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Characterization and functional analyses of Sox gene fish-hook in Drosophila embryonic development
Multicellular organisms develop from a single cell. The developmental program takes a fertilized egg through cell division, differentiation and morphogensis, to produce the adult. These processes are controlled by the genes present in the fertilized egg. Therefore, transcriptional regulation of these genes plays an essential role in development. Studying the functional mechanisms of transcriptional regulators will gain key insights into the complex processes of development. Transcriptional regulators that control the pattern of gene expression in the developing embryo are essential for the development of a symmetric body. One such gene is fish-hook (fish). Observations of fish mutant embryos indicate Fish has important functions in embryonic segmentation and CNS development (Nambu and Nambu 1996; Russell et al., 1996). The sequencing analyses indicated that fish encodes a Droosphila high mobility group (HMG) Sox protein. Fish protein has a single HMG domain, which shares over 50% identity with other Sox proteins' HMG domains. Sox protein's HMG domain can bind to the consensus DNA sequences and induce strong DNA bending. Some of the Sox proteins have transcriptional activation capability. To reveal Fish functions during Drosophila embryonic development, genetic and molecular approaches were used to (1) characterize Fish protein, including studying the Fish protein expression pattern during embryonic development, its' DNA binding and bending properties, and its transcriptional activation capability; and (2) uncover the gene regulatory functions of Fish in Drosophila embryonic segmentation and CNS midline development. Characterization of Fish protein revealed that Fish protein is initially expressed in a 7 stripe pattern during early blastoderm, which is rapidly replaced by strong neuroectoderm expression. Fish HMG domain, like other Sox protein's HMG domains, can bind to the vertebrate Sox protein consensus DNA binding sequences, AACAAT and AACAAAG, and this binding induces an 85 degree DNA bend. In addition, the NH2-terminal portion of Fish protein has the transcription activation capability (Ma et al., 1998). Gene regulatory functions of Fish were first investigated in embryonic segmentation. Fish directly regulates the expression of the pair rule gene, even-skipped (eve), by binding to multiple sites located in eve downstream regulatory regions that direct formation of eve stripes 1, 4, 5, and 6. Genetic interactions between fish and pdm mutants suggest that Fish may function along with the Drosophila POU domain proteins Pdm1 and Pdm2 to regulate eve transcription (Ma et al., 1998). Studies of Fish functions in embryonic CNS midline development indicated that Fish and Drifter, a POU domain protein, function along with the PAS domain protein Single-minded (Sim) to control CNS midline development and gene expression. Fish, Drifter and Sim are co-expressed in the developing midline cells. Genetic analyses indicate that fish, drifter and sim synergistically regulate CNS midline development and slit midline expression. Both Fish and Drifter interact with the slit 1.0 kb enhancer element, which contains a CNS Midline Element (CME), the Sim binding site. Fish can directly associate with Drifter and Sim proteins. Further more, these three proteins can form a ternary complex. The direct associations between the Sox protein Sox2 and the PAS domain protein Trh or the POU domain protein Oct3 were also detected, and this indicates the interactions between Sox/POU and Sox/PAS proteins are conserved. These conserved interactions may reveal novel gene regulatory mechanisms that involve these three distinct classes of transcription factors.
Ma, Yue, "Characterization and functional analyses of Sox gene fish-hook in Drosophila embryonic development" (2000). Doctoral Dissertations Available from Proquest. AAI9978523.