Dr. Jamrich has been working on embryonic pattern formation for several years and his group has discovered and characterized a number of developmental control genes that have a critical importance for normal vertebrate development. Most recently we have described the identification of a novel Xenopus homeobox gene PV.1, which is capable of mediating induction of ventral mesoderm. PV.1 is expressed in the ventral marginal zone zone of blastulae and later in the posterior ventral area of gastrulae and neurulae. PV.1 is inducible in uncommitted ectoderm by the ventralizing growth factor BMP4 and counteracts the dorsalizing effects of the dominant negative BMP4 receptor. Over-expression of PV.1 yields ventralized tadpoles. In animal caps, PV.1 ventralizes induction by activin and inhibits expression of dorsal specific genes. These observation suggest that PV.1 is a critical component in the formation of ventral mesoderm and possibly mediates the effects of BMP4.In addition, Dr. Jamrich's laboratory isolated a novel homeobox gene, Rx1 (for Retinal homeobox), which is the earliest specific marker of retinal development in Xenopus laevis. Rx1 is first expressed in the future anterior neural plate of late gastrulae in the region of presumptive retinal precursor cells. During early retinal morphogenesis, Rx1 becomes restricted to the multipotent retinal stem cells comprising the ciliary margin. Overexpression of Rx1 in Xenopus embryos results in the formation of ectopic retinal pigment epithelium (RPE) and the duplication of the retina. The expression pattern and the functional characteristics of the Rx1 gene product suggest that Rx1 has a crucial role in determination of the vertebrate eye. The importance of this gene for eye development is further underscored by the fact that the Drosophila homologue of this gene is also expressed in the eye primordia.
