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Analysis of gene trapped embryonic stem cells and characterization of Hox gene expression pattern in additional sex combs like-1 (ASXL1) mutants Lee, Chun Lam Iris


Cells differentiate into different cell types through the development process. To maintain cell identity, trithorax and Polycomb proteins, which are responsible for the active state and silent state respectively, play an important role by maintaining the gene expression pattern of a mother cell during cell division, so the gene expression pattern can be passed on to its daughter cell. To date, many of these Polycomb group proteins have been identified in Drosophila. We look at a member of Enhancer of trithorax and Polycomb (ETP), called the Additional sex combs (Asx) protein because it is necessary for repression and activation maintenance functions in Drosophila. No ETP has been molecularly characterized. Our lab is studying the mammalian homologs of Asx in mice, called (Additional sex combs-like) Asxl1, Asxl2, and Asxl3. We have successfully created Asxl1 mutant mice using homologous recombination by Cynthia Fisher, our former PhD student. 1) Using a gene trapped ES cell line, we would like to create another mutant mice, Asxl2, by gene trapped method. The characterization of ES cell line shows that this cell line is not ideal to make chimera mice because it has double integration. This will be difficult for future molecular analysis. 2) I also would like to characterize the expression pattern of Hox genes of Asxl1 embryos by mRNA in-situ hybridization since homeotic transformations are observed in these mutants. The analysis of Hox genes in Asxl1 mutant shows that all three HOX genes I examined, Hox a4, a7, and c8, show anterior shift of the anterior boundaries; Hox c8 in the head region is suppressed in Asxl1 mutants. My results provide evidence that homeotic transformation in Asxl1 mutants is due to mis-expression of Hox genes. Results also support that Asxl1 is a true ETP because the mutants show both derepression and repression of Hox genes expression.

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