| Popis: |
This thesis describes work that arose from studies of the imprinting of GNAS1, on human chromosome 20q13. Null mutations in GNAS1 cause the hormone-resistance syndrome pseudohpoparathyroidism type 1a (PHP1a). It was demonstrated that GNAS1 is imprinted, as predicted from the anomalous inheritance of PHP1a, but that its allele-specific regulation is highly complex. This gene is shown to encode several protein products: (i) the alpha subunit of the stimulatory G protein Gs; this protein is biallelically derived; (ii) NESP55, a neuroendocrine secretory protein, expressed exclusively from the maternal allele; (iii) XLas, a Golgi-specific G protein that is expressed exclusively from the paternal allele. Many known imprinted genes lie in clusters that may span several hundred of kb, and may be co-ordinately regulated by a imprinting control region. To assess whether GNAS1 is part of such an imprinted gene cluster, genomic clones were analysed for the presence of other nearby transcripts. This resulted in the identification of two novel genes, CTSZ and CGI107, as well as a number of putative transcripts that lie within GNASl. One of the latter forms part of a spliced polyadenylated antisense transcript that spans the upstream region of NESP55. The CTSZ gene was shown to comprise 6 exons and 5 introns, spanning ~ 12 kb. It encodes cathepsin Z, a cysteine protease whose precise function is undefined. The CG1107 gene was shown to comprise 6 exons and 5 introns, spanning ~ 10 kb, encoding 194 amino acid protein of unknown function, but showing sequence similarity to the kisir protein in Drosophila. Four chromosomally dispersed processed pseudogenes of CG1107 were identified. Together with the biallelic expression of another neighbouring gene TH1, these results suggest the possibility that GNAS1 may not after all be part of an extensive cluster of imprinted genes. This has implications for further studies of the mechanism of imprinting control in this region. |
