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The RNA-binding protein Rbm24 is transiently expressed in myoblasts and is required for myogenic differentiation during vertebrate development.
RNA-binding proteins (RBP) contribute to gene regulation through post-transcriptional events. Despite the important roles demonstrated for several RBP in regulating skeletal myogenesis in vitro, very few RBP coding genes have been characterized during skeletal myogenesis in vertebrate embryo. In the present study we report that Rbm24, which encodes the RNA-binding motif protein 24, is required for skeletal muscle differentiation in vivo. We show that Rbm24 transcripts are expressed at all sites of skeletal muscle formation during embryogenesis of different vertebrates, including axial, limb and head muscles. Interestingly, we find that Rbm24 protein starts to accumulate in MyoD-positive myoblasts and is transiently expressed at the onset of muscle cell differentiation. It accumulates in myotomal and limb myogenic cells, but not in Pax3-positive progenitor cells. Rbm24 expression is under the direct regulation by MyoD, as demonstrated by in vivo chromatin immunoprecipitation assay. Using morpholino knockdown approach, we further show that Rbm24 is required for somitic myogenic progenitor cells to differentiate into muscle cells during chick somitic myogenesis. Altogether, these results highlight Rbm24 as a novel key regulator of the myogenic differentiation program during vertebrate development.
Rbm24 is expressed at all sites of skeletal muscle formation during vertebrate development. (A–E) Detection of Seb4 (A–C), XMyoD (D) and XMyf5 (E) expression by whole-mount in situ hybridization on stage 28 (A) and stage 37 (B–E) Xenopus embryos. (A,A′) Seb4 is expressed in all somites (so) and specifically in the myotome (my) of the somites as shown on transverse vibratome section (A′) of the embryo shown in A at the level of the somite. It is also expressed in non-muscle territories including lens (le) and otic vesicle (ov), and is transiently expressed in developing heart at the stage 28 (he). (B,B′,C) Seb4 expression in hypaxial migrating cells (hyp) (B) as well as in the following branchiomeric cranial muscles: levatores mandibulae muscles anlagen (lev), quadrato-hyoangularis and orbitohyoideus muscles anlagen (qho), and interhyoideus muscle analgen (int.hy). B′ is a transverse vibratome section through the embryo in B, at the level of the head. (D,E) Cranial muscles also express XMyoD (D) but not XMyf5 except for the interhyoideus muscle analgen (E). (F–N) Detection of mouse Rbm24 expression by whole-mount in situ hybridization on E10.5 (F–H), E11.5 (I–K) and E12.5 (L–N) mouse embryos. Rbm24 is expressed in the entire myotomal compartment of all developing somites (so) at all stages. (F–H) At E10.5, it is also expressed in the lens (le), otic vesicle (ov), heart (he) and weakly in the mesodermal core of the first and second branchial arches (arrows in F). It is not detected in developing forelimbs (asterisks in F and G) and hindlimbs (asterisks in H). (I–K) At E11.5, Rbm24 is detected in all appendicular muscle masses at the forelimb (fl) and hindlimb (hl) levels (arrowheads in I) and in further developing head muscles (hm). (L–N) At E12.5, the expression of Rbm24 persists in appendicular muscle masses and developing head muscles. Strong expression can be observed in the limb (arrowheads in L). (M) Diaphragm muscle (dia) also expresses mRbm24 at this stage. (O–T) Analysis of chick Rbm24 expression by whole-mount in situ hybridization on 3 days (stage HH20) (O–Q) and 3.5 days (stage HH23) (R–T) chick embryos. As in mouse embryos, chick Rbm24 is expressed in the entire myotomal compartment of all developing somites (so) at all stages. It is not detected in limb buds at 3 days of development (asterisks in O–Q) but is observed in developing forelimbs (fl) and hindlimbs (hl) at 3.5 days of development (arrowheads in R and S). Chick Rbm24 is expressed in the mesodermal core of the first and second branchial arches at 3 days of development (arrows in T). Other expression sites include otic vesicle (ov), lens (le) and heart (he).