{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,3]],"date-time":"2026-08-03T15:04:41Z","timestamp":1785769481756,"version":"3.56.0"},"reference-count":47,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2021,8,17]],"date-time":"2021-08-17T00:00:00Z","timestamp":1629158400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Animals"],"abstract":"<jats:p>It was the aim of this study to characterize the development of the gonads and genital ducts in the equine fetus around the time of sexual differentiation. This included the identification and localization 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 23-fold from 45 to 60 days of gestation, and an even greater increase was observed in the 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 &lt; 0.05) by fetal sex. Most primordial germ cells (86.8 \u00b1 3.2% in females and 84.6 \u00b1 4.7% in males) were characterized as pluripotent according to co-localization with CD117. However, only a very small percentage of primordial germ cells were proliferating (7.5 \u00b1 1.7% in females and 3.2 \u00b1 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.<\/jats:p>","DOI":"10.3390\/ani11082422","type":"journal-article","created":{"date-parts":[[2021,8,17]],"date-time":"2021-08-17T21:27:40Z","timestamp":1629235660000},"page":"2422","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Sexual Differentiation and Primordial Germ Cell Distribution in the Early Horse Fetus"],"prefix":"10.3390","volume":"11","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9599-0830","authenticated-orcid":false,"given":"Dragos","family":"Scarlet","sequence":"first","affiliation":[{"name":"Obstetrics, Gynecology and Andrology, Department for Small Animals and Horses, University of Veterinary Medicine Vienna, Veterin\u00e4rplatz 1, 1210 Vienna, Austria"},{"name":"Institute of Veterinary Anatomy and Clinic of Reproductive Medicine, Vetsuisse Faculty Z\u00fcrich, Winterthurerstrasse 260, 8057 Z\u00fcrich, Switzerland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stephan","family":"Handschuh","sequence":"additional","affiliation":[{"name":"Vetcore Facility for Research, University of Veterinary Medicine Vienna, Veterin\u00e4rplatz 1, 1210 Vienna, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9709-0919","authenticated-orcid":false,"given":"Ursula","family":"Reichart","sequence":"additional","affiliation":[{"name":"Vetcore Facility for Research, University of Veterinary Medicine Vienna, Veterin\u00e4rplatz 1, 1210 Vienna, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8046-6254","authenticated-orcid":false,"given":"Giorgia","family":"Podico","sequence":"additional","affiliation":[{"name":"Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, IL 61802, USA"},{"name":"Department of Comparative Biosciences, College of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, IL 61802, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7337-8002","authenticated-orcid":false,"given":"Robyn E.","family":"Ellerbrock","sequence":"additional","affiliation":[{"name":"Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, IL 61802, USA"},{"name":"Department of Comparative Biosciences, College of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, IL 61802, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3286-2441","authenticated-orcid":false,"given":"Sebasti\u00e1n","family":"Demyda-Peyr\u00e1s","sequence":"additional","affiliation":[{"name":"Department of Animal Production, School of Veterinary Sciences, National University of La Plata and CONICET CCT-La Plata, Calle 60 and 118 S\/N, 1900 La Plata, Argentina"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3799-6641","authenticated-orcid":false,"given":"Igor F.","family":"Canisso","sequence":"additional","affiliation":[{"name":"Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, IL 61802, USA"},{"name":"Department of Comparative Biosciences, College of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, IL 61802, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5038-188X","authenticated-orcid":false,"given":"Ingrid","family":"Walter","sequence":"additional","affiliation":[{"name":"Vetcore Facility for Research, University of Veterinary Medicine Vienna, Veterin\u00e4rplatz 1, 1210 Vienna, Austria"},{"name":"Institute of Pathology, Department of Pathobiology, University of Veterinary Medicine Vienna, Veterin\u00e4rplatz 1, 1210 Vienna, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6077-7362","authenticated-orcid":false,"given":"Christine","family":"Aurich","sequence":"additional","affiliation":[{"name":"Center for Artificial Insemination and Embryo Transfer, University of Veterinary Medicine Vienna, Veterin\u00e4rplatz 1, 1210 Vienna, Austria"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,8,17]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"240","DOI":"10.1038\/346240a0","article-title":"A gene from the human sex-determining region encodes a protein with homology to a conserved DNA-binding motif","volume":"346","author":"Sinclair","year":"1990","journal-title":"Nature"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1152\/physrev.00009.2006","article-title":"Sex determination and gonadal development in mammals","volume":"87","author":"Wilhelm","year":"2007","journal-title":"Physiol. Rev."