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Multiplicity of functions for the otu gene products during Drosophila oogenesis
1Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208.
Abstract:
The ovarian tumor gene behaves as if it encodes a product (OGP), which is required during several early steps in the transformation of oogonia into functional oocytes. Seventeen ethyl methane sulfonate-induced mutations have been studied, and their mutant phenotypes can be explained as graded responses by individual germ cells to different levels of OGP synthesized by the mutant germ cells themselves. The lowest and highest levels of OGP appear to be produced by otu10 and otu14, respectively. The 15 mutants with intermediate OGP levels are temperature sensitive; subnormal temperatures improve ovarian development, while above-normal temperatures suppress it. A subgroup of these mutants are unable to form a system of actin microfilament bundles in the cortical cytoplasm of their nurse cells during stage 10B, and these defective nurse cells are unable to transport their cytoplasm to the oocyte, as normally happens between stages 10B and 12. In addition to its role in the actin-mediated transport of nurse cell cytoplasm, OGP also appears to alter the morphology of giant polytene chromosomes, which form as the nurse cells undergo endocycles of DNA replication. Genetic evidence suggests that otu also encodes a second product (SP) that is utilized late in oogenesis. SP is required for the synthesis in the ooplasm of glycogen-rich, beta yolk spheres. Products of the otu gene also play a vital but unknown role in embryogenesis.
Insights
The ovarian tumor (otu) gene product is essential for early oocyte development, including actin-mediated cytoplasm transport and yolk sphere synthesis. Mutations reveal temperature sensitivity and crucial roles in oogenesis and embryogenesis.
Area of Science:
- Developmental Biology
- Genetics
- Cell Biology
Background:
- The ovarian tumor (otu) gene is crucial for oogenesis.
- Its product, ovarian tumor gene product (OGP), is involved in early oocyte development.
- Mutations in otu affect various stages of female germ cell differentiation.
Purpose of the Study:
- To investigate the function of the ovarian tumor (otu) gene and its products.
- To characterize the phenotypes of ethyl methane sulfonate-induced otu mutations.
- To understand the role of OGP in oocyte development and nurse cell function.
Main Methods:
- Analysis of 17 ethyl methane sulfonate-induced otu mutations.
- Phenotypic characterization of mutant germ cells under varying temperatures.
- Microscopic examination of actin microfilament bundles and giant polytene chromosomes.
- Genetic analysis to identify a second otu gene product (SP).
Main Results:
- Mutant phenotypes correlate with different levels of OGP, with otu10 and otu14 representing extreme levels.
- 15 intermediate mutants exhibit temperature sensitivity, with optimal development at subnormal temperatures.
- A subset of mutants shows defects in actin-mediated nurse cell cytoplasm transport to the oocyte.
- OGP influences polytene chromosome morphology, and a second product (SP) is required for yolk sphere synthesis.
Conclusions:
- The otu gene encodes at least two products essential for distinct stages of oogenesis.
- OGP plays a critical role in early oocyte development, including actin-dependent transport and chromosome structure.
- SP is vital for late oogenesis, specifically yolk sphere formation.
- The otu gene products have essential, though currently unknown, functions in embryogenesis.