A transgenic zebrafish model for the in vivo study of the blood and choroid plexus brain barriers using claudin 5

Abstract

The central nervous system (CNS) has specific barriers that protect the brain from potential threats and tightly regulate molecular transport. Despite the critical functions of the CNS barriers, the mechanisms underlying their development and function are not well understood, and there are very limited experimental models for their study. Claudin 5 is a tight junction protein required for blood brain barrier (BBB) and, probably, choroid plexus (CP) structure and function in vertebrates. Here, we show that the gene claudin 5a is the zebrafish orthologue with high fidelity expression, in the BBB and CP barriers, that demonstrates the conservation of the BBB and CP between humans and zebrafish. Expression of claudin 5a correlates with developmental tightening of the BBB and is restricted to a subset of the brain vasculature clearly delineating the BBB. We show that claudin 5a-expressing cells of the CP are ciliated ependymal cells that drive fluid flow in the brain ventricles. Finally, we find that CP development precedes BBB development and that claudin 5a expression occurs simultaneously with angiogenesis. Thus, our novel transgenic zebrafish represents an ideal model to study CNS barrier development and function, critical in understanding the mechanisms underlying CNS barrier function in health and disease.

Physiology and molecular biology of barrier mechanisms in the fetal and neonatal brain

“…Van Leewen et al . () provide additional evidence for the proposal that in early development vascularization of the choroid plexuses compared to that of the brain indicates that the plexuses are likely to be a more important route of entry into the brain early on (Johansson et al . ).…”

“…) although in zebrafish it is apparently also expressed at the blood–CSF barrier (van Leewen et al . ). Angiogensis and blood–brain barrier formation appear to be linked and occur simultaneously; by using genetic mouse models, the effectors of Wnt/b‐catenin signaling, including Lef1, Apcdd1 and tnfrsf19, have been shown to control these processes (reviewed in Daneman & Prat, 2015).…”

“…Van Leewen et al . () have used a similar approach to Umans et al . () and report that the tight junction protein claudin 5 is present in both cerebral endothelial cells and choroid plexus epithelial cells.…”

Lnc-ECAL-1controls cerebrovascular homeostasis by targeting endothelium-specific tight junction proteinCldn5b

“…The core roles of tight junction protein Claudin5 (CLDN5) in blood-brain barrier permeability of mammals have been identified (Nitta et al, 2003) (He et al, 2015). In zebrafish, Cldn5a expanded the expression in brain vessels from 72 hpf (van Leeuwen et al, 2018), while Cldn5b is enriched in brain vasculature at 48 hpf (Xie et al, 2010). Cldn5a is involved in brain ventricular development (Zhang et al, 2010), and the function of Cldn5b remains unknown.…”

The role of motile cilia in the development and physiology of the nervous system

“…As such, the choroid plexuses make up a barrier between the blood and the CSF, tightly controlling the CSF content. Interestingly, the choroid plexus cells exhibit cilia, which are motile in zebrafish [155], but mostly immotile in mice [156]. The function of these cilia is not fully understood, yet in zebrafish, they may contribute to CSF flow [155], while in mice they are suggested to serve a chemosensory function [156].…”