Das B et al. (2002), Multiple thyroid hormone-induced muscle growth ...

XB-ART-6596

Proc Natl Acad Sci U S A 2002 Sep 17;9919:12230-5. doi: 10.1073/pnas.182430599.

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Multiple thyroid hormone-induced muscle growth and death programs during metamorphosis in Xenopus laevis.

Das B , Schreiber AM , Huang H , Brown DD .

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Xenopus laevis tadpole tails contain fast muscle fibers oriented in chevrons and two pairs of slow muscle "cords" along the length of the tail. When tail resorption is inhibited by a number of different treatments, fast muscle but not the slow cord muscle still is lost, demonstrating that the fast tail muscle is a direct target of the thyroid hormone-induced death program. Expression of a dominant negative form of the thyroid hormone receptor (TRDNalpha) was restricted to tadpole muscle by means of a muscle-specific promoter. Even though the transgene protects fast tail muscle from thyroid hormone (TH)-induced death, the tail shortens, and the distal muscle chevrons at the tail tip are degraded. This default pathway for muscle death is probably caused by the action of proteolytic enzymes secreted by neighboring fibroblasts. Non-muscle tissues that are sensitive to TH, such as the fibroblasts, are not protected by the transgene when it is expressed solely in muscle. If allowed to develop to metamorphosis, these transgenic animals die at the climax of metamorphosis before tail resorption has begun. Their limbs have very little muscle even though the rest of limb morphology is normal. Thus, fast tail muscle and limb muscle have their own cell autonomous death and growth programs, respectively, that are independent of the fate of the other neighboring cell types. In contrast, death of the slow muscle is controlled by the other cell types of the tail.

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Species referenced: Xenopus laevis
Genes referenced: thra
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	Fig 1. The expression profile of tadpoles transgenic for pCar/GFP. (a) Ventral view of the head region of a 1-wk-old tadpole expressing GFP in cardiac and skeletal muscle. (b) GFP expression in the muscle of the developing limb at NF stage 54. (c) GFP expression in the limb muscle of a juvenile frog. (d) GFP expression in muscle fibers in the middle of the tail region of a stage 57 tadpole. (e) GFP expression in the mid-tail region of a stage 63 tadpole, demonstrating the loss of GFP fibers in the fast muscle chevrons. (f) GFP expression in the slow muscle cords of the tail in a stage 64 tadpole. (g) Loss of GFP-labeled muscle fibers in the tail of a stage 63 tadpole. [Bars = 500 μm (a, b, and f) and 1 mm (c–e and g).]
	Fig 2. Assaying muscle loss by using a muscle-specific antibody (MF20) after the 2-wk assay of tadpoles with TH. (a) Tail of an animal treated with 10 nM T3 for 7 days. Note the loss of muscle fibers and disorganization of the chevron structures. (b) Tail of an untreated animal. (c) Tail of a pCar/TRDNα transgenic animal treated with 10 nM T3 for 7 days. (d–f) In situ hybridization of tail cross sections obtained from animals in a–c, respectively, with collagenase-3 antisense probe. (g–i) Changes in the head of the animals in a–c, respectively, after the 2-wk assay. [Bars = 500 μm (a–c and g–i), 100 μm (d and e), and 50 μm (f).]
	Fig 3. Caspase-3 activity in the tadpole tails in the 2-wk assay and retention of muscle in tail tip. (a) Tail from a wild-type animal treated with 10 nM T3 for 4 days. Note the caspase-3-positive muscle fibers (examples are shown with arrowheads). (b) Tail from an untreated control animal. (c) Tail from a pCar/TRDNα-expressing animal treated with 10 nM T3 for 4 days. Note the caspase-3-positive epidermal cells similar to a but the lack of caspase-positive muscle fibers. (d–f) Tips of the tail stained with MF20 (red) and anti-active caspase-3 antibody (green) of 10 nM T3-treated (7 days) wild-type, untreated wild-type, and 10 nM T3-treated (7 days) pCar/TRDNα tadpoles, respectively. [Bars = 100 μm (a–c) and 200 μm (d–f).]
	Fig 4. Inhibition of activation of caspase-3 in tail muscle during spontaneous metamorphosis. (a) Cross section through the mid tail region of a wild-type tadpole at NF stage 62 stained with active caspase-3 antibody (red) and MF20 (green) and counterstained with 4′,6-diamidino-2-phenylindole (DAPI; blue). (b) Similarly stained cross section through the mid-tail region of a pCar/TRDNα tadpole. (Bars = 100 μm.)
	Fig 5. Inhibition of muscle formation in the limbs in the pCar/TRDNα animal. (a) Wild-type and pCar/TRDNα tadpoles at stage 63. The transgenic animal will die at this stage. (b) The skinned hind limbs of the animals shown in a, demonstrating the reduced muscle formation in the transgenic tadpole. (c) Bone (red) and cartilage (blue) staining of the same hind limbs. [Bars = 1 cm (a) and 500 μm (b and c).]

References [+] :

Berry, The expression pattern of thyroid hormone response genes in the tadpole tail identifies multiple resorption programs. 1998, Pubmed, Xenbase