Smarcd3 is required for LR axis specification in zebrafish. (A–E) Expression of smarcd3 (A–C and E are lateral views, anterior to left, and D is a caudal view, dorsal to top). (A) During gastrulation. (B) Expression in the developing tailbud. (C and D) Early somitogenesis. (E) Mid-somitogenesis. Knockdown of smarcd3 randomizes direction of heart looping in embryos 40 h after fertilization (F–H). A, atrium; V, ventricle. In H, red bars show normal looping and blue bars show reversed looping. Heart looping is partially rescued by smarcd3 RNA. (I–L) Altered expression of lefty1 (lft1) in the diencephalon and lefty2 (lft2) in the heart field of 22- to 24-somite-stage embryos. (I) Normal left-sided expression. (J) Right-sided expression. (K) Bilateral expression. (L) Absence of expression. Expression of lft1 in the midline is unaltered. (M–R) Quantification of alterations in asymmetric gene expression patterns in smarcd3 morphants. (M and P) southpaw (spaw) expression in the LPM (19- to 21-somite stage). (N and Q) lft1 expression. (O and R) lft2 expression. L, left-sided; R, right-sided; B, bilateral; A, absent.
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