Cell Type-Specific Localization of c-Myc Protein in the Mouse Uterus: Modulation by Steroid Hormones and Analysis of the Periimplantation Period*

Estrogen has been shown to induce a rapid transient increase in c-myc mRNA in the rat uterus. However, no studies of the cell specificity of c-myc expression in the uterus have been reported, and nothing is known about the expression of c-myc in response to other steroids or during normal uterine preparation for implantation. To this end, the cell type-specific localization of c-myc protein was determined in the ovariectomized mouse uterus after progesterone (P4) and/or 17 beta-estradiol (E2) injection as well as during the periimplantation period. After E2 injection, a rapid accumulation of c-myc protein was detected exclusively in the uterine luminal and glandular epithelial nuclei in the ovariectomized mouse. Essentially all of these cells contained immunoreactive c-myc by 12 h postinjection. In contrast, after P4 injection, rapid accumulation of c-myc was noted exclusively in some of the stromal cell nuclei. Pretreatment of the ovariectomized mouse for 4 days with P4 (P4 priming) followed by E2 injection resulted in an increase in the number of c-myc-positive stromal cells, but few, if any, c-myc-positive cells were detected in the luminal and glandular epithelia. These uterine cell type-specific localizations of c-myc protein, induced by E2 or P4 injection, were followed within 18-24 h by DNA synthesis ([ 3H]thymidine incorporation) restricted to the epithelia or stroma, respectively. c-Myc was detected in the nuclei of luminal and glandular epithelia during proestrus and on days 1 and 2 of pregnancy, a period when the uterus is under the influence of estrogen. c-Myc-positive cells were detected in the stroma on day 3, and by day 4 a large number of stromal cell nuclei were c-myc positive. These changes are coincident with increasing P4 levels during early pregnancy. At the implantation chamber on day 5, many cells in the primary decidual zone as well as some of the deeper stromal cells were c-myc protein positive, whereas on day 6, c-myc protein was detected only in the secondary decidual zone. During this period of uterine preparation for embryo implantation and subsequent decidualization, there was a positive correlation between c-myc protein localized in specific populations of uterine cells and subsequent DNA synthesis in those cell types. Thus, both E2 and P4 induce cell type-specific accumulation of c-myc protein in the uterus of the ovariectomized mouse, with E2 induction of c-myc being restricted to epithelia, and P4 induction restricted to stroma.(ABSTRACT TRUNCATED AT 400 WORDS)