The actin nucleator Cordon-bleu is required for development of motile cilia in zebrafish

Abstract

The Cordon-bleu (Cobl) gene is widely conserved in vertebrates, with developmentally regulated axial and epithelial expression in mouse and chick embryos. In vitro, Cobl can bind monomeric actin and nucleate formation of unbranched actin filaments, while in cultured cells it can modulate the actin cytoskeleton. However, an essential role for Cobl in vivo has yet to be determined. We have used zebrafish as a model to assess the requirements for Cobl in embryogenesis. We find that cobl shows enriched expression in ciliated epithelial tissues during zebrafish organogenesis. Cobl protein is enriched in the apical domain of ciliated cells, in close proximity to the apical actin cap. Reduction of cobl by antisense morpholinos reveals an essential role in development of motile cilia in organs such as Kupffer's vesicle and the pronephros. In Kupffer's vesicle, the reduction in Cobl coincides with a reduction in the amount of apical F-actin. Thus, Cobl represents a molecular activity that couples developmental patterning signals with local intracellular cytoskeletal dynamics to support morphogenesis of motile cilia.

sept7b is essential for pronephric function and development of left–right asymmetry in zebrafish embryogenesis

“…Staining for acetylated tubulin revealed a significant reduction in the length of cilia in the dilated pronephric tubules in sept7b morphants and this resembled several other mutants and morphants that lead to defective pronephric function (Clément et al, 2011;Kramer-Zucker et al, 2005a;Ravanelli and Klingensmith, 2011;Sun et al, 2004). The cilia and basal bodies of the sept7b morphants were also misoriented and resembled the phenotype of zebrafish with mutations in intraflagellar transport proteins that cause defects in basal body orientation and planar polarity (Cao et al, 2010;Jones et al, 2008).…”

“…In sept7b morphants, the normal asymmetry of two different markers, spaw (lateral plate mesoderm) and cmlc2 (a heart marker), was randomized. Similar defects in asymmetrical organ patterning, kidney function and ciliogenesis have been observed in cdc14B phosphatase morphants and mutants, and actin nucleator cordon-bleu morphants (Clément et al, 2011;Ravanelli and Klingensmith, 2011).…”

“…This led to defects in fluid flow and, thereby, to the formation of pronephric cysts and edema, hydrocephaly and to abnormalities in left-right asymmetry. A number of genes are involved in regulating ciliogenesis and cilia function -including genes that control basal body formation and localization, intraflagellar transport, integrity of the axoneme and cytoskeletal organization (Cao et al, 2010;Essner et al, 2005;Kramer-Zucker et al, 2005a;Ravanelli and Klingensmith, 2011;Sullivan-Brown et al, 2008;Sun et al, 2004). Our study links the role of septins in ciliogenesis (Hu et al, 2010;Kim et al, 2010) to the function of several vertebrate tissues -including the kidney, central canal and Kupffer's vesicle -that require cilia in vivo.…”

“…Because a well-organized actin cytoskeleton is required for the migration and docking of the basal bodies to the apical plasma membrane, and for cilia elongation (Boisvieux-Ulrich et al, 1990;Pan et al, 2007;Ravanelli and Klingensmith, 2011;Tamm and Tamm, 1988), a sept7b-dependent disruption of actin organization could contribute to the defects in ciliogenesis. Alternatively, the reduced number of basal bodies upon sept7b knockdown could also lead to reduced cortical actin, as a dense apical actin cap has been shown to form around basal bodies after their apical docking (Pan et al, 2007;Werner et al, 2011).…”

The role of hair cells, cilia and ciliary motility in otolith formation in the zebrafish otic vesicle

“…These organelles are present on the apical surface of most vertebrate cells and are involved in sensory, signalling and mechanical processes (Bisgrove and Yost, 2006;Ishikawa and Marshall, 2011). Every cell of the zebrafish OV epithelium is monociliated (Riley et al, 1997), and many genes involved in ciliogenesis, intraflagellar transport, ciliary movement, stability and function are expressed in the OV (Tsujikawa and Malicki, 2004;Bisgrove et al, 2005;Omori and Malicki, 2006;Pathak et al, 2007;Omori et al, 2008;SullivanBrown et al, 2008;van Rooijen et al, 2008;Yu et al, 2008;Colantonio et al, 2009;Wilkinson et al, 2009;Gao et al, 2010;Glazer et al, 2010;Kang et al, 2010;May-Simera et al, 2010;Becker-Heck et al, 2011;Clément et al, 2011;Pathak et al, 2011;Ravanelli and Klingensmith, 2011;Rothschild et al, 2011;Yu et al, 2011). Sensory hair cells in the ear each bear a specialised cilium known as the kinocilium.…”