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We cloned two isoforms of the Xenopus Eya1 orthologue. They show identical patterns of expression that closely resemble the previously described expression of XSix1, but partly differ from the expression of Eya1 in other vertebrates. XEya1 is expressed in the somites and hypaxial muscle precursors, but not in the pronephros. Moreover, all ectodermal placodes except the lens placode strongly express XEya1. At neural plate stages, ectodermal XEya1 expression starts in two domains, the anterior neural folds and a domain lateral to the neural folds. At tailbud stages, XEya1 expression continues in the adenohypophysis, all neurogenic placodes and placodally-derived structures including cranial ganglia, the otic vesicle and lateral line primordia.
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11335132
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Fig. 3. Spatiotemporal expression of XEya1 during Xenopus development (lateral views). (A) At neural plate stages (stage 14), an ectodermal domain (arrow) lateral to the neural folds expresses XEya1. (B) At neural fold stages (stage 18; insert, same specimen in oblique anterior view) this domain has separated into a profundal/trigeminal placodal area (pPrV) and a posterior placodal area (pp). The latter corresponds to the ‘dorsolateral placodal area’ of Schlosser and Northcutt (2000), but has been assigned a more neutral label here, because XEya1 expression suggests that it may be the precursor not only of lateral line and otic placodes but also of epibranchial placodes. XEya1 also starts to be expressed in the anterior placodal area (ap) of the anterior neural folds, the precursor of adenohypophysis and olfactory placodes. (C) At early tailbud stages (stage 22), XEya1 expression is maintained in the olfactory placodes (pOl), the developing adenohypophysis (data not shown), and the profundal/trigeminal placodal area. Within the posterior placodal area of XEya1 expression, it is now possible to distinguish the otic placode (pOt) and two ventral extensions. The anterior extension (app) is closely apposed to the profundal/trigeminal placodal area. It will give rise to the anterodorsal and anteroventral lateral line placodes and the facial epibranchial placode. The posterior extension (ppp) will broaden later and give rise to the remaining lateral line, epibranchial and hypobranchial placodes. (D) At mid-tailbud stages (stage 26), XEya1 continues to be expressed in the shrinking profundal and trigeminal placodes (pPrV), in the otic vesicle (vOt), in the anterodorsal (pAD) and anteroventral (pAV) lateral line placode, as well as in the facial epibranchial placode (epVII). The apparently contiguous XEya1 expression domain anterior to the otic vesicle reflects the close apposition of these placodes (Schlosser and Northcutt, 2000). The middle (pM) lateral line placode and the developing glossopharyngeal (epIX) epibranchial placode but not the lens placode (lp) also express XEya1. Moreover, XEya1 transcripts are now detectable in the somites (s). (E) At stage 30, XEya1 is expressed in all neurogenic placodes, including the newly developed posteriorlateral line placode (pP), vagal epibranchial placodes (epX1 and epX2/3), and hypobranchial placodes (hp1), in the somites and in the hypaxial muscle precursors (white arrowheads), but not in the lens (l). (F) At early tadpole stages (stage 41), XEya1 expression persists in placodally-derived structures such as the otic vesicle (vOt) and in the primordia of lateral lines derived from the anterodorsal (e.g. supraorbital line, so), anteroventral (e.g. hyomandibular line, hm; other lines, asterisk), middle (e.g. aortic lateral line, ao), and posteriorlateral line placodes (dorsal, middle and ventraltrunk lines, d, m, v). The XEya1 positive hypaxial muscle precursors (white arrowheads) have migrated further ventrally. Bar in (A): 0.1 mm (A–F).
Fig. 4. Expression of XEya1 (B,E) compared to other placodal markers XSix1 (A,D) and XSox2 (C,F) in lateral views (A–C) and transverse sections at the level of the otic vesicle (D–F) of stage 30–34 Xenopus embryos. Patterns of expression of XEya1 (B,E) and XSix1 (A,D) are largely identical in the adenohypophysis (data not shown), olfactory placodes (pOl), the otic vesicle(vOt), lateral line placodes (pAV, pAD, pM, pP), epibranchial (epVII, epIX, epX1, epX2/3) and hypobranchial placodes (hp1). Co-expression of both genes is also observed in cranial ganglia that have a placodally-derived component, e.g. in the profundal/trigeminal ganglionic complex (data not shown), in the fused ganglia of the facial, anteroventral and anterodorsal lateral line nerves (gVII/AV/AD in D,E), and in the fused ganglia of the glossopharyngeal and middle lateral line nerves (gIX/M in D,E). Additionally, XEya1 and XSix1 are co-expressed in the somites (s in A,B), in hypaxial muscle precursors (white arrowheads in A,B) and weakly in the pharyngeal pouches (asterisks in D,E). Placodal expression of XSox2 (C,F) overlaps with the expression of XEya1 and XSix1 in the adenohypophysis (data not shown), the olfactory placode, the otic vesicle and the lateral line placodes, as well as in some cranial ganglia (e.g. gVII/AV/AD in F). In contrast to XEya1 and XSix1, however, XSox2 is not expressed in the profundal/trigeminal placodes or ganglia (data not shown) and in the epibranchial placodes (C), whereas it is strongly expressed in the neural tube (nt), the lens (l), and the pharyngeal pouches (asterisks). Bar in (A): 0.1 mm (A–C). Bar in (D): 0.1 mm (D–F).
