title: Bcl-x and Bax regulate mouse primordial germ cell survival and apoptosis during embryogenesis.
abstract: Restricted germ cell loss through apoptosis is initiated in the fetal gonad around embryonic day 13.5 (E13.5) as part of normal germ cell development. The mechanism of this germ cell attrition is unknown. We show that Bcl-x plays a crucial role in maintaining the survival of mouse germ cells during gonadogenesis. A bcl-x hypomorphic mouse was generated through the introduction of a neomycin (neo) gene into the promoter of the bcl-x gene by homologous recombination. Mice that contained two copies of the hypomorphic allele had severe reproductive defects attributed to compromised germ cell development. Males with two mutant alleles lacked spermatogonia and were sterile; females showed a severely reduced population of primordial and primary follicles and exhibited greatly impaired fertility. Primordial germ cells (PGCs) in bcl-x hypomorph mice migrated to the genital ridge by E12.5 but were depleted by E15.5, a time when Bcl-x and Bax were present. Two additional bcl-x transcripts were identified in fetal germ cells more than 300 bp upstream of previously reported start sites. Insertion of a neo cassette led to a down-regulation of the bcl-x gene at E12.5 in the hypomorph. Bax was detected by immunohistochemistry in germ cells from bcl-x hypomorph and control testes at E12.5 and E13.5. Bcl-x function was restored, and animals of both genders were fertile after removal of the neo selection cassette using Cre-mediated recombination. Alternatively, the loss of Bcl-x function in the hypomorph was corrected by the deletion of both copies of the bax gene, resulting in a restoration of germ cell survival. These findings demonstrate that the balance of Bcl-x and Bax control PGC survival and apoptosis.
authors.affiliation: Laboratory of Genetics and Physiology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: E B
authors.initials: EB
authors.lastname: Rucker
authors.forename: P
authors.initials: P
authors.lastname: Dierisseau
authors.forename: K U
authors.initials: KU
authors.lastname: Wagner
authors.forename: L
authors.initials: L
authors.lastname: Garrett
authors.forename: A
authors.initials: A
authors.lastname: Wynshaw-Boris
authors.forename: J A
authors.initials: JA
authors.lastname: Flaws
authors.forename: L
authors.initials: L
authors.lastname: Hennighausen
mesh_terms: D000818:Animals; D001483:Base Sequence; D002470:Cell Survival / Q000235:genetics; D004622:Embryo, Mammalian / Q000166:cytology*; D005314:Embryonic and Fetal Development / Q000235:genetics; D005260:Female; D018507:Gene Expression Regulation, Developmental; D005854:Germ Cells / Q000502:physiology*; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008817:Mice, Mutant Strains; D008969:Molecular Sequence Data; D009865:Oocytes / Q000473:pathology; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics* / Q000378:metabolism; D013093:Spermatogonia / Q000473:pathology; D013737:Testis / Q000196:embryology; D014158:Transcription, Genetic; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: C494827:Bax protein, mouse; C494812:Bcl2l1 protein, mouse; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein