|M.Sc Student||Cohen Lior|
|Subject||Identifying the Chromosomal Binding Sites of the Homeotic|
Cofactor Homothorax (HTH)
|Department||Department of Medicine||Supervisor||Professor Adi Salzberg|
The homothorax (hth) gene is involved in multiple developmental processes in the fruit fly, Drosophila melanogaster. It encodes for a homeodomain containing protein of the MEIS family and was shown to regulate the nuclear localization of the homeotic cofactor Extradenticle (EXD). HTH was shown to bind DNA in vitro as a part of ternary HTH/EXD/HOX complexes and was shown to be required for activating the transcription of downstream target genes. Despite extensive research describing the great biological importance of HTH, little is known about the number and nature of its target genes. To identify direct target genes of HTH, we have performed a comparative microarray analysis and mapped the chromosomal binding sites of HTH on polytene chromosomes. Combining the two approaches was designed to help us identify direct downstream targets of HTH and avoid 'false positive' genes whose expression is affected by HTH indirectly. One hundred thirteen of approximately 150 chromosomal binding sites of HTH were mapped to specific cytological intervals: 25 sites on chromosome X, 15 sites on the left arm of chromosome 2 (2L), 21 sites on 2R, 26 sites on 3L and 26 sites on 3R. The microarray analysis revealed 371 genes whose expression was elevated significantly when a chimeric transcriptional-activating form of HTH was expressed ubiquitously in embryos. Sixty of these genes were up-regulated at least 2.8 fold and were further examined. Thirty eight of these 60 genes are located in the vicinity of one of the HTH binding sites and have therefore been considered as potential direct targets of HTH.