Recent data on the structure of rabbit milk protein genes and on the mechanism of the hormonal control of their expression.
Mammary explants or isolated mammary cells from rabbit have been cultured in the presence of insulin, prolactin and cortisol alone or in combination. The cellular content in alpha s1-casein, beta-casein and whey acidic protein (WAP) mRNA have been evaluated using the corresponding cDNA as probes. In all cases alpha s1-casein mRNA was the most abundant and WAP mRNA the least abundant mRNA. The three genes showed essentially similar dependency towards hormones. Prolactin stimulated mRNA accumulation and insulin and cortisol amplified this stimulation. The induction by prolactin was rapid whereas stimulation by insulin was slower. Fragments of rabbit genomic DNA inserted in lambda phage and containing alpha s1-casein, and WAP genes have been cloned. The primary sequence around the CAP site of the three genes has been established. A comparison of the sequences located upstream from the CAP site shows several striking homologies with the corresponding genes from cow, rat and guinea-pig. This suggests that these sequences participate in the transcriptional control of the genes by hormones. The mechanism involved in the transduction of the prolactin message to milk protein genes in unknown. Using mammary explants in culture, several classical mechanisms of transduction have been examined. Phorbol ester, phorbol -12, 13-dibutyrate (PdiBu) inhibited prolactin action. However, another tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA), did not alter prolactin action. Kinase C inhibitor H7 did not prevent prolactin action and did not overcome the inhibition by PdiBu. Kinase C is therefore not essential for the transduction of the prolactin message to milk protein gene. Neomycin, which inhibits phosphatidylinositol hydrolysis by phosphorylase C, prevented prolactin action, whereas other inhibitors of phosphatidylinositol metabolism remained uneffective. Degradation of phosphatidylinositol is therefore likely not an essential step of prolactin action on milk protein genes. Inhibitors of tyrosine kinase and phosphatase exhibited a poor capacity to modify the prolactin response. Hence, transduction mechanisms using tyrosine kinase activity likely cannot account for prolactin action.
Devinoy
E
E
I.N.R.A., Jouy-en-Josas, France.
Hubert
C
C
Jolivet
G
G
Thepot
D
D
Clergue
N
N
Desaleux
M
M
Dion
M
M
Servely
J L
JL
Houdebine
L M
LM
D000818:Animals; D001483:Base Sequence; D002364:Caseins / Q000235:genetics; D002478:Cells, Cultured; D004247:DNA / Q000032:analysis / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects*; D006854:Hydrocortisone / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D008321:Mammary Glands, Animal / Q000166:cytology* / Q000187:drug effects; D008894:Milk Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D011388:Prolactin / Q000494:pharmacology*; D011817:Rabbits
D002364:Caseins; D007328:Insulin; D008894:Milk Proteins; C024471:whey acidic proteins; D011388:Prolactin; D004247:DNA; D006854:Hydrocortisone