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Mech Dev
2000 May 01;931-2:49-58. doi: 10.1016/s0925-4773(00)00265-3.
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Neuroectodermal specification and regionalization of the Spemann organizer in Xenopus.
Fetka I
,
Doederlein G
,
Bouwmeester T
.
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During gastrulation in Xenopus convergence and extension movements, mediated by mediolateral intercalations, are the driving force for early neural plate morphogenesis. Here we show that the winged helix transcriptional regulator, Xfd-12' is dynamically expressed in medial neural plate precursors that undergo convergence and extension movements. These medial neuraxial progenitors are specified in and beyond the Spemann organizer prior to specification of the basal anlage of the neural plate. The initiation of Xfd-12' expression coincides with the induction of mesendoderm by Nodal-related growth factors at the late blastula stage. Comparative expression analysis suggests that cellular rearrangements at the pre-gastrulation stage account for regionalization of the Spemann organizer into head and trunk organizer compartments, the latter in which medial neural plate progenitors reside. While the maintenance of Xfd-12' expression in the dorsal non-involuting marginal zone requires FGF signalling, its subsequent positioning along the medial aspect of the neuraxis depends on signalling by Wnt and Nodal-related family members. Based on these findings we propose that XFD-12' is a trunk organizer component that might control convergence and extension movements of medial neural plate precursors during gastrulation.
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10781939
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Fig. 2. Xfd-12′ is expressed during medial neural plate morphogenesis. Whole-mount in situ hybridization was used to reveal the spatio-temporal expression pattern of Xfd-12′. (A) Stage 9; expression is initiated in the presumptive dorsal marginal zone. (B) Stage 10.5; expression increases in the dorsal circumblastoporal zone. (C,D) Stages 11 and 11.5; expression constricts in the dorsal midline. (E,J) Stage 12, sagittal and transverse sections; Xfd-12′ expression is restricted to the neuraxial midline. (F,G) Stages 12 and 12.5; strong expression in the prospective floorplate and the dorsal periblastoporal zone. (H,I) Stages 13 and 14; down-regulation in the rostral neuraxial midline. (K) Stage 17; expression remains high in the dorso-posterior region. (L) Stage 25; caudal expression in the tailbud. (M–O) Stage 25, frontal, sagittal and transverse sections; expression is observed in the chordoneural hinge (ch) and the tip of the posterior wall (pw). From stage 12 onwards expression is in addition found in the mid-hindbrain junction. Black arrowheads point to the lateral extent of dorsal circumblastoporal expression during neuraxial constriction and red arrowheads point to mid-hindbrain expression. Embryos are viewed (A,B) vegetally with dorsal up, (C,D) dorso-vegetally, (F–I) dorsally with anterior up, (K) dorsally with anteriorleft and (L) laterally with anteriorleft.
Fig. 3. Xfd-12′ marks medial neuraxial progenitors prior to shh activation in the floorplate. Whole-mount in situ hybridization analysis was used to compare the spatio-temporal expression of pintallavis (A,E,I,M), shh (B,F,J,N), sox-2 (C,G,K,O) and Xfd-12′ (D,H,L,P) during gastrulation at stage 10.5–11 (A–D), stage 11.5–12 (E–H), stage 12.5–13 (I–L) and neurulation at stage 14 (M–P). Arrows point to the dorsal blastopore. Embryos in (A–D) are viewed vegetally with dorsal up, whereas all other embryos are viewed from the dorsal perspective with anterior up.
Fig. 6. Medial neural plate progenitors become localized to the trunkorganizer. Comparative expression analysis at peri gastrulation stages. Serial sections of single stage 9 blastula (A,C,E,G) and stage 10.5 gastrula (B,D,F,H,I) embryos that were stained by in situ hybridization for cerberus (A,B), pintallavis (C,D), Xbra (E,F), Xfd-12′ (G,H) and goosecoid (I) expression.
Stages 12 and 12.5; strong expression
( Xfd-12')in the prospective floorplate and the dorsal periblastoporal zone. If unbleached, the blastopore would be visible as a ring.
Stages 12 and 12.5; strong expression
(Xfd-12â²) in the prospective floorplate and the dorsal periblastoporal zone.
