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Positive and negative regulation of muscle cell identity by members of the hedgehog and TGF-beta gene families.

Du SJ, Devoto SH, Westerfield M, Moon RT - J. Cell Biol. (1997)

Bottom Line: We have examined whether the development of embryonic muscle fiber type is regulated by competing influences between Hedgehog and TGF-beta signals, as previously shown for development of neuronal cell identity in the neural tube.We found that ectopic expression of Hedgehogs or inhibition of protein kinase A in zebrafish embryos induces slow muscle precursors throughout the somite but muscle pioneer cells only in the middle of the somite.We propose that a Hedgehog signal first induces the formation of slow muscle precursor cells, and subsequent Hedgehog and TGF-beta signals exert competing positive and negative influences on the development of muscle pioneer cells.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, University of Washington, School of Medicine, Seattle 98195, USA.

ABSTRACT
We have examined whether the development of embryonic muscle fiber type is regulated by competing influences between Hedgehog and TGF-beta signals, as previously shown for development of neuronal cell identity in the neural tube. We found that ectopic expression of Hedgehogs or inhibition of protein kinase A in zebrafish embryos induces slow muscle precursors throughout the somite but muscle pioneer cells only in the middle of the somite. Ectopic expression in the notochord of Dorsalin-1, a member of the TGF-beta superfamily, inhibits the formation of muscle pioneer cells, demonstrating that TGF-beta signals can antagonize the induction of muscle pioneer cells by Hedgehog. We propose that a Hedgehog signal first induces the formation of slow muscle precursor cells, and subsequent Hedgehog and TGF-beta signals exert competing positive and negative influences on the development of muscle pioneer cells.

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Ectopic Dorsalin-1 represses muscle pioneer cell induction by Hedgehogs. Embryos were double labeled with anti-myc  antibody to monitor expression of dsl-1myc and with the 4D9 antibody to monitor muscle pioneer cells. (A) Embryos injected with  Shhfs RNA as control. (B) Embryos coinjected with twhh-bGFP  DNA and zebrafish Shh RNA show induction of extra muscle pioneer cells. (C) Embryos coinjected with twhh-dsl-1myc DNA and  zebrafish Shh RNA also show induction of extra muscle pioneer  cells, but not in the region (bracket) near the notochord cell expressing Dorsalin-1 (arrowhead). Embryos are oriented in side  views, with anterior to the left and dorsal to the top. Bar, 50 μm.
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Figure 6: Ectopic Dorsalin-1 represses muscle pioneer cell induction by Hedgehogs. Embryos were double labeled with anti-myc antibody to monitor expression of dsl-1myc and with the 4D9 antibody to monitor muscle pioneer cells. (A) Embryos injected with Shhfs RNA as control. (B) Embryos coinjected with twhh-bGFP DNA and zebrafish Shh RNA show induction of extra muscle pioneer cells. (C) Embryos coinjected with twhh-dsl-1myc DNA and zebrafish Shh RNA also show induction of extra muscle pioneer cells, but not in the region (bracket) near the notochord cell expressing Dorsalin-1 (arrowhead). Embryos are oriented in side views, with anterior to the left and dorsal to the top. Bar, 50 μm.

Mentions: These results demonstrate that Hedgehogs can induce slow muscle cells, including both muscle pioneers and non–muscle pioneer slow muscle cells, and that Dorsalin-1 can specifically inhibit the development of muscle pioneer cells. Dorsalin-1 could act by inhibiting the expression of hedgehog genes in the notochord, or by antagonizing Hedgehog protein activity. If Dorsalin-1 represses expression of hedgehog genes, then overexpression of Hedgehog should overcome the inhibitory effect of Dorsalin-1 on muscle pioneer formation. We tested this prediction by coinjecting Hedgehog RNAs with twhh-dsl-1myc DNA and analyzing the injected embryos by double labeling with anti-myc antibody (labeling myc-tagged Dorsalin-1) and with the 4D9 antibody (labeling muscle pioneer cells). Compared to embryos injected with control RNA (Fig. 6 A), the expression of Dorsalin-1 in the notochord (Fig. 6 C, arrowhead) inhibited development of muscle pioneers in adjacent somites (Fig. 6 C, bracket), regardless of whether embryos were coinjected with RNA encoding Tiggy-winkle hedgehog (100%, n = 65; not shown) or Sonic hedgehog (100%, n = 43). In contrast, induction of muscle pioneers by Hedgehogs was unaffected in embryos coinjected with Sonic hedgehog RNA and the control DNA construct twhh-bGFP (Fig. 6 B). These data suggest that Dorsalin-1 blocks the differentiation of slow muscle precursor cells into muscle pioneer cells by antagonizing the activity of Hedgehogs rather than by simply inhibiting their expression.


