1. Department of Animal Breeding and Genetics, National Institute of Animal Industry, Tsukuba Norin Danchi, Ibaraki-ken 305–0901, Japan.
2. Basic Research Division, Prima Meatpackers, Tsuchiura-shi, Ibaraki-ken 300–0841, Japan.
3. Laboratory of Developmental Biology, The Rockefeller University, New York, NY 10021, USA.