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Proc Natl Acad Sci U S A
1997 Aug 05;9416:8602-5. doi: 10.1073/pnas.94.16.8602.
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Relax promotes ectopic neuronal differentiation in Xenopus embryos.
Ravassard P
,
Vallin J
,
Mallet J
,
Icard-Liepkalns C
.
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We previously isolated a novel rat cDNA encoding a basic helix-loop-helix transcription factor named Relax, whose expression in the developing central nervous system is strictly limited to discrete domains containing precursor cells. The timing of Relax expression coincides with neuronal differentiation. To investigate the involvement of Relax in neurogenesis we tested whether Relax activated neural genes in the ectoderm by injecting Relax RNA into Xenopus embryos. We demonstrate that ectopic Relax expression induces a persistent enlargement of the neural plate and converts presumptive epidermal cells into neurons. This indicates that Relax, when overexpressed in Xenopus embryos, has a neuronal fate-determination function. Analyses both of Relax overexpression in the frog and of the distribution of Relax in the rat neural tube strongly suggest that Relax is a neuronal fate-determination gene.
Figure 1
Phenotype of Relax/XE12-injected Xenopus embryos at stage 14. (Top) In situ hybridization of an N-CAM digoxygenin-labeled riboprobe in noninjected (a) and Relax/XE12-RNA-injected (b) embryos. (Bottom) Schematic representation of both embryos; dark gray represents the N-CAM label. The injected side (i) and the noninjected side (ni) of the embryo are indicated. The symmetric axis is represented by two vertical lines. All injected embryos presented a phenotype similar to those shown here.
Figure 2
Persistence of the ectopic expression of Relax at the late neurula stage. Immunocytochemistry with N-CAM (a–c) and β-tubulin (d) antibodies (1:100) of noninjected (a), XE12 RNA-injected (b), and Relax/XE12 RNA (c and d) embryos at development stage 20. The adhesion organ (ao), the optic vesicle (ov), and the injected (i) and the noninjected sides (ni) of the embryo are indicated. Arrows indicate neural tube labeling; arrowheads indicate ectopic labeling. The symmetric axis is represented by two vertical lines. All the injected embryos presented a phenotype similar to those shown here.
Figure 3
Ectopic N-CAM expression in Xenopus embryos injected with Relax/XE12. Immunocytochemistry with N-CAM antibody (1:100) of Relax-XE12-injected embryos at development stage 20: the injected left side (a), the noninjected right side (b), and the ventral side (c). (Lower) Twofold magnification of the marked area shown in a, b, and c, respectively. The injected (i) and the noninjected (ni) sides of the embryo are indicated. The dotted lines indicate the dorsal midline of the embryo. Open arrows indicate ectopic N-CAM-positive cells. All the injected embryos presented a phenotype similar to those shown here.
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