Stage11 chick embryo showing somites and unsegmented PSM. Posterior to the left

Vertebrate Segmentation

As vertebrate embryos elongate posteriorly, a succession of equal-sized mesodermal segments – somites – are generated at the anterior of an unsegmented precursor domain, the presomitic mesoderm (PSM). Repeated formation of intersomitic boundaries is driven by a molecular oscillator (segmentation clock) which drives cyclic transcription of a variety of genes in a series of pulses whose periodicity corresponds to that of somitogenesis (Palmeirim et al., 1997)

We have shown that periodic accumulation of cycling transcripts is due to pulsed initiation of transcription, and that a relatively small region of the mouse lunatic fringe promoter is sufficient to drive cyclic transcription in the PSM of transgenic embryos. The equivalent region of the human lunatic fringe promoter behaves similarly. More detailed analysis of this clock element has led to a working model that its cycling is driven by oscillatory Notch signalling (Morales et al , 2002). However, it has also been suggested that cyclic Wnt signalling underlies the primary segmentation clock and regulates periodic Notch activation.

Mouse embryos at the same developmental stage exhibit dynamic expression of lunatic fringe transcripts in the presomitic mesoderm. (Posterior is downwards.)

Current research interests:

1. Defining the molecular nature of the segmentation clock, in particular, the relative roles of Notch and Wnt signalling in driving oscillations. We are using transgenic mice to manipulate the synthesis of putative clock components in order to alter clock periodicity and define components that define the primary, rate-limiting oscillator.
2. Defining functional requirements for lunatic fringe in driving the clock and in somite boundary formation
3. Defining conserved regulatory elements that drive periodic transcription in order to identify factors that recognise these motifs and through which the segmentation clock should work.
4. Functional analysis of genes expressed and active during segmentation. Amongst the techiques we use are transgenic mice, gene transfer in chicken embryos, and injection into zebrafish embryos.
5. Investigating the basis of axial growth of the embryo, in particular, by molecular characterisation of the axial stem cells via single-cell transcriptional profiling and of signals from surrounding cells required for stem cell specification and maintenance.

Techniques

Gene transfer in chicken embryos; Mouse transgenics; In situ hybridisation; Injection into zebrafish embryos; Cell culture.

Lab members: Michael Stauber, Sheena Pinchin, Charalampos (Babis) Rallis, Christina Morgenstern, Christian Dillon, Krzysztof Wicher