Comparison of endocrine and cellular mechanisms regulating the corpus luteum of primates and ruminants.

The corpus luteum (CL) is a transient endocrine organ that is essential for maintenance of pregnancy in both ruminants and primates. The cellular and endocrine mechanisms that regulate the CL in these species have commonalities and some distinct and intriguing differences. Both species have similar cellular content with large luteal cells derived from the granulosa cells of the follicle, small luteal cells from follicular thecal cells, and large numbers of capillary endothelial cells that form the vasculature that has an essential role in optimal CL function. Intriguingly, the large luteal cells in ruminants grow larger than in primates and acquire a capacity for high constitutive progesterone (P4) production that is independent of stimulation from LH. In contrast, the primate CL and the granulosa lutein cells from primates continue to require stimulation by LH/CG throughout the luteal phase. Although the preovulatory follicle of women and cows had similar size and steroidogenic output (10 to 20 mg/h), the bovine CL had about ten-fold greater P4 output compared to the human CL (17.4 vs. 1.4 mg/h), possibly due to the development of high constitutive P4 output by the bovine large luteal cells. The continued dependence of the primate CL on LH/CG/cAMP also seems to underlie luteolysis, as there seems to be a requirement for greater luteotropic support in the older primate CL than is provided by the endogenous LH pulses. Conversely, regression of the ruminant CL is initiated by PGF from the nonpregnant uterus. Consequently, the short luteal phase in ruminants is primarily due to premature secretion of PGF by the nonpregnant uterus and early CL regression, whereas CL insufficiency in primates is related to inadequate luteotropic support and premature CL regression. Thus, the key functions of the CL, pregnancy maintenance and CL regression in the absence of pregnancy, are produced by common cellular and enzymatic pathways regulated by very distinct luteotropic and luteolytic mechanisms in the CL of primates and ruminants.

Growth, morphogenesis, and differentiation during mouse prostate development in situ, in renal grafts, and in vitro.

BACKGROUND: In vitro organ culture and renal grafting of the urogenital sinus (UGS) have both been used as models of prostate development. However, neither has been rigorously examined for its fidelity to replicate the canonical process of prostate differentiation in situ. METHODS: We assessed size, morphology, histology, and the mRNA expression of differentiation marker genes of the E14 male mouse UGS grown for 0-28 days as sub-renal capsule allografts in nude mice or in culture containing androgen and compared these to UGS development in situ. RESULTS: Development of grafted tissues was morphologically and histologically similar to development in situ but differentiation occurred more rapidly. UGS growth in organ culture resulted in bud formation, but did not trigger cellular differentiation. However, the potential for differentiation was maintained and could be rescued by grafting tissues into nude mice. CONCLUSIONS: In vitro organ culture and renal grafting of UGS tissues may be appropriate models for studying prostatic bud formation, but only grafting is an appropriate model for prostatic differentiation.

Externalization of host cell protein kinase C during enteropathogenic Escherichia coli infection.

Enteropathogenic Escherichia coli (EPEC) is a common cause of diarrhea in children in developing countries. Protein kinase C (PKC), a serine- and threonine-directed protein kinase, is rapidly activated following EPEC infection and this is accompanied by its translocation to a membrane-bound location where it is tightly bound to phosphatidylserine (PS). EPEC infection causes host cell death, one of whose features is externalization of PS. We hypothesized that externalization of PS would be accompanied by externalization of PKC as well. We report that EPEC infection triggers the externalization of PKC to the outer surface of the host cell. Ecto-PKC remains firmly tethered to the cell but can be released by incubation with peptide or protein substrates for the enzyme. Ecto-PKC is intact and biologically active and able to phosphorylate protein substrates on the surface of the host cell. Phosphorylation of whole EPEC bacteria or EPEC-secreted proteins could not be detected. Externalization of PKC could be reproduced by the combination of an apoptotic stimulus (ultraviolet (UV) irradiation) and phorbol myristate acetate (PMA), a procedure which resulted in externalization of >25% of the total cellular content of PKC-alpha. In the presence of ATP, ecto-PKC inhibited UV-induced cell shrinkage, membrane blebbing, and propidium iodide uptake but not the activation of caspases 3 and 7. This is the first report that expression of an ecto-protein kinase is altered by a microbial pathogen and the first to note that externalization of PKC can accompany apoptosis.