Messenger RNAs encoding the beta subunits of guinea pig (Cavia porcellus) luteinizing hormone (gpLH) and putative chorionic gonadotropin (gpCG) are transcribed from a single-copy gpLH/CG beta gene

Neither gene locus nor gene sequence characterizations have been reported f or the beta subunits of guinea pig (gp) LH and putative gp chorionic gonado tropin (CC). Descriptions of this locus would allow comparison with functio nally relevant molecular genetic features of other species' homologous loci including the single-copy equid LH/CG beta gene and the primate LH beta -C G beta gene cluster locus. Contiguous cDNA and genomic DNA fragments spanni ng the entire mature coding sequence of gpLH beta mRNA, gpCG beta mRNA and a homologous gpLH/CG beta gene were amplified using PCR methodologies. With the exception of one silent mutation, the two cDNA and the genomic sequenc es were identical where they overlapped. Comparison of guinea pig coding se quence with LH beta, CG beta and LH/CG beta sequences of other vertebrate s pecies revealed the following order of similarity expressed as per cent cod ing sequence identity: rhinoceros LH beta (83.6%)>pig LH beta (81.8%)>donke y LH/CG beta =bovine LH beta (81.5%)> horse LH/CG beta (80.6%)>dog LH beta (79.7%)>human LH beta (78.2%)>rat LH beta (77.9%)>human CG beta (75.8%)>tur key LH beta (52.7%); values that are generally consistent with recently pos tulated phylogenetic relationships. Like the consensus mammalian LH beta ge ne, the 5'-flanking region of the gpLH/CG beta gene contains a single TATA sequence 37 bp upstream of the translation start codon. The first in-frame stop codon occurred at codon position +122 which is consistent with the 121 amino acid residue length of the consensus mammalian mature LH beta peptid e. To estimate gene copy number, full-length gpLH beta cDNA was radiolabele d and hybridized to Southern blots of guinea pig genomic DNA digested with a panel of six restriction endonucleases. Tho resulting simple hybridizatio n pattern strongly suggested that there is a single-copy gpLH/CG beta gene. Northern analysis of total pituitary RNA using the same probe indicated th at gpLH beta transcript size is indistinguishable from that of consensus ma mmalian pituitary LH beta mRNAs (similar to 750 nucleotides). Despite ampli fying gpCG beta from placental RNA, positive signal was not detected in Nor thern blot lanes containing guinea pig tc,tal RNA prepared front placentae collected at three gestational ages (17.3 days, 24.3 days and 68 days (term )). Other data suggest that inability to detect Northern blot signal could have been due to low relative tissue concentrations of gpCG beta transcript and/or sampling at gestational time-points that missed peak periods of mRN A expression. We conclude that, with respect to gene copy number, coding se quence and pituitary mRNA size, the gpLH/CG beta gene locus reflects the CT P-less consensus mammalian LH beta condition. However, based on the capacit y of this single-copy gene to express in both pituitary and placental tissu es, gpLH/CG beta also exhibits functional similarities with the single-copy equine LH/CG beta locus.