Genetic dissection of X-linked interspecific hybrid placental dysplasia incongenic mouse strains

Interspecific hybridization in the genus Mus results in male sterility and X-linked placental dysplasia. We have generated several congenic laboratory mouse lines (Mus musculus) in which different parts of the maternal X chro mosome were derived from M spretus. A strict positive correlation between p lacental weight and length of the M. spretus-derived part of the X chromoso me was shown. Detailed analysis was carried out with one congenic strain th at retained a M. spretus interval between 12.0 and 30.74 cM. This strain co nsistently produced hyperplastic placentas that exhibited an average weight increase of 180% over the weight of control placentas. In derived subconge nic strains, however, increased placental weight could no longer be observe d. Morphometric analysis of these placentas revealed persistence of abnorma l morphology. Fully developed placental hyperplasia could be reconstituted by recombination of proximal and central M, spretus intervals with an inter vening il I. musculus region. These results may suggest that placental dysp lasia of interspecific mouse hybrids is caused by multiple loci clustered o n the X chromosome that act synergistically. Alternatively, it is possible that changes in chromatin structure in interspecific hybrids that influence gene expression are dependent on the length of the alien chromosome.