NeuN
Encyclopedia
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NeuN is a neuronal nuclear antigen
and was first described in 1994 by Mullen et al., who raised a series of monoclonal antibodies
to mouse antigens with the original intent of finding mouse species specific immunological markers for use in transplantation experiments. In the event they isolated a hybridoma
line, called mAb A60, which proved to bind an antigen expressed only in neuronal nuclei and to a lesser extent the cytoplasm of neuronal cells, and which appeared to work on all vertebrates. This unknown antigen was therefore known as NeuN for "Neuronal Nuclei". A few neuronal cell types were not recognized by the NeuN antibody, such as cerebellar Purkinje cells, olfactory Mitral cells and retinal photoreceptors. However the vast majority of neurons are strongly NeuN positive, and NeuN immunoreactivity has been widely used to identify neurons is tissue culture and in sections and to measure the neuron/glial ratio in brain regions. NeuN immunoreactivity becomes obvious as neurons mature, typically after they have downregulated expression of Doublecortin
, a marker seen in the earliest stages of neuronal development. The NeuN protein was not at the time characterized, though the molecular weight was shown to be closely spaced bands running at 46kDa and 48kDa on SDS-PAGE
. However the exact identity of the NeuN protein remained a mystery for many years. Despite this the mAb A66 antibody has become very widely used as a robust marker of neurons, and a May 2011 Medline search using the keyword "NeuN" produced over 1,100 hits. Recently Kim et al. used proteomic methods to show that NeuN corresponds to Fox-3. Fox-3 is one of a family of mammalian homologues of the Fox-1, originally discovered in the nematode
worm Caenorhabditis elegans
as a gene involved in sex determination. Fox is in fact an acronym of "Feminizing locus on X". The mammalian genome contains three genes homologous to C. elegans Fox-1, called Fox-1, Fox-2 and Fox-3. All these Fox proteins are about 46kDa in size, and each includes a central highly conserved so called RRM or RNA recognition motif
. This motif corresponds to a small ~70 amino acid module consisting of 4 strands forming a beta sheet
structure and two alpha helices. RRM domains are one of the most common domains in the human genome
and are found in numerous proteins which bind RNA molecules. An alternate name for Fox-3 is hexaribonucleotide binding protein 3, and the Fox proteins are believed to have a role in the regulation of mRNA splicing. For a review of the Fox family of proteins see this reference.
NeuN is a neuronal nuclear antigen
Antigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
and was first described in 1994 by Mullen et al., who raised a series of monoclonal antibodies
Monoclonal antibodies
Monoclonal antibodies are monospecific antibodies that are the same because they are made by identical immune cells that are all clones of a unique parent cell....
to mouse antigens with the original intent of finding mouse species specific immunological markers for use in transplantation experiments. In the event they isolated a hybridoma
Hybridoma
Hybridoma technology is a technology of forming hybrid cell lines by fusing a specific antibody-producing B cell with a myeloma cell that is selected for its ability to grow in tissue culture and for an absence of antibody chain synthesis...
line, called mAb A60, which proved to bind an antigen expressed only in neuronal nuclei and to a lesser extent the cytoplasm of neuronal cells, and which appeared to work on all vertebrates. This unknown antigen was therefore known as NeuN for "Neuronal Nuclei". A few neuronal cell types were not recognized by the NeuN antibody, such as cerebellar Purkinje cells, olfactory Mitral cells and retinal photoreceptors. However the vast majority of neurons are strongly NeuN positive, and NeuN immunoreactivity has been widely used to identify neurons is tissue culture and in sections and to measure the neuron/glial ratio in brain regions. NeuN immunoreactivity becomes obvious as neurons mature, typically after they have downregulated expression of Doublecortin
Doublecortin
Doublecortex; lissencephaly, X-linked , also known as DCX, is a gene.Doublecortin is a microtubule-associated protein expressed by neuronal precursor cells and immature neurons in embryonic and adult cortical structures...
, a marker seen in the earliest stages of neuronal development. The NeuN protein was not at the time characterized, though the molecular weight was shown to be closely spaced bands running at 46kDa and 48kDa on SDS-PAGE
SDS-PAGE
SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis, describes a collection of related techniques widely used in biochemistry, forensics, genetics and molecular biology to separate proteins according to their electrophoretic mobility...
. However the exact identity of the NeuN protein remained a mystery for many years. Despite this the mAb A66 antibody has become very widely used as a robust marker of neurons, and a May 2011 Medline search using the keyword "NeuN" produced over 1,100 hits. Recently Kim et al. used proteomic methods to show that NeuN corresponds to Fox-3. Fox-3 is one of a family of mammalian homologues of the Fox-1, originally discovered in the nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
worm Caenorhabditis elegans
Caenorhabditis elegans
Caenorhabditis elegans is a free-living, transparent nematode , about 1 mm in length, which lives in temperate soil environments. Research into the molecular and developmental biology of C. elegans was begun in 1974 by Sydney Brenner and it has since been used extensively as a model...
as a gene involved in sex determination. Fox is in fact an acronym of "Feminizing locus on X". The mammalian genome contains three genes homologous to C. elegans Fox-1, called Fox-1, Fox-2 and Fox-3. All these Fox proteins are about 46kDa in size, and each includes a central highly conserved so called RRM or RNA recognition motif
RNA recognition motif
RNA recognition motif, RNP-1 is a putative RNA-binding domain of about 90 amino acids that are known to bind single-stranded RNAs. It was found in many eukaryotic proteins....
. This motif corresponds to a small ~70 amino acid module consisting of 4 strands forming a beta sheet
Beta sheet
The β sheet is the second form of regular secondary structure in proteins, only somewhat less common than the alpha helix. Beta sheets consist of beta strands connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet...
structure and two alpha helices. RRM domains are one of the most common domains in the human genome
Human genome
The human genome is the genome of Homo sapiens, which is stored on 23 chromosome pairs plus the small mitochondrial DNA. 22 of the 23 chromosomes are autosomal chromosome pairs, while the remaining pair is sex-determining...
and are found in numerous proteins which bind RNA molecules. An alternate name for Fox-3 is hexaribonucleotide binding protein 3, and the Fox proteins are believed to have a role in the regulation of mRNA splicing. For a review of the Fox family of proteins see this reference.