Fig. 5. Early Hro-eve transcripts appear to be associated with chromatin of cells in mitosis. Brightfield (Nomarski optics) images of embryos processed by in situ hybridization for Hro-eve. (A) Ventral view of a stage 7 embryo. On the right, regions of an m bandlet are in focus. The M teloblast is out of focus, but 4 m blast cells in the proximal bandlet (one cell wide because the primary blast cells have not yet divided) are in view. Distal to this, the bandlet is in focus again, now two cells wide; in each pair of secondary m blast cells, m.l is on the left and m.m is on the right; perinuclear localization of the Hro-eve transcripts in the blast cells can be seen, as in Fig. 4 (arrowheads). Cell m.l divides prior to m.m in Helobdella (Bissen and Weisblat, 1989) (E. K. Schimmerling, BA Honors thesis, University of California, 1986). In this embryo, the in situ signal in successive m.l cells is punctate instead of perinuclear, which corresponds to the younger cell (arrow) in prophase, and the older cell (yoked arrows) in telophase. The other m bandlet is largely out of focus, but one m.l in that bandlet exhibits punctate staining. (B) Schematic drawing of the embryo in A. (C) In a late two-cell embryo, punctate staining (arrow) marks the metaphase chromatin of cell CD. Diffuse background staining of teloplasm is also evident. Scale bar: 100 µm.

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