Chromatin diminution and chromosome elimination in four Japanese hagfish species

Abstract

Cytogenetic examination of four Japanese hagfish species belonging to the order Myxinida (Eptatretus okinoseanus, E. burgeri, Paramyxine atami, and Myxine garmani) revealed differences in chromosome number between germ cells (spermatocytes and spermatogonia) and somatic cells (liver, blood, gill, and kidney). The differences in chromosome number between spermatogonia (54, 52, 48, and 16) and somatic cells (34, 36, 34, and 14) were 20, 16, 14, and 2 in E. okinoseanus, E. burgeri, P. atami, and M. garmani, respectively. The amount of DNA in a somatic cell (2C) relative to that in a germ cell (2C) averaged 54.6% (E. okinoseanus type A), 44.9% (E. okinoseanus type B), 79.1 % (E. burgeri), 60.0% (P. atami), and 70.2 % (M. garmani). These results clearly indicate that chromosome elimination takes place during early cleavage in the four hagfish species of Myxinida living in Japanese waters, except in the ancestral germline cells. C-banding of metaphase chromosome preparations of germline and somatic cells from each hagfish species revealed that the C-band-positive chromatin in the ancestral somatic cells had been almost completely eliminated. Three patterns of elimination of this chromatin are discussed.

Germ line-restricted supernumerary (B) chromosomes in <i>Eptatretus okinoseanus</i>

“…The results of C-banding by means of our modified C-banding technique were consistent with those obtained by Sumner's (1972) barium/saline/Giemsa (BSG) technique, described in a previous report (Nakai et al. 1991).…”

“…The present data on chromosome numbers, as shown in Tables I and II. give the modal chromosome number of somatic cells as 34 and that of spermatogonia as 54 in all type A speci mens, as in the previous report (Nakai et al, 1991), whereas the modal number for spermatogonia varied between 54 and 62 in type B specimens. Moreover, intraindividual variations in the chromosome number of spermatogonia from both types were clearly found.…”

“…Nakai andKohno (1987). andNakai et al (1991) reported that chromosome elimination occurs in all four species of Japanese hagfish (Eptatretus okino seanus, E. burgeri, Paramyxine atami, and M yxine garmani [Cyclostomata, Vertebrata]) during their early embryogenesis. Except for M. garmani, the chromosomes (or parts of chromo somes) that are eliminated consist of C-band-positive chroma tin: consequently, the somatic cells have no C-band-positive chromatin.…”

“…andNakai et al (1991) reported that chromosome elimination occurs in all four species of Japanese hagfish (Eptatretus okino seanus, E. burgeri, Paramyxine atami, and M yxine garmani [Cyclostomata, Vertebrata]) during their early embryogenesis. Except for M. garmani, the chromosomes (or parts of chromo somes) that are eliminated consist of C-band-positive chroma tin: consequently, the somatic cells have no C-band-positive chromatin.In a previous paper (Nakai et al, 1991), we reported the chromosome number in somatic cells of E. okinoseanus as 2n = 34 and that in spermatogonia as 2n = 54. Furthermore, in this species, there are two types of individuals with respect to the quantity and distribution of C-band-positive chromatin in germ cells.…”

Adult murine neurons: their chromatin and chromosome changes and failure to support embryonic development as revealed by nuclear transfer

“…That the majority of adult cerebral neurons display chromosome changes was quite unexpected. Chromosomal or DNA deletions occur in the early development of some animals, such as the nematode Ascaris megalocephala (Boveri, 1887;Tobler et al, 1992), the fly Sciara coprophila (Metz and Schmauck, 1931;Gerbim, 1986), the copepod (Cyclops divulsus) (Beermann, 1977), and the jawless hagfish (Nakai et al, 1991). These deletions usually occur during early embryonic cleavage and appear to facilitate the separation of the germ-cell line from the somatic-cell lineage (Di Berardino, 1997).…”