THE STRUCTURE AND REGULATION OF EXPRESSION OF THE MOUSE GROWTH-HORMONE RECEPTOR AND BINDING-PROTEIN

The mouse growth hormone receptor (mGHR) and the mouse growth hormone- binding protein (mGHBP) are products of a single gene which are genera ted by alternative splicing. The factors that regulate the expression of mGHR and mGHBP mRNA and protein during pregnancy in the mouse are i ncompletely understood. During pregnancy in the mouse, there are paral lel increases in circulating mouse growth hormone (mGH), liver mGHR, a nd serum mGHBP. The increase in both hepatic mGHR and serum mGHBP begi ns on Day 9 of gestation and by late gestation the hepatic mGHR conten t has increased 8-fold and serum mGHBP has increased 30-fold compared with values in nonpregnant controls. A parallel increase occurs in the steady state levels of liver GHR and GHBP encoding mRNAs. The increas e in both messages begins on Day 9 of gestation; however, the GHR mRNA reaches maximum levels by Day 13, while the GHBP mRNA continues to in crease until the end of pregnancy. The magnitude of the increase in th e GHR-encoding message is 15- to all-fold between nonpregnant and late pregnant mice, and the magnitude of the increase in the GHBP-encoding message is 30- to 50-fold. Both pituitary mGH and the number of conce ptuses influence the receptors and binding protein for mGH during preg nancy.