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Dev Dyn
2009 Jan 01;2381:204-9. doi: 10.1002/dvdy.21826.
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Samba, a Xenopus hnRNP expressed in neural and neural crest tissues.
Yan CY
,
Skourides P
,
Chang C
,
Brivanlou A
.
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RNA binding proteins regulate gene expression at the posttranscriptional level and play important roles in embryonic development. Here, we report the cloning and expression of Samba, a Xenopus hnRNP that is maternally expressed and persists at least until tail bud stages. During gastrula stages, Samba is enriched in the dorsal regions. Subsequently, its expression is elevated only in neural and neural crest tissues. In the latter, Samba expression overlaps with that of Slug in migratory neural crest cells. Thereafter, Samba is maintained in the neural crest derivatives, as well as other neural tissues, including the anterior and posterior neural tube and the eyes. Overexpression of Samba in the animal pole leads to defects in neural crest migration and cranial cartilage development. Thus, Samba encodes a Xenopus hnRNP that is expressed early in neural and neural crest derivatives and may regulate crest cells migratory behavior.
Figure 3. Samba is expressed in the neural and neural crest derivatives as seen by in situ hybridization. A: Vegetal view of stage 10 embryos with dorsal side to the right. Samba expression is concentrated in the dorsal region. B: Neurula stage embryo. Samba is present in the neural plate and crest domain. C: Anterior-dorsal view of late neurula stage embryo. Arrows point to the outer edge of the forming migratory crest domain, which expresses Samba. D: Double in situ for Slug and Samba show that Samba overlaps with Slug-expressing migrating streams but is not restricted to neural crest domain. Slug probe was developed with a violet stain and Samba with blue stain. E: Anterior-lateral view of tail bud stage embryo indicates that Samba is expressed in migrating lateral streams of crest cells (arrow) and optic vesicles. F: Lateral view of tail bud stage embryo showing that Samba remains in the crest cells, optic vesicle, and now appears in the otic vesicle as well. G: Dorsal view of a late tail bud stage embryo. H,I: Higher magnification of cranial expression in Figures F and G.
Figure 4. Overexpression of Samba does not affect neural and crest markers. Embryos co-injected with 200 pg of Samba and 100 pg of beta-galactosidase in one blastomere at two-cell stage were processed for in situ hybridization for the neural markers Sox2 and Sox3 and the crest markers Slug, Msx1, and Twist. None of the markers altered their expression pattern in the presence of excess Samba.
Figure 5. Samba inhibits migration of crest cells and formation of crest derivatives. A: Diagram of the cranial neural crest transplantation procedure and the resulting embryo. Green fluorescent protein (GFP) -positive crest cells migrating from the transplant generated the characteristic streams of migration in control embryos injected with 500 pg of GFP (for details see the Experimental Procedures section). B-D: Crest cell migration was limited in red fluorescent protein (RFP) embryos that received transplants from donors co-injected with 200 pg of Samba and GFP. Green channel showing GFP-positive transplanted cells (B); red channel showing RFP-positive host cells (C) and overlay of green and red channels (D). E-G: In contrast, when the transplants expressed only GFP and were inserted into RFP-Samba-overexpressing embryos, crest cell migration was normal. Green channel showing GFP (E); red channel showing RFP (F) and overlay of green and red channels (G). H: Ventral view of an Alcian-blue-stained embryo injected with GFP on the left animal pole. Arrow points to the left maxillary cartilage. F: Embryo injected with 200 pg of Samba lacks the left maxillary cartilage (arrow).
