DEVELOPMENT OF CYTOCHROME-P-450 SIDE-CHAIN CLEAVAGE MESSENGER-RNA LEVELS IN NEONATAL OVARIES OF NORMAL AND HYPOGONADAL (HPG) MICE

Cytochrome P-450 side chain cleavage (P-450(SCC)) is vital for biosynthesis of gonadal steroids. In this study changes in P-450(SCC) mRNA levels and cholesterol side-chain cleavage (CSCC) enzyme activity have been measured during development in the ovary of the normal mouse and the hypogonadal (hpg) mouse which lacks circulating gonadotrophins. Levels of P-450(S)CC mRNA were measured using a semi-quantitative reverse transcription-polymerase chain reaction technique for which part of the 5' sequence of a mouse P-450(SCC) cDNA was sequenced. On the day of birth P-450(S)CC mRNA was present at low levels in the mouse ovary. Thereafter there was no change in P-450(S)CC mRNA levels for 5 days after which time levels increased significantly to reach a peak around day 10. Activity of CSCC showed a similar pattern of development although activity was not detectable on days 1 and 3. In the hpg mouse P-450(S)CC mRNA levels were normal on day 1 but did not increase thereafter up to 15 days. These results show that there is gonadotrophin-independent expression of P-450(S)CC mRNA in the mouse ovary at birth when only primordial follicles and stromal tissue are present. As the ovary develops after 5 days changes in P-450(S)CC mRNA levels become gonadotrophin-dependent and coincide with maturation of secondary follicles.