Gap junction is a cell‑cell communication junction type found in virtually all mammalian epithelia and endothelia and provides the necessary “signals” to coordinate physiological events to maintain the homeostasis of an epithelium and/or endothelium under normal physiological condition and...

The blood‑brain barrier refers to the very low permeability across microvessels in the Central Nervous System (CNS), created by the interaction between vascular endothelial cells and surrounding cells of the neurovascular unit. Permeability can be modulated (increased and decreased) by a...

The inner blood‑retinal barrier (inner BRB) is created by complex tight junctions of retinal capillary endothelial cells. Although this barrier prevents the free diffusion of substances between the circulating blood and the neural retina, the inner BRB efficiently supplies nutrients to the...

Spermatozoa undergo a posttesticular maturation in the epididymis to acquire motility and the capacity to fertilize. Sperm maturation depends in part upon the creation of a specific microenvironment within the epididymal lumen. This environment is conditioned by proteins secreted by the...

Spermatogenesis involves precise co-ordination of multiple cellular events that take place in the seminiferous epithelium composed of Sertoli cells and developing germ cells during the seminiferous epithelial cycle. Given the cyclic and co-ordinated nature of spermatogenesis, temporal and...

Intestinal epithelium serves as a key interface between internal body compartments and the gut lumen. The epithelial layer forms a physical barrier that protects the body from the harmful environment of the lumen and also mediates vectorial fluxes of fluids, nutrients and waste. Increased...

Endothelial and epithelial cells form selectively permeable barriers that separate tissue compartments. These cells coordinate movement between the lumen and tissue via the transcellular and paracellular pathways. The primary determinant of paracellular permeability is the tight junction,...

The blood‑testis barrier (BTB) is known for its ability to create an immune privilege site in the seminiferous epithelium, but less is known of the blood‑epididymal barrier (BEB). It is already established that the fully functional BTB and BEB are much more complex and consist of...

The epithelium lining the female reproductive tract forms a selectively permeable barrier that is responsible for creating an optimal luminal fluid microenvironment essential to the success of various reproductive events. The selective permeability of the epithelial barrier to various ions is...

Drug transport in the central nervous system can be highly regulated by the expression of numerous influx and efflux transport proteins not only at the blood‑brain barrier and blood‑cerebrospinal fluid barrier but also in brain parenchymal cellular compartments (i.e., astrocytes,...

The blood‑testis barrier (BTB), similar to other blood‑tissue barriers, such as the blood‑brain barrier and the blood‑retinal barrier, is used to protect the corresponding organ from harmful substances (e.g., xenobiotics) including drugs and foreign compounds. More importantly, the BTB...

Tight junction (TJ) composes of an intriguing class of cell junction molecules, for which these molecules share similar organizations and structure features among different organs. Four types of transmembrane molecules namely occludins, claudins, junctional adhesion molecules and...

The Blood-retina barrier (BRB) is composed of both an inner and an outer barrier. The outer BRB refers to the barrier formed at the retinal pigment epithelial (RPE) cell layer and functions, in part, to regulate the movement of solutes and nutrients from the choroid to the sub-retinal space....

Src family kinases (SFKs), in particular c‑Src and c‑Yes, are nonreceptor protein tyrosine kinases that mediate integrin signaling at focal adhesion complex at the cell‑extracellular matrix interface to regulate cell adhesion, cell cycle progression, cell survival, proliferation and...

The blood‑testis barrier (BTB) is one of the tightest blood‑tissue barriers in mammals including rodents and humans. It is used to sequester meiosis I and II, postmeiotic spermatid development via spermiogenesis and the release of sperm at spermiation from the systemic circulation, such...

The Scribble polarity complex or module is one of the three polarity modules that regulate cell polarity in multiple epithelia including blood‑tissue barriers. This protein complex is composed of Scribble, Lethal giant larvae (Lgl) and Discs large (Dlg), which are well conserved across...