Information about Neurofilament

neurofilament, light polypeptide 68kDa
Identifiers
Symbol	NEFL
Entrez	4747
HUGO	7739
OMIM	162280
RefSeq	NM_006158
UniProt	P07196
Other data
Locus	Chr. 8 p21

neurofilament, heavy polypeptide 200kDa
Identifiers
Symbol	NEFH
Entrez	4744
HUGO	7737
OMIM	162230
RefSeq	NM_021076
UniProt	P12036
Other data
Locus	Chr. 22 q12.1-13.1

neurofilament 3 (150kDa medium)
Identifiers
Symbol	NEF3
Entrez	4741
HUGO	7734
OMIM	162250
RefSeq	NM_005382
UniProt	P07197
Other data
Locus	Chr. 8 p21

Neurofilaments are the 10 nanometer (10nm) or intermediate filaments found specifically in neurons. The subunits of neurofilaments are related structurally to the 10nm or intermediate filaments of other tissues such as the keratin subunits, which make 10nm filaments expressed specifically in epithelia.

Classification

Class IV: NF-L, NF-M and NF-H

The family of proteins making intermediate filaments is divided into 5 major classes, the keratins forming the classes I and II. The neurofilament subunits occupy the class IV family of intermediate filaments, and was originally thought to contain only three proteins named NF-L, NF-M and NF-H.

These names come from the apparent molecular weight of the mammalian subunits on SDS-PAGE:

• the light or lowest (NF-L) runs at 68-70kDa
• the medium or middle (NF-M) runs at about 145-160kDa
• the heavy or highest (NF-H) runs at 200-220kDa

The SDS-PAGE molecular weights vary between mammalian species, with larger species usually having larger proteins. Neurofilaments are found in vertebrate neurons in especially high concentrations along the axons, where they appear to regulate axonal diameter.

In the adult mammal neurofilament subunit proteins coassemble in vivo, forming a heteropolymer that contain NF-L plus NF-M or NF-H. The NF-H and NF-M proteins have lengthy C-terminal tail domains that appear to control the spacing between neighboring filaments, generating aligned arrays with a fairly uniform interfilament spacing.

Class IV: Other

A fourth class IV subunit alpha-internexin, a.k.a. NF66, is found in association with NF-L, NF-M and NF-H in many situations.

A fifth protein belonging to class IV, Nestin, is found in developing neurons and glia, and the presence of this protein is widely used to define neural stem cells. This protein is lost as development proceeds.

Class III

The class III intermediate filament protein subunit peripherin is found in neurofilaments along with the class IV subunits in a few neurons, mostly in the peripheral nervous system.

Finally another class III intermediate filament subunit, vimentin, is found in developing neurons and a few very unusual neurons in the adult in association with class IV proteins, such as the horizontal neurons of the retina.

Growth

During axonal growth, new neurofilament subunits are incorporated all along the axon in a dynamic process that involves the addition of subunits along the filament length, as well as the addition of subunits at the filament ends.

After an axon has grown and connected with its target cell, the diameter of the axon may increase as much as fivefold.

Neurofilaments are repulsive. This is because their purpose is to set the diameter of dendrites and axons. They do this by repelling each other because of their polarity and move away from each other.

The level of neurofilament gene expression seems to directly control axonal diameter, which in turn controls how fast electrical signals travel down the axon.^[1]

See also

• Intermediate filament

References

•  • [ e] Histology: nervous tissue
Neurons (gray matter)	soma, axon (axon hillock, axoplasm, axolemma, neurofibril/neurofilament), dendrite (Nissl body, dendritic spine) types (bipolar, pseudounipolar, multipolar, pyramidal, Purkinje, granule)
Afferent nerve/Sensory nerve/Sensory neuron	GSA, GVA, SSA, SVA, fibers Ia, Ib or Golgi, II or Aβ, III or Aδ or fast pain, IV or C or slow pain
Efferent nerve/Motor nerve/Motor neuron	GSE, GVE, SVE, Upper motor neuron, Lower motor neuron (Aα motorneuron, Aγ motorneuron)
Synapses	neuropil, synaptic vesicle, neuromuscular junction, electrical synapse - Interneuron (Renshaw)
Sensory receptors	Free nerve ending, Meissner's corpuscle, Merkel nerve ending, Muscle spindle, Pacinian corpuscle, Ruffini ending, Olfactory receptor neuron, Photoreceptor cell, Hair cell, Taste bud
Glial cells	astrocyte, oligodendrocyte, ependymal cells, microglia, radial glia
Myelination (white matter)	Schwann cell, oligodendrocyte, nodes of Ranvier, internode, Schmidt-Lanterman incisures, neurolemma
Related connective tissues	epineurium, perineurium, endoneurium, nerve fascicle, meninges

•  • [ e] Proteins of the cytoskeleton
Microfilaments	Actins - Actin-binding proteins - Actinin - Arp2/3 complex - Cofilin - Destrin - Gelsolin - Myosins - Profilin - Tropomodulin - Troponin (T, C, I) - Tropomyosin - Wiskott-Aldrich syndrome protein
Intermediate filaments	type 1 and 2 (Cytokeratin, type I, type II) - type 3 (Desmin, GFAP, Peripherin, Vimentin) - type 4 (Internexin, Nestin, Neurofilament, Synemin, Syncoilin) - type 5 (Lamin A, B)
Microtubules	Dyneins - Kinesins - MAPs (Tau protein, Dynamin) - Tubulins - Stathmin
Catenins	Alpha catenin - Beta catenin - Plakoglobin (gamma catenin) - Delta catenin
Nonhuman	Major sperm proteins - Prokaryotic cytoskeleton (Crescentin, FtsZ, MreB)
Other	APC - Dystrophin (Dystroglycan) - plakin (Desmoplakin, Plectin) - Spectrin - Talin - Utrophin - Vinculin