Novel expression of luteinizing hormone subunit genes in the rat testis

Abstract

The two gonadotropins, LH and FSH, are thought to be synthesized and secreted solely by the anterior pituitary. We present here evidence for expression of the LH beta and common alpha-subunit (C alpha) genes in the rat testis. The LH beta and C alpha-subunit messenger RNAs (mRNAs) were detected by reverse transcriptase-polymerase chain reaction in the rat testis and pituitary with primer pairs producing 247- and 199-base pair complementary DNA (cDNA) fragments, corresponding to nucleotides 154-400 of LH beta and nucleotides 250-448 of C alpha cDNA, respectively. The specificity of the cDNA species generated was verified by Southern hybridization using nested [32P]cDNA or oligonucleotide probes, and identity with the published rat LH beta and C alpha-subunit gene structures was determined by sequencing. The mRNA bands with specific hybridization to complementary RNA (cRNA) probes corresponding to nucleotides 154-368 of the rat LH beta cDNA and nucleotides 250-448 of the rat C alpha cDNA were found in the rat pituitary and testis by Northern hybridization. The major C alpha mRNA had a size of 0.8 kilobases (kb) in the pituitary and testis. The major LH beta transcripts were 0.8 and 2.7 kb in the pituitary and testis, respectively. To further characterize the larger testicular LH beta-subunit transcript, rapid amplification of the 3'-end of cDNA (3'-RACE) was performed using an oligo(deoxythymidine-17) adapter and a specific 5'-primer. Southern hybridization of the 3'-RACE product of rat testicular RNA with a LH beta [32P]cDNA probe had the same size as the 3'-RACE product of pituitary RNA. The pituitary and testicular RNAs were then cut into two segments using oligonucleotide-directed ribonuclease H digestion and subjected to Northern hybridization using a cRNA probe specific to the 5'-end segment. The digested 5'-end segments of the pituitary and testicular mRNAs were 0.4 and 2.3 kb, respectively, indicating that the testicular LH beta mRNA has a 1.9-kb 5'-extension, compared to the cognate pituitary mRNA. This was further verified by Northern hybridization using a cRNA probe corresponding to nucleotides -790 to -10 upstream of the pituitary initiation site of LH beta gene transcription. Specific hybridization of a 2.7-kb mRNA transcript was found in the rat testis, but none in the pituitary. Hence, the 3'-end polyadenalytion site of the LH beta mRNA is the same in rat pituitary and testis, and the different transcript sizes are due to a difference at the 5'-end.