Vertebrate homologues of the Drosophila melanogaster gene prospero have been
identified in many species. Whilst the function and regulation of prospero has been
well studied in Drosophila the function and regulation of the homologous vertebrate
gene, praxl, is not known.
We describe the identification of the prox genes as members of a multigene family in
vertebrates through the isolation of new members of the Prox gene family in
zebrafish, Fugu rubripes, Tetraodon nigroviridis, mouse, and human. We examined
the phylogeny of this new multigene family and we characterised the expression of
these novel genes in zebrafish.
Analysis of the expression of these genes identified the slow muscle as site of
expression for prox 1 that did not overlap with the novel zebrafish Prox genes.
Therefore, we studied the function ofprox 1 in the slow muscle using a combination
of DNA, and morpholino injections. We demonstrate that prox 1 in not required for
the specification of slow muscle as determined by the expression of markers of
terminal differentiation. We also show that the medial lateral migration of the slow
muscle is unaffected by the loss of prox 1. However, ectopic expression of prox 1
specifically in the fast muscle causes a defect in nuclear patterning. In normal
development the fast muscle cells fuse early to form a multinucleate syncytium. The
nuclei in this syncytium are normally evenly spaced. Ectopic expression of prox 1
resulted in the nuclei of the fast cells being positioned at the centre of the syncytium
similarly to the situation observed in the mononucleate slow muscle. Furthermore
loss of Prox 1 results in the disrupted patterning of the slow fibres, demonstrating a
role for Prox 1 in the patterning of the slow muscle fibres.
An understanding of the 3-dimensional (3D) pattern of gene expression can often
lead to a better understanding of gene function. Optical projection tomography
(OPT) is a new method for obtaining 3D data about an object. OPT generates a 3D
digital model of a sample and allows it to be virtually sectioned, or rendered to
produce a 3D image. OPT was developed for use on mouse embryos and had not
been tested with zebrafish. We describe the difficulties of using OPT on samples as
small as zebrafish embryos and the development of techniques to overcome these
problems and allow its use in zebrafish.