PMC

Summary of developmental mechanisms underlying brain ventricle formation, function of the brain ventricular system, and associated abnormalities. See text for details.

Cartoon representation of adult human brain ventricles. Blue represents brain tissue and yellow shows brain ventricles. Choroid plexuses are in red, blue arrows designate direction of CSF flow.
LV: lateral ventricle, 3V: third ventricle, 4V: fourth ventricle.

Cartoon depicting eCSF secretion and function. Inset: dorsal view of embryonic brain, after initial lumen inflation, with enlarged area (hindbrain) boxed. Ion pumps and proteolgycan secretion are thought to form an osmotic gradient regulating fluid flow. Signaling and growth factors are also secreted. Both fluid pressure and growth factors stimulate cell proliferation and gene expression within the surrounding neuroepithelium. Not drawn to scale. PG: proteoglycans. Circular cells at ventricular surface are mitotic cells.

A. Schematic showing zebrafish neuroepithelium as it opens into the brain ventricles. After neurulation, the zebrafish neuroepithelium is a closed neural tube (i) connected by apical actin junctions and surrounded by a basement membrane (i,iii). As the brain ventricles open, the neuroepithelium bends in locations of apical constriction (white asterisks) and basal constriction at MHB (ii,iii).
B. Schematic depicting stages of neurulation in mammals, beginning with the columnar epithelium of the neural plate (i). Neurulation and hinge-point formation occur concurrently (ii), resulting in an open neural tube with hinge-points already formed. The lumen remains open and expands after neurulation is complete (iii).
C. Schematic depicting stages of neurulation in zebrafish, beginning with the columnar neural plate (i). Neurulation progresses through a “neural keel” stage (ii) and ends with a closed neural tube (iii). Subsequently, the neural tube opens and forms hinge-points to shape the ventricles (iv).
D. Cartoons of transverse sections of the midbrain ventricle depicting several phenotypes observed when neuroepithelium morphogenesis does not occur normally in zebrafish. When junctions are completely disrupted (i), neurulation does not proceed and ventricle formation is impossible. When the midline does not form correctly (ii), the midline cannot separate to form the ventricles. Some mutants show normal midline formation, but still do not separate at the midline and form hinge-points (iii). F: forebrain ventricle, M: midbrain ventricle, H: hindbrain ventricle, MHB: midbrain-hindbrain boundary.

A. Schematic of vertebrate embryonic brain development. Shown are lateral views of the neural tube as it undergoes early embryonic brain morphogenesis to form the primary brain vesicles.
B. Conservation of embryonic brain ventricle structure. Tracings of embryonic brain ventricles at similar corresponding stages in development, all lateral views. Human embryo brain ventricles, stage 17 (approximately 43 days post fertilization), traced from the Carnegie Embryological Collection. Rat embryo brain ventricles, stage E14 (14 days post fertilization), traced from (); Chick embryo brain ventricles, stage 16 (approximately 2.5 days post fertilization), traced from (); Zebrafish embryo brain ventricles, 24 hours post fertilization.
C. Comparison of early embryonic and adult brain ventricles. Colors correspond to the same ventricle regions in the embryo and adult.
Not to scale. F: forebrain (telencephalon plus diencephalon), M: midbrain (mesencephalon), H: hindbrain (rhombencephalon), MHBC: midbrain hindbrain boundary constriction, LV: lateral ventricle, 3V: third ventricle, 4V: fourth ventricle.
In part A, F M H refer to brain vesicles. In parts B and C, F M H refer to ventricles.