title: Loss of mitogen-activated protein kinase kinase kinase 4 (MAP3K4) reveals a requirement for MAPK signalling in mouse sex determination.
abstract: Sex determination in mammals is controlled by the presence or absence of the Y-linked gene SRY. In the developing male (XY) gonad, sex-determining region of the Y (SRY) protein acts to up-regulate expression of the related gene, SOX9, a transcriptional regulator that in turn initiates a downstream pathway of testis development, whilst also suppressing ovary development. Despite the requirement for a number of transcription factors and secreted signalling molecules in sex determination, intracellular signalling components functioning in this process have not been defined. Here we report a role for the phylogenetically ancient mitogen-activated protein kinase (MAPK) signalling pathway in mouse sex determination. Using a forward genetic screen, we identified the recessive boygirl (byg) mutation. On the C57BL/6J background, embryos homozygous for byg exhibit consistent XY gonadal sex reversal. The byg mutation is an A to T transversion causing a premature stop codon in the gene encoding MAP3K4 (also known as MEKK4), a mitogen-activated protein kinase kinase kinase. Analysis of XY byg/byg gonads at 11.5 d post coitum reveals a growth deficit and a failure to support mesonephric cell migration, both early cellular processes normally associated with testis development. Expression analysis of mutant XY gonads at the same stage also reveals a dramatic reduction in Sox9 and, crucially, Sry at the transcript and protein levels. Moreover, we describe experiments showing the presence of activated MKK4, a direct target of MAP3K4, and activated p38 in the coelomic region of the XY gonad at 11.5 d post coitum, establishing a link between MAPK signalling in proliferating gonadal somatic cells and regulation of Sry expression. Finally, we provide evidence that haploinsufficiency for Map3k4 accounts for T-associated sex reversal (Tas). These data demonstrate that MAP3K4-dependent signalling events are required for normal expression of Sry during testis development, and create a novel entry point into the molecular and cellular mechanisms underlying sex determination in mice and disorders of sexual development in humans.
authors.affiliation: Mammalian Genetics Unit, Medical Research Council (MRC) Harwell, Oxfordshire, United Kingdom.
authors.forename: Debora
authors.initials: D
authors.lastname: Bogani
authors.forename: Pam
authors.initials: P
authors.lastname: Siggers
authors.forename: Rachel
authors.initials: R
authors.lastname: Brixey
authors.forename: Nick
authors.initials: N
authors.lastname: Warr
authors.forename: Sarah
authors.initials: S
authors.lastname: Beddow
authors.forename: Jessica
authors.initials: J
authors.lastname: Edwards
authors.forename: Debbie
authors.initials: D
authors.lastname: Williams
authors.forename: Dagmar
authors.initials: D
authors.lastname: Wilhelm
authors.forename: Peter
authors.initials: P
authors.lastname: Koopman
authors.forename: Richard A
authors.initials: RA
authors.lastname: Flavell
authors.forename: Hongbo
authors.initials: H
authors.lastname: Chi
authors.forename: Harry
authors.initials: H
authors.lastname: Ostrer
authors.forename: Sara
authors.initials: S
authors.lastname: Wells
authors.forename: Michael
authors.initials: M
authors.lastname: Cheeseman
authors.forename: Andy
authors.initials: A
authors.lastname: Greenfield
mesh_terms: D000818:Animals; D012734:Disorders of Sex Development; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D048768:MAP Kinase Kinase Kinase 4 / Q000172:deficiency* / Q000235:genetics; D020935:MAP Kinase Signaling System; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010053:Ovary / Q000166:cytology / Q000196:embryology; D017354:Point Mutation; D019849:Sex Determination Processes; D051876:Sex-Determining Region Y Protein / Q000235:genetics / Q000378:metabolism; D013737:Testis / Q000166:cytology / Q000196:embryology
chemical_list: D051876:Sex-Determining Region Y Protein; D048768:MAP Kinase Kinase Kinase 4