The general aim of this project is to identify, characterize and elucidate the function of protein factors that regulate gene expression in vertebrate embryos. This is being approached in several ways. One strategy has been to identify transcription factors that activate specific genes in the early embryo. Initially, the focus of this approach was an epidermal keratin gene, XK81A1, expressed in the Xenopus laevis embryo. Analysis of cis-regulatory elements in this gene lead to the discovery that a Xenopus homolog of a mammalian transcription factor, AP-2 (XAP-2) plays an important role in keratin regulation, and is probably involved in other aspects of epidermal differentiation, both in frogs and in mammals. This work has continued, and is currently aimed at the regulation of the XAP-2 gene, itself a marker for early ectoderm. A parallel project is aimed at the regulation of XDll2, an epidermis-specific homeodomain gene. The cis-regulatory DNA for this gene has been mapped to about 900 bp of 5' flanking sequence. This element drives epidermis-specific expression in both Xenopus embryos and in primary murine keratinocytes induced to differentiate in vitro. A second strategy is directed at signal transduction mechanisms in cranial neural crest, a tissue induced to differentiate into a variety of cell types critical in formation of the vertebrate head. PCR-based techniques have been used to clone neural crest-derived cDNAs encoding protein kinases, a number of which have been obtained, falling into several categories. Most attention has been directed at a receptor tyrosine kinase in the Eph family, christened Pagliaccio (Pag), which is expressed in a localized pattern in brain and head structures. The PCR has also been used to clone members of the cadherin family of cell-cell adhesion molecules from embryonic neural tube of the zebrafish (Brachydanio rerio). Cadherins are thought to play a role in neural crest migration and differentiation. This hypothesis will be tested by engineering transgenic fish in which the expression of specific cadherins can be experimentally altered.
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