Expression of c-myc and c-fos protooncogenes in the anterior pituitary gland of the rat. Effect of estrogen.

Thymidine incorporation into the DNA of the anterior pituitary gland is stimulated by estrogen. We studied the relationship between this effect and expression of the protooncogenes c-myc and c-fos. Within one hour after estrogen administration, the level of c-myc and c-fos mRNA increased in the anterior pituitary gland and remained high throughout the experimental period (16 to 22 hrs). Transcription of the prolactin gene, one of the targets of estrogen action, was stimulated at the same time intervals. There were no modifications in the growth hormone mRNA level. Thus, estrogen induced the expression of c-myc and c-fos in the anterior pituitary gland in an early period.