Jingxia Xu

Date of Award

12-2011

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biochemistry and Molecular Biology

Advisor

Thomas Gridley

Second Committee Member

Gregory Cox

Third Committee Member

Mary Ann Handel

Abstract

Bidirectional communication between the oocyte and surrounding somatic cells, termed granulosa cells, is essential for development of an egg competent for fertilization and embryogenesis. The Notch signaling pathway plays an essential role during oocyte development in Drosophila. In the mouse ovary, Notch pathway receptors (Notch2, Notch3 and Notch4) are expressed in granulosa cells, while Notch ligands (Jag1 and Jag2) are expressed in the oocytes, suggesting that there may be an important role for Notch signaling in folliculogenesis in mice. Notch2 is the most abundant receptor expressed in granulosa cells, but homozygous null mice are embryonic lethal. Using a cre/loxP conditional knockout system, we deleted the Notch2 gene specifically in granulosa cells of the ovary using Amhr2-Cre mice, and show that the Notch2 gene is required for early folliculogenesis. Notch2 gene deletion in granulosa cells resulted in reduced fertility in female mice, a reduced number of normal primordial follicles, persistent multiple oocytes follicles, and hemorrhagic cysts. The mutants had more oocytes than the littermate controls at postnatal day 2. There was no extended oocyte proliferation after embryonic day 16.5, nor was there a defect in granulosa cell proliferation. TUNEL staining showed a significant decrease in both the number of apoptotic oocytes and pre-granulosa cells in postnatal day 1 mutant ovaries. Our data indicate that the Notch2 gene is important in germ cell cyst breakdown and the endowment of primordial follicles. These results show that the Notch signaling pathway plays an important role in oocyte-granulosa cell communication, and is required for follicle development and fertility in mice.

The Jag2 gene is required for craniofacial, limb and T cell development. Jag2 homozygous null mice die at birth from cleft palate, precluding study of Jag2 function in postnatal mice. We have generated a Jag2 conditional null allele by flanking the first two exons of the Jag2 gene with loxP sites. Cre-mediated deletion of the Jag2flox allele generates the Jag2del2 allele, which behaves genetically as a Jag2 null allele. This Jag2 conditional null allele will enable investigation of Jag2 function in a variety of tissue-specific contexts, including the function of Jag2 in folliculogenesis.

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