Name: tight junction proteins and cell barriers
Uploaded: 2023-04-30T11:55:38.000Z
Duration: 1 min 29 s
Channel: JoVE

En órganos como los riñones y los intestinos, las células epiteliales están selladas entre sí con uniones estrechas para evitar el flujo de macromoléculas, iones y solutos pequeños a través del espacio paracelular.
Las uniones estrechas comprenden principalmente proteínas transmembrana de claudina y ocludina, cada una con cuatro alfa-hélices que abarcan la membrana.
Hileras de claudinas y ocludinas polimerizan en la membrana, formando una red de hebras de sellado.
Estas hebras se unen a hebras similares de proteínas en la célula adyacente por sus bucles extracelulares, manteniendo así unidas las dos membranas.
En el lado citoplasmático, las colas C-terminales de estas proteínas se asocian con los dominios PDZ de grandes proteínas de andamiaje llamadas zonula occludens o ZO.
Las proteínas ZO tienen múltiples dominios de unión a proteínas y, por lo tanto, pueden unirse a claudinas, ocludinas, actina y otras proteínas ZO, formando una malla que organiza y estabiliza estas hebras de sellado.
Además de sellar el espacio paracelular, las uniones estrechas también impiden el movimiento lateral de las proteínas, como los transportadores de glucosa, a lo largo de la membrana. Esto ayuda a localizar estas proteínas en la superficie apical del epitelio intestinal para la absorción de glucosa.

<ol>
	<li>Sawada, Norimasa. "Enfermedades humanas relacionadas con las uniones estrechas". Patología Internacional 63.1 (2013): 1-12. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7168075/">Enlace</a></li>
	<li>Anderson, James M. y Christina M. Van Itallie. "Fisiología y función de la unión estrecha". Perspectivas de Cold Spring Harbor en biología 1.2 (2009): a002584. <a href="https://cshperspectives.cshlp.org/content/1/2/a002584.full">Enlace</a></li>
	<li>Mariano, Cibelle, et al. "Una mirada a la tricelulina y su papel en la formación y mantenimiento de uniones estrechas". Revista europea de biología celular 90.10 (2011): 787-796. <a href=" https://d1wqtxts1xzle7.cloudfront.net/52322075/A_look_at_tricellulin_and_its_role_in_ti20170327-17112-1qhpwe8-libre.pdf?1490608194=&response-content-disposition=inline%3B+filename%3DA_look_at_tricellulin_and_its_role_in_ti.pdf&Expires=1654205963&Signature=IelR0FUZCC6ZcqAcJvs1JTGe6liRDBX6aqaYzcw4sMZ2yqyhu5BuZ9DDbujaDRUN9SwX20yuCRLRyzxl6MWAa4QfY2cZ1wtZb4qfoi5otW~z0rhB3ba231uB1~pdP0rZpdHB4~snYhLr-~nZRsoaUqTFJmJaJXpxtHnoBGC4HFP29Q8D3q0rNHNDJGq9Qx9SfcLWmDISH7n8IfsUozT6rdpn421eOVufn5lNVunpqMX6iiRAT4D7p8bJEPpfd2~3cygJP7Ltc32RiIm2RHGvp9CRUoXs015y2aR4A7--dka7UzL97Aa~DDZ8ES90wX9D58qA~jX24DnmzNeNwlAayg__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA">Link</a></li>
</ol>

juntas apretadas

Tight Junctions

Las uniones estrechas son sellos moleculares entre células que evitan la fuga de líquidos, iones y otros pequeños solutos a través de cavidades y compartimentos en organismos multicelulares. Están compuestos principalmente por proteínas transmembrana claudina y ocludina, y otras proteínas como la tricelulina y JAM (molécula de adhesión de la unión). Todas estas proteínas son proteínas transmembrana de 4 pasos, excepto JAM, que es una proteína transmembrana de un solo paso que pertenece a la superfamilia de las inmunoglobulinas. Los dominios extracelulares de estas proteínas de unión estrecha interactúan con los de la membrana celular adyacente, uniendo y sellando así las dos células adyacentes.

Permeabilidad selectiva de uniones estrechas

Existen múltiples isoformas de la claudina transmembrana, con hasta 24 tipos diferentes expresados en humanos. La diversidad de la proteína claudina confiere permeabilidad selectiva a diferentes uniones estrechas. Por ejemplo, la claudina-16, expresada en el epitelio del riñón, aumenta la permeabilidad a los iones de magnesio, permitiendo así su recaptación de la sangre durante la filtración. Por el contrario, la claudina-5 expresada en las células endoteliales de los capilares cerebrales disminuye selectivamente la permeabilidad iónica a través de la barrera hematoencefálica.

