Application of recombinant DNA techniques to structure-function studies of equine protein hormones.

Complementary (c)DNA libraries have been made from horse pituitary gland and endometrial cup tissues with the aim of isolating the genes for the horse gonadotrophins (FSH, LH and CG) and growth hormone (GH). Southern (DNA) and Northern (RNA) blotting techniques were used to demonstrate that several heterologous (human and ovine) cDNA probes would be adequate for isolating the horse genes. A human cDNA probe was then used to isolate the horse gonadotrophin alpha-subunit cDNA from the pituitary and endometrial cup libraries. The nucleotide sequences from both tissue sources were identical, thereby confirming that there is a single gene for the alpha-subunit in the horse. As soon as the gonadotrophin beta-subunit sequences become available, they will be expressed along with the alpha-subunit to obtain biologically active hormones. Horse GH cDNA has also been isolated by using a sheep cDNA probe and its DNA sequence has been determined. It was subsequently used to demonstrate that horse endometrial cups, but not the allantochorion taken at the same stage of gestation, contains mRNA for a GH-like protein. This mRNA could be due to a low level of expression of the GH gene or to expression of the gene(s) for a GH-related protein such as prolactin or placental lactogen.