XB-ART-26360Cell. December 1, 1989; 59 (5): 893-903.
A Xenopus mRNA related to Drosophila twist is expressed in response to induction in the mesoderm and the neural crest.
We have cloned a Xenopus cDNA related to the twist gene, which is required for mesodermal differentiation in Drosophila. Northern blots of dissected embryos and in situ hybridization show that the corresponding mRNA, called Xtwi, first appears in early gastrulae, and is present only in mesodermal cells. Within the mesoderm, Xtwi is expressed in the notochord and lateral plate, but not in the myotome; therefore there is a complementary pattern of Xtwi and muscle-specific gene expression in the mesoderm. Xtwi expression therefore marks the subdivision of the mesoderm. Xtwi is also activated a few hours later in the early development of the neural crest. This gene is thus expressed in response to two sequential early inductions in frog development.
PubMed ID: 2590945
Article link: Cell.
Genes referenced: actc1 actl6a foxi1 tbx2 twist1
Article Images: [+] show captions
|Figure 1. Sequence of the Xenopus twist-related cDNA 118 The two overlapping poly(A) addition signals are underlined. Asterisk indicates translation stop.|
|Figure 2. Comparison of the Predicted Protein Sequences of Drosophila twist and Xenopus Xtwi The Xtwi protein is homologous to parts of the C-terminal region of twist. The bold box surrounds the DNA binding and dimerization domain as defined by Murre et al. (WQQ), and the light box another region of similarity. Double dots indicate identities, single dots indicate conservative substitutions, and dashes indicate spaces inserted to improve the match.|
|Figure 3. Expression of Xtwi through Early Xenopus Development (A) Northern blot containing 10 pg of total staged (Nieuwkoop and Faber, 1997) embryo RNA per lane probed with random-primed fragments (Feinberg and Volgelstein, 1983) made from the tl8 cDNA. Ethidium bromide staining of the 18s rRNA shows roughly equal loading. (6) Graph of numbers of Xtwi transcripts per embryo through da velopment based on densitometry of appropriately exposed autoradio graphs of the blot shown in (A). The line plotted refers to one class of transcripts, and so the total number of Xhvi transcripts is about double the value shown.|
|Figure 4. Xtwi Expression in Tailbud (Stage 26) Embryos (A) and (B) are Northern blots of RNA from dissected embryo parts hybridized successively with probes made from tl6, a cardiac actin gene-specific sequence (Mohun et al., 1964), and a cDNA encoding the translation factor EFla, which is expressed in all cells (Krieg et al., 1969). The cardiac actin probe detects transcripts only in muscle, and the EF-la probe shows the relative amounts of total RNA in each sample. In (A), the rest of the head actually consisted of the internal head cells left after the other parts had been dissected away, and thus contained various cell types, including mesoderm and neural crest. In (B), although both cardiac actin and Xtwi are expressed in the somite fraction, cardiac actin is probably restricted to the myotome, and Xtwi to loose mesenchymal cells next to the notochord, possibly the sclerotome (see text and Figure 9C). The whole embryo sample contains an amount of total RNA similar to that in the dissected tissue samples, which are pooled from several embryos. lat mes, lateral mesoderm.|
|Figure 5. The Dorsal Axial Structuresof a Late Neurula (Stage 16) The pictures show (A) the mesodermal and (B) the ectodermal layers exposed by dissection and viewed from the ventral side. Anterior is to the left. Scale bars represent 400 urn.|
|Figure 6. Northern Analysis of Dissected Parts of Stage 16 Neurectoderm The blot was probed as described in the legend to Figure 4. The neural crest sample contains RNA from the segments of the cephalic neural crest shown in Figure 5. The dorsal (dl) mesoderm sample analyzed for comparison includes somites and notochord.|
|Figure 7. Xtwi Expression in Midneurulae Transverse sections of stage 14-16 embryos hybridized with Xtwi ([A) and [C)) and cardiac actin ([B) and [D)) probes. (A) and (B) are sections about a quarter of the way through the embryo from the anterior end, at the level of the most anterior somites. In such sections Xtwi is expressed in the lateral plate (lp) and in the notochord (n), in contrast to cardiac actin, which is expressed only in the somites (s). In (A), labeling by Xtwi of the forming neural crest is just detectable (unlabeled arrows). Sections cut about halfway through the embryo show Xtwi expression restricted to the notochord (C) and cardiac actin in only the somites (D).|
|Figure B. Xtwi Is Expressed in the Mesoderm and Neural Crest of Late ·Neurulae transcripts (Figure 48). Apart from the neural crest, the only tissues labeled by Xtwi at these early stages are of mesodermal origin. It might be thought that a low level of (A) and (B) are sections a quarter of the way, (C) and (D) a third of the way, and (E) and (F) about halfway through stege 18-19 embryos counting from the anterior end, hybridized with Xtwi and cardiac actin probes. Note the strong expression of Xtwi in the an1erior neural crest (nc). Mesodermal labeling by Xtwi is restricted to the notochord (n) and anterior lateral plate mesoderm (lp), whereas cardiac actin labels only the somites (s).|
|Figure 9. Xtwi Expression in Tailbud Embryos (A) and (B) are sections from stage 23-24 embryos one-tenth and one-fifth from the anterior end, showing patches of labeled tissue corresponding to neural crest cells that have migrated into the head. (C) and (E) are middle and posterior sections, respectively, from a stage 27-28 embryo showing labeling in (C) of paranotochordal mesenchyme (m; possibly the sclerotome, see text), and in (E) of the notochord and lateral plate mesoderm (lp), as illustrated by the diagram (D). nt, neural tube; s, somites.|
|Figure 10. Xtwi Expression Is Activated in Response to Two Successive Inductions Northern blots were probed with Xtwi and EMa probes (see legend to Figure 4). (A) Stage 3 l/2 blastulae were dissected into animal, equatorial, and vegetal pieces, and these cultured with control stage 13. Animal and vegetal pieces were also cultured in combination. (B) Early gastrulaectoderm (ect) was cultured alone or in combination with mesoderm (mns) from the dorsal (dl) or ventral (VI) sides of midgastrulae until control embryos reached the tailbud stage. The mesoderm was then removed before analysis of the ectoderm fragments. The whole embryo sample included for comparison contains an amount of total RNA similar to that in the ectoderm fragments.|