An In Vitro Assay to Monitor Sertoli Cell Blood-Testis Barrier (BTB) Integrity.

In this chapter, we detail a reliable, effective, and easy to perform assay to monitor the Sertoli cell blood-testis barrier (BTB) integrity. While the BTB in the testis is composed of the tight junction (TJ) barrier and basal ES (ectoplasmic specialization, a testis-specific actin-rich adherens junction (AJ) type), this method is applicable to all other blood-tissue barrier in vitro, including endothelial TJ-barrier of the blood-brain barrier (BBB). Furthermore, this method does not require expensive set up, and can be rapidly performed by any standard biochemistry/cell biology/molecular biology laboratory. The basic idea is built on the concept that a functional blood-tissue barrier, such as the BTB conferred by Sertoli cells in the testis, is capable of blocking the diffusion of a small membrane impermeable biotin (e.g., EZ-Link Sulfo-NHS-LC-biotin, Mr. 556.59) across the barrier. However, when this barrier is compromised, such as following treatment with a toxicant or knockdown of a relevant gene necessary to confer the TJ-barrier function, the biotin will permeate the barrier, reaching the Sertoli cell cytosol. Biotin can be subsequently visualized by using streptavidin conjugated to a fluorescence tag such as Alexa Fluor 488 (green fluorescence) which can be easily visualized by a standard fluorescence microscope.