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Abstract SOX7, first described in Xenopus laevis by Shiozawa et al. [Biochim. Biophys. Acta 1309(1996)73], is a member, along with SOXs 17 and 18, of the F subgroup of SOX-type transcription factors. As part of a study of maternal SOX proteins that may modulate beta-catenin signaling, we isolated a XSOX7 cDNA from oocyte RNA and examined the pattern of XSOX7 expression during early development. While present maternally cell-type specific expression was first observed in the ciliated cells within the epidermis of early neurula stage embryos. As development proceeds, the pattern of XSOX7 expression becomes increasingly complex. XSOX7 is expressed in the aortic arch, the olfactory pit, the stomodeal depression, the procardiac tube, within cells of the developing embryonic vasculature, in the notochord, and within the hindbrain. XSOX7 expression continues within the hindbrain in 3-day old ( approximately stage 40) larvae. Given its widespread expression, XSOX7 is likely to be involved in a number of developmental processes.
Fig. 1. (A) RT-PCR analysis reveals the presence of XSOX7 RNA in eggs and throughout early development. Primers for EF1α, expressed throughout development, were used as a positive control; in the absence of RT, no amplification was observed. Whole-mount in situ hybridization staining using antisense (B) and sense (C) probes reveals the presence of easily detectable levels of XSOX7 throughout the early embryo. The animal hemispheres of the embryos are shown.
Fig. 2. Whole-mount in situ hybridization of stage 14 embryos with antisense (A) and sense (B) XSOX7 probes. Ciliated cells, scattered evenly through the non-neural ectoderm, are clearly stained with the antisense probe (arrows). No such staining is observed with the sense probe. There is weak background staining visible in the neural plate area of both sense and antisense probes.
Fig. 3. Localization of XSOX7 RNA in stage 27 embryos. (Panel A) An embryo stained for XSOX7 RNA (‘XSOX7’) is compared to an embryo stained for X-msr RNA (‘X-msr’). There is strong XSOX7 staining in the posterior cardinal veins (pcv), hindbrain (hb), aorotic arch (aa), vitilline veins (vv), and the procardiac tube (pct). In transversally sectioned embryos stained for X-msr (B) or XSOX7 (C) the staining of the posterior cardinal veins by both probes is clearly visible. The XSOX7 probe also stains epidermal ciliated cells (cc) and the dorsal aspect of the neural tube (dnt). (D) A transverse section through the hindbrain region reveals XSOX7 staining in the endocardium of the procardiac tube, the aortic arch and the hindbrain.
Fig. 4. (Panel A) Lateral view of the stage 33/34 larvae stained by whole-mount in situ for XSOX7 reveals that XSOX7 RNA is still present in the posterior cardinal veins (pcv), hindbrain (hb), and aortic arches (aa). Staining is also visible the branching intersomatic arteries (ia), epithelial straps (es), olfactory pit (op), and stomodeal depression (sd) and the notochord (not). XSOX7 is still present in ciliated cells (cc). (Panel B) In a front view of a stage 33/34 embryo, it is possible to see more clearly that XSOX7 is expressed in the stomodeal depression, the olfactory pit and in the ‘V-shaped’ epithelial straps. The position of the cement gland (cg) in marked. (Panel C) A ventral view of an embryo reveals the strong expression of XSOX7 in the epithelial straps, while a dorsal view (Panel D) reveals the strong staining of regions of the hindbrain. (Panel E) A cross section through the hindbrain region of a stained larvae reveals presence of XSOX7 RNA in the aortic arches and the outer edges of the rhombencephalon.
Fig. 5. (Panel A) whole-mount in situ hybridization with antisense XSOX7 probe of a 3-day old larvae (stage 40) reveals XSOX7 expression in the hindbrain (hb) and aortic arch (aa). (Panel B) No staining is seen using a sense XSOX7 probe. Hindbrain expression at this stage appears as either a single (C) or a pair of structure (D) on each side of the embryo.