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"7","DOI":"10.1159\/000338612","article-title":"How to make a gonad: Cellular mechanisms governing formation of the testes and ovaries","volume":"7","author":"Ungewitter","year":"2013","journal-title":"Sex Dev."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1095\/biolreprod1.Supplement_1.1","article-title":"Development of Mammalian Testes and Genital Ducts1","volume":"1","author":"Gier","year":"1969","journal-title":"Biol. Reprod."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"589","DOI":"10.1093\/humrep\/dem411","article-title":"Expression of pluripotent stem cell markers in the human fetal ovary","volume":"23","author":"Kerr","year":"2008","journal-title":"Hum. Reprod."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"15961","DOI":"10.1038\/s41598-017-15931-3","article-title":"Temporal expression pattern of genes during the period of sex differentiation in human embryonic gonads","volume":"7","author":"Mamsen","year":"2017","journal-title":"Sci. Rep."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"366","DOI":"10.1095\/biolreprod65.2.366","article-title":"Temporal and spatial localization patterns of Gata4 during porcine gonadogenesis","volume":"65","author":"McCoard","year":"2001","journal-title":"Biol. Reprod."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"513","DOI":"10.1530\/rep.0.1210513","article-title":"Fetomaternal interactions and influences during equine pregnancy","volume":"121","author":"Allen","year":"2001","journal-title":"Reproduction"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"244","DOI":"10.1111\/evj.12556","article-title":"Changes in maternal androgens and oestrogens in mares with experimentally-induced ascending placentitis","volume":"49","author":"Canisso","year":"2017","journal-title":"Equine. Vet. J."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"445","DOI":"10.1530\/REP-17-0239","article-title":"Equine fetal adrenal, gonadal and placental steroidogenesis","volume":"154","author":"Legacki","year":"2017","journal-title":"Reproduction"},{"key":"ref_11","first-page":"389","article-title":"Dehydroepiandrosterone synthesis by the fetal foal and its importance as an oestrogen precursor","volume":"32","author":"Pashen","year":"1982","journal-title":"J. Reprod. Fertil. Suppl."},{"key":"ref_12","unstructured":"Walt, M.L., Stabenfeldt, G.H., Hughes, J.P., Neely, D.P., and Bradbury, R. (1979). Development of the equine ovary and ovulation fossa. J. Reprod. Fertil. Suppl., 471\u2013477."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"118","DOI":"10.1016\/j.theriogenology.2017.11.036","article-title":"Reproductive system development in male and female horse embryos and fetuses: Gonadal hyperplasia revisited","volume":"108","author":"Barreto","year":"2018","journal-title":"Theriogenology"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"34","DOI":"10.1016\/j.anireprosci.2014.01.014","article-title":"Sex determination in horses\u2014current status and future perspectives","volume":"146","author":"Aurich","year":"2014","journal-title":"Anim. Reprod. Sci."},{"key":"ref_15","first-page":"180","article-title":"The role of ovarian surface epithelium in folliculogenesis during fetal development of the bovine ovary: A histological and immunohistochemical study","volume":"7","author":"Kenngott","year":"2013","journal-title":"Sex. Dev. Genet. Mol. Biol. Evol. Endocrinol. Embryol. Pathol. Sex Determ. Differ."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"579","DOI":"10.1111\/j.1440-169X.1992.00579.x","article-title":"Co-Expression of Cytokeratins and Vimentin in Sheep Cumulus-Oocyte Complexes. Alteration of Intermediate Filament Distribution by Acrylamide","volume":"34","author":"Gall","year":"1992","journal-title":"Dev. Growth Differ."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"153","DOI":"10.1159\/000369203","article-title":"Expression of Intermediate Filaments and Germ Cell Markers in the Developing Bovine Ovary: An Immunohistochemical and Laser-Assisted Microdissection Study","volume":"200","author":"Kenngott","year":"2014","journal-title":"Cells Tissues Organs."