Abstract
ABSTRACTThe conserved multi-protein MuvB core associates with the Myb oncoproteins and with the RB-E2F-DP tumor suppressor proteins in complexes that regulate cell proliferation, differentiation, and apoptosis. Drosophila Mip120, a homolog of LIN54, is a sequence-specific DNA-binding protein within the MuvB core. A mutant of Drosophila mip120 was previously shown to cause female and male sterility. We now show that Mip120 regulates two different aspects of oogenesis. First, in the absence of the Mip120 protein, egg chambers arrest during the transition from stage 7 to 8 with a failure of the normal program of chromosomal dynamics in the ovarian nurse cells. Specifically, the decondensation, disassembly and dispersion of the endoreplicated polytene chromosomes fail to occur without Mip120. The conserved carboxy-terminal DNA-binding and protein-protein interaction domains of Mip120 are necessary but not sufficient for this process. Second, we show that a lack of Mip120 causes a dramatic increase in the expression of benign gonial cell neoplasm (bgcn), a gene that is normally expressed in only a small number of cells within the ovary including the germline stem cells.
Highlights
Three different avenues of research led to the discovery and initial characterization of the Mip120 and LIN54 family of proteins—biochemistry, genetics in model organisms, and bioinformatics
The Mip120 protein was first identified in Drosophila as a component of a multi-protein complex that bound to the origin of DNA replication within a chorion locus that undergoes developmentally programmed gene amplification in ovarian follicle cells during oogenesis (Beall et al, 2002)
Loss of Mip120 causes an arrest of oogenesis during the transition between stages 7 and 8: We began our investigation of the role of Mip120 in oogenesis by obtaining the only reported mutant allele of mip120, which was kindly provided by the laboratory of Michael Botchan (UC Berkeley)
Summary
Three different avenues of research led to the discovery and initial characterization of the Mip120 and LIN54 family of proteins—biochemistry, genetics in model organisms, and bioinformatics. The Mip120 protein was first identified in Drosophila as a component of a multi-protein complex that bound to the origin of DNA replication within a chorion locus that undergoes developmentally programmed gene amplification in ovarian follicle cells during oogenesis (Beall et al, 2002). This complex contained the dMyb oncoprotein, the p55 CAF1 histone chaperone, and three novel Myb-interacting proteins that were named based on their relative molecular weights in kilodaltons—Mip130, Mip120, and Mip (Figure 1, MMC). The proteins present in this complex except for dMyb later became known as the MuvB core, because of their homology to proteins encoded by synMuvB group genes in C. elegans (Lipsick, 2004)
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