Our laboratory is interested in the regulatory strategies that determine the entry of a mesodermal cell into the myogenic programme. We use the mouse embryo as a model and focus on Pax3 (with its paralogue Pax7) and Myf5 which play a key upstream role in the formation of skeletal muscle. In the case of Pax3 we have created a number of gain of function and loss of function alleles which give new insight into its role. These mutants carry nlacZ or GFP markers which makes it possible to follow and isolate by FACS the cells which express the gene. Using this approach with the different mutants, we are looking for Pax3 targets.

We are also looking at the signalling molecules which control Pax3 expression (collaboration with G. Cossu). Pax3 is present in presomitic mesoderm prior to segmentation ; the nature of the cells which express it and its potential function in these cells represent another collaborative project within the network (with I. Palmeirin). In the case of the Myf5 gene we have devoted efforts to understanding its regulation. The locus is complicated with the presence of a second myogenic gene, Mrf4, which has a distinct expression pattern. We have isolated a number of key regulatory sequences lying 5’ to these genes and are currently studying their control. They reveal the range of spatiotemporal controls exerted on this myogenic determination gene at different sites where skeletal muscle will form during embryogenesis.

Part of the challenge is to understand how this is effected. Sonic hedgehog has been implicated in the regulation of Myf5 and analysis of a number of transgenes carrying different Myf5 regulatory elements on a Gli2/Gli3 mutant background will be carried out in collaboration with A.-G. Borycki. Another collaboration within the network (with M. Hargrave in Ph. Ingham’s laboratory) focusses on the prdm1 gene in the mouse, encoding the zinc finger factor Blimp1, which lies downtream in the Hedgehog regulatory cascade and which has interesting effects on skeletal myogenesis, as indicated by the U-boot mutation in zebrafish. Stéphane Vincent in our laboratory who is also working on Myf5 regulation, mutated the prdm1 gene when he was a postdoc in E. Robertson’s laboratory. The aim in this project is to examine the expression and role of the gene during mouse myogenesis.