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Figure 2. Developmental expression of XTbx1. Whole mount in situ hybridization was used to detect XTbx1 expression in Xenopus embryos. A: Ventral view of embryos between stages 10.5 to 11.5 shows weak XTbx1 expression (purple staining) throughout the presumptive mesoderm. B: Embryos at stage 15 (bottom row) and stage 16 (top row) shown in dorsal (embryos at left) and lateral (embryos at right) views. Weak expression is seen at stage 15 in the lateral plate mesoderm extending from the anterior to mid-trunk level. Stronger XTbx1 expression is seen at stage 16 along the entire length of the lateral plate and head mesoderm but is not present in the neural tube. C: Expression of XTbx1 is seen in the pharyngeal arches at stage 26 (top). The first indication of XTbx1 expression in the anterior, ventral quadrant of the otic vesicle appears at stage 28 (bottom embryo). Pharyngeal arch expression has become stronger and extended further posterior. D,E: XTbx1 expression becomes further elaborated in the pharyngeal arches between stages 31 and 36. At stage 31 (D, bottom), expression in the otic vesicle extends further posterior and dorsal. At stage 32 (D, top), XTbx1 is absent from only the dorsal-most part of the otic vesicle. Low levels of XTbx1 expression are also seen in the somites. By stage 35 (E, bottom), XTbx1 is expressed throughout the otic vesicle and in the head mesoderm between the eye and cement gland at stage 36 (E, top). F,G: Transverse sections through a stage 32 embryo at the planes marked in D. XTbx1 is present in the mesenchyme adjacent to the outflow tract of the heart (arrowhead, F) as well as in the head mesenchyme (hm) but not the condensing cartilage (cc) of the pharyngeal arches (G). |
