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Rethinking progesterone regulation of female reproductive cyclicity
Saturday, 2016/04/16 | 07:39:59
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Kaiyu Kubota, Wei Cui, Pramod Dhakal, Michael W. Wolfe, M. A. Karim Rumi, Jay L. Vivian, Katherine F. Roby, and Michael J. Soares PHYSIOLOGY SignificanceProgesterone possesses an essential role in regulating female fertility, with prominent actions throughout the female reproductive axis. The neuroendocrine actions of progesterone have been viewed as critical for the control of the female reproductive cycle. This basic principle has been reinforced by in vivo experimental paradigms, using hormone replacement as well as pharmacologic and genetic disruption of the progesterone receptor (PGR). Phenotypic characterization of Pgr null rats strengthens roles for progesterone in the regulation of female fertility, but not roles for progesterone as an essential determinant of female reproductive cyclicity, challenging an elemental principle of mammalian reproductive biology. Such findings demonstrate the benefits of genome editing in expanding available animal models for physiologic investigation. AbstractThe progesterone receptor (PGR) is a ligand-activated transcription factor with key roles in the regulation of female fertility. Much has been learned of the actions of PGR signaling through the use of pharmacologic inhibitors and genetic manipulation, using mouse mutagenesis. Characterization of rats with a null mutation at the Pgr locus has forced a reexamination of the role of progesterone in the regulation of the female reproductive cycle. We generated two Pgr mutant rat models, using genome editing. In both cases, deletions yielded a null mutation resulting from a nonsense frame-shift and the emergence of a stop codon. Similar to Pgr null mice, Pgr null rats were infertile because of deficits in sexual behavior, ovulation, and uterine endometrial differentiation. However, in contrast to the reported phenotype of female mice with disruptions in Pgr signaling, Pgr null female rats exhibit robust estrous cycles. Cyclic changes in vaginal cytology, uterine histology, serum hormone levels, and wheel running activity were evident in Pgr null female rats, similar to wild-type controls. Furthermore, exogenous progesterone treatment inhibited estrous cycles in wild-type female rats but not in Pgr-null female rats. As previously reported, pharmacologic antagonism supports a role for PGR signaling in the regulation of the ovulatory gonadotropin surge, a result at variance with experimentation using genetic ablation of PGR signaling. To conclude, our findings in the Pgr null rat challenge current assumptions and prompt a reevaluation of the hormonal control of reproductive cyclicity.
See http://www.pnas.org/content/113/15/4212.full PNAS April 12 2016; vol.113; no.15: 4212–4217
Fig. 1. Phenotypic characterization of PgrΔ136E1 null female rats. (A) Temporal assessment of vaginal opening in wild-type (+/+) and PgrΔ136E1 null (−/−) female rats (n = 50/genotype). (B and C) Fertility tests and litter sizes from wild-type males mated to wild-type and PgrΔ136E1 null female rats and PgrΔ136E1 null males mated to wild-type females. (n = 6/mating scheme). (D) Sexual behavior in wild-type and PgrΔ136E1 null female rats. The ratio of female lordosis behavior to male mounting was quantified (n = 6/genotype; Movie S1). (E–J) Effects of exogenous gonadotropins on ovulation (E), ovarian weight (F), gene expression (G), and hematoxylin and eosin-stained paraffin-embedded ovarian tissue sections (H–J) in wild-type and PgrΔ136E1 null female rats (n = 6/genotype). (J) Trapped oocyte within an unruptured follicle. (K–M) Examination of artificial decidualization in wild-type and PgrΔ136E1 null female rats. (K) Schematic presentation of hormone treatments (E2, estradiol; P4, progesterone). (L) Gross responses of uterine tissue to a deciduogenic stimulus. (M) Quantification of uterine horn weights from nonstimulated (Nonstim) and stimulated (Stim) uterine horns (n = 6/genotype). (N and O) Mammary gland development in hormonally treated wild-type and PgrΔ136E1 null female rats. (P) Examination of acute uterine responses to progesterone in wild-type and PgrΔ136E1 null rats. Progesterone responsive transcripts were monitored by quantitative RT-PCR (qRT-PCR) (n = 6/group; C, vehicle; P, progesterone). Results are presented as mean ± SEM. Asterisks or different letters above bars signify differences between means (P < 0.05). |
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