Positive and negative regulation of muscle cell identity by members of the hedgehog and TGF-beta gene families.

Du SJ, Devoto SH, Westerfield M, Moon RT - J. Cell Biol. (1997)

Ectopic Dorsalin-1 represses muscle pioneer cell induction by Hedgehogs. Embryos were double labeled with anti-myc  antibody to monitor expression of dsl-1myc and with the 4D9 antibody to monitor muscle pioneer cells. (A) Embryos injected with  Shhfs RNA as control. (B) Embryos coinjected with twhh-bGFP  DNA and zebrafish Shh RNA show induction of extra muscle pioneer cells. (C) Embryos coinjected with twhh-dsl-1myc DNA and  zebrafish Shh RNA also show induction of extra muscle pioneer  cells, but not in the region (bracket) near the notochord cell expressing Dorsalin-1 (arrowhead). Embryos are oriented in side  views, with anterior to the left and dorsal to the top. Bar, 50 μm.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2139815&req=5

Figure 6: Ectopic Dorsalin-1 represses muscle pioneer cell induction by Hedgehogs. Embryos were double labeled with anti-myc antibody to monitor expression of dsl-1myc and with the 4D9 antibody to monitor muscle pioneer cells. (A) Embryos injected with Shhfs RNA as control. (B) Embryos coinjected with twhh-bGFP DNA and zebrafish Shh RNA show induction of extra muscle pioneer cells. (C) Embryos coinjected with twhh-dsl-1myc DNA and zebrafish Shh RNA also show induction of extra muscle pioneer cells, but not in the region (bracket) near the notochord cell expressing Dorsalin-1 (arrowhead). Embryos are oriented in side views, with anterior to the left and dorsal to the top. Bar, 50 μm.
Mentions: These results demonstrate that Hedgehogs can induce slow muscle cells, including both muscle pioneers and non–muscle pioneer slow muscle cells, and that Dorsalin-1 can specifically inhibit the development of muscle pioneer cells. Dorsalin-1 could act by inhibiting the expression of hedgehog genes in the notochord, or by antagonizing Hedgehog protein activity. If Dorsalin-1 represses expression of hedgehog genes, then overexpression of Hedgehog should overcome the inhibitory effect of Dorsalin-1 on muscle pioneer formation. We tested this prediction by coinjecting Hedgehog RNAs with twhh-dsl-1myc DNA and analyzing the injected embryos by double labeling with anti-myc antibody (labeling myc-tagged Dorsalin-1) and with the 4D9 antibody (labeling muscle pioneer cells). Compared to embryos injected with control RNA (Fig. 6 A), the expression of Dorsalin-1 in the notochord (Fig. 6 C, arrowhead) inhibited development of muscle pioneers in adjacent somites (Fig. 6 C, bracket), regardless of whether embryos were coinjected with RNA encoding Tiggy-winkle hedgehog (100%, n = 65; not shown) or Sonic hedgehog (100%, n = 43). In contrast, induction of muscle pioneers by Hedgehogs was unaffected in embryos coinjected with Sonic hedgehog RNA and the control DNA construct twhh-bGFP (Fig. 6 B). These data suggest that Dorsalin-1 blocks the differentiation of slow muscle precursor cells into muscle pioneer cells by antagonizing the activity of Hedgehogs rather than by simply inhibiting their expression.

Bottom Line: We have examined whether the development of embryonic muscle fiber type is regulated by competing influences between Hedgehog and TGF-beta signals, as previously shown for development of neuronal cell identity in the neural tube.We found that ectopic expression of Hedgehogs or inhibition of protein kinase A in zebrafish embryos induces slow muscle precursors throughout the somite but muscle pioneer cells only in the middle of the somite.We propose that a Hedgehog signal first induces the formation of slow muscle precursor cells, and subsequent Hedgehog and TGF-beta signals exert competing positive and negative influences on the development of muscle pioneer cells.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, University of Washington, School of Medicine, Seattle 98195, USA.

ABSTRACT
We have examined whether the development of embryonic muscle fiber type is regulated by competing influences between Hedgehog and TGF-beta signals, as previously shown for development of neuronal cell identity in the neural tube. We found that ectopic expression of Hedgehogs or inhibition of protein kinase A in zebrafish embryos induces slow muscle precursors throughout the somite but muscle pioneer cells only in the middle of the somite. Ectopic expression in the notochord of Dorsalin-1, a member of the TGF-beta superfamily, inhibits the formation of muscle pioneer cells, demonstrating that TGF-beta signals can antagonize the induction of muscle pioneer cells by Hedgehog. We propose that a Hedgehog signal first induces the formation of slow muscle precursor cells, and subsequent Hedgehog and TGF-beta signals exert competing positive and negative influences on the development of muscle pioneer cells.

Show MeSH
Related in: MedlinePlus