Three types of cilia including a novel 9+4 axoneme on the notochordal plate of the rabbit embryo

Motile monocilia play a pivotal role in left‐right axis determination in mouse and zebrafish embryos. Cilia with 9+0 axonemes localize to the distal indentation of the mouse egg cylinder (“node”), while Kupffer's vesicle cilia in zebrafish show 9+2 arrangements. Here we studied cilia in a prototype mammalian embryo, the rabbit, which develops via a flat blastodisc. Transcription of ciliary marker genes Foxj1 , Rfx3 , lrd , polaris , and Kif3a initiated in Hensen's node and persisted in the nascent notochord. Cilia emerged on cells leaving Hensen's node anteriorly to form the notochordal plate. Cilia lengthened to about 5 μm and polarized from an initially central position to the posterior pole of cells. Electron‐microscopic analysis revealed 9+0 and 9+2 cilia and a novel 9+4 axoneme intermingled in a salt‐and‐pepper‐like fashion. Our data suggest that despite a highly conserved ciliogenic program, which initiates in the organizer, axonemal structures may vary widely within the vertebrates. Developmental Dynamics 235:3348–3358, 2006. © 2006 Wiley‐Liss, Inc.