Embryonic-cerebrospinal fluid (E-CSF) plays crucial roles in early brain development including the control
of neurogenesis. Although FGF2 and lipoproteins present in the E-CSF have previously been shown
to be involved in neurogenesis, the main factor triggering this process remains unknown. E-CSF contains
all-trans-retinol and retinol-binding protein involved in the synthesis of retinoic acid (RA), a neurogenesis
inducer. In early chick embryo brain, only the mesencephalic-rombencephalic isthmus (IsO) is able to
synthesize RA. Here we show that in chick embryo brain development: (1) E-CSF helps to control RA synthesis
in the IsO by means of the RBP and all-trans-retinol it contains; (2) E-CSF has retinoic acid activity,
which suggests it may act as a diffusion pathway for RA; and (3) the influence of E-CSF on embryonic
brain neurogenesis is to a large extent due to its involvement in RA synthesis. These data help to
understand neurogenesis from neural progenitor cells
