title: Early gonadogenesis in mammals: significance of long and narrow gonadal structure.
abstract: In mammalian embryogenesis, the gonadal primordium arises from the thickening of the coelomic epithelium, which results in a pair of extremely long and narrow gonadal structures along the anteroposterior axis. These gonadal structures are conserved in various mammalian species, suggesting a great advantage in properly receiving migrating primordial germ cells (PGCs) that are widely scattered throughout the hindgut tube. Soon after the PGCs settle, the bipotential gonads undergo sex determination into testes or ovaries by the sex-determining gene, Sry, which is expressed in supporting cell precursors in a center-to-pole manner. Such a long, narrow gonadal structure bestows a considerable time lag on Sry expression between the center and pole regions, but testiculogenesis with cord formation and Leydig cell differentiation occurs synchronously throughout the whole organ. This synchronous testiculogenesis could be explained by a positive-feedback mechanism between SOX9 (another SRY-related transcription factor) and FGF9 downstream of Sry. FGF signals are likely secreted from the center region, rapidly diffuse into the poles, and then induce the establishment of SOX9 expression in Sertoli cells in the pole domains. This work focuses on recent knowledge of the molecular and cellular events of PGC migration, gonadogenesis, and testiculogenesis, and their biological significance in mammalian embryogenesis.
authors.affiliation: Department of Veterinary Anatomy, The University of Tokyo, Tokyo, Japan.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Harikae
authors.forename: Kento
authors.initials: K
authors.lastname: Miura
authors.forename: Yoshiakira
authors.initials: Y
authors.lastname: Kanai
mesh_terms: D000818:Animals; D002465:Cell Movement; D053595:Embryonic Stem Cells / Q000166:cytology; D005260:Female; D018507:Gene Expression Regulation, Developmental; D024282:Genes, sry; D005854:Germ Cells / Q000166:cytology; D006066:Gonads / Q000196:embryology*; D008297:Male; D008322:Mammals; D055758:SOX9 Transcription Factor / Q000235:genetics; D012733:Sex Differentiation / Q000235:genetics; D013737:Testis / Q000196:embryology
chemical_list: D055758:SOX9 Transcription Factor