| |
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 posterior lateral 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 posterior lateral line placodes (dorsal, middle and ventral trunk lines, d, m, v). The XEya1 positive hypaxial muscle precursors (white arrowheads) have migrated further ventrally. Bar in (A): 0.1 mm (A–F). |
