. Le bulletin biologique. Biologie ; zoologie ; biologie ; biologie marine. O . IV o J 30 40 50 60 70 80 90 100 temps après la pièce jointe (minutes) Figure 11. L'adhérence des Hemicentrotus pulcherrimus embryons pour le plat de verre poly-L-lysine. Le chiffre en haut à droite de chaque photographie dans un indique le temps après la pièce jointe pour le verre plat. Les chiffres romains (I à IV) en A et B indiquent la même d'embryons. Les embryons gastrulated presque normalement si elles avaient été attaché après l'invagination (embryon I et II). Si les embryons ont été seulement dans l'invagination primaire lorsque

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. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. O . IV o J 30 40 50 60 70 80 90 100 Time after the attachment (minute) Figure 11. Adhesion of Hemicentrotus pulcherrimus embryos to the glass dish coated with poly-L-lysine. The numeral at the top right corner in each photograph in A indicates the time after the attachment to the glass dish. Roman numerals (I-IV) in A and B indicate the same embryos. The embryos gastrulated almost normally if they had been attached after the primary invagination (embryo I and II). If the embryos had been just in the primary invagination when attached, the rate of elongation of the arch- enteron was slowed and the archenteron could not reach the apical plate (embryo III and IV). The scale bar indicates 100 /j.m. The initial phase of gastrulation In both species of embryos, bottle cells (Nakajima and Burke, 1996) were observed in the vegetal plate (Fig. 5D, G, arrows). The appearance of bottle cells in the vegetal plate may lead to the first step of invagination. if the archenteron cells retain the monolayer arrangement (Gustafson and Wolpert, 1963, 1967). Unlike the archenteron cells in H. puk-lieirimux embryos (Fig. 5C. D), those in S. mirabilis embryos were variable in shape and were not organized into a complete monolayer sheet (Fig. 5G, H). As a result, the force produced by bottle cells does not necessarily cause the bending of the vegetal plate. Other forces seem to be nec- essary to produce the invagination of the vegetal plate cells in S. iniruhilis embryos. In this study, several types of cells were observed on SEM images. The role of each type of cell is unknown. If cells are pulled apically or basally, they should become skewed, be- cause cells are connected with extracellular matrix (Wessel and McClay, 1987; Burke et «/.. 1991: Berg et ai. 1996). If a monolayer cell sheet is bent, wedge-shaped cells should appear at the bending point. Thus, the shapes of cells are signs of the existence of the forces g

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• bookauthorlilliefrankrat
• booksubjectbiology
• booksubjectzoology