Avian hairy Gene Expression Identifies a Molecular Clock Linked to Vertebrate Segmentation and Somitogenesis

Abstract

We have identified and characterized c-hairy1, an avian homolog of the Drosophila segmentation gene, hairy. c-hairy1 is strongly expressed in the presomitic mesoderm, where its mRNA exhibits cyclic waves of expression whose temporal periodicity corresponds to the formation time of one somite (90 min). The apparent movement of these waves is due to coordinated pulses of c-hairy1 expression, not to cell displacement along the anteroposterior axis, nor to propagation of an activating signal. Rather, the rhythmic c-hairy mRNA expression is an autonomous property of the paraxial mesoderm. These results provide molecular evidence for a developmental clock linked to segmentation and somitogenesis of the paraxial mesoderm, and support the possibility that segmentation mechanisms used by invertebrates and vertebrates have been conserved.

From segment to somite: Segmentation to epithelialization analyzed within quantitative frameworks

“…This represents a rapid change of state, such as the changes in adhesive and migratory behavior of PSM cells as they form somites. Support for the existence of a segmentation clock came from the discovery that several genes exhibit periodic expression along the PSM, with cycling times equal to the time taken to form one new pair of somites (Palmeirim et al, 1997;Pourquie, 2001Pourquie, , 2003. For example, during the formation of one somite, bands of chairy 1 and lunatic fringe expression sweep along the PSM, coming to rest within the newly forming somite.…”

Induction and patterning of the primitive streak, an organizing center of gastrulation in the amniote

“…It would also be an interesting hypothesis that the Wnt8c and nodal expression domain may reflect the first gastrulation movements of the endoderm. However, gene expression is often dynamic during embryogenesis (Palmeirim et al, 1997) and does not necessarily serve as a marker for a particular cell lineage or fate (Fig. 5).…”

Groucho proteins: transcriptional corepressors for specific subsets of DNA-binding transcription factors in vertebrates and invertebrates

“…In vertebrates, family members have been shown to be involved in neurogenesis and somite formation (Kageyama and Nakanishi 1997;Palmeirim et al 1997). Additionally, members of this family such as the Drosophila Enhancer of split genes and certain mammalian Hairy/Enhancer of s គplit (HES) genes are important effectors of the Notch signaling pathway, which controls neuronal cell fate decisions in both vertebrates and Drosophila (Kageyama and Nakanishi 1997;Robey 1997;Fisher and Caudy 1998).…”