Robert Grainger, W. L. Lyons Brown Professor of Biology at the University of Virginia, uses NCRR support to develop genomic and genetic resources for Xenopus tropicalis, the western clawed frog of Africa. "Combining the new genomic and genetic tools with the power that frogs provide for studying early embryonic development should create a golden future for the X. tropicalis model," Grainger says. He views X. tropicalis as a much-needed complement to a related research frog, X. laevis, whose value is limited by its complex genome and long generation times.

Grainger and colleagues have so far created about 100 different genetically altered lines of X. tropicalis for use in studies of development. They manipulate the genomes of these frogs with a technique called transgenesis, or gene transfer, using parts of genes known as control or regulatory elements. These elements control gene expression-the degree to which a gene's protein product gets produced within the cell-by either promoting or repressing the transcription of the gene's DNA sequence into messenger RNA (mRNA).

The scientists first take a regulatory element that promotes the expression of some particular gene of interest. They then hook up this promoter sequence with a reporter gene-a gene that produces an easily detectable protein product such as green fluorescent protein. When this transgenic construct is introduced into frog embryos, the result is embryos whose tissues light up with the reporter-gene product whenever and wherever the original gene of interest is expressed in the developing frog. Simultaneous development of different tissues can be visualized by combining specific promoters with reporter genes that produce differently colored proteins.

Grainger also uses transgenes to interfere with the normal expression of a gene. One experiment introduced mutations to block expression of the gene Otx2, important for brain formation. This led to a form of blindness similar to an inherited human form of blindness known as coloboma. Grainger also is randomly introducing mutations in genes to see which ones produce developmental abnormalities and is then mapping and identifying the genes responsible.



Posted by: Kelly    Source