Partial purification and characterization of proteins with growth promoting activities from ovine mammary gland secretions

Developmental regulation of growth promoting activities in mammary secretio ns of pregnant Awassi ewes was defined, and growth factors contained in the se secretions were partially purified and characterised. Mammary secretions from pregnant ewes enhanced fibroblast cell (AKR-2B) and mammary cell (CID -9 cell strain) proliferation to levels comparable to that induced by 10% F oetal calf serum. Major milk proteins in mammary secretions collected from pregnant ewes one month prior to lambing up to one week after lambing, were resolved by SDS-PAGE, while gelatinases were resolved by zymography. Gelat inase activity was noted prior to P134 and decreased thereafter to reach a minimum during lactation. This decrease was concomitant with the onset of c asein production. It is during this critical developmental period that high est growth promoting activity in mammary secretions was detected. Secretions with highest growth promoting activity were fractionated by ion exchange and gel filtration chromatography. Two heat-resistant, trypsin/chy motrypsin sensitive, growth-promoting activities were characterised. The fi rst, designated ovine mammary derived growth factor-1 (oMDGF-1), had around a 30 kDa molecular weight and eluted at 0.65 M NaCl gradient on cation ion exchange chromatography. The second, oMDGF-2, eluted under gel filtration conditions at a molecular weight of 50 kDa and 150 kDa. oMDGF-1 induced cha nges in Connexin 43, but not in beta -casein mRNA expression by CID-9 mamma ry cells. In conclusion, growth factor activities in ewe mammary secretions peak duri ng gestation at a period that overlaps maximal gelatinase expression and pr ecedes milk protein synthesis. The factors modulate mammary cell function a nd may play a role in mammary gland development. (C) 2001 Elsevier Science Inc. All rights reserved.