The right column shows stg mRNA patterns, visualized by in situ hybridization of a stg cDNA probe to whole embryos. The left column shows the same embryos stained for DNA with Hoechst 33258. Embryos A-D were hybridized with 35S probe, which detects expression through several layers of tissue. Embryos E-H were hybridized with 3H probe, which detects only surface expression. The anterior of each embryo is to the left.
We have labeled the regions of stg RNA expression with the numbers of the mitotic domains (MDs) mapped by . stg expression corresponds perfectly with these domains, but begins 25–35 min before the onset of mitosis in a given domain. A: ventral view, showing the first zygotic stg expression in MD10 (10), and what is probably residual maternal RNA in the pole cells (P). B: dorsal view, just at the onset of gastrulation, about 25 min before the first mitoses. stg expression can be seen in MDs 1–10. C: dorsal view showing the beginning of expression in five spots within MD11, about 15 min before the first mitoses. D: dorsolateral view, showing expanded expression in MD11. The first mitoses, in MDs 1–8, are in progress in this embryo. E: ventrolateral view of an embryo the same age as D. stg expression can be seen in MDs 1, 2, 5, 8, 9, 11, 14, and 15. Mitoses are occurring in domains 1, 2, 5, 8, and 9, but have not yet begun in MDs 11, 14, or 15. The embryo just above this (not labeled) is slightly older and shows segmentally repeated spots of expression in MDs 16 and 17. F: ventrolateral view showing stg expression and mitoses in MD N. Note that expression has diminished in MDs 1–15, which have already divided. Also note the lack of expression in the amnioserosa (A), a nondividing polyploid tissue. G: lateral view, showing cycle 14 expression in MDs N and M, which are dividing. Cycle 15 expression is evident in a number of spots in the head, and in a segmental pattern in the dorsolateral epidermis and mesectoderm.