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Relative Contribution of Promoter and Intragenic Sequences in the Hormonal Regulation of Rat β-Casein Transgenes

Kuo-Fen Lee^*, Suzanne H. Atiee, Susan J. Henning and Jeffrey M. Rosen

Department of Cell Biology, Baylor College of Medicine Houston, Texas 77030

Address requests for reprints to: Jeffrey M. Rosen, Department of Cell Biology, Baylor College of Medicine, 1 Baylor Plaza, Houston, Texas 77030-3498.

Abstract

In order to identify DNA sequences responsible for the regulation β-casein gene expression, lines of transgenic mice bearing the entire rat β-casein gene and two rat β-casein promoter chloramphenicol acetyltransferase (CAT) fusion genes have been established. All three transgenes have been shown previously to be regulated in a tissue- and stage specific manner. To investigate the relative contribution of promoter and intragenic sequences in the hormonal regulation of the β-casein gene, mammary explant cultures derived from these lines of mice have now been performed, and the effects of PRL and glucocorticoids on transgene as compared with endogenous β-casein gene expression have been quantified. After the addition of PRL to cultures performed in the presence of insulin and glucocorticoids, a 25- to 40-fold induction of endogenous mouse β-casein mRNA was observed after 48 hr. A comparable greater than 25-fold induction of transgene expression after PRL addition was observed in explant cultures derived from a line of mice expressing the entire rat β-casein gene. In contrast, PRL addition elicited only a 1- to 4.5-fold increase in CAT activity in cultures derived from two lines of mice bearing casein-CAT fusion genes with either 524 or 2300 base pairs of 5'-flanking DNA. In the presence of insulin, glucocorticoid or PRL addition alone increased endogenous β-casein gene expression 2- to 2.5-fold and 5- to 10-fold, respectively, but only a 1.2- to 2.5-fold induction of CAT activity was observed for each hormone. These results are consistent with the hypothesis that while the β-casein promoter contains elements important for its tissueand stage-specific expression and PRL-induced transcription, intragenic sequences are important for the processing and stabilization of β-casein mRNA in response to hormones

FOOTNOTES

^* Present address: Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, Massachusetts 02142.

Present address: Department of Biology, University of Houston, Houston, Texas 77204.

These studies were supported by USDA Grant 86-CRCR-1-2250 and NIH Grant CA-16303 (to J.M.R.) and NIH Senior Fellowship HD-07100 (to S.J.H.).

Received for publication November 9, 1988. Revision received December 7, 1988. Accepted for publication December 7, 1988.

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