Fundamental studies of a developing heteromorphic sex chromosome pair in hynobiid salamanders.

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Hynobius leechii in Cheju Island (Korea) has a pair of female heteromorphic sex chromosomes in which the W chromosome shows polymorphism in its size and shape according to its habitat (Ikebe unpublished data). On the other hand, Hynobius tokyoensis in Kanto district (Japan) also has the same kind of sex chromosomes with polymorphism and the W chromosomes in this species are different from those of H.leechii. Heteromorphism in the two species are clearly caused by increase of heterochromatin in their W chromosomes. On the contrary, most of H.neburosus which inhabits between the habitats of H.leechii and H.tokyoensis, does not have a heteromorphic sex chromosome pair (Ikebe ＆ Kohno 1979, Ikebe et al. l987). Namely, it is natural to understand that the heteromorphic sex chromosome pairs should be developed independently in these two species.For obtaining the fundamental knowledge in promoting factors of heteromorphism in the sex chromosome pair of the two species, first, we tried to detect the repeat sequences which amplified in W chromosomes in H.leechii. Microdissection of the chromosomes was carried on the heterochromatin region and the centromeric region of the W chromosomes in metaphases of embryos from Songpanak (collected in 1998) and Kyorairi (collected in 2000). By using the microcloning, the three step degenerate oligonucleotide primed polymerase chain reaction (DOP-PCR), and the Southern blot hybridization, one DNA fragment which is originated in genomic DNA of H.leechii was isolated. The fragment was seqenced and the size was 208 base pairs. It was not specific to the female genomic DNA of H.leechii..In near future, we have to isolate the sequence which consists of heterochromatin in W chromosomes of H.leechii and have to compare it to that of H.tokyoensis.