DUPLICATION OF THE SOUTHERN WHITE RHINOCEROS (CERATOTHERIUM-SIMUM SIMUM) LUTEINIZING-HORMONE BETA-SUBUNIT GENE

Luteotropic glycoprotein hormones (LGH) include luteinizing hormone (L H) and chorionic gonadotropin (CG). The order Primates is the only phy logenetic clad known to exhibit more than one LGH beta subunit gene pe r haploid genome. In the present study, we report the discovery of a s econd case of LGH beta gene replication, in the white (w) rhinoceros ( r or rhino). The presence of more than one gene was strongly suggested by a complex banding pattern observed on Southern blots of DNA prepar ed from two unrelated white rhinos. The existence of two LGH beta gene s per haploid genome was estimated by genomic equivalence assay. Howev er, genomic restriction-site mapping studies, together with other find ings, suggested that the replicates are probably not tandemly arranged as occurs in primates. A simple band pattern was observed in Southern blots of four other perissodactyl species, indicating that a single-c opy LH beta gene is the consensus condition. Two distinct white rhino LH beta genomic clones (wrLH beta 1 and wrLH beta 2) were isolated. Th e nucleotide sequence of wrLH beta 1 was identical with that of wrLH b eta 2, except that the latter lacked the consensus mammalian LGH beta second intron. Sequences of the TATA-containing proximal 5'-flanking r egions of the two genes were homologous to at least. -57 relative to t he site of pituitary transcriptional initiation. We conclude that wrLH beta 1 is the extant form of the ancestral perissodactyl LH beta gene , whereas wrLH beta 2 is a randomly integrated cDNA element (processed gene) reverse transcribed from a partially spliced ancestral wrLH bet a 1 mRNA. That wrLH beta 2 was heritable demonstrates that wrLH beta 1 was transcribed in gametes or early conceptus cells contributing to t he germline at some point in time since the divergence of white rhinos from other members of the family Rhinocerotidae. Furthermore, because homologous proximal (pituitary) promoter sequence is present in wrLH beta 2, it can be concluded that the wrLH beta 1 mRNA template from wh ich wrLH beta 2 is derived was transcribed from a secondary promoter l ocated upstream of the consensus TATA-regulated pituitary promoter.