279. Expression of oestrogen receptor-α and modulators of steroid receptor signalling, proline-rich nuclear receptor-2 and peptidylprolyl isomerade-D, in the hypothalamus of suckled and weaned postpartum beef cows

The aim was to characterise gene expression in the hypothalamus of suckled and weaned postpartum beef cows. The hypothalamus was obtained at slaughter from 12 primiparous Brahman cows (Zebu, Bos indicus) at 27 and 34 days postpartum. Six cows were weaned 7 days or 14 days before slaughter. Hypothalamic regions used for gene expression were: H1 (SC-POA, APVN, anterior hypothalamic nucleus, anterior portion of the arcuate nucleus, nearby areas of the diagonal band of Broca, and medial septum); H2 (basal hypothalamus-median eminence, ventromedial hypothalamus, posterior portion of the arcuate nucleus, and anterior part of the mammillary body). Gene expression was determined using the Agilent bovine 44k DNA microarray and differential expression (DE) was ascertained by mixed model analysis. A total of 122 genes were DE in H1 and 84 genes were DE in H2; 41 DE genes were common to H1 and H2. Functional clustering of DE genes using DAVID (www.david.abcc.ncifcrf.gov) revealed DE gene clusters in H1 associated with signalling events and ion binding, and DE gene clusters in H2 associated with hormone activity and ligand-receptor interactions. Of the DE genes, ~25% were linked with oestrogen signalling. This included oestrogen receptor-α (ESR1) that showed lower DE in H2 for weaned cows. Two modulators of steroid receptor signalling, proline-rich nuclear receptor coactivator-2 (PNRC2)1 and peptidylprolyl isomerase D (PPID)2, showed altered expression. In weaned cows, expression level of PNRC2 was lower in H1 and H2, while that of PPID was decreased in H1. The overlapped hypothalamic regions H1 and H2 are known to contain GnRH neuron terminals and kisspeptin neurons. Weaning promotes the resumption of cyclic ovarian function in postpartum cows, and the similar shifts in DE of ESR1, PNRC2 and PPID provided further evidence of a role for oestradiol at the hypothalamus in regulating postpartum reproduction. (1) Zhou D et al. 2006 Nucleic Acids Res 34:5974–86 (2) Kumar P et al. 2001 Biochem Biophys Res Commun 284:219–25