},{"key":"ref_18","first-page":"1315","article-title":"Expression of Epithelial and Mesenchymal Differentiation Markers in the Early Human Gonadal Development","volume":"300","author":"Martinovic","year":"2017","journal-title":"Anat. Rec. Hoboken N. J. 2007"},{"key":"ref_19","first-page":"335","article-title":"Differential distribution of laminin chains in the development and sex differentiation of mouse internal genitalia","volume":"39","author":"Ekblom","year":"1995","journal-title":"Int. J. Dev. Biol."},{"key":"ref_20","first-page":"151","article-title":"Sex-specific localization of laminin alpha 5 chain in the differentiating rat testis and ovary","volume":"64","author":"Miner","year":"1999","journal-title":"Differ. Res. Biol. Divers."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"197","DOI":"10.1007\/s00441-016-2371-4","article-title":"Role of Notch signaling in granulosa cell proliferation and polyovular follicle induction during folliculogenesis in mouse ovary","volume":"365","author":"Terauchi","year":"2016","journal-title":"Cell Tissue Res."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"371","DOI":"10.1292\/jvms.55.371","article-title":"Developmental changes in paramesonephric and mesonephric ducts and the external genitalia in swine fetuses during sexual differentiation","volume":"55","author":"Inomata","year":"1993","journal-title":"J. Vet. Med. Sci."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1002\/ar.1090810102","article-title":"The relation of the growing m\u00fcllerian duct to the wolffian duct and its importance for the genesis of malformations","volume":"81","author":"Gruenwald","year":"1941","journal-title":"Anat. Rec."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"223","DOI":"10.1111\/j.1439-0264.2007.00835.x","article-title":"Expression and distribution of intermediate-filament proteins and laminin during the development of the bovine Mullerian duct","volume":"37","author":"Kenngott","year":"2008","journal-title":"Anat. Histol. Embryol."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"281","DOI":"10.1159\/000364935","article-title":"Molecular Genetics of M\u00fcllerian Duct Formation, Regression and Differentiation","volume":"8","author":"Mullen","year":"2014","journal-title":"Sex. Dev."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"493","DOI":"10.1016\/j.ydbio.2007.03.027","article-title":"Cellular mechanisms of M\u00fcllerian duct formation in the mouse","volume":"306","author":"Orvis","year":"2007","journal-title":"Dev. Biol."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Childs, A.J., Cowan, G., Kinnell, H.L., Anderson, R.A., and Saunders, P.T. (2011). Retinoic Acid signalling and the control of meiotic entry in the human fetal gonad. PLoS ONE, 6.","DOI":"10.1371\/journal.pone.0020249"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"438","DOI":"10.1095\/biolreprod.108.075747","article-title":"Global gene expression in the human fetal testis and ovary","volume":"81","author":"Houmard","year":"2009","journal-title":"Biol. Reprod."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"2343","DOI":"10.1089\/scd.2011.0730","article-title":"LIN28 is selectively expressed by primordial and pre-meiotic germ cells in the human fetal ovary","volume":"21","author":"Childs","year":"2012","journal-title":"Stem. Cells Dev."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"e174","DOI":"10.1111\/j.1365-2605.2011.01148.x","article-title":"Expression and interdependencies of pluripotency factors LIN28, OCT3\/4, NANOG and SOX2 in human testicular germ cells and tumours of the testis","volume":"34","author":"Gillis","year":"2011","journal-title":"Int. J. Androl."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"909","DOI":"10.1038\/nature08210","article-title":"A role for Lin28 in primordial germ-cell development and germ-cell malignancy","volume":"460","author":"West","year":"2009","journal-title":"Nature"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"701390","DOI":"10.1155\/2015\/701390","article-title":"High LIN28A Expressing Ovarian Cancer Cells Secrete Exosomes That Induce Invasion and Migration in HEK293 Cells","volume":"2015","author":"Enriquez","year":"2015","journal-title":"Biomed. Res. Int."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"477","DOI":"10.1093\/molehr\/gas025","article-title":"The pluripotency factor LIN28 in monkey and human testes: A marker for spermatogonial stem cells?","volume":"18","author":"Aeckerle","year":"2012","journal-title":"Mol. Hum. Reprod."