title: Temperature-dependent sex determination in the American alligator: AMH precedes SOX9 expression.
abstract: Gonadal morphogenesis is very similar among mammals, birds, and reptiles. Despite this similarity, each group utilises quite different genetic triggers for sex determination. In mammals, testis development is initiated by action of the Y-chromosome gene SRY. Current evidence suggests that SRY may act together with a related gene, SOX9, to activate another gene(s) in the pathway of testicular differentiation. A downstream candidate for regulation by SRY and SOX9 is AMH. In mouse, Sox9 is expressed in the Sertoli cells of the embryonic testis and it precedes the onset of Amh expression. During mouse gonadogenesis, Amh is confined to the embryonic testis, although it later shows postnatal expression in the ovary. Reptiles such as the American alligator, which exhibit temperature-dependent sex determination (TSD) do not have dimorphic sex chromosomes and apparently no SRY orthologue. SOX9 is expressed during testis differentiation in the alligator; however, it appears to be expressed too late to cause testis determination. Here we describe the cloning and expression of the alligator AMH gene and show that AMH expression precedes SOX9 expression during testis differentiation. This is the opposite to that observed in the mouse where SOX9 precedes AMH expression. The data presented here, as well as findings from recent expression studies in the chick, suggest that AMH expression is not regulated by SOX9 in the non-mammalian vertebrates.
authors.affiliation: Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Victoria, Australia.
authors.forename: P S
authors.initials: PS
authors.lastname: Western
authors.forename: J L
authors.initials: JL
authors.lastname: Harry
authors.forename: J A
authors.initials: JA
authors.lastname: Graves
authors.forename: A H
authors.initials: AH
authors.lastname: Sinclair
mesh_terms: D000489:Alligators and Crocodiles / Q000196:embryology* / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D054304:Anti-Mullerian Hormone; D001483:Base Sequence; D002645:Chickens; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006023:Glycoproteins; D006131:Growth Inhibitors / Q000737:chemistry / Q000235:genetics*; D006609:High Mobility Group Proteins / Q000235:genetics*; D006801:Humans; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009024:Morphogenesis / Q000502:physiology*; D009095:Mullerian Ducts / Q000196:embryology; D055758:SOX9 Transcription Factor; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D019849:Sex Determination Processes; D013696:Temperature; D013735:Testicular Hormones / Q000737:chemistry / Q000235:genetics*; D013737:Testis / Q000196:embryology; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D006023:Glycoproteins; D006131:Growth Inhibitors; D006609:High Mobility Group Proteins; D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human; C527933:Sox9 protein, mouse; D013735:Testicular Hormones; D014157:Transcription Factors; D054304:Anti-Mullerian Hormone