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. 2013 Jan 10;10(1):3.
doi: 10.1186/2045-8118-10-3.

Genetic Mouse Models to Study Blood-Brain Barrier Development and Function

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Free PMC article

Genetic Mouse Models to Study Blood-Brain Barrier Development and Function

Fabien Sohet et al. Fluids Barriers CNS. .
Free PMC article

Abstract

The blood-brain barrier (BBB) is a complex physiological structure formed by the blood vessels of the central nervous system (CNS) that tightly regulates the movement of substances between the blood and the neural tissue. Recently, the generation and analysis of different genetic mouse models has allowed for greater understanding of BBB development, how the barrier is regulated during health and its response to disease. Here we discuss: 1) Genetic mouse models that have been used to study the BBB, 2) Available mouse genetic tools that can aid in the study of the BBB, and 3) Potential tools that if generated could greatly aid in our understanding of the BBB.

Figures

Figure 1
Figure 1
Representation of genetic mouse models. 1) Knockout out of specific genes. A neomycin cassette is inserted by homologous recombination either into an exon (1A) of a gene of interest or replacing the whole gene of interest (1B). 2) Methods to control the cell specificity and timing of gene deletion. Homologous recombination is used to insert lox-p sites surrounding an exon of the gene of interest. To conditionally delete the gene in a specific cell type, the Cre recombinase is expressed by a tissue specific promoter and deletes the loxP flanked region (2A). To regulate the timing, one can use a transgene encoding a Cre recombinase fused with the modified estrogen receptor (Cre-ERT) that will move into the nucleus upon injection of tamoxifen (2B). 3) Ectopic expression of a transgene. A common method is to utilize a lox-stop-lox cassette which can be removed by Cre recombinase. A transgene is generated with a stop codon that is flanked with two loxP sites upstream of the transgene of interest. The transgene can be introduced to the genome at a specific locus by homologous recombination or randomly inserted in the genome. When the Cre recombinase deletes the stop codon, the transgene can be transcribed (3A). This technique is available with the Cre-ERT system (3B). 4) To reversibly express a transgene. A common method is the use of the TRE/tTA or TRE/rtTA systems. A transgene is generated with the gene of interest downstream of the tetracycline responsive element (TRE). A second transgene is generated with a tissue specific promoter controlling the expression of tTA (Tet-Off, 4A) or rtTA (Tet-ON, 4B). For Tet-OFF, the tTA activates transcription of the transgene downstream of the TRE promoter, only in the absence of doxycycline. For Tet-ON, the rtTA activates transcription of the transgene downstream of the TRE promoter only in the presence of doxycycline.
Figure 2
Figure 2
Schematic representation of the BBB in health and diseases. Schematic representation of the blood–brain barrier in health (left side) and during pathological breakdown during injury and disease (right side). CNS endothelial cells (pink) form BBB properties, and interact with cells in the blood (RBC-red, leukocyte-blue) and in the neural tissue (pericyte-green, astrocytes-taupe). Many of the BBB properties are altered during diseases such as stroke and MS.
Figure 3
Figure 3
Abcb1a/Abcb1b/Bcrp triple knockout mice have a leaky BBB to Rhodamine123. Adult wild type (C) or Abcb1a/Abcb1b/Bcrp triple knockout mice (3KO) were given an intravenous injection of Rhodamine123 (10 ng). After 1 hour the blood compartment was removed by transcardiac perfusion with PBS, the brains were removed, hemisected down the midline and imaged for Rhodamine123 fluorescence with a Fujifilm imager LAS 4000. Figure 3 represents an image of the hemisected brains with the cerebellum at the top of the image and frontal cortex towards the bottom of the image. More Rhodamine123 (dark color) was observed in Abcb1a/Abcb1b/Bcrp triple knockout mice compared with littermate controls. To demonstrate the consistency of the phenotype between different animals, 3 wild-type and 3 Abcb1a/Abcb1b/Bcrp triple knockout mice brains were utilized.

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