Abstract
BackgroundDevelopment and maintenance of the blood-brain and blood-retinal barrier is critical for the homeostasis of brain and retinal tissue. Despite decades of research our knowledge of the formation and maintenance of the blood-brain (BBB) and blood-retinal (BRB) barrier is very limited. We have established an in vivo model to study the development and maintenance of these barriers by generating a transgenic zebrafish line that expresses a vitamin D-binding protein fused with enhanced green fluorescent protein (DBP-EGFP) in blood plasma, as an endogenous tracer.ResultsThe temporal establishment of the BBB and BRB was examined using this transgenic line and the results were compared with that obtained by injection of fluorescent dyes into the sinus venosus of embryos at various stages of development. We also examined the expression of claudin-5, a component of tight junctions during the first 4 days of development. We observed that the BBB of zebrafish starts to develop by 3 dpf, with expression of claudin-5 in the central arteries preceding it at 2 dpf. The hyaloid vasculature in the zebrafish retina develops a barrier function at 3 dpf, which endows the zebrafish with unique advantages for studying the BRB.ConclusionZebrafish embryos develop BBB and BRB function simultaneously by 3 dpf, which is regulated by tight junction proteins. The Tg(l-fabp:DBP-EGFP) zebrafish will have great advantages in studying development and maintenance of the blood-neural barrier, which is a new application for the widely used vertebrate model.
Highlights
Development and maintenance of the blood-brain and blood-retinal barrier is critical for the homeostasis of brain and retinal tissue
The Blood Retinal Barrier (BRB) and Blood Brain Barrier (BBB) is established at 3 dpf in zebrafish To determine the temporal sequence of establishment of the brain (BBB) and blood-retinal (BRB) and blood-brain barrier (BBB) in zebrafish, we injected two fluorescent dyes into the circulatory system of Tg(flk1:mCherry) [22,23] embryos at 2 dpf, 2.5 dpf and 3 dpf
We examined the permeability of the brain vasculature, the central arteries such as middle mesencephalic central artery (MMCtA), posterior mesencephalic central artery (PMCtA), and cerebellar central artery (CCtA)
Summary
Development and maintenance of the blood-brain and blood-retinal barrier is critical for the homeostasis of brain and retinal tissue. The blood-brain barrier (BBB) and the blood-spinal cord barrier are endothelial barriers located within the cerebral vessels of the brain and the spinal cord, whereas the barrier between blood and the cerebrospinal fluid (blood-CSF barrier) is formed by the epithelial cells of the choroid plexus [1,2]. Both the endothelial and epithelial barriers have tight junctions, which seal the intercellular cleft of endothelial or epithelial cells and restrict paracellular diffusion of water-soluble molecules[4]. Claudin 5a has been recently shown to be essential for the establishment of a neuroepithelial barrier and zebrafish brain ventricular lumen expansion[7]
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