FUNDAMENTAL STUDIES OF DNA DIMINUTION (CHROMOSOME ELIMINATION) IN LOWER FISH DURING DIFFERENTIATION INTO SOMATIC CELLS.

从体细胞(肝、血、鳃、肾)的生殖细胞(精母细胞和精原细胞)中分离到4种日本鳗和1种东太平洋鳗，它们的染色体数目不同。精原细胞(54、52、48、16和54)与体细胞(34、36、34、14和34)的染色体数目之差分别为20、16、14、2和20。在松材线虫的生殖细胞中，观察到C阳性染色质较多的生殖细胞和数量较少的生殖细胞。生殖细胞DNA相对清除量分别为43.6%(E.O.A型)、55.1%(E.O.B型)、20.9%(E.B.)、40.0%(P.A.)、29.8%(M.G.)。和48.7%(E.S)。这些结果清楚地表明，在生活在日本和加拿大P…的粘液纲5种鳗鱼中除原始生殖细胞外，染色体的消除主要发生在卵裂的早期阶段。从松材线虫(A型、B型)、伯格氏乳杆菌和加尔马尼乳杆菌的生殖系细胞和体细胞中提取DNA，并用30种限制性内切酶进行酶切。琼脂糖凝胶电泳法显示，两种酶(Bam HI、Dra I)在两种类型的松材线虫胚系DNA中均产生弱条带。DNA过滤杂交实验证明，Bam HI扩增出的两个DNA片段大小约为125bp，仅存在于被剔除的松材线虫DNA中，可能分别占种系总DNA的1.25%和1.32%。这些值分别相当于二倍体的8.5x10^5和9.0x10^5个拷贝。这些片段在另外两个物种的种系基因组和体细胞基因组中几乎不包含。原位杂交实验表明，该DNA片段位于两种类型生殖细胞中都有限的几条小染色体上，并且在okinoseanus中为C-带阳性染色质。较少

Four Japanese and one East Pacific Canadian hagfish in the order Myxinida, Eptatretus okinoseanus, Eptatretus burgeril Paramyxine atami, Myxine garmani and Eptatretus stoutil have been possess different chromosome numbers in their germ cells (spermatocytes and spermatogonia) from somatic cells (liver, blood, gill and kidney). The difference of the chromosome numbers between spermatogonia (54, 52, 48, 16 and 54) and somatic cells (34, 36, 34, 14 and 34) was 20, 16, 14, 2 and 20, in E. okinoseanus, E. burgeri, P. atami, M. garmani and E. stoutii, respectively. In E. okinoseanus, two types of germ cells, those having large amount of C-positive chromatin and those having small amount were observed. The relative amount of DNA eliminated from germ cells averaged 43.6%, (E. o. type A), 55.1% (E. o. type B), 20.9% (E. b.), 40.0% (P. a.), 29.8% (M. g.) and 48.7% (E. s.), respectively. These results clearly indicate that, in the 5 hagfish species in Myxinida which live in Japanese and Canadian P … More acific waters, chromosome elimination takes place during the early stages of cleavage except for the ancestral germ cells.DNA from germ line cells and somatic cells in E. okinoseanus (type A, type B), E. burgeri and M. garmani bad been isolated and digested with 30 kinds of restriction enzymes. Two enzymes (Bam H I, Dra I) generated weak bands limited to germ line DNA in both types of E. okinoseanus by agarose gel electrophoresis. DNA filter hybridization experiments proved that two DNA fragments by Bam HI, about 125 bp long, are contained only in the eliminated DNA of E. okinoseanus and may account about 1.25% and 1.32% of the total germ line genomic DNA. These values would correspond to approximate 8.5x10^5 and 9.0X10^5 copies in diploid, respectively. These fragments are hardly contained in the germ line genomes and somatic genomes of the other two species. In situ hyubridization experiments demonstrated that this DNA fragments are located on several small chromosomes which are limited in germ cells in both types and which are C-band positive chromatin in E. okinoseanus. Less