We investigated LIF expression in a carnivore, the Western spotted skunk, that exhibits a 6- to 7-mo period of embryonic diapause. It has been hypothesized that the uterine environment is inadequate to support implantation during the period of arrested blastocyst development, at which time the uterus is quite small and secretes reduced levels of uterine-specific proteins. Corpora lutea are also small and appear relatively inactive, yet sufficient steroids are secreted to maintain pregnancy. Renewed embryonic development in the spotted skunk begins in late March to early April and is induced by increasing day length and prolactin (PRL) secretion. Blastocysts increase in diameter, renew mitosis in the inner cell mass, and exhibit increased RNA and protein synthesis. antibiotic levaquin
In synchrony with blastocyst activation, the uterus undergoes several changes including increases in weight, number of active-appearing secretory gland cells, synthesis of uterine secretory proteins, abundance of epidermal growth factor receptor (EGF-R) mRNA, and EGF-induced protein tyrosine kinase activity. The temporal pattern of LIF expression in the uterus of mice, rabbits, mink, and humans and the failure of blastocysts to implant in LIF mice suggest that LIF may be required for implantation. This led us to hypothesize that embryonic diapause in the spotted skunk is due to insufficient uterine expression of LIF during delayed implantation whereas resumption of embryonic development and implantation are associated with increased LIF expression. We also investigated the effects of progesterone, estrogen, PRL, and EGF on LIF mRNA expression in the uterus.