Figure 5. Myosin occupies a wider-than-normal zone in asterless cells. Cyan, anti-tubulin; yellow, Hoechst; magenta, anti-phospho-myosin. (A and B) Untreated 16-cell sand dollar embryos. Projection of 24 0.5-µm sections, vegetal view (A); and 19 0.6-µm sections, side view (B). (C and D) 16-cell sand dollar embryos fixed 10 min after adding 25 µM TSA. (C) A projection of 18 0.5-µm sections through the middle portion of the macromeres. (D) A projection of 28 0.5-µm sections through the middle portion of the mesomeres. A–D are from the same batch fixed at the same time. Normally, phospho-myosin is virtually absent outside of ∼10 µm furrow zone. In TSA-treated cells, phosphomyosin is not as thoroughly excluded from the poles but is still enriched equatorially, with definite zones around ingressing furrows (brackets in D), even though no spindle microtubules approach the cortex. A′–D′ are 2× enlarged views of the cells indicated by the white marks in A–D.
Figure 5.

Myosin occupies a wider-than-normal zone in asterless cells. Cyan, anti-tubulin; yellow, Hoechst; magenta, anti-phospho-myosin. (A and B) Untreated 16-cell sand dollar embryos. Projection of 24 0.5-µm sections, vegetal view (A); and 19 0.6-µm sections, side view (B). (C and D) 16-cell sand dollar embryos fixed 10 min after adding 25 µM TSA. (C) A projection of 18 0.5-µm sections through the middle portion of the macromeres. (D) A projection of 28 0.5-µm sections through the middle portion of the mesomeres. A–D are from the same batch fixed at the same time. Normally, phospho-myosin is virtually absent outside of ∼10 µm furrow zone. In TSA-treated cells, phosphomyosin is not as thoroughly excluded from the poles but is still enriched equatorially, with definite zones around ingressing furrows (brackets in D), even though no spindle microtubules approach the cortex. A′–D′ are 2× enlarged views of the cells indicated by the white marks in A–D.

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