Differentiation of the Corpus Luteum of the Mink (Mustela vison): Mitogenic and Steroidogenic Potential of Luteal Cells from Embryonic Diapause and Postimplantation Gestation

Abstract

The mink corpus luteum (CL) involutes after ovulation and remains dormant, synthesizing low amounts of progesterone until reactivated to terminate embryonic diapause. We examined the mitotic and steroid synthetic capacity of luteal cells from the diapause and postimplantation phases of mink gestation. Cells from diapause divided in vitro, reaching confluence in 7-8 days. Three phenotypes were distinguishable: a fusiform cell in whorls, a hypertrophied epithelioid cell, and a small epithelioid cell. The first and second cell types divided in vitro after confluence, evidenced by localization of proliferating cell nuclear antigen (PCNA) in their nuclei. The small epithelioid cells were present in cell nests and showed no PCNA activity. Cells derived from reactivated CL did not reach confluence and had no PCNA activity. Progesterone accumulation was enhanced in luteal cells from diapause by LH, FSH, and dibutyryl (Bu2)cAMP, and by LH and (Bu2)cAMP in cells from reactivated CL. In luteal cells from the diapause phase of gestation, LH and (Bu2)cAMP induced increases in mRNA coding for steroidogenic acute regulatory protein, while cytochrome P450 side-chain cleavage enzyme mRNA was increased by prolactin, LH and (Bu2)cAMP. Cellular concentrations of 3beta-hydroxysteroid dehydrogenase-delta5-4-isomerase mRNA were increased by prolactin and (Bu2)cAMP. Thus, luteinization in the mink CL does not engender exit from the cell cycle, as both fusiform and hypertrophied cells from diapause divide in vitro. Reactivation appears to represent terminal differentiation. LH is capable of stimulating steroidogenesis in vitro in luteal cells from diapause, and prolactin and LH appear to have both specific and overlapping stimulatory effects on the CL of this species.

Unique biphasic progestagen profile in parturient and non-parturient giant pandas (Ailuropoda melanoleuca) as determined by faecal hormone monitoring

“…This includes earlier suggestions that the duration of the secondary phase is less variable than that of the primary phase (Enders 1952, Murphy & Moger 1977, Allais & Martinet 1978, Papke et al 1980, Canivenc & Bonnin 1981, Mead 1981, Foresman & Daniel 1983. Enders (1952) first postulated that the second, enhanced P 4 rise was associated with implantation of a previously free-floating embryo, a concept later proven for the mink (Allais & Martinet 1978, Murphy et al 1993, Douglas et al 1998, European badger (Canivenc & Bonnin 1981, Yamaguchi et al 2006) and spotted skunk (Mead 1981). What is much less well understood is the mechanism(s) responsible for provoking this significant P 4 surge.…”

“…What is much less well understood is the mechanism(s) responsible for provoking this significant P 4 surge. Early morphological studies in several carnivore species have revealed that corpora lutea (CL) form rapidly post-ovulation and remain unchanged until lutein cells increase in size, change in cellular ultrastructure and secrete more progestagens coincident with implantation (Wimsatt 1963, Mead 1986, Douglas et al 1998). An intriguing area for future research is determining how CL rejuvenation or enhancement is mediated and whether an extra-gonadal source of steroid contributes to the hormonal milieu associated with the secondary progestagen rise.…”

Expression of Vascular Endothelial Growth Factor Isoforms and Receptors Flt-1 and KDR During the Peri-Implantation Period in the Mink, Mustela vison1

“…The defining characteristics of obligate diapause are the developmental arrest of the embryo and the lack of an active corpus luteum, with attendant low levels of progesterone secretion [33]. In other species, estrogen and progesterone upregulate VEGF expression [24].…”

Embryonic diapause: development on hold

“…Increased circulating prolactin following the equinox induces expression of both prolactin and LH receptors in the mink corpus luteum, and these two hypophyseal factors then drive progesterone synthesis (Murphy and Rajkumar, 1985;Douglas et al, 1998a). A peculiarity of the mink corpus luteum of diapause is that the cells are not terminally differentiated by luteinization as in other species, but retain their capacity to divide (Douglas et al, 1998b). Implantation requires secretion of an as yet unknown factor from the corpus luteum .…”