Abstract
The dorsal medial region of the developing mammalian telencephalon plays a central role in the patterning of the adjacent brain regions. This review describes the development of this specialized region of the vertebrate brain, called the cortical hem, and the formation of the various cells and structures it gives rise to, including the choroid plexus, Cajal-Retzius cells and the hippocampus. We highlight the ontogenic processes that create these different forebrain derivatives from their shared embryonic origin and discuss the key signalling pathways and molecules that influence the patterning of the cortical hem. These include BMP, Wnt, FGF and Shh signalling pathways acting with Homeobox factors to carve the medial telencephalon into district progenitor regions, which in turn give rise to the choroid plexus, dentate gyrus and hippocampus. We then link the formation of the lateral ventricle choroid plexus with embryonic and postnatal neurogenesis in the hippocampus.
Highlights
The regulation of forebrain patterning has been an area of intense interest over the past few years
The orchestrated patterning of the dorsal telencephalic midline (DTM) region and correct positioning of the cortical hem (CH) depend on the antagonistic properties of the rostral telencephalic organizer (RTO) source of fibroblast growth factors (FGFs) signalling with Wnt and royalsocietypublishing.org/journal/rsob Open Biol. 11: 210042 (a) coronal view lv
While recent findings have led to tremendous progress in our understanding of the role cerebrospinal fluid (CSF) in neural development, future work needs to further elucidate the dynamic morphogenetic processes guiding choroid plexus (ChP) formation, identify CSF factors that promote neurogenesis and how altered development of these structures contributes to brain disorders
Summary
The regulation of forebrain patterning has been an area of intense interest over the past few years. By E12.5, the CH is delineated by the expression of three Wnt genes, Wnt2b, Wnt3a and Wnt5a, forming a distinct boundary with the hippocampal primordium dorsally and the CH ventrally [5]. The rostral telencephalic organizer (RTO) has been identified as an additional signalling centre that restricts the boundary of the CH forming region in the medial telencephalon. In addition to an inductive role in the telencephalon, the RTO patterns the neuroepithelium into functional domains, defining the anterior limit of the CH [7]. In addition to repressing the extent of Lhx expression in the forebrain, FGF8 signalling decreases Wnt expression in the CH domain, thereby defining the anterior boundary of the CH [7].
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