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The community effect describes a process required for Xenopus muscle progenitor cells to progress to the expression of myogenic genes. Past work has suggested that this effect is dependent on secreted factors released by dorsolateral or dorsal lip cells. We show here that known dorsalizing molecules as well as other natural dorsal lip factors contribute to, but do not wholly account for, the community effect. We conclude that, in addition to dorsalizing molecules, the community effect requires factors or conditions peculiar to the dorsolateral mesoderm, a region of the embryo that contains muscle progenitor cells.
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9240569
???displayArticle.link???Int J Dev Biol ???displayArticle.grants???[+]
Fig. 1. Diagram to illustrate the experimental procedures used. Dissection, eelf
dissociation, reaggregation and sandWIch construction rook less chan one hour.
Sandwiches were cultured for 18 h at f8ce. until control embryos reached stage 18.
The procedure for dissection of dorsolateral mesoderm tissue from Stage 70'/2
embryos is descflbed by Gurdon er al. (1993b)
Fig. 2. Dorsalizing molecules contribute
to the community effect in
Xenopus myogenesis. RLD>i.-
labeled dorsolateral mesoderm cells
of gastrulae were implanred smgly.
or m groups of different Sizes, into
blastula animal cap sandwiches, and
were immunosrained for MyoD at
the equivalenr of stage 18(see Gurdon
et al.. 1993b. for methods). The animal
cap sandwIch tissues derived
from blastulae were injected with
100 pg mRNA for noggin or Siamois
mRNAs; NIL. anima/caps not mjected
with mRNA. Sections are of sand.
wiches with small (10-50 cell)
reaggregates. vIewed for MyoD anrlbody
stam (left), RLDx (middle), or
Hoechst (right!. MyoD-posirive nuclei
are seen m the noggin and Siamois
injecred samples.
Fig. 3. Siamois and noggin reduce the size of a reaggregate required
forthe community effect. In dorsolateral cell reaggregares of 2000rmore
cells. inserred Into uninjected sandwiches, up to 40% of cells will e.\press
MyoD. In noggin and Siamois injected sandwiches. at leasr 15 adjacenr
dorsolateral cefls are required for MyoD expression. 965, 800 and 525 cells
were scored, and 6 sandwiches were tested per condition.
Fig. 4. Sandwiches of dorsal lip tissue can induce small groups of
implanted mesoderm cells from ventral !AI or dorsolateral (B) regions
to express MyoD. At least 15 cells must be enclosed in a reaggregate for
some of them to e\press MyoD In dorsal lip sandwiches (A and BI Animal
cap sandwiches are totally unable to induce MyoD. As a result. veneral
mesoderm cells are not Induced to express MyoD at afl in animal cap
sandwiches (AI, over 100 dorsolateral cells must be reaggregated and
placed In uninjecred animal cap sandwiches If they are to become positive
for MyoD (BI
