Small heat shock protein HSPB1 regulates growth of embryonic zebrafish craniofacial muscles

► High HspB1 expression levels characterize craniofacial muscles in zebrafish embryos. ► HspB1 does not associate with myofibrils during normal development. ► Morpholino injection was used to reduce HspB1 expression in zebrafish embryos. ► Loss of HspB1 specifically reduces myofibril size in embryonic craniofacial muscles. ► Loss of HspB1 does not affect embryonic craniofacial tissues lacking HspB1.