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James V Constantino, Ana Carranza-Martin, Christopher Premanandan, Brian W Kirkpatrick, Milo C Wiltbank, and Alvaro Garcia-Guerra

In brief

The bovine high fecundity allele, Trio, results in the occurrence of multiple ovulations and is characterized by antral follicles that develop slower and acquire ovulatory capacity at smaller sizes. This study provides novel information on the effect of the Trio allele on early folliculogenesis.


The bovine high fecundity allele, Trio, causes overexpression in granulosa cells (GCs) of SMAD6, an inhibitor of BMP15-activated SMAD signalling. Furthermore, the Trio allele results in antral follicles that develop slower, acquire ovulatory capacity at smaller sizes, and have three-fold greater ovulation rate compared to half-sib non-carriers. The present study was designed to determine preantral follicle numbers and size in Trio carrier and non-carrier cattle testing the hypothesis that inhibition of SMAD signalling would alter preantral follicle activation and/or growth. Ovarian tissues from Trio carrier (n = 12) and non-carrier (n = 12) heifers were obtained by laparotomy after follicle wave synchronization. Follicle numbers and dimensions were determined for each stage of development (primordial, transitional, primary, and secondary) from paraffin-embedded sections. There were no differences in the number of primordial, transitional, or secondary follicles or in antral follicle count, circulating AMH, or ovarian volume between carriers and non-carriers. Trio carriers had ~2.5-fold greater (P < 0.01) number of primary follicles than non-carriers, and transitional and primary follicles were larger (~1.2-fold; P < 0.1) in Trio carriers. Oocyte volume of primordial and transitional follicles was not different between genotypes; however, oocytes were larger (P < 0.05) in primary (~1.3-fold) and secondary (~1.8-fold) follicles for Trio carriers. Granulosa cell numbers were not different (P > 0.3) between carriers and non-carriers, irrespective of the stage of development. These results suggest that, after primordial follicle activation, follicles in Trio carrier cattle have slower progression through the primary stage, hence the larger oocyte and greater number of primary follicles.

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Riley E Thompson, Aime K Johnson, Pouya Dini, Margherita Y Turco, Tulio M Prado, Christopher Premanandan, Graham J Burton, Barry A Ball, Brian K Whitlock, and Budhan S Pukazhenthi

The endometrium, the inner uterine lining, is composed of cell layers that come in direct contact with an embryo during early pregnancy and later with the fetal placenta. The endometrium is responsible for signals associated with normal reproductive cyclicity as well as maintenance of pregnancy. In the mare, functionally competent in vitro models of the endometrium have not been successful. Furthermore, the ability to study various reproductive processes in vitro may allow critical evaluation of signaling pathways involved in the reproductive diseases of animals that cannot be handled frequently, such as various wildlife species. Here we report the establishment of organoids, 3D structures, derived from fresh and frozen–thawed equine endometrium (Equus ferus caballus and E. f. przewalskii). Although organoids from domestic mares responded to exogenous hormonal stimuli, organoids from Przewalski’s horse failed to respond to exogenous hormones. The present study represents a ‘first’ for any large animal model or endangered species. These physiologically functional organoids may facilitate improved understanding of normal reproductive mechanisms, uterine pathologies, and signaling mechanisms between the conceptus and endometrium and may lead to the development of novel bioassays for drug discovery.