Faculty Bibliography

The notochord and dorsal ectoderm induce dorsoventral compartmentalization of the vertebrate neural tube through the differential regulation of genes such as HNF-3beta, Pax3, Pax6 and snail. Here we analyze the expression of HNF-3beta and snail homologues in the ascidian, Ciona intestinalis, a member of the subphylum Urochordata, the earliest branch in the chordate phylum. A combination of in situ hybridization and promoter fusion analyses was used to demonstrate that the Ciona HNF-3beta homologue is expressed in the ventralmost ependymal cells of the neural tube, while the Ciona snail homologue is expressed at the junction between the invaginating neuroepithelium and dorsal ectoderm, similar to the patterns seen in vertebrates. These findings provide evidence that dorsoventral compartmentalization of the chordate neural tube is not an innovation of the vertebrates. We propose that precursors of the floor plate and neural crest were present in a common ancestor of both vertebrates and ascidians.

A 2935-bp cDNA clone encoding glutamine synthetase (GS) was isolated from a cDNA library prepared from four-blastomere Paracentrotus lividus sea urchin embryos. The sequence consists of a 75-bp 5' untranslated region (5'-UTR) followed by a 1095-bp coding region corresponding to a 365-amino-acid (aa) protein, a 1747-bp 3'-UTR and a terminal 18-bp poly(A) tail. The encoded protein shows about 66% identical residues, as compared with human and lobster class-II GS. The sequence contains the Mn(2+)-binding aa and the highly conserved aa regions observed in other GS. Northern blot analyses show that the GS mRNA is present in the sea urchin egg and is developmentally regulated in the embryo.

In order to isolate genes important in controlling embryonic development in Tunicates, a genomic library from the ascidian Ciona intestinalis was screened with a degenerate oligodeoxyribonucleotide encoding the third helix of Antennapedia-type homeoboxes. Fourteen C. intestinalis homeobox genes, corresponding to several classes of homeodomains, have been identified. Five of the isolated homeoboxes show their highest homology to members of the Vertebrate HOX clusters. mRNAs for two of the isolated homeoboxes are present in unfertilized C. intestinalis eggs.