LUTEINIZING-HORMONE CHORIONIC-GONADOTROPIN BIOACTIVITY IN THE COMMON MARMOSET (CALLITHRIX-JACCHUS) IS DUE TO A CHORIONIC-GONADOTROPIN MOLECULE WITH A STRUCTURE INTERMEDIATE BETWEEN HUMAN CHORIONIC-GONADOTROPINAND HUMAN LUTEINIZING-HORMONE

Chorionic gonadotropin (CG), a pregnancy-specific heterodimeric hormon e found in primates, is responsible for CL rescue with pregnancy maint enance. Of the primates, the human and baboon gene sequences are the o nly structures so far determined, In order to study the structure and function of CG in other primates, we have isolated and sequenced the c oding regions for the two subunits of marmoset CG (mCG) by the reverse transcription/polymerase chain reaction method. Study of multiple clo nes confirmed a high degree of homology with the human sequences (88% and 80% for the alpha and beta nucleotide sequences, respectively), Ma rmoset CG alpha has an extra four amino acids compared to hCG alpha, w hereas the mCG beta sequence has a 3-bp deletion that maintains the re ading frame and C-terminal amino acid sequence. Most of the difference s between hCG beta and mCG beta peptides occur in the C-terminal regio n, which includes the loss of two of the O-linked glycosylation consen sus sequences and the presence of an N-linked glycosylation consensus sequence. When mCG alpha and beta were co-expressed in CHO cells, asse mbly of biologically active hormone was confirmed by induced steroid s ecretion by MA10 cells, Partially purified mCG beta was used to raise anti-mCG antibodies, To date, an antibody has been obtained that is ca pable of detecting recombinant mCG beta, recombinant mCG dimer, and mC G dimer secreted by cultured marmoset trophoblast. Marmoset CG alpha a nd beta were also detectable at the transcriptional level in cultured trophoblast by in situ hybridization, This suggests that the LH/CG bio activity reported from marmoset placentae and embryos is due to a mole cule with structural features common to hLH (glycosylation pattern) an d hCG (CG beta C-terminal structure).