International Mammalian Genome Society

The 13th International Mouse Genome Conference
October 31-November 3, 1999

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G5 The Identification and Cloning of a Novel Candidate Gene for the Amnionless Mutation

E. Lacy, S. Kalantry, S. Manning, C. Tomihara-Newberger, Y. Zhang, O. Haub, and K. Manova. Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10021

Histological and marker expression studies on amnionless (amn) have previously demonstrated that this recessive transgene insertional mouse mutation specifically blocks the assembly of the middle primitive streak, the portion of the streak that gives rise to paraxial and lateral trunk mesoderm during gastrulation. The formation of the middle streak region must be mediated by a pathway that is genetically separable from those directing the assembly of the proximal and distal streak regions, as these are functionally intact in the amn mutant. Furthermore, the disrupted amn gene must play a key role in this pathway.

Chimera analysis has shown that the amn gene acts not in the epiblast, which contains the middle streak precursors, but in an extraembryonic tissue, either extraembryonic ectoderm or visceral endoderm. Characterization of the mutant and wild type loci has recently identified only one gene that is physically disrupted by the transgene insertion. The disrupted gene is an excellent candidate for amn as it is expressed during gastrulation exclusively in the visceral endoderm, one of the extraembryonic tissues implicated in the chimera analysis as the site of amn function. Moreover, its expression is perturbed in mutant embryos. Consistent with the model that amn disrupts a required interaction between the epiblast and the extraembryonic visceral endoderm, this amn candidate encodes a novel gene product that is predicted to be a type I transmembrane protein. Targeted disruption as well as BAC rescue experiments are underway to assess the candidacy of this novel gene.


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