Quantitative Analysis of Striped Coat-Color Patterns in Large White→Duroc Chimeric Pigs With Special Reference to the Genetic Control Mechanisms of the Dominant Black-Eyed White Phenotype

Coat colors of four chimeric pigs produced by the microinjection of dissociated blastomeres of (Landrace × Large White) blastocysts to the blastocyst cavity of (Duroc × Duroc) blastocysts (Kashiwazaki et al., 1992) exhibited characteristic horizontal stripe-patterns. We carried out quantitative analysis of those patterns in order to derive information concerning the genetic regulatory mechanisms of the dominant black-eyed white phenotypes in the pig. In the four chimeras, the theoretical mean widths of the single-clone stripe calculated from the estimated widths of minimal recognizable stripe (MRS) (Tachi, 1988) were 2.1 ± 0.1, 2.23 ± 0.15,1.89 ± 0.06, and 1.93 ± 0.28 cm respectively. The estimated number of single-clone stripes in the thoracico-lumbar region of those animals were 42.3, 40.7, 46.3, 44.2, and about twice the mean number of vertebrae in the same region (Duroc, 20 or 21; Large White, 21 or 22). Furthermore, the mean length of thoracico-lumbar vertebrate in two of the chimeric pigs, as measured on X-ray radiographs, was approximately twice the mean single-clone stripe width. It was concluded that the stripe-patterns of the chimeric pigs probably represented the dermatome patterns of epidermis; and in the pig, a single somite was likely to be derived from the clones of two primordial cells, as originally proposed by Gearhart & Mintz (1972) in the mouse. It was suggested, furthermore, that in the Large White→Duroc chimeric pigs, melanocytes that migrated into the region of skin formed by a Large White dermatome could not survive, thus creating a clearly demarcated white stripe. Possible involvement of KL or c-kit in the dominant black-eyed white phenotype of the pig is discussed.