
(1995). TLE expression correlates with mouse embryonic
segmentation, neurogenesis, and epithelial determination. Mech.
Dev. 53,369
-381.[CrossRef][Medline]
Dubrulle, J. and Pourquie, O. (2004). Coupling
segmentation to axis formation. Development
131,5783
-5793.
Haraguchi, S., Kitajima, S., Takagi, A., Takeda, H., Inoue, T.
and Saga, Y. (2001). Transcriptional regulation of Mesp1 and
Mesp2 genes: differential usage of enhancers during development.
Mech. Dev. 108,59
-69.[CrossRef][Medline]
Hirata, H., Bessho, Y., Kokubu, H., Masamizu, Y., Yamada, S.,
Lewis, J. and Kageyama, R. (2004). Instability of Hes7
protein is crucial for the somite segmentation clock. Nat.
Genet. 36,750
-754.[CrossRef][Medline]
Huppert, S. S., Ilagan, M. X., De Strooper, B. and Kopan, R.
(2005). Analysis of Notch function in presomitic mesoderm
suggests a gamma-secretase-independent role for presenilins in somite
differentiation. Dev. Cell
8, 677-688.[CrossRef][Medline]
Iulianella, A., Melton, K. R. and Trainor, P. A.
(2003). Somitogenesis: breaking new boundaries.
Neuron 40,11
-14.[CrossRef][Medline]
Kanno, J., Aisaki, K., Igarashi, K., Nakatsu, N., Ono, A.,
Kodama, Y. and Nagao, T. (2006). "Per cell"
normalization method for mRNA measurement by quantitative PCR and microarrays.
BMC Genomics 7,64
.[CrossRef][Medline]
Kawamura, A., Koshida, S., Hijikata, H., Ohbayashi, A., Kondoh,
H. and Takada, S. (2005). Groucho-associated transcriptional
repressor ripply1 is required for proper transition from the presomitic
mesoderm to somites. Dev. Cell
9, 735-744.[CrossRef][Medline]
Koizumi, K., Nakajima, M., Yuasa, S., Saga, Y., Sakai, T.,
Kuriyama, T., Shirasawa, T. and Koseki, H. (2001). The role
of presenilin 1 during somite segmentation.
Development 128,1391
-1402.[Abstract]
Kraus, F., Haenig, B. and Kispert, A. (2001).
Cloning and expression analysis of the mouse T-box gene Tbx18.
Mech. Dev. 100,83
-86.[CrossRef][Medline]
Leitges, M., Neidhardt, L., Haenig, B., Herrmann, B. G. and
Kispert, A. (2000). The paired homeobox gene Uncx4.1
specifies pedicles, transverse processes and proximal ribs of the vertebral
column. Development 127,2259
-2267.[Abstract]
Monsoro-Burq, A. H. and Le Douarin, N. (2000).
Duality of molecular signaling involved in vertebral chondrogenesis.
Curr. Top. Dev. Biol.
48, 43-75.[Medline]
Morales, A. V., Yasuda, Y. and Ish-Horowicz, D.
(2002). Periodic Lunatic fringe expression is controlled during
segmentation by a cyclic transcriptional enhancer responsive to notch
signaling. Dev. Cell 3,63
-74.[CrossRef][Medline]
Morimoto, M., Takahashi, Y., Endo, M. and Saga, Y.
(2005). The Mesp2 transcription factor establishes segmental
borders by suppressing Notch activity. Nature
435,354
-359.[CrossRef][Medline]
Morimoto, M., Kiso, M., Sasaki, N. and Saga, Y.
(2006). Cooperative Mesp activity is required for normal
somitogenesis along the anterior-posterior axis. Dev.
Biol. 300,687
-698.[CrossRef][Medline]
Nakajima, Y., Morimoto, M., Takahashi, Y., Koseki, H. and Saga,
Y. (2006). Identification of Epha4 enhancer required for
segmental expression and the regulation by Mesp2.
