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First published online 30 January 2008
doi: 10.1242/dev.006742
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Department of Molecular Genetics, The Ohio State University, 984 Biological Sciences Building, 484 West 12th Avenue, Columbus, OH 43210-1292, USA.
Author for correspondence (e-mail:
cole.354{at}osu.edu)
Accepted 20 December 2007
The Notch pathway plays multiple roles during vertebrate somitogenesis,
functioning in the segmentation clock and during rostral/caudal (R/C) somite
patterning. Lunatic fringe (Lfng) encodes a glycosyltransferase that
modulates Notch signaling, and its expression patterns suggest roles in both
of these processes. To dissect the roles played by Lfng during
somitogenesis, a novel allele was established that lacks cyclic Lfng
expression within the segmentation clock, but that maintains expression during
R/C somite patterning (Lfng
FCE1). In the absence of
oscillatory Lfng expression, Notch activation is ubiquitous in the
PSM of Lfng
FCE1 embryos.
Lfng
FCE1 mice exhibit severe segmentation
phenotypes in the thoracic and lumbar skeleton. However, the sacral and tail
vertebrae are only minimally affected in Lfng
FCE1
mice, suggesting that oscillatory Lfng expression and cyclic Notch
activation are important in the segmentation of the thoracic and lumbar axial
skeleton (primary body formation), but are largely dispensable for the
development of sacral and tail vertebrae (secondary body formation).
Furthermore, we find that the loss of cyclic Lfng has distinct
effects on the expression of other clock genes during these two stages of
development. Finally, we find that Lfng
FCE1 embryos
undergo relatively normal R/C somite patterning, confirming that Lfng
roles in the segmentation clock are distinct from its functions in somite
patterning. These results suggest that the segmentation clock may employ
varied regulatory mechanisms during distinct stages of anterior/posterior axis
development, and uncover previously unappreciated connections between the
segmentation clock, and the processes of primary and secondary body
formation.
Key words: Lunatic fringe, Notch, Segmentation clock, Somitogenesis, Secondary body formation, Mouse
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