Fig. 2. Expression of XTbx5 mRNA during organogenesis. (A) Stage 17 embryo, lateral view. The arrow shows faint expression of XTbx5 mRNA in the lateral mesoderm. (B) Stage 20 embryo, lateral view. Expression is detected in the eye (e) and the cardiac field (c). (C) Stage 25 embryo, lateral view. Expression of XTbx5 in the lateral mesoderm is greatest near the ventral midline and tapers off dorsally. (D) Ventral view of the same embryo in C. XTbx5 mRNA is not expressed across the ventral midline. (E) Stage 30 embryo, lateral view. Expression has moved further ventrally and has fused across the ventral midline, but some expression persists in lateral mesoderm. (F) Ventral view of the same embryo in E. Notice the heart-shaped expression along the ventral midline. (G) Stage 35 embryo. The expression of XTbx5 condenses in the lateral mesoderm, marking the sinus venosus (sv) (Nieuwkoop and Faber, 1967). (H) Dorsal-lateral view of a stage 35 embryo cleared in benzyl benzoate/benzyl alcohol (BBA). Notice that the expression of XTbx5 leaving the atrium branches onto either side of the embryos marking the developing sinus venosus. (I) Stage 40 embryo. The sinus venosus (sv) has moved further dorsally to lie just below the somites. Notice the lack of XTbx5 expression in the anterior portion of the pericardial cavity. (J) Stage 40 embryo in BBA. Notice the horseshoe-shaped expression marking the sinus venosus (sv). (K) XMLC2 expression, stage 30 embryo ventral view. Expression is seen further anteriorly than XTbx5 along the ventral midline and does not resemble the heart-shaped XTbx5 expression. (L) XMLC2 expression at stage 40. In contrast to XTbx5, XMLC2 is detected throughout the pericardial cavity. Abbreviations used in the figure are: atrium (a), bulbus cordis (bc), sinus venosus (sv) and ventricle (v). (M) Stage 28 embryo used to show the positions of the sections shown in N and O. (N) A section through the eye shows that XTbx5 is expressed only in the outer edge of the ciliary marginal zone (cmz), marking the stem cell population. There is also expression along the dorsal surface of the retina. (O) A section through the developing heart region shows that XTbx5 is expressed in the lateral and ventral mesoderm.
Image published in: Horb ME and Thomsen GH (1999)
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