Laminin

Laminins are major proteins in the basal lamina (one of the layers of the basement membrane), a protein network foundation for most cells and organs. The laminins are an important and biologically active part of the basal lamina, influencing cell differentiation, migration, adhesion as well as phenotype and survival.

Laminins are trimeric proteins that contain an α-chain, a β-chain, and a γ-chain, found in five, four, and three genetic variants, respectively. The laminin molecules are named according to their chain composition. Thus, laminin-511 contains α5, β1, and γ1 chains. Fourteen other chain combinations have been identified in vivo. The trimeric proteins intersect to form a cross-like structure that can bind to other cell membrane and extracellular matrix molecules. The three shorter arms are particularly good at binding to other laminin molecules, which allows them to form sheets. The long arm is capable of binding to cells, which helps anchor organized tissue cells to the membrane.

The laminins are a family of glycoproteins that are an integral part of the structural scaffolding in almost every tissue of an organism. They are secreted and incorporated into cell-associated extracellular matrices. Laminin is vital for the maintenance and survival of tissues. Defective laminins can cause muscles to form improperly, leading to a form of muscular dystrophy, lethal skin blistering disease (junctional epidermolysis bullosa) and defects of the kidney filter (nephrotic syndrome).

Types
Fifteen laminin trimers have been identified. The laminins are combinations of different alpha-, beta-, and gamma-chains.


 * There are five forms of alpha-chains: LAMA1, LAMA2, LAMA3, LAMA4, LAMA5
 * There are four of beta-chains: LAMB1, LAMB2, LAMB3, LAMB4
 * There are three of gamma-chains: LAMC1, LAMC2, LAMC3

Laminins were previously called Laminin-1, Laminin-2 etc… but the nomenclature was recently changed to describe which chains are present in each isoform. For example, laminin-511 contains an α5-chain, a β1-chain and a γ1 chain.

Networks
Laminins form independent networks and are associated with type IV collagen networks via entactin, fibronectin , and perlecan. They also bind to cell membranes through integrin receptors and other plasma membrane molecules, such as the dystroglycan glycoprotein complex and Lutheran blood group glycoprotein. Through these interactions, laminins critically contribute to cell attachment and differentiation, cell shape and movement, maintenance of tissue phenotype, and promotion of tissue survival. Some of these biological functions of laminin have been associated with specific amino-acid sequences or fragments of laminin. For example, the peptide sequence [GTFALRGDNGDNGQ], which is located on the alpha-chain of laminin, promotes adhesion of endothelial cells.

Pathology
Dysfunctional structure of one particular laminin, laminin-211, is the cause of one form of congenital muscular dystrophy. Laminin-211 is composed of an α2, a β1 and a γ1 chains. This laminin's distribution includes the brain and muscle fibers. In muscle, it binds to alpha dystroglycan and integrin alpha7—beta1 via the G domain, and via the other end binds to the extracellular matrix. Abnormal laminin-332, which is essential for epithelial cells, leads to dissociation of keratinocytes of the skin and cells covering the gastrointestinal tract from the basal lamina with severe skin blisters and loss of cells in the mouth, pharynx, and gastrointestinal tract. A called congential muscular dystrophy that leads to death in early infancy. Malfunctional laminin-521 in the kidney filter causes leakage of protein into the urine and nephrotic syndrome.

Laminins in cell culture
Recently, several publications have demonstrated that laminins can be used to culture cells, such as pluripotent stem cells, that are difficult to culture on other substrates. Mostly two types of laminins have been used. Laminin-111 extracted from mouse sarcomas is one popular laminin type, as well as a mixture of laminins 511 and 521 from human placenta. Various laminin isoforms are practically impossible to isolate from tissues in pure form due to extensive cross-linking and the need for harsh extraction conditions such as proteolytic enzymes or low pH that cause degradation. However, professor Tryggvason's group at the Karolinska Institute in Sweden showed how to produce recombinant laminins using HEK293 cells in 2000. Kortesmaa et al. 2000. This opened the possibility test if laminins could have a significant role in vitro as they have in the human body. In 2008, two groups independently showed that mouse embryonic stem cell can be grown for months on top of recombinant laminin-511. Later on Rodin et al showed that recombinant laminin 511 can be used to create a totally xenon-free and defined cell culture environment to culture human pluripotent ES cells and human iPS cells.

Laminin is frequently used in scientific research for use in cell culture and for studying cellular interactions with the extracellular environment. Many suppliers such as Trevigen, SigmaAldrich, MerckMillipore and other manufacture Mouse Laminin I. However only BioLamina produces multiple human recombinant laminins that can be used to create a xeno-free and defined stem cell culture environment. Laminins can be used to recreate the 3D cellular environment for assessing cellular differentiation, morphology, and angiogenic potential, as well as assays which measure cell adhesion, proliferation, migration, and invasion through the extracellular matrix.

Role in neural development
Laminin-111 is a major substrate along which nerve axons will grow, both in vivo and in vitro. For example, it lays down a path that developing retinal ganglion cells follow on their way from the retina to the tectum. It is also often used as a substrate in cell culture experiments. Interestingly, the presence of laminin-1 can influence how the growth cone responds to other cues. For example, growth cones are repelled by netrin when grown on laminin-111, but are attracted to netrin when grown on fibronectin. This effect of laminin-111 probably occurs through a lowering of intracellular cyclic AMP.

Laminin Domain I
LAMA1;    LAMA2;     LAMA3;     LAMA4;     LAMA5;

Laminin Domain II
LAMA1;    LAMA2;     LAMA3;     LAMA4;     LAMA5;

Laminin B (Domain IV)
HSPG2;    LAMA1;     LAMA2;     LAMA3;     LAMA5;     LAMC1;     LAMC2;     LAMC3;

Laminin EGF-like (Domains III and V)
AGRIN;    ATRN;      ATRNL1;    CELSR1;    CELSR2;    CELSR3;    CRELD1;    HSPG2; LAMA1;    LAMA2;     LAMA3;     LAMA4;     LAMA5;     LAMB1;     LAMB2;     LAMB3; LAMB4;    LAMC1;     LAMC2;     LAMC3;      MEGF10;    MEGF12;    MEGF6; MEGF8;    MEGF9;     NSR1;      NTN1;      NTN2L;     NTN4;      NTNG1;     NTNG2; RESDA1;   SCARF1;    SCARF2;    SREC;      STAB1;     USH2A;

Laminin G domain
AGRIN;    CASPR4;    CELSR1;    CELSR2;    CELSR3;    CNTNAP1;   CNTNAP2;   CNTNAP3;   CNTNAP4; CNTNAP5;  COL11A1;   COL11A2;   COL24A1;   COL5A1;    COL5A3;    CRB1;      CRB2; CSPG4;    EGFLAM;    FAT;       FAT2;      FAT4;      GAS6;      HSPG2;     LAMA1; LAMA2;    LAMA3;     LAMA4;     LAMA5;     NELL2;     NRXN1;     NRXN2;     NRXN3; PROS1;    RESDA1;    SLIT1;     SLIT2;     SLIT3;     USH2A;

Laminin N-terminal (Domain VI)
LAMA1;    LAMA2;     LAMA3;     LAMA5;     LAMB1;     LAMB2;     LAMB3;     LAMB4; LAMC1;    LAMC3;     NTN1;      NTN2L;     NTN4;      NTNG1;     NTNG2;     USH2A;