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a AgResearch, Wallaceville Animal Research Centre, Upper Hutt, New Zealand
Animals heterozygous (I+) for the Inverdale prolificacy gene (FecXI) have an increased ovulation rate whereas those homozygous (II) for FecXI are infertile with "streak" ovaries and follicular development arrested at the primary (type 2 follicle) stage. The streak ovaries also contain small oocyte-free nodules with granulosa-like cells and often tumor-like structures. It has been hypothesized that these abnormal structures are of granulosa cell origin, and the aim of this study was to determine whether genes normally expressed in granulosa cells are also expressed in the nodules and tumor-like structures. The mRNAs encoding c-kit and its ligand stem cell factor (SCF), FSH receptor (FSH-R), follistatin, 
-inhibin subunit, and the ßA- and ßB-activin/inhibin subunits were localized in ovaries of ewes with 0 (++), 1 (I+), or 2 (II) copies of the FecXI gene (n = 4–9 animals per genotype per gene) using in situ hybridization. Ontogeny of expression of all mRNAs examined was similar between ++ and I+ ewes. Expression of c-kit mRNA was observed in the oocyte of all follicular types present in ++, I+, and II ewes. Moreover, granulosa cells of type 2 (II) and type 2 and larger follicles (++, I+) expressed SCF mRNA. The mRNAs encoding FSH-R, follistatin, -inhibin subunit, and ßB-activin/inhibin subunit were identified in type 3 and larger follicles of ++ and I+ ewes but not in follicles of II ewes that were only at the type 1, 1a, or 2 stages of development. However, the cells within the oocyte-free nodules of II ewes expressed all of these genes. The mRNAs encoding c-kit and ßA-activin/inhibin subunit were not observed in granulosa cells until antrum formation (type 5 follicles) or in the nodules of II ewes. Tumors from 4 ewes were obtained and classified as cystic, semisolid, or solid structures containing granulosa-like cells or as solid structures containing predominately fibroblast- and luteal-like cells. Often, two tumors were present on the same ovary. Tumors containing granulosa-like cells (n = 3–4 per gene) expressed the mRNAs encoding -inhibin subunit, ßA-, and ßB-activin/inhibin subunits, follistatin, and the FSH-R but did not contain detectable amounts of mRNA for c-kit or SCF. Tumors composed predominately of fibroblast- and luteal-like cells expressed very low levels of SCF mRNA; of the other mRNAs examined, none were detected. Also, none of the genes examined were found to be expressed by the surface epithelium, theca externa, fibroblast, or vascular cells within the ovary of animals of any genotype. These findings are consistent with the hypothesis that the somatic cells in oocyte-free nodules and tumor-like tissue in II ewes originate from the granulosa cells of the small follicles.
1 Supported by New Zealand Foundation for Research, Science and Technology.
2 Correspondence: Jennifer L. Juengel, Wallaceville Animal Research Centre, PO Box 40063, Upper Hutt, New Zealand. FAX: 64 4 922 1380; juengelj{at}agresearch.cri.nz
3 Current address: National Centre for Disease Investigation, Ministry of Agriculture and Forestry, PO Box 40742, Upper Hutt, New Zealand.
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