Luteotropic glycoprotein hormones (LGH) include luteinizing hormone (LH) and chorionic gonadotropin (CG). The order Primates is the only phylogenetic clad known to exhibit more than one LGH subunit gene per haploid genome. In the present study, we report the discovery of a second case of LGH 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 prepared from two unrelated white rhinos. The existence of two LGH genes per haploid genome was estimated by genomic equivalence assay. However, genomic restriction-site mapping studies, together with other findings, 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-copy LH gene is the consensus condition. Two distinct white rhino LH genomic clones (wrLH 1 and wrLH 2) were isolated. The nucleotide sequence of wrLH 1 was identical with that of wrLH 2, except that the latter lacked the consensus mammalian LGH second intron. Sequences of the TATA-containing proximal 5 -flanking regions of the two genes were homologous to at least 57 relative to the site of pituitary transcriptional initiation. We conclude that wrLH 1 is the extant form of the ancestral perissodactyl LH gene, whereas wrLH 2 is a randomly integrated cDNA element (processed gene) reverse transcribed from a partially spliced ancestral wrLH 1 mRNA. That wrLH 2 was heritable demonstrates that wrLH 1 was transcribed in gametes or early conceptus cells contributing to the 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 2, it can be concluded that the wrLH 1 mRNA template from which wrLH 2 is derived was transcribed from a secondary promoter located upstream of the consensus TATA-regulated pituitary promoter.
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