UCHIDA RAT (RSEY) - A NEW MUTANT RAT WITH CRANIOFACIAL ABNORMALITIES RESEMBLING THOSE OF THE MOUSE SEY MUTANT

A new mutant rat with small eyes (rSey) which was found in the course of breeding Sprague-Dawley rats is described. Genetic analysis demonst rates that rSey is inherited as an autosomal dominant mutation. Hetero zygotes (rSey/+) have small eyes, while homozygotes (rSey/rSey) do not develop lens and nasal placodes, resulting in lack of eyes and the no se and perinatal death. rSey does not affect Rnv other cranial regions including the maxilla, mandible, hyoid arch and otic vesicles. The ge netics and phenotype of the mutant rat closely resemble the Sey mutati on in the mouse, suggesting that rSey is the rat counterpart of the Se y mouse. Tissue recombination studies indicate that ectoderm from homo zygotes (rSey/ rSey) never differentiates into lens tissue even if it is cultured with normal optic vesicles from rSey/+ or +/+ embryos. In contrast, lens differentiation occurs when ectoderm from rSey/+ or +/ embryos is cultured with optic vesicles from rSey/+ or +/+ as well as rSey/rSey embryos. These results suggest that the failure of head ect oderm from rSey/rSey embryos to differentiate into lens results from d efects in the early differentiation signaling from the neural plate or underlying mesenchyme before the optic vesicle grows out to contact t he head ectoderm.