International Mammalian Genome Society

17th International Mouse Genome Conference

9-12 November 2003, Braunschweig, Germany


POSTER 177 - GENETIC INCOMPATIBILITY BETWEEN X-LINKED LOCI AND TWO AUTOSOMAL REGIONS CAUSES HYBRID BREAKDOWN BETWEEN TWO MOUSE SUBSPECIES

Oka A
Department of Mammalian Genetics, National Institute of Genetics

Co-Authors: 1) Mita A, 1) Sakurai N, 1) Yamamoto H, 2) Takagi N, 3) Takano-Shimizu T, 4) Toshimori K, 5) Moriwaki K, 1) Shiroishi T
Institutions: 1) Department of Mammalian Genetics, National Institute of Genetics, 2) Hokkaido University, 3) Department of Population Genetics, National Institute of Genetics, 4) Chiba University 5) RIKEN BioResource Center

Hybrid breakdown is a type of reproductive failure that appears after F2 generation of crosses between different species or subspecies. It is caused by incompatibility between alleles of interacting genes. We have studied the hybrid breakdown using a consomic strain, C57BL/6J-X MSM, in which the X chromosome of C57BL/6J (derived mostly from Mus musculus domesticus) is substituted by the X chromosome of the MSM/Ms strain (M. m. molossinus). Males of this consomic strain are sterile due to the abnormal sperm head morphology, whereas F1 hybrids between C57BL/6J and MSM/Ms are completely fertile. This finding implies that incompatibility between X-linked gene(s) and other chromosomal gene(s) causes the hybrid breakdown observed in C57BL/6J-XMSM. The previous our study revealed that at least three X-linked QTLs are responsible for the sperm head abnormality and the hybrid breakdown. We conducted the whole-genome scan to detect autosomal and/or Y chromosomal regions, which interact with the X-linked QTLs and underlie the genetic incompatibility. The result suggested that Chromosome 1 and 11 interact with the X-linked QTLs for proper male reproduction in parental MSM/Ms strain, and disruption of this interaction causes the hybrid breakdown. Furthermore, we characterized the sperm head abnormality in detail in C57BL/6J-XMSM. In spermiogenesis, nuclear protein histone is replaced by protamine, spermatid- and sperm-specific basic proteins, and it leads to chromatin condensation in spermatids. We found that this replacement did not occur properly in C57BL/6J-XMSM, which may cause the abnormal sperm head morphology.


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