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1. Chromosomal features in the spermatogonial metaphase and anaphase. The investigations have been undertaken based on the chromosomal slides prepared according to the current air-drying squash method. Chromosomes were examined in spermatogonial metaphase and early anaphase in the following 7 butterfly-species: Papilio maackii (2n,60); Papilio bianor (2n,60); Polygonia c-aureum (2n,62); Argyreus hyperbius (2n,62); Curetis acuta (2n,58); Favonius latifasciatus (2n,48); and Narathura japonica (2n,48). They are reproduced in Figs.1-12. In general, the mitotic chromosomes have been furnished as objects for the determination of chromosomal form in organisms in numerous surveys of karyological studies. As a whole, the mitotic chromosomes provide favorite materials for chromosome analysis from the following reason that the chromosomes of M-I cells are usually presented by a structure of bivalents characterized by their chiasmata. On the basis of the chromosomal aspects derived from the mitotic metaphases observed in the above-mentioned species, the author was not able to obtain any evidence indicating that V- or J-shaped metacentric chromosomes are included in the diploid complements of the butterfly. As seen in micrographs of early anaphases shown in Figs.7-12, every chromosome divided each into two elements which took a parallel arrangement. With the advance of the stage these sister chromatids took the start-action to each opposite pole. The chromosomal features and behavior as seen at the early anaphase were nearly identical to those observed in some Hemiptera such as Euschistus and Solubea by HUGHES-SCHRADER & SCHRADER (1961). The latter authors have described in their paper that in anaphasic disjunction the separating chromatids remain parallel to each other as they move "broadside on" to the pole. 2. Chromosomal features and behavior in the M-I metaphase and anaphase. The following investigations were undertaken based on the chromosome preparations according to the ordinary acetoorcein squash method, and also phase contrast was applied for more detailed analysis. Chromosome features depicted at M-I metaphase and anaphase in the following two species: Graphium sarpedon (n,20) (butterfly) and Eumeta variegata (n,31) (moth), are presented in Figs.13-25. The prereductional phenomenon of the bivalents in Lepidoptera had been established on the basis of the behavior of fragment chromosomes studied through the mitotic and meiotic divisions of G. sarpedon (MAEKI and HAYASHI, 1979). It was shown that the first division was reductional, whereas the second division was equational. Here, noteworthy was the finding that the bivalent chromosomes of Lepidoptera were constructed by "a ring of four" (LA COUR, 1952) at the M-I metaphase (Figs.13-17,22-23). The general features of chromosomes of G.sarpedon and E. variegata at the M-I anaphase are remarkable by the appearance displaying "pseudo-V-shape" in outline (see Figs.18-21, 24-25). In the course of the first anaphase the two sister chromatids moved to the same pole, and then the two chromatids (or a half-bivalent) having the pseudo-V-shape spread gradually along a straight line from each other. It appeared that the spindle fibers attached themselves to the whole poleward surface of the two rods of each sister chromatid. This behavior followed closely the synchronized activity of their spindle fibers. Most reasonable estimation from the above observations seems to be in favor of the view that the formation of the "pseudo-V-shaped" chromosome results from the association of the two rod-shaped elements equipped with the diffuse kinetochore structure. 3. Chromosome morphology and behavior in the M-II cells. In the equatorial plate of M-II metaphase two sister chromatids of a rod-type appeared taking a linear arrangement in each, as seen in Fig.26. If the chromosomes were telocentric carrying a kinetochore at their terminal ends, those two sister chromatids should be arranged in parallel condition at the M-II metaphase. Further, the dyads with the parallel arrangement would appear radially directing their kinetochores toward the cell center, as schematically shown by OGUMA (1942)(Fig.49). Every chromosome divided, however, each into two elements taking a linear arrangement at metaphase and early anaphase as seen in figs. 26-40. Under this condition each chromosomal element appeared taking a form like "a tadpole" or "the head of a writing brush" in outline (Figs.26-31). This feature would be resulted from a bundle formation of the spindle-fibers : The fibers gather to the chromosomal part close to the cell pole, while condense longwise in another part. The above features of chromatids at the M-II metaphase would be related also to the location of