Germ line-restricted,highly repeated DNA sequences and their chromosomal localization in a Japanese hagfish (Eptatretus okinoseanus)

The various species of Japanese hagfish, namely, Eptatretus okinoseanus (types A and B), Eptatretus burgeri and Myxine garmani, are known to eliminate a fraction of their chromosomes during early embryogenesis. High molecular weight DNA from germ line cells and somatic cells of these hagfish species was isolated and digested with different restriction enzymes. The DNA fragments were separated by agarose gel electrophoresis. Digestion with BamHI and DraI generated two weak bands and one weak band, respectively, that were estimated to be about 90, and 180 bp and about 90 bp long and were limited to the germ line DNA in both types of E. okinoseanus. DNA filter hybridization experiments showed that the two BamHI fragments and the one DraI fragment were present almost exclusively in the germ line DNA of E. okinoseanus. Thus, these DNA fragments appear to be eliminated during embryogenesis. Moreover, evidence was obtained that these fragments are highly and tandemly repeated. Molecular cloning and sequence analysis revealed that the BamHI fragments are mainly composed of a family of closely related sequences that are 95 bp long (EEEo1, for Eliminated Element of E. okinoseanus 1), and the DraI fragment is composed of another family of closely related sequences that are 85 bp long (EEEo2). The two DNA families account for about 19% of the total eliminated DNA in E. okinoseanus type A. Fluorescence in situ hybridization experiments demonstrated that the two families of DNA are located on several C-band-positive, small chromosomes that are limited to germ cells in both types of E. okinoseanus.by W. Hennig