Lhx8 is a member of the LIM-homeobox transcription factor family and preferentially expressed in oocytes and germ cells within the mouse ovary. We discovered that Lhx8 knockout females lose oocytes within 7 days after birth. At the time of birth, histological examination shows that Lhx8-deficient (Lhx8−/−) ovaries are grossly similar to the newborn wild-type ovaries. Lhx8−/− ovaries fail to maintain the primordial follicles, and the transition from primordial to growing follicles does not occur. Lhx8−/− ovaries misexpress oocyte-specific genes, such as Gdf9, Pou5f1, and Nobox. Very rapid loss of oocytes may partly be due to the drastic downregulation of Kit and Kitl in Lhx8−/− ovaries. We compared Lhx8−/− and wild-type ovaries using an Affymetrix 430 2.0 microarray platform. A total of 80 (44%) of 180 of the genes downregulated more than 5-fold in Lhx8−/− ovaries were preferentially expressed in oocytes, whereas only 3 (2%) of 146 genes upregulated more than 5-fold in the absence of Lhx8 were preferentially expressed in oocytes. In addition, the comparison of genes regulated in Lhx8−/− and Nobox−/− newborn ovaries discovered a common set of 34 genes whose expression level was affected in both Lhx8- and Nobox-deficient mice. Our findings show that Lhx8 is a critical factor for maintenance and differentiation of the oocyte during early oogenesis, and it acts in part by downregulating the Nobox pathway.
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Vol. 79 • No. 3