Recombinant inbred and congenic strains of the rat for genetic analysis of limb morphogenesis

Recombinant inbred (RI) and congenic strains carrying the polydactyly-luxate syndrome (PLS) provide an experimental model for the analysis of polygenic control of limb development. PLS is determined by a major gene Lx whose phenotypic expression is strongly influenced by the genetic background upon which it operates. The morphometric analysis of the skeleton of front and hind legs has been carried out. The morphotypes of PLS in RI strains exhibit a continuous variability and transgressive variation compared to BN.Lx and SHR.Lx morphotypes, which strongly indicates the polygenic effects on PLS manifestation. Quantitative trait loci (QTL) were searched for through correlation of genetic markers and morphometric traits. The association analysis revealed statistically significant correlations (P0.0003) of morphometric traits with two markers on chromosome 4 (Il6 and A2m) associated with the number of front feet and hind feet phalanges, respectively, one marker on chromosome 7 (D7Mit17) associated with the tibia length, and the somatostatin gene on chromosome 11 associated with the number of front feet phalanges. In addition, suggestive associations of morphometric traits with markers on further nine chromosomes have been found (correlation coefficients ranging from 0.5 to 0.6). The verification of all these findings is in progress by means of double congenic strains which, in addition to the Lx gene, carry differential chromosome segments with putative modifiers.