Zhao H et al. (2007), Myoskeletin, a factor related to Myocardin, is ...

XB-ART-35925

Int J Dev Biol 2007 Jan 01;514:315-20. doi: 10.1387/ijdb.062260hz.

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Myoskeletin, a factor related to Myocardin, is expressed in somites and required for hypaxial muscle formation in Xenopus.

Zhao H , Rebbert ML , Dawid IB .

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Myoskeletin was identified as a gene induced by activin in animal cap explants of Xenopus laevis. This gene encodes a protein related to the transcription factor Myocardin. Whereas Myocardin is expressed in the heart and is known to be involved in heart and smooth muscle formation, Myoskeletin is expressed in the somites and in hypaxial muscle precursors as they migrate away from the somites during tadpole stages. Myoskeletin is required for hypaxial muscle formation, as reduction of its expression through injection of an antisense morpholino oligonucleotide leads to suppression of hypaxial muscle formation. In overexpression experiments in animal caps, Myoskeletin is capable of inducing multiple genes including skeletal muscle, cardiac muscle and smooth muscle-specific genes. We conclude that Myoskeletin is a somite and hypaxial muscle-specific member of the Myocardin family that is required for hypaxial muscle formation.

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Species referenced: Xenopus laevis
Genes referenced: mef2a mmut myf5 myh4 myh6 myocd myos nkx2-5 srf tbxt
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	Fig. 2 (Left). Expression pattern of MyoS. (A) MyoS expression assayed by RT-PCR. (B-E) In situ hybridization. No pattern of expression is seen at stage 10.5 (B), but strong expression in the somites is apparent as stages 18 (C), 24 (D) and 37/38 (E). At stage 37/38, strong expression is also seen in hypaxial muscles and in head musculature.
	Fig. 3 (Right). MyoS is required for hypaxial muscle differentiation. MyoS-MO (A,C) or Control (C)-MO (B,D) were injected at a level of 20 ng into each blastomere at the 2-cell stage. (A,B) Staining with 12/101 antibody at stage 39. (C,D) In situ hybridization with MyoS probe at stage 33/34. Strong reduction or complete absence of antibody staining was seen in 31/31 MyoS-MO-injected embryos (A), while 34/37 C-MO- injected embryos showed intense staining equivalent to that in uninjected embryos (B); three separate experiments were carried out. Using MyoS staining, 27/27 embryos showed strong suppression (C), while 35/36 C- MO-injected embryos showed normal expression (D).
	Fig. 4 (Left). Rescue of hypaxial muscle differentiation. Embryos were injected into one side with MyoS-MO (20 ng) or MyoS-MO plus MyoS mRNA (0.5 ng); the injected side was marked by lacZ RNA. Embryos were stained with 12/101 antibody and for β-galactosidase. (A) MyoS-MO, injected side (3/16 or 20% of embryos showed medium to strong staining, 13/16 weak to negative staining); (A uninjected side (16/16 strong staining). (B) MyoS- MO plus mut-MyoS mRNA, injected side (8/13 or 60% medium to strong staining, 5/13 weak to negative); (B uninjected side (13/13 strong staining).
	Fig. 5 (Right). MyoS induces muscle genes in animal explants. MyoS RNA was injected into the animal region of 2-cell embryos, animal caps were dissected at blastula, cultured to equivalent stage 12.5 and the expression of various genes was assayed by RT-PCR. In (A), 1 and 2ng mRNA was injected per embryo, in (B) the doses were 0.2 and 1ng. AC, uninjected animal caps; -RT, without reverse transcriptase.
	myos (myoskeletin) gene expression in Xenopus laevis embryo via in situ hybridization, NF stage 18, dorsal view, anterior left.
	myos (myoskeletin) gene expression in Xenopus laevis embryo via in situ hybridization, NF stage 24, lateral view, anterior left, dorsal up.
	myos (myoskeletin) gene expression in Xenopus laevis embryo via in situ hybridization, NF stage 38, lateral view, anterior left, dorsal up.