PARENT SESSION
OVARY - C

Wednesday, August 4, 2004
10:30 AM–12:30 PM
Buchanan Courtyard

(798) KIT LIGAND PROMOTES FOLLICLE ACTIVATION IN CULTURED NEONATAL MOUSE OVARIES BUT NOT IN CULTURED RABBIT OVARIAN CORTICAL EXPLANTS.

Hutt, Karla¹, McLaughlin, Eileen², Holland, Michael³, ¹ Pest Animal Control Cooperative Research Centre, Canberra, ACT, Australia² ARC Centre of Excellence in Biotechnology and Development, Newcastle, NSW, Australia³ Monash Institute of Reproduction and Development, Melbourne, VIC, Australia

ABSTRACT- In mice and rats, signalling via the pleiotropic cytokine Kit Ligand (KL), and its receptor C-Kit, has been reported to promote primordial follicle activation and oocyte growth. To extend these findings, we investigated the effects of KL on the initial recruitment of primordial follicles in ovaries from juvenile rabbits, a non-rodent species. Eight-week-old rabbit ovarian cortical explants and whole 3-day-old mouse ovaries were maintained in organ culture for 8 days and selected explants and ovaries were co-cultured with 150 ng/ml recombinant mouse KL and/or neutralising KL antibody. Rabbit ovarian cortical explants were also treated with 150 ng/ml recombinant rabbit KL protein. Oocyte diameter and the proportion of total follicles remaining in the primordial follicle stage of development were compared with controls and between treatment groups for each species. As anticipated the analysis of mouse ovaries indicates that KL promotes primordial follicle activation. Of the follicles present in untreated cultured mouse ovaries 33.00 ± 3.15% were in the primordial stage whereas primordial follicles were found to comprise only 10.77 ± 1.46% of all follicles in KL treated ovaries (p<0.05). KL also promoted an increase in the diameter of small mouse oocytes from 19.04 ±0.26 m in untreated ovaries to 21.31 ± 0.28 m in KL treated ovaries (mean ± sem, p<0.05). These effects were completely inhibited by co-culture with neutralising anti-recombinant mouse KL antibody. In contrast neither recombinant mouse KL or recombinant rabbit KL had a stimulatory effect on primordial follicle recruitment in cultured rabbit ovarian explants. However, the diameters of small rabbit oocytes increased significantly with KL treatment (31.66 ± 0.17 m vs. 37.59 ± 0.28 m, mean ± sem, p<0.05). Though rabbit primordial follicles failed to activate in response to exogenous KL, RT-PCR and immunohistochemical analysis confirmed that nearly all rabbit oocytes express C-Kit prior to and throughout the culture process. Taken together these data demonstrate that KL stimulates primordial follicle activation in the mouse but not in the rabbit, implying differences in the mechanism of follicle activation between these species.

KEY WORDS: primordial, folliculogenesis, kit ligand, activation