The L1 family is a family of

cell adhesion molecule Cell adhesion molecules (CAMs) are a subset of cell surface proteins that are involved in the binding of cells with other cells or with the extracellular matrix (ECM), in a process called cell adhesion. In essence, CAMs help cells stick to each ...

s that includes four different L1-like proteins. They are members of the immunoglobulin superfamily (

IgSF CAM IgSF CAMs (Immunoglobulin-like Cell Adhesion Molecules) are cell adhesion molecules that belong to Immunoglobulin superfamily. It is regarded as the most diverse superfamily of CAMs. This family is characterized by their extracellular domains cont ...

). The members of the L1-family in humans are called L1 or L1cam,

CHL1 Neural cell adhesion molecule L1-like protein also known as close homolog of L1 (CHL1) is a protein that in humans is encoded by the ''CHL1'' gene. CHL1 is a cell adhesion molecule closely related to the L1. In melanocytic cells CHL1 gene expres ...

(close homologue of L1),

Neurofascin Neurofascin is a protein that in humans is encoded by the ''NFASC'' gene. Function Neurofascin is an L1 family immunoglobulin cell adhesion molecule (see L1CAM) involved in axon subcellular targeting and synapse formation during neural develop ...

and NRCAM (NgCAM related cell adhesion molecule). L1 family members are found on neurons, especially on their axons. Sometimes they are found on glia, such as Schwann cells,

radial glia Radial glial cells, or radial glial progenitor cells (RGPs), are bipolar-shaped progenitor cells that are responsible for producing all of the neurons in the cerebral cortex. RGPs also produce certain lineages of glia, including astrocytes and ol ...

and

Bergmann glia Radial glial cells, or radial glial progenitor cells (RGPs), are bipolar-shaped progenitor cells that are responsible for producing all of the neurons in the cerebral cortex. RGPs also produce certain lineages of glia, including astrocytes and ol ...

cells and, as such, are important for neural cell migration during development. L1 family members are expressed throughout the vertebrate and invertebrate kingdoms. L1 family members are able to bind to a number of other proteins. As cell adhesion molecules, they often bind "homophilically" to themselves; for example L1 on one cell binding to L1 on an adjacent cell. L1 family members also bind "heterophilically" to members of the contactin or

CNTN1 Contactin 1, also known as CNTN1, is a protein which in humans is encoded by the ''CNTN1'' gene. Function The protein encoded by this gene is a member of the immunoglobulin superfamily. It is a glycosylphosphatidylinositol (GPI)-anchored neuron ...

family. L1 family members bind to many cytoplasmic proteins such as

Ankyrin Ankyrins are a family of proteins that mediate the attachment of integral membrane proteins to the spectrin-actin based membrane cytoskeleton. Ankyrins have binding sites for the beta subunit of spectrin and at least 12 families of integral mem ...

s, ezrin-moesin-radixin (ERM) proteins, signaling molecules like src (

src gene Tyrosine-protein kinase CSK also known as C-terminal Src kinase is an enzyme that, in humans, is encoded by the CSK gene. This enzyme phosphorylates tyrosine residues located in the C-terminal end of Src-family kinases (SFKs) including SRC, HCK, ...

) and erk (

Extracellular signal-regulated kinases In molecular biology, extracellular signal-regulated kinases (ERKs) or classical MAP kinases are widely expressed protein kinase intracellular signalling molecules that are involved in functions including the regulation of meiosis, mitosis, and p ...

) and proteins important in trafficking, such as AP-2. NrCAM and neurofascin both have class 1 PDZ domain binding motifs at their COOH termini. NrCAM can bind to SAP102 and other members of the MAGUK family.

Function

The importance of L1 in neural development has been revealed in several ways. In humans, mutations in the L1 gene can have devastating consequences. In extreme cases, babies are born with a fatal condition of

hydrocephalus Hydrocephalus is a condition in which an accumulation of cerebrospinal fluid (CSF) occurs within the brain. This typically causes increased intracranial pressure, pressure inside the skull. Older people may have headaches, double vision, poor ...

("water on the brain"). Children with less severe mutations typically exhibit mental retardation and difficulty in controlling limb movements (spasticity). Autopsies on patients that have died of an L1-deficiency disease reveal a remarkable condition: they are often missing two large nerve tracts, one that runs in the two halves of the brain and the other that runs between the brain and the spinal cord. The absence of such nerve tracts suggests that L1 is involved in the growth of axons within the embryonic nervous system."**

Function

References

Further reading