Chromosome elimination in three Baltic, south Pacific and north-east Pacific hagfish species.

We have confirmed that chromosome elimination occurs in the cells of Myxine glutinosa, collected from the Baltic Sea off Sweden, Eptatretus cirrhatus from the south Pacific Ocean off the east coast of New Zealand, and E. stoutii from the north-east Pacific Ocean off Canada, similar to cells of four Japanese hagfish species. In M. Glutinosa, E. cirrhatus type A, E. cirrhatus type B and E. stoutii, the differences in chromosome number between spermatogonia (44, 72, 80 and 48) and somatic cells (28, 34, 34 and 34) were 16, 38, 46 and 14 respectively. The amount of DNA eliminated from presumptive somatic cells averaged 43.5%, 48.7%, 54.6% and 52.8% respectively. Euchromatic chromosomes and/or parts of chromosomes in addition to heterochromatic chromosomes were clearly eliminated in E. cirrhatus and E. stoutii. Adding our previous observations of four Japanese hagfish species, chromosome elimination occurs in all seven of the hagfish species. These results suggest that this phenomenon, chromosome elimination, generally occurs in the order Myxinida. In addition, B-chromosomes were observed in the germ cells of E. cirrhatus and E. stoutii, similar to the cells of E. okinoseanus, E. burgeri and Paramyxine atami (E. atami). This fact suggests that B-chromosomes might exist generally in the family Eptatretidae.