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Fig. 3. Expression of X-bhh in mesoderm and ectodermal derivatives. Whole embryos, hybridized in situ with a probe specific for X-bhh transcripts, were embedded in paraffin and sectioned (see Materials and methods). (A) Sagittal section of a stage 14 neurula with anterior to the left. X-bhh transcripts are most prominent in the sub-epithelial and epithelial layers of the neuroectoderm but are also present at lower levels in the underlying chordamesoderm (see arrows in the insert), (np) neural plate, (a) archenteron. (B) Parasagittal section through the head of a stage 28 tailbud embryo with anterior to the left. X-bhh-expressing cells are seen in the sub-epithelial layer of the ectoderm (arrows), just dorsal to the cement gland (cg); (e) eye. (C) Transverse section of a stage 28 embryo at the level of the eye (e). X-bhh expression is found in both the superficial and deep layers throughout the roof of the mesencephalon (me). Expression is also observed prominently in the prospective retinal layer of the eye vesicle (e). (D) Transverse section of a stage 28 embryo at the level of the otic vesicle (ov). X-bhh expression is seen in the dorsal roof of the rhombencephalon (rh), and in the epithelial layer of the ectoderm. Expression is also prominent in the otic vesicle (ov), (n), notochord. (E) Para-sagittal section through the head of a stage 28 embryo with anterior to the left. X- bhh transcripts are detected in the dorsal mesencephalon and rhombencephalon (arrows) and in the branchial arches (arrowheads). (F) Dorsal view of a whole tailbud embryo (stage 23) with anterior to the left. The embryo has been double-labeled by in situ hybridization with a probe specific for X-bhh transcripts prior to immunostaining with monoclonal antibody 12/101, specific for the myotomal portion of the somite (Kintner and Brockes, 1984). A block of two adjacent somites (s) is delimited by the arrows. (G) Lateral view of the embryo in F, at higher magnification, and with anterior to the left. The brown 12/101 stain highlights the myotome of each somite (area between two arrows); the dark blue X-bhh stain is localized to a single central portion of the dermatome of each somite (see text; data not shown). (H) Glancing section in the plane of the dermatome of an embryo similar to that in F with anterior to the left. The arrows demarcate the boundaries of a single somite and the arrowhead denotes X-bhh staining. |