Uniones tricelulares

Además de sellar los espacios entre dos células, las uniones estrechas también sellan los espacios formados en la unión de tres células: una unión tricelular. La estructura de las uniones tricelulares se observó por primera vez en la década de 1970 mediante microscopía electrónica de fractura por congelación. En estas uniones, los hilos de sellado están orientados perpendicularmente a los hilos de las uniones estrechas bicelulares. El punto de contacto tricelular forma así un tubo vertical estrecho de unos 10 nm de diámetro que controla el movimiento paracelular de las moléculas.

La tricelulina fue la primera proteína identificada que se concentra en estas uniones tricelulares. Comparte homología de secuencia con las proteínas ocludina y exhibe cuatro isoformas en humanos. Curiosamente, se ha demostrado que las mutaciones en el gen de la tricelulina, TRIC, causan discapacidad auditiva, lo que demuestra su importancia para mantener sellos herméticos como los necesarios en el órgano de Corti, una estructura del oído interno.

Juntas apretadas

Las uniones herméticas son sellos moleculares entre células que evitan la fuga de fluidos, iones y otros solutos pequeños a través de cavidades y compartimentos en ...

Education

Educación

JoVE Core

Cell Biology

Biología Celular

Unit 1

Unidad 1

Cell-Cell Interactions

Interacciones célula-célula

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

tight junction proteins and cell barriers

Tight junction proteins form seals between neighboring cells. These molecular barriers help stop fluids, ions, and other small solutes from leaking across body cavities and tissue compartments in multicellular organisms. They are an important part of cell barriers in places where controlled movement matters.

The main tight junction proteins are claudin and occludin. Other proteins include tricellulin and JAM, which stands for junctional adhesion molecule. Most of these proteins are 4-pass transmembrane proteins, meaning they cross the cell membrane four times. JAM is different because it is a single-pass transmembrane protein in the immunoglobulin superfamily. The extracellular parts of these proteins interact with matching parts on the nearby cell membrane. This brings two adjacent cells together and helps seal them.

Claudin proteins are especially important because there are many isoforms, or forms, of claudin. Humans express up to 24 different types. This diversity gives tight junctions selective permeability, which means some substances pass more easily than others. For example, claudin-16 in kidney epithelium increases permeability to magnesium ions. This helps magnesium move back into the body during filtration. In contrast, claudin-5 in endothelial cells of brain capillaries lowers ion permeability across the blood-brain barrier.

Tight junctions also seal tricellular junctions, which are the gaps where three cells meet. These junctions were first seen in the 1970s with freeze-fracture electron microscopy. At these contact points, the sealing strands run perpendicular to the strands in bicellular tight junctions. The center of the tricellular contact forms a narrow vertical tube about 10 nm wide. This structure helps control paracellular movement, which is movement between cells.

Tricellulin is the first protein known to concentrate at tricellular junctions. It is related in sequence to occludin and has four isoforms in humans. Mutations in the tricellulin gene, TRIC, can cause hearing impairment. This shows how important tight seals are in the organ of Corti, a structure in the inner ear.

Tight Junction Proteins and Cell Barriers

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tight junctions

Tight junction proteins form seals between neighboring cells. These molecular barriers help stop fluids, ions, and other small solutes from leaking across body cavities and tissue compartments in multicellular organisms. They are an important part of cell barriers in places where controlled movement matters. The main tight junction proteins are claudin and occludin. Other proteins include tricellulin and JAM, which stands for junctional adhesion molecule. Most of these proteins are 4-pass...

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key terms and concepts

Learn how claudin, occludin, tricellulin, and JAM seal cells, control selective permeability, and support barriers like the blood-brain barrier.

Tight Junction Proteins and Cell Barriers | JoVE K12

cell biology

JoVE Core Biología Celular ilustra procesos celulares complejos mediante completos vídeos animados fáciles de entender. Esta colección se centra en los componentes esenciales de las células y su funcionamiento, incluyendo los orgánulos y las membranas, el transporte celular y el metabolismo energético celular. Todo este material se complementa con los vídeos de científicos en acción, que muestran la aplicación de la biología celular en experimentos reales de investigación.

Tight Junction Proteins and Cell Barriers

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