FIGURE 3.

Reissner’s fiber (RF, green) in different chordates and during development. (A) In the neural tube of cephalochordates RF is secreted by the infundibular organ of the floor plate (FP) (IO) and floats in the CSF-filled neural or central canal (NCa). (B–D) Reissner’s fiber in teleost fish [(B), early embryonic; (C), middle stage; (D), advanced]. Note that in teleosts, the flexural organ (FO, possibly homologous to the IO in cephalochordates) is replaced by the subcommissural organ (SCO) in the roof plate (RP) as the secreting organ of RF. Note also the CSF-contacting neurons (CSF-cn) with an axon (inferior process) and a dendrite or cilium that enters the CSF and contacts RF.