Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Sexual Differentiation and Primordial Germ Cell Distribution in the Early Horse Fetus

Version 1 : Received: 25 June 2021 / Approved: 28 June 2021 / Online: 28 June 2021 (14:14:06 CEST)

A peer-reviewed article of this Preprint also exists.

Scarlet, D.; Handschuh, S.; Reichart, U.; Podico, G.; Ellerbrock, R.E.; Demyda-Peyrás, S.; Canisso, I.F.; Walter, I.; Aurich, C. Sexual Differentiation and Primordial Germ Cell Distribution in the Early Horse Fetus. Animals 2021, 11, 2422. Scarlet, D.; Handschuh, S.; Reichart, U.; Podico, G.; Ellerbrock, R.E.; Demyda-Peyrás, S.; Canisso, I.F.; Walter, I.; Aurich, C. Sexual Differentiation and Primordial Germ Cell Distribution in the Early Horse Fetus. Animals 2021, 11, 2422.

Journal reference: Animals 2021, 11, 2422
DOI: 10.3390/ani11082422

Abstract

It was the aim of this study to provide a more precise timeframe of development of the gonads and genital ducts in the equine fetus around the time of sexual differentiation. This included the identification and localisation of the primordial germ cell population. Equine fetuses between 45 and 60 days of gestation were evaluated using a combination of micro-computed tomography scanning, immunohistochemistry, and multiplex immunofluorescence. Fetal gonads increased in size by 23-fold from 45 to 60 days of gestation, paralleled by a greater increase in metanephros volume. Signs of mesonephros atrophy were detected during this time. Tubular structures of the fetal testes were present from day 50 onwards, whereas cell clusters dominated in the fetal ovary. The genital ducts were well-differentiated and presented a lumen in all samples. No sign of mesonephric or paramesonephric duct degeneration was detected. Expression of AMH was strong in the fetal testes but absent in ovaries. Irrespective of sex, primordial germ cells selectively expressed LIN28. Migration of primordial germ cells from the mesonephros to the gonad was detected at 45 days, but not at 60 days of development. Their number and distribution within the gonad were influenced (p<0.05) by fetal sex. Most primordial germ cells (86.8 ± 3.2% in females and 84.6 ± 4.7% in males) were characterized as pluripotent according to co-localization with CD117. However, only a very small percentage of primordial germ cells was proliferating (7.5 ± 1.7% in females and 3.2 ± 1.2% in males) based on co-localization with Ki67. It can be concluded that gonadal sexual differentiation in the horse occurs asynchronously with regard to sex but already before 45 days of gestation.

Keywords

gonad; germ cell; genital duct; fetus; horse

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