},{"key":"ref_34","doi-asserted-by":"crossref","unstructured":"Curran, S., Urven, L., and Ginther, O.J. (1997). Distribution of putative primordial germ cells in equine embryos. Equine. Vet. J. Suppl., 72\u201376.","DOI":"10.1111\/j.2042-3306.1997.tb05105.x"},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Lee, G., Jung, H., and Yoon, M. (2016). The Lin28 expression in stallion testes. PLoS ONE, 11.","DOI":"10.1371\/journal.pone.0165011"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"39","DOI":"10.1016\/j.anireprosci.2014.11.004","article-title":"The KIT is a putative marker for differentiating spermatogonia in stallions","volume":"152","author":"Jung","year":"2015","journal-title":"Anim. Reprod. Sci."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"77","DOI":"10.1016\/j.theriogenology.2019.09.025","article-title":"Assessment of peripheral markers and ultrasonographic parameters in pregnant mares receiving intramuscular or intrauterine cloprostenol","volume":"142","author":"Podico","year":"2020","journal-title":"Theriogenology"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"1156","DOI":"10.1071\/RDv32n2Ab61","article-title":"Low plasma progestin concentration during the early postovulatory phase impairs equine conceptus development in the late preimplantation phase","volume":"32","author":"Okada","year":"2020","journal-title":"Reprod. Fertil. Dev."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"968","DOI":"10.1016\/j.theriogenology.2008.05.059","article-title":"Expression of anti-Mullerian hormone (AMH) in equine granulosa-cell tumors and in normal equine ovaries","volume":"70","author":"Ball","year":"2008","journal-title":"Theriogenology"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"676","DOI":"10.1038\/nmeth.2019","article-title":"Fiji: An open-source platform for biological-image analysis","volume":"9","author":"Schindelin","year":"2012","journal-title":"Nat. Methods"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"412","DOI":"10.1111\/age.12543","article-title":"Sex chromosomal abnormalities associated with equine infertility: Validation of a simple molecular screening tool in the Purebred Spanish Horse","volume":"48","author":"Anaya","year":"2017","journal-title":"Anim. Genet."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"14","DOI":"10.1016\/j.ydbio.2011.01.011","article-title":"Two distinct origins for Leydig cell progenitors in the fetal testis","volume":"352","author":"DeFalco","year":"2011","journal-title":"Dev. Biol."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"2883","DOI":"10.1242\/dev.126.13.2883","article-title":"Mesonephric cell migration induces testis cord formation and Sertoli cell differentiation in the mammalian gonad","volume":"126","author":"Tilmann","year":"1999","journal-title":"Development"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"166","DOI":"10.1111\/j.1439-0442.1989.tb00717.x","article-title":"Origin of m\u00fcllerian duct and its later developmental changes in relation to wolffian duct in bovine fetuses","volume":"36","author":"Inomata","year":"1989","journal-title":"J. Vet. Med. Ser. A"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"385","DOI":"10.1007\/BF00196840","article-title":"The role of fibronectin and laminin in development and migration of the avian Wolffian duct with reference to somitogenesis","volume":"183","author":"Jacob","year":"1991","journal-title":"Anat. Embryol."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"1967","DOI":"10.1242\/dev.056143","article-title":"\u03b2-Catenin is essential for M\u00fcllerian duct regression during male sexual differentiation","volume":"138","author":"Kobayashi","year":"2011","journal-title":"Development"},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"533","DOI":"10.1016\/j.tvjl.2014.08.026","article-title":"Expression of putative markers of pluripotency in equine embryonic and adult tissues","volume":"202","author":"Esteves","year":"2014","journal-title":"Vet. J."}],"container-title":["Animals"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2076-2615\/11\/8\/2422\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T06:45:54Z","timestamp":1760165154000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2076-2615\/11\/8\/2422"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,8,17]]},"references-count":47,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2021,8]]}},"alternative-id":["ani11082422"],"URL":"https:\/\/doi.org\/10.3390\/ani11082422","relation":{"has-preprint":[{"id-type":"doi","id":"10.20944\/preprints202106.0662.v1","asserted-by":"object"}]},"ISSN":["2076-2615"],"issn-type":[{"value":"2076-2615","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,8,17]]}}}