Casein, Actin, and Tubulin Expression During Early Involution in Bovine and Murine Mammary Tissue

Abstract

Hybridization methods and in vitro translation were used to examine the expression and functional condition of messenger RNA encoding caseins and cytoskeletal proteins in the mammary gland during early involution. In the mouse, steady state mRNA levels for α-, β-, and γ-caseins coordinately decreased to 20% of initial levels between 12 and 72h after pup removal. In vitro translatability of mouse casein mRNA, as determined by immunoprecipitation, electrophoresis, and gel slice counting, revealed a pattern that closely paralleled mRNA expression. In contrast, bovine casein mRNA levels were only slightly reduced by 72h postmilking, whereas in vitro translatability decreased by about one-half. Northern blot analysis of total mouse mammary RNA that were hybridized with probes to cytoskeletal proteins showed a gradual decrease of α-tubulin mRNA, but an increase in β-actin mRNA during early involution. Two-dimensional gel analysis of in vitro translated products indicated a concordant increase in β-γ-actin. In the cow, β-actin mRNA at 72h of involution was equal to or greater than that during lactation. These results demonstrate the generally slower involution response in the cow and suggest that differing regulations are involved. Early events of cellular involution may be related to a reorganization of the cytoskeleton.