SEQUENCE OF THE BOVINE HDL-RECEPTOR (SR-BI) CDNA AND CHANGES IN RECEPTOR MESSENGER-RNA EXPRESSION DURING GRANULOSA-CELL LUTEINIZATION IN-VIVO AND IN-VITRO

Steroidogenic activity in the mature corpus luteum of most mammals dep ends upon provision of cholesterol from the circulating lipoproteins. In cattle, as in many species, high-density lipoprotein (HDL) is the m ajor lipoprotein involved. The recent identification of the scavenger receptor SR-BI as an HDL-receptor allows control of this process to be investigated more closely. In this study, we have sequenced the bovin e SR-BI HDL-receptor and examined changes in expression of the recepto r mRNA during corpus luteum development in vivo and granulosa cell lut einization in vitro. Sequencing of the bovine HDL-receptor showed that it codes for a protein of 509 amino acids with close identity to hams ter, mouse, rat and human sequences. Examination of the tissue distrib ution of the HDL-receptor mRNA showed high levels in adrenal cortex an d corpus luteum and lower levels in spleen and liver. Using a semi-qua ntitative, reverse transcription-polymerase chain reaction technique l evels of HDL-receptor mRNA were measured in corpora lutea from cattle at known stages of the oestrus cycle and in bovine granulosa cells lut einized in culture. Levels of HDL-receptor mRNA were low in isolated b ovine granulosa cells, but increased 7-fold during corpus luteum devel opment in vivo and 5-fold during granulosa cell luteinization in cultu re. Results show that luteinization of granulosa cells is associated w ith an increase in HDL-receptor RNA levels which, along with changes i n steroidogenic enzyme activity, is likely to explain the marked incre ase in steroidogenic capacity which occurs during corpus luteum format ion. (C) 1997 Elsevier Science Ireland Ltd.