Effects of prolactin and progesterone on expression of casein genes. Titration of casein mRNA by hybridization with complementary DNA.

Prolactin injected into pseudopregnant rabbits induced lactogenesis. Progesterone injected simultaneously considerably reduced this effect. The content of mRNA for casein in total cellular RNA and in total polysomal RNA was estimated during these two hormonal actions using a hybridization technique. The synthesis of DNA complementary to casein mRNA was carried out with mRNA obtained from polysomes immunoprecipitated with anti-casein antibody. The content of casein mRNA was determined by hybridization of this cDNA with the RNA fractions. This technique revealed that prolactin induced the synthesis of mRNA for casein whereas progresterone greatly limited this effect of prolactin. These variations of casein mRNA content are in good agreement with values previously determined by translation and with the ability of mammary gland to synthesize casein.