centrosomes occurring in the meiosis-II stage and to the non-synchronized activity of the spindle-fibers. In the course of the second anaphase the two sister chromatids moved to the opposite poles: The anaphasic movement was found to be end-first to the pole. Then it seems probable that the chromatid being in the direction vertical to the pole may be shifted gradually to the horizontal direction. The horizontal arrangement of each monad through the anaphasic movement of the M-II chromosomes failed to be confirmed in detail in this investigation. This behavior is closely associated with the synchronized activity of their spindlefibers. The morphology and behavior of the M-II chromosomes in the lepidopteran species seemed to be in close coincidence to those observed in Cimex-species (Hemiptera) by UESHIMA (1966). The situation occurring in the chromosomes at M悠I metaphase and anaphase could be well understood only in the chromosomes equipped by the diffuse kinetochore structure. On the basis of the above findings it can be allowed to state that, in striking contrast to the mitotic behavior of chromosomes, the male meiosis of lepidopteran insects may be characterized by a definite restriction of kinetochore activity in the M-I and M-II chromosomes, as fairly demonstrated by HUGHES-SCHRADER & SCHRADER (1961) in hemipteran species. 4. Gamma-ray induced fragments of chromosomes in Graphium sarpedon. The radiation treatment was made in the Radiation Laboratory through the courtesy of Mr. H. Terada, the Research Institute of Microbial Disease, Osaka University. The materials for this study consisted of over 100 male larvae of Graphium sarpedon at the last-instar which had been bred in the laboratory from 1974 to 1973. The condition of irradiation was as follows: Distance 75cm; field size 12cm×12cm; dosage rate 53.5 R/min; Cobalt-60 gamma irradiation unit (Shimazu). In order to induce the fragmentation of chromosomes, 50 larvae were irradiated in each year: 12 larvae in group were irradiated each at dosages of 800R, 1000R, 1500R, and 2000R. Irradiated specimens were killed at intervals of 18, 21, 24, 27, and 30 hrs after exposure. On dissection one testis from two males which were received the same dosage were prepared following the aceto-orcein squash method, while the other testis was fixed with Allen's P.F.A.-3 solution for the routine study. On cytological examinations, the specimens treated at 1500R and 2000R showed remarkable aberrations of chromosomes at the meiotic stage. The normal haploid chromosome-number of G. sarpedon was 20. The nuclear plates shown in Figs.53-54 and Fig.60 showed 21 chromosomes at the M-I metaphase, while Fig.59 showed 19 chromosomes in the same M-I phase. The above features resulted from the chromosomal fusion as well as from fragmentation during meiosis. Another noticeable was the feature that some of the chromosomes were being in a way ready to divide in part, as shown in Figs.51-52 and Figs.57-58. The chromosomes induced by the present gamma-irradiation experiments were represented by two divided elements each showing an ordinary kinetic manner as seen in Figs.55-56. The situation is suggestive of that the induced fragment chromosomes carry the kinetochore in each. 5.Behavior of a fragment chromosome in Graphium sarpedon. The author had an opportunity to find a supernumerary chromosome represented by a fragment in a larva of G. sarpedon bred in the laboratory in 1975. The supernumerary element occurred without exception in all nuclei of the spermatogonial cells (Figs.63-64). It seems apparent that the fragment may be produced by chromosome fragmentation which had taken place in certain early periods of spermatogonial proliferation. All nuclei at M-I always contained the element of the same nature (Figs.65-67), while there were two kinds of the M-II nuclei, one carrying the supernumerary and another having no such element in a proportion of 1:1 (Figs.69-70). The fragment chromosome divided in n, 21 nuclei into two elements: this picture was well illustrated in Figs.68 and 69. Thus, the evidence is indicative of that G. sarpedon is a species belonging to the pre-reduction group at meiosis. The fragment chromosome behaved in a quite regular manner during the whole course of both mitotic and meiotic divisions as shown in Figs.63-70. The above findings are strongly suggestive of that the fragment chromosome carries the kinetochore or centromere. General recognition available to us is that the chromosomes of lepidopteran insects are characterized by the holokinetic organization in general; it has been expected early in relation to genetic information in Lepidoptera.
日本鱗翅学会の論文
1981-09-20

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前木孝道
関西学院大・理・生

鱗翅類の染色体について

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