Survival of motor neuron or survival motor neuron (SMN) is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

that in humans is encoded by the ''

SMN1 Survival of motor neuron 1 (''SMN1''), also known as component of gems 1 or ''GEMIN1'', is a gene that encodes the SMN protein in humans. Gene ''SMN1'' is the telomeric copy of the gene encoding the SMN protein; the centromeric copy is ter ...

'' and '' SMN2''

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

s. SMN is found in the cytoplasm of all animal cells and also in the nuclear gems. It functions in transcriptional regulation, telomerase regeneration and cellular trafficking. SMN deficiency, primarily due to

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...

s in ''SMN1'', results in widespread splicing defects, especially in spinal

motor neuron A motor neuron (or motoneuron), also known as efferent neuron is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly o ...

s, and is one cause of spinal muscular atrophy. Research also showed a possible role of SMN in neuronal migration and/or differentiation.

Function

The SMN protein contains GEMIN2-binding, Tudor and YG-Box domains. It localizes to both the

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

and the nucleus. Within the nucleus, the protein localizes to subnuclear bodies called gems which are found near coiled bodies containing high concentrations of small

ribonucleoprotein Nucleoproteins are proteins conjugated with nucleic acids (either DNA or RNA). Typical nucleoproteins include ribosomes, nucleosomes and viral nucleocapsid proteins. Structures Nucleoproteins tend to be positively charged, facilitating inter ...

s (snRNPs). This protein forms heteromeric complexes with proteins such as GEMIN2 and GEMIN4, and also interacts with several proteins known to be involved in the

biogenesis Spontaneous generation is a Superseded scientific theories, superseded scientific theory that held that living creatures could arise from abiotic component, non-living matter and that such processes were commonplace and regular. It was Hypoth ...

of snRNPs, such as hnRNP U protein and the small nucleolar RNA binding protein.

SMN complex

''SMN complex'' refers to the entire multi-protein complex involved in the assembly of snRNPs, the essential components of spliceosomal machinery. The complex, apart from the "proper" survival of motor neuron protein, includes at least six other proteins ( gem-associated protein 2, 3, 4, 5, 6 and 7.

Interactions

SMN has been shown to interact with: * Bcl-2, * Coilin, * DDX20, * DHX9, * FBL, * FUBP1, * GAR1, * GEMIN2, * GEMIN4, * GEMIN5, * GEMIN7, * HNRNPR, *

KPNB1 Importin subunit beta-1 is a protein that in humans is encoded by the ''KPNB1'' gene. Function Nucleocytoplasmic transport, a signal- and energy-dependent process, takes place through nuclear pore complexes embedded in the nuclear envelope. T ...

, * P53, * SNRPD1, and * SNRPD2.

Evolutionary conservation

SMN is evolutionarily conserved including the

Fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

kingdom, though only fungal organisms with a great number of

intron An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e., a region inside a gene."The notion of the cistron .e., gen ...

s have the ''Smn'' gene (or the splicing factor spf30 paralogue). Surprisingly, these are filamentous fungus which have

mycelia Mycelium (: mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Its normal form is that of branched, slender, entangled, anastomosing, hyaline threads. Fungal colonies composed of mycelium are fo ...

, so suggesting analogy to the neuronal axons.

References

External links