Fig. 2

Structure of the zebrafish Xirp family and gene expression patterns.

(A) Phylogenetic analysis of Xirp family members. The zebrafish Xirp family comprises three members which are orthologous to their two mammalian counterparts. Phylogenetical distances calculated according to the ClustalW slow/accurate method are indicated. Danio rerio (D.r.); Gallus gallus (G.g.); Mus musculus (M.m.). (B) As for mammalian Xirp1, intraexonic splicing of zebrafish xirp1 results in three alternative isoforms: xirp1α (6894 bp), xirp1β (4452 bp), xirp1γ (2006 bp). Xirp1β is identical to the N-terminus of Xirp1α and harbours Xin-repeats; Xirp1γ is identical to the C-terminus of Xirp1α and harbours a Filamin C binding domain (FilC BD). Antibodies specific against isoforms Xirp1α/β (P43) and Xirp1α/γ (P47) were generated. Black asterisks indicate the position of protein truncation in the xirp1^sa0046 mutant. Concerning Xirp2a and Xirp2b, differential splicing leads to various isoforms classified as long (containing Xin-repeats) or short (lacking a large exon encoding Xin-repeats and resulting in the encoding of a LIM domain). Here, we represented schematically the long isoforms and their respective antibody. (C) Summary panel of xirp gene family expression with whole-mount in situ hybridization probes designed to exclusively cover the long isoforms of these genes. xirp1 has the earliest and widest expression of all three xirp genes. After initial expression within adaxial cells during somitogenesis, xirp1 expression decreases within somitic tissue after 24 hpf. xirp1 is the only xirp family member harboring Xin-repeats that is expressed within the heart during cardiogenesis. In comparison, xirp2a and xirp2b mRNAs are strongly expressed within somitic muscle after 24 hpf where they localize to the somite boundaries. Both xirp1 and xirp2a are expressed within other types of skeletal muscle including those of the fin buds, whereas xirp2b expression remains restricted to somitic muscle. Asterisks indicate the heart; arrowheads point at fin buds. Black scale bars: 250 μm, red scale bars: 200 μm.