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RESEARCH INTERESTS
Chromosome organization and function in Drosophila melanogaster
The overall interest of our lab is to understand the relationship between chromosome structure and function. The chromosomes of most eukaryotes exhibit three prominent structural features: the ends of each linear chromosome, called telomeres; the division into broad domains of euchromatin and heterochromatin; and, the primary constriction, or centromere. We are primarily interested in functional aspects of telomeres and heterochromatin. Our studies are carried out using the model organism, Drosophila melanogaster. The multitude of genetic, molecular and cytological tools that have been developed for Drosophila make it an ideal choice.
Telomeres carry out the specialized function of allowing a cell to discriminate a natural chromosome end from chromosome damage in the form of a DNA double strand break (DSB). The variety of responses that cells exhibit to telomere loss, e.g. cell cycle arrest, cell death, and end-to-end chromosome fusion, can reasonably be thought of as the consequences of seeing a chromosome end as an irreparable DSB.
We developed a method for producing a single non-telomeric end in developing Drosophila. Cells of the fly exhibit two distinctly different, tissue-specific responses to this controlled telomere loss. Somatic cells undergo a cell cycle arrest that can last for several days, followed by apoptosis, similar to the response of mammalian somatic cells to telomere shortening. However, in the Drosophila germline, cells very efficiently construct a new telomere on the non-telomeric chromosome end. Telomeric DNA is not added during this process, but the components that hide the end and prevent the cell from seeing it as a DSB are assembled on the new end. Our current interests are to understand the differential regulation of the somatic and germline responses to telomere loss, and to identify components of the Drosophila telomere in order to understand how the fly builds telomeres de novo.
Our second major area of interest is to understand the function and regulation of heterochromatin. The Y chromosome of Drosophila is entirely heterochromatic. It does not determine sex, but is needed for male fertility. We have discovered that a distinctive and general feature of the Y chromosome is that it is subject to genomic imprinting. This is apparent by observing the expression of transgenic reporters inserted on the Y. These reporter genes generally show reduced expression when the Y chromosome is transmitted paternally, rather than maternally. We are carrying out genetic screens and using a candidate gene approach to identify the genes that mediate this differential chromosomal imprint.
A third aspect of our research is the continued development and refinement of methods for gene targeting by homologous recombination in Drosophila. This
technique adds to the arsenal of tools that can be brought to bear to understand
chromosome structure and function. In addition to carrying out classical
phenotype-directed screens to identify the components of a particular biological process, we can now examine the contribution of genes that are initially identified only by genomic sequencing. Gene targeting is used to generate the animals that carry mutations in these genes. Moreover, as a part of this work, tools to generate controlled DSBs in the genome have been developed, and they provide a useful complement to the telomere studies.
Representative publications:
Ahmad, Kami and Kent G. Golic, 1999 Telomere loss in somatic cells of Drosophila causes cell cycle arrest and apoptosis. Genetics 151: 1041-1051
Rong, Yikang S. and Kent G. Golic, 2000 Gene targeting by homologous recombination in Drosophila. Science 288: 2013-2018
Rong, Y. S., S. Titen, H. B. Xie, M. M. Golic, M. Bastiani, P. Bandyopadhyay, B. M. Olivera, M. Brodsky, G. M. Rubin and K. G. Golic, 2002 Targeted mutagenesis by homologous recombination in Drosophila melanogaster. Genes and Development 16: 1568-1581
Maggert, K. A. and K. G. Golic, 2002 The Y chromosome of Drosophila melanogaster exhibits chromosome-wide imprinting. Genetics 162: 1245-1258
Gong, W. and K. G. Golic, 2003 Ends-out, or replacement, gene targeting in Drosophila. Proc. Natl. Acad. Sci. USA 100: 2556-2561
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