Development 133,2517
-2525.
Nomura-Kitabayashi, A., Takahashi, Y., Kitajima, S., Inoue, T.,
Takeda, H. and Saga, Y. (2002). Hypomorphic Mesp allele
distinguishes establishment of rostrocaudal polarity and segment border
formation in somitogenesis. Development
129,2473
-2481.
Ohtsuka, T., Ishibashi, M., Gradwohl, G., Nakanishi, S.,
Guillemot, F. and Kageyama, R. (1999). Hes1 and Hes5 as notch
effectors in mammalian neuronal differentiation. EMBO
J. 18,2196
-2207.[CrossRef][Medline]
Pourquie, O. (2003). The segmentation clock:
converting embryonic time into spatial pattern.
Science 301,328
-330.
Rida, P. C., Le Minh, N. and Jiang, Y. J.
(2004). A Notch feeling of somite segmentation and beyond.
Dev. Biol. 265,2
-22.[CrossRef][Medline]
Saga, Y. and Takeda, H. (2001). The making of
the somite: molecular events in vertebrate segmentation. Nat. Rev.
Genet. 2,835
-845.[CrossRef][Medline]
Saga, Y., Hata, N., Koseki, H. and Taketo, M. M.
(1997). Mesp2: a novel mouse gene expressed in the presegmented
mesoderm and essential for segmentation initiation. Genes
Dev. 11,1827
-1839.
Sakai, K. and Miyazaki, J. (1997). A transgenic
mouse line that retains Cre recombinase activity in mature oocytes
irrespective of the cre transgene transmission. Biochem. Biophys.
Res. Commun. 237,318
-324.[CrossRef][Medline]
Takahashi, Y., Koizumi, K., Takagi, A., Kitajima, S., Inoue, T.,
Koseki, H. and Saga, Y. (2000). Mesp2 initiates somite
segmentation through the Notch signalling pathway. Nat.
Genet. 25,390
-396.[CrossRef][Medline]
Takahashi, Y., Inoue, T., Gossler, A. and Saga, Y.
(2003). Feedback loops comprising Dll1, Dll3 and Mesp2, and
differential involvement of Psen1 are essential for rostrocaudal patterning of
somites. Development
130,4259
-4268.
Yagi, T., Tokunaga, T., Furuta, Y., Nada, S., Yoshida, M.,
Tsukada, T., Saga, Y., Takeda, N., Ikawa, Y. and Aizawa, S.
(1993). A novel ES cell line, TT2, with high
germline-differentiating potency. Anal. Biochem.
214, 70-76.[CrossRef][Medline]
Yasuhiko, Y., Haraguchi, S., Kitajima, S., Takahashi, Y., Kanno,
J. and Saga, Y. (2006). Tbx6-mediated Notch signaling
controls somite-specific Mesp2 expression. Proc. Natl. Acad. Sci.
USA 103,3651
-3656.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati 
Twitter What's this?
Related articles in Development:
This article has been cited by other articles:
|
|
 |
|
  J. Feller, A. Schneider, K. Schuster-Gossler, and A. Gossler Noncyclic Notch activity in the presomitic mesoderm demonstrates uncoupling of somite compartmentalization and boundary formation Genes & Dev., August 15, 2008; 22(16): 2166 - 2171. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Oginuma, Y. Niwa, D. L. Chapman, and Y. Saga Mesp2 and Tbx6 cooperatively create periodic patterns coupled with the clock machinery during mouse somitogenesis Development, August 1, 2008; 135(15): 2555 - 2562. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. C. Dunty Jr, K. K. Biris, R. B. Chalamalasetty, M. M. Taketo, M. Lewandoski, and T. P. Yamaguchi Wnt3a/ -catenin signaling controls posterior body development by coordinating mesoderm formation and segmentation Development, January 1, 2008; 135(1): 85 - 94. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
