Cell cycles in embryos of the silkworm, Bombyx mori: G2-arrest at diapause stage.

In the silkworm, Bombyx mori, diapause occurs at a specific embryonic stage, i.e. after formation of the germ band with cephalic lobes and telson and sequential mesoderm segmentation. As long as the eggs are incubated at 25° C, cell divisions and morphological development of the embryos cease. To examine changes in percentage of embryonic cells in the G1, S and G2 phases during embryogenesis, nuclear fractions were isolated from embryos, stained with propidium iodide and then subjected to flow cytometric analysis. The percentages of embryonic cells in G1, S and G2 were 10, 35 and 55%, respectively, at the stage of formation of cephalic lobes, whilst 98% of cells were in G2 at diapause stage. After termination of diapause by acclimation at 5° C or by a combination of chilling and HCl, cell division resumed in the embryos. During this period, the cells rapidly entered S phase through G1 from G2, suggesting that their G1 phase was short. In eggs in which diapause was averted by HCl-treatment after incubation at 25° C for 20 h after oviposition, embryonic development proceeded continuously for 9.5 days at 25° C until hatching. Along with this development, the G1 fraction increased to levels of about 90%. These results indicate that embryonic cells are arrested in G2 at diapause and suggest that, concomitant with further embryonic development, cell cycles become slower in proportion to an increasing length of G1. Finally, most of the cells may be arrested in G1, while there is only a small fraction of cells continuously cycling.

M chromosome of the wild silkworm, Bombyx mandarina (n = 27), corresponds to two chromosomes in the domesticated silkworm, Bombyx mori (n = 28).

Chromosomes of Bombyx mori (n = 28) and of Bombyx mandarina (n = 27) were studied cytogenetically to resolve the origin of the large M chromosome in the Japaneses type of B. mandarina. In the F1 progeny from the reciprocal cross between B. mandarina and B. mori, the mitotic chromosome number was 2n = 55, and a chromosome configuration of 26 bivalents plus 1 trivalent was observed at metaphase I of germ cells. The trivalent chromosome consisted of the M chromosome from B. mandarina and two chromosomes from B. mori. When males of B. mori were mated to the F1 females, nuclei with two types of chromosome number (2n = 55 and 2n = 56) and two sets of chromosome pairs (26 bivalents plus 1 trivalent versus 28 bivalents) were observed in the metaphase I stage. Linkage analysis showed that the 14th chromosome of B. mori was involved in these two types of chromosome segregation. This result indicates that the M chromosome in B. mandarina arose from a fusion between a chromosome corresponding to the 14th linkage group and another, yet unidentified linkage group.

[Evaluation of coronary flow reserve using Doppler guide wire in patients with ampulla cardiomyopathy: three case reports].

Coronary flow velocity recordings were obtained in three patients with ampulla (Takotsubo) cardiomyopathy using Doppler guide wire. Immediately after admission, coronary angiography demonstrated no significant stenosis and normal coronary flow in the epicardial coronary artery. Left ventriculography showed abnormal wall motion of the left ventricle mimicking ampulla shape in all patients. The coronary flow velocity pattern was normal, but coronary flow reserve of the left anterior descending coronary artery was decreased by adenosine administration in all patients. The coronary flow reserve in the left circumflex and right coronary artery also decreased. Cardiac catheterization was performed during the follow-up period in two patients. Left ventriculography revealed almost normal wall motion of the left ventricle. The coronary flow reserve normalized in one patient.