Mechanism for generation of left isomerism in Ccdc40 mutant embryos.
Leftward fluid flow in the mouse node is generated by cilia and is critical for initiating asymmetry of the left-right axis. Coiled-coil domain containing-40 (Ccdc40) plays an evolutionarily conserved role in the assembly of motile cilia and establishment of the left-right axis. Approximately one-third of Ccdc40lnks mutant embryos display situs defects and here we investigate the underlying mechanism. Ccdc40lnks mutants show delayed induction of markers of the left-lateral plate mesoderm (L-LPM) including Lefty1, Lefty2 and Nodal. Consistent with defective cilia motility compromising fluid flow across the node, initiation of asymmetric perinodal Cerberus like-2 (Cerl2) expression is delayed and then randomized. This is followed by delayed and then randomized asymmetric Nodal expression around the node. We propose a model to explain how left isomerism arises in a proportion of Ccdc40lnks mutants. We postulate that with defective motile cilia, Cerl2 expression remains symmetric and Nodal is antagonized equally on both sides of the node. This effectively reduces Nodal activation bilaterally, leading to reduced and delayed activation of Nodal and its antagonists in the LPM. This model is further supported by the failure to establish Nodal expression in the left-LPM with reduced Nodal gene dosage in Ccdc40lnks/lnks;NodalLacZ/+ mutants causing a predominance of right not left isomerism. Together these results suggest a model where cilia generated fluid flow in the node functions to ensure robust Nodal activation and a timely left-sided developmental program in the LPM.
Institute for Biomedical Sciences, The George Washington University, Washington, DC, United States of America.|Center for Neuroscience Research, Children's Research Institute, Children's National Medical Center, Washington, DC, United States of America.
Kelsey F
KF
Sugrue
Center for Neuroscience Research, Children's Research Institute, Children's National Medical Center, Washington, DC, United States of America.
Irene E
http://orcid.org/0000-0001-7688-682X
IE
Zohn
D000818:Animals; D019521:Body Patterning / Q000235:genetics*; D002923:Cilia / Q000378:metabolism / Q000473:pathology; D018507:Gene Expression Regulation, Developmental; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D055458:Left-Right Determination Factors / Q000235:genetics / Q000378:metabolism; D008648:Mesoderm / Q000378:metabolism; D051379:Mice; D009154:Mutation; D055457:Nodal Protein / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000235:genetics* / Q000378:metabolism
C556027:CCDC40 protein, mouse; C119003:Dte protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D055458:Left-Right Determination Factors; C111386:Lefty1 protein, mouse; C526162:Lefty2 protein, mouse; D055457:Nodal Protein; C526008:Nodal protein, mouse; D011506:Proteins