CLONING OF BOVINE PARATHYROID HORMONE-RELATED PROTEIN (PTHRP) CDNA AND EXPRESSION OF PTHRP MESSENGER-RNA IN THE BOVINE MAMMARY-GLAND

Parathyroid hormone-related protein (PTHrP) produced by the mammary gl and has been postulated to have multiple functions in both the mother and neonate. In humans, alternative 3'-mRNA splicing and endoproteolyt ic processing result in multiple bioactive PTHrP peptides. Multiple PT HrP peptides also have been reported in bovine milk. To investigate th e source of molecular heterogeneity of PTHrP in bovine milk, bovine PT HrP was cloned from a bovine brain cDNA library, sequenced and used to characterize the mammary PTHrP transcript. A 1065 bp clone (bP1) for bovine PTHrP was isolated from a brain cDNA library. The bP1 clone con tained the entire coding sequence of PTHrP and 61 and 473 nucleotides of the 5'- and 3'-untranslated regions (UTRs) respectively. The predic ted amino acid sequence of bovine PTHrP was 72-92% homologous to the s equences of chicken, rat, mouse, human, and canine PTHrP with the high est sequence divergence present in the C-terminal region of the peptid e. The 5'- and 3'-UTRs of bovine brain PTHrP have a high degree of hom ology to exons 4 and 9 of human PTHrP respectively. PTHrP was expresse d as a single 1200 nucleotide mRNA transcript in lactating bovine mamm ary tissue. RT-PCR using region-specific oligonucleotide primers deriv ed from bP1 demonstrated that PTHrP mRNA transcripts in bovine brain a nd lactating mammary gland utilize the same 5'- and 3'-UTRs. Expressio n of PTHrP mRNA was localized to secretory and ductular epithelial cel ls within the lactating mammary gland, as detected using in situ hybri dization. Expression of PTHrP mRNA was demonstrated in the mammary gla nd during late pregnancy and throughout lactation in cows.