Nicolas N et al. (2000), Neural and hormonal control of expression of my...

XB-ART-10980

Dev Dyn 2000 May 01;2181:112-22. doi: 10.1002/(SICI)1097-0177(200005)218:1<112::AID-DVDY10>3.0.CO;2-D.

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Neural and hormonal control of expression of myogenic regulatory factor genes during regeneration of Xenopus fast muscles: myogenin and MRF4 mRNA accumulation are neurally regulated oppositely.

Nicolas N , Mira JC , Gallien CL , Chanoine C .

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With the aim to investigate the influence of both innervation and thyroid hormone, on the expression of the MRFs during muscle regeneration, we performed cardiotoxin injury-induced regeneration experiments on fast muscles of adult Xenopus laevis subjected to different experimental conditions, including denervation and T3 treatment, and analyzed the accumulation of the four myogenic regulatory factors (MRFs) using RT-PCR and in situ hybridization. We show here that manipulation of hormone levels or innervation resulted in differential alterations of MRF expression. Denervation and T3 treatment transiently down-regulated Myf-5 mRNA levels at the beginning of the regeneration process. Myf-5 was the only myogenic factor subject to thyroid hormone influence. Muscle denervation persistently reduces the levels of MRF4 transcripts as early as the first stages of regeneration, whereas the levels of myogenin mRNA were increased in the late stages of regeneration. This suggests that MRF4 expression may be induced by innervation and hence may be involved in mediating transcriptional responses to innervation and that myogenin expression may compensate for the down-regulation of MRF4 gene. This switch in MRF gene expression following denervation could have important consequences for the ability of Xenopus regenerating muscles to recover function after denervation.

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Species referenced: Xenopus laevis
Genes referenced: myf5 myf6 myog myrf

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	Figure 2. RNAse protection for acetylcholine receptor (α subunit) and EF-1α RNA. Amounts used were 5 μg total RNA per assay; innervated (C) and denervated (D) regenerating muscles taken at 15 days following cardiotoxin injury.
	Figure 4. In situ hybridization using antisense riboprobes to Myf-5 on transverse sections of control (A, D), T3-treated (B) and denervated (C) regenerating muscle at 11 days P-I. Using sense riboprobes, we did not detect hybridization signals (data not shown). A, B and C are darkfield photomicrographs. D is a brightfield photomicrograph of the same section that is shown in A. Scale bar = 200 μm
	Figure 5. In situ hybridization using antisense riboprobes to MRF4 on transverse sections of control (C), T3-treated (D) and denervated (A,B) regenerating muscle at 11 days P-I. Using sense riboprobes, we did not detect hybridization signals (data not shown). B, C and D are darkfield photomicrographs. A is a brightfield photomicrograph of the same section that is shown in B. Scale bar = 200 μm
	Figure 6. In situ hybridization using antisense riboprobes to MRF4 on transverse sections of control (A, C), T3-treated (D), denervated (B), and denervated/T3-treated (E) regenerating muscle at 20 days P-I. Using sense riboprobes, we did not detect hybridization signals (data not shown). B, C, D, and E are darkfield photomicrographs. A is a brightfield photomicrograph of the same section that is shown in C. A: Scale bar = 200 μm; D, E: Scale bar = 150 μm
	Figure 7. In situ hybridization using antisense riboprobes to myogenin on transverse sections of control (C, G, H), T3-treated (A, B), denervated (D, E, I) and denervated/T3-treated (F) regenerating muscle at 20 (A) and 30 (G) days P-I. Using sense riboprobes, we did not detect hybridization signals (data not shown). B, C, E, F, H, I are darkfield photomicrographs. A, D, G are brightfield photomicrographs. Scale bar = 200 μm