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???displayArticle.abstract??? XLPOU3 is a member of the Xenopus POU domain family of genes, encoding a class of homeodomain-containing transcription factors implicated in cell differentiation during development. Here we describe the isolation and characterisation of XLPOU3b, an allelic genomic counterpart of the XLPOU3 cDNA previously described (Baltzinger et al. (1992) Nucleic Acids Res. 20, 1993), and the spatio-temporal transcription patterns of this gene during development, as determined by Northern blotting and whole-mount in situ hybridisation. Like other genes encoding POU domains of class III, XLPOU3b is intronless. XLPOU3 and XLPOU3b proteins share 82% amino acid identity with the mammalian N-Oct-3/Brn-2 proteins. XLPOU3 mRNA, which is first detected at the neurula stage, is expressed in the developing brain and spinal cord. In addition, XLPOU3 transcription is observed in a restricted region of the auditory vesicle during development. The results suggest that XLPOU3 may participate in patterning the central nervous system during early Xenopus development.
Fig. 4. Localisation of the XLPOU3 transcripts during early development by whole-mount in situ hybridisation. Embryos in (A-F) were hybridised
with an antisense XLPOU3 probe while the control embryo in (G) was hybridised with an XLPOU3 sense probe. The embryo of (D,E) is albino. Anterior
is to the left and dorsal is up, except in (E). (A) Early neurula stage embryo (stage 14); two anterior patches of XLPOU3 expression are seen
(arrowheads) on the medial region of the neural plate. (B) In mid-neurula (stage 17118) and (C) early tailbud (stage 22/23) embryos, the hybridisation
signal extends along the anterior-posterior axis and appears most abundant in the head region. (D) At stage 27 (hatching), the three major subdivisions
of the brain (fore-, mid-, hindbrain) are involved and expression continues to extend along the posterior axis. (E) At stage 27 (dorsal view), the absence
of staining-along the middling of the brain shows that there are no transcripts in the floor and roof plate cells. A signal is detected in the auditory vesicles
(white arrowheads). (F) At stage 32, the regions expressing XLPOU3 are the same as in (D,E). Blue staining is detected in the branchial arches
and, although not observed in embryos hybridised with the sense probe, this signal is most likely artifactual, since it is observed inconsistently. (Cl) No
signal is revealed with a sense XLPOU3 probe hybridised to a tailbud stage embryo. The dark coloration of the cement gland (cg) is due to pigmentation
and does not constitute a positive signal. All embryos were cleared in Murray reagent prior to photography.
Fig. 6. Distribution of XLPOU3 transcripts in the developing brain, spinal cord and auditory vesicle of tailbud stage 30 embryos. (A-F) Representative
transverse sections, along the anterior-posterior axis. Dorsal is up. (A) A section through the rostral diencephalon, just in front of the optic vesicles,
shows a broad distribution of XLPOU3 mRNA. (B,C) Sections at the level of the optic vesicles show the preponderant dorsal distribution of the
XLPOU3 mRNA. The faint signal in the optic vesicles in (C) is not systematically observed. (D) A section at the level of the auditory vesicle indicates
the presence of XLPOU3 mRNA still in the dorsal half of the hindbrain, excluding the roof plate but also in a restricted region of the auditory vesicle
(arrows). (E,F) Sections through the rhombencephalon and spinal cord show the presence of XLPOU3 mRNA near the ventricular zone when moving
caudally. e, eye vesicle; av, auditory vesicle; cg, cement gland; nc, notochord.
Fig. 7. The distribution of XLPOU3 mRNA along the dorsal-ventral axis i
hindbrain region of a stage 27 embryo (A,B) or stage 32 embryo (CD) al
more dorsal as development proceeds. av, auditory vesicle.
