Expression studies on homeobox and bmp homologues in echinoderm neuronal regeneration. neuroscience

Recent years have seen an expansion of interest in the use of echinoderms as models for the study of gene expression in development. In particular, emphasis has been placed on patterning genes and their role in the determination cell lineage and fate. In our laboratory, we have focussed on the remarkable powers of regeneration exhibited by this invertebrate phylum with close phylogenetic links to chordates. Our investigations have involved cloning a BMP2/4 homologue from crinoids (AnBMP2/4) and the identification of a number of homeobox homologues in asteroids. In situ hybridisation indicates an important role for AnBMP2/4 during the early stages of blastemal regeneration at a time when fundamental patterns are being established. AnBMP2/4 expression was first detected in cells from the coelomic epithelium, and subsequently in coelomocytes of the regenerating blastema. To date, the function of BMP2/4 found in other system, as well as AnBMP2/4, as a neural inhibitor or an epidermal inducer is under investigation. However, this expression in an adult system shows similarities with recent studies in sea urchin embryos where a BMP2/4 homologue is involved in the regulation of the ectoderm/endoderm boundary and epidermal/non epidermal fate decisions. In asteroids we have cloned a number of Hox genes including homologues of Hox1, Hox4/5, SpHbox1/TgHbox1, Hox9/10, Gbx and, uniquely a Mox homologue. These have all been identified by RT-PCR in cDNAs prepared from regenerating radial nerve cord (RNC) at days post ablation (pa). Immunocytochemistry using an antibody against the product of Hox1 homologue has revealed its expression pattern during neural regeneration, particularly at day 10, in Asterias rubens.