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???displayArticle.abstract??? xPAK1, a probable effector of stress activated MAP-kinase SAPK1/JNK activation and cytoskeletal dynamics, was found to be ubiquitously expressed within the Xenopus laevis ear and lateral line system during the development and differentiation of these organs. xPAK1 expression was very strong in the otic placode from its condensation, and expression continued in the otic vesicle up until stage 35/36, after which it abruptly ceased. At stage 29/30 expression occurred specifically in the epithelium of the otic vesicle, which includes the prospective sensorial epithelium. Expression of xPAK1 was also observed in the lateral line system from stage 35/36, at which stage the lateral lineprimordia have begun to migrate from the region of the otic vesicle. Lateral line expression continued at least until stage 37/38, at which time xPAK1 was noted in association with the differentiating lateral line organs. To our knowledge, xPAK1 is the first ubiquitouslateral line marker that is also expressed in the ear. In the context of previous studies, our data suggest that xPAK1 either plays a role in the differentiation of the mechano-sensors of the auditory system or in the formation of the otic vesicleepithelium and the lateral lineprimordia.
Fig. 3. Expression of xPAK1 in the otic placode and vesicle. Lateral views of whole-mount in situ hybridization of xPAK1 transcripts in X. laevis embryos at (A) stage 23/24, (B) stage 25, (C) stage 26, dorso-lateral view, (D) stage 29. (G-H) Sequential sections of a xPAK1 hybridized stage 29/30. (I) Whole-mount TUNEL staining [(Hensey and Gautier, 1998) as modified by Poitras et al. manuscript submitted] of anterior region of a stage 27 embryo. (J) Magnified view of TUNEL staining over the eye of a stage 27 embryo showing colocalization of stain with cell nuclei, as revealed by Hoechst 33258 fluorescence. Op, otic placode; ov, otic vesicle. Bar in A to D, 1 mm; in E to H, 50 μm; in I 0.5 mm; and in J 100 μm.
Fig. 4. Expression of xPAK during lateral line development. (A) Stage 35/36, (B-H) stage 37/38. (A-E) Whole-mount in situ hybridization. (F,G and H) Transverse sections of stage 37/38 whole mount embryos sectioned after hybridization with xPAK1. ov, otic vesicle; o, olefactory placode; nc, notochord; e, eye; a, d, io, so, hm, respectively the aortic, dorsal, infraor- bital, supraorbital and hyomandibular lateral lines; t, tail. Bar in A to C,1 mm; in D, 0.3 mm; in E and F, 0.16 mm; and in G and H, 0.3 mm.
Fig. 2. Expression of xPAK1
mRNA and protein. (A) Northern
blot of xPAK1 mRNA during
early development. The positions
of 18S and 28S rRNAs are indicated
and the ethidium bromide
stained 18S band shown below
the Northern blot. (B) Quantitative
RT-PCR of xPAK1 mRNA from
embryos confirms the quantitation
by Northern blot and in (D) shows
the relative expression of mRNA
in isolated adult tissues. For a
given RNA source three gel tracks
are shown corresponding to PCR
reactions with 2 fold increasing
aliquots of reverse transcribed
RNA. Western analyses of endogenous
xPAK1 protein showing
its relative abundance (C) during
early development and (D) in
isolated adult tissues. In (D) the
relative abundance of xPAK1p is
indicated as �-�, �+�, etc, and �?�
indicates an unidentified peptide
present in liver.
pak1 (p21 protein (Cdc42/Rac)-activated kinase 1) gene expression in Xenopus laevis embryos, NF stage 25, as assayed by in situ hybridization. Lateral view: anteriorleft, dorsal up.
pak1 (p21 protein (Cdc42/Rac)-activated kinase 1) gene expression in Xenopus laevis embryos, NF stage 37, as assayed by in situ hybridization. Lateral view: anteriorleft, dorsal up.
