Brown DD et al. (2006), Xtn3 is a developmentally expressed cardiac and...

XB-ART-34591

Gene Expr Patterns 2006 Oct 01;68:913-8. doi: 10.1016/j.modgep.2006.03.003.

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Xtn3 is a developmentally expressed cardiac and skeletal muscle-specific novex-3 titin isoform.

Brown DD , Davis AC , Conlon FL .

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Titin proteins play an essential role in maintaining muscle function and structure. Recent work has implicated the involvement of the novex-3 titin isoform in sarcomere restructuring and disease. Unlike avian and mammalian systems, Xenopus laevis myogenesis is characterized by a wave of primary myogenesis followed by apoptosis of the primary muscles and formation of new muscles by secondary myogenesis. We show here that the Xenopus laevis novex-3 titin isoform (Xtn3) is developmentally expressed throughout the somites, heart, and primary muscles of the developing embryo. Downregulation of Xtn3 expression at tadpole stages appears to coincide with the change in myofiber composition from solely embryonic "fast" fiber types to myofibers containing both "fast" and "slow" fiber types. We demonstrate that Xtn3 is expressed early in the presomitic mesoderm and remains expressed in the somites, ventral myoblasts, and developing jaw muscles through late tailbud stage. Furthermore, we show that Xtn3 is expressed in the cardiac primordia prior to linear heart tube formation and remains expressed in the heart until tadpole stage, at which point it is downregulated in the heart except in discrete patches of cardiac cells. Finally, we demonstrate that Xtn3 transcripts are detectable in adult heart and muscle tissues.

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Species referenced: Xenopus laevis
Genes referenced: actc1 actl6a myh6 pc.1 tbx20 tn3 ttn

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	Fig. 2. Xtn3 is developmentally expressed throughout the somites, heart, and jaw myoblasts from early neurula to late tailbud stages. (A–P) In situ hybridization showing expression of the Xtn3 at the indicated stages. (A–C) Neurula stage embryos. Anterior is to the left. (A and C) Dorsal views. (B) Lateral view. (D–M) Tailbud stage embryos. (E, G, I, K, and M) Ventral anterior views. Anterior is up. (H) Inset shows higher magnification of somite region. Bracket indicates one individual somite. (N) Tadpole stage embryo. Note the lack of staining in trunk and heart. Some light staining remains in facial muscles. (O and P) Adult heart lacking global Xtn3 expression. (P) A magnification of (O). Black arrowhead indicates isolated group of Xtn3-expressing cells. h, heart; hp, heart primordia; jm, jaw myoblasts; psm, presomitic mesoderm; pc, pigment cells; vm, ventral myoblasts; s, somites; t, trunk.
	Fig. 3. Histology of Xtn3 expression. Paraffin embedded embryos were sectioned at a depth of 16 μm after in situ hybridization. (A, C, E, and G) Transverse sections through developing somites. (B, D, F, and H) Transverse sections through developing cardiac region. (I) Transverse section showing jaw myoblasts in the head. a, atrium; ec, endocardium; hp, heart primordia; jm, jaw myoblasts; mc, myocardium; nc, notochord; nt, neural tube; s, somites; v, ventricle; vm, ventral myoblasts.
	tn3 (titin novex-3) gene expression in Xenopus laevis embryos, NF stage 40, as assayed by in situ hybridization, lateral view, anterior left, dorsal up. Key: jm=jaw muscle, h=heart; vm=ventral myoblasts, also called hypaxial muscles.
	Fig. 4. Xtn3 is expressed in adult heart and skeletal muscle. RNA from St.13 embryos, St.38 embryos, adult heart, and adult muscle tissue was isolated and 100 ng of RNA subjected to RT-PCR. Xtn3 RT-PCR shows expression in St.38, adult heart and adult muscle tissues. “−RT” controls lack reverse transcriptase to show lack of genomic contamination. Tbx20 primers serve as controls for heart tissue, MHCα and muscle actin serve as controls for muscle tissue, and EF1α serves as loading control.
	tn3 (titin novex-3) gene expression in Xenopus laevis embryos, NF stage 40, as assayed by in situ hybridization, transverse section through head at eye level, dorsal up. Key: jm= jaw muscle.

References [+] :

Bang, The complete gene sequence of titin, expression of an unusual approximately 700-kDa titin isoform, and its interaction with obscurin identify a novel Z-line to I-band linking system. 2001, Pubmed