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

Abstract

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.

Genome Duplication in Early Vertebrates: Insights from Agnathan Cytogenetics

“…Twelve families of these repetitive DNA sequences are eliminated elements that have been characterized and named according to the eptatretine species from which they were originally isolated: EEEo1 and EEEo2 (i.e. eliminated element of E. okinoseanus 1 and 2) from E. okinoseanus [Kubota et al, 1993]; EEPa1 from P. atami ; EEEc1, EEEc2 and EEEc3 from E. cirrhatus [Goto et al, 1998]; EEEb1 and EEEb2 from E. burgeri , and EEPs1-4 from P. sheni ( table 3 ) [Kojima et al, 2010]. A minor fraction of these latter sequences remains in somatic cells after chromosome elimination in P. sheni , where various germline repetitive elements accumulate also at all ends of Cband-negative chromosomes and are eliminated together with the whole C-band-positive chromosomes during germline-soma differentiation.…”

Isolation of a new germ line-specific repetitive DNA family in <i>Acricotopus</i> by microdissection of polytenized germ line-limited chromosome sections from a permanent larval salivary gland preparation

“…The genetic phenomenon of a chromosomal germ line-soma differentiation with the occurrence of additional chromosomes, present only in germ line cells, was established in the dipteran families Cecidomyiidae, Chironomidae and Sciaridae, and also in some hagfish species (Vertebrata, Cyclostomata) (Kohno et al, 1986;Tobler, 1986;Kubota et al, 1993;Goday and Esteban, 2001;Redi et al, 2001). In the Orthocladiinae, a subfamily of the Chironomidae, the germ line-limited chromosomes (Ks; K being derived from "Keimbahn") and the soma chromosomes (Ss) pass through a complex chromosome cycle with interesting genetic features such as elimination mitoses and monopolar movements of chromosome complements (Bauer and Beermann, 1952;Bauer, 1970).…”

Circadian Rhythms in Locomotor Activity of the Hagfish, Eptatretus burgeri VI. The Effects of Cutting the Spinal Cord

“…For example, it has been reported for all hagfish investigated that predetermined chromosomes and DNA fragments are eliminated during a stage of cell division in somatic cells, but not in germ-line cells. The phenomenon, called chromosomal elimination, has not been observed in any other vertebrates (Kohno et al, 1986;Kubota et al, 1992Kubota et al, , 1993Kubota et al, , 1997Kubota et al, , 2001Kohno, 1998;Nabeyama et al, 2000;Kloc and Zagrodzinska, 2001). The functions, roles, mechanisms, and evolutionary origin of this strange phenomenon are unclear.…”