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 residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

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 term ...

'' and ''

SMN2 Survival of motor neuron 2 (''SMN2'') is a gene that encodes the SMN protein (full and truncated) in humans. Gene The ''SMN2'' gene is part of a 500 kb inverted duplication on chromosome 5q13. This duplicated region contains at least four ge ...

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

s. SMN is found in the cytoplasm of all animal cells and also in the

nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: * Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics *Nuclear space *Nuclear ...

gems Gems, or gemstones, are polished, cut stones or minerals. Gems or GEMS may also refer to: Arts, entertainment and media * ''Gems'' (Aerosmith album), 1988 * ''Gems'' (Patti LaBelle album), 1994 * ''Gems'' (Michael Bolton album), 2011 * Gems TV, ...

. It functions in

transcriptional regulation In molecular biology and genetics, transcriptional regulation is the means by which a cell regulates the conversion of DNA to RNA (transcription), thereby orchestrating gene activity. A single gene can be regulated in a range of ways, from al ...

telomerase Telomerase, also called terminal transferase, is a ribonucleoprotein that adds a species-dependent telomere repeat sequence to the 3' end of telomeres. A telomere is a region of repetitive sequences at each end of the chromosomes of most euka ...

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 replication, DNA or viral repl ...

s in ''SMN1'', results in widespread splicing defects, especially in spinal motor neurons, and is one cause of spinal muscular atrophy. Research also showed a possible role of SMN in

neuronal migration The development of the nervous system, or neural development (neurodevelopment), refers to the processes that generate, shape, and reshape the nervous system of animals, from the earliest stages of embryonic development to adulthood. The fiel ...

and/or differentiation.

Function

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

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

and the

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom * Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...

. 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 int ...

s (snRNPs). This protein forms heteromeric complexes with proteins such as GEMIN2 and

GEMIN4 Gem-associated protein 4 is a protein that in humans is encoded by the ''GEMIN4'' gene. Function The product of this gene is part of the SMN protein complex localized to the cytoplasm, nucleoli, and to discrete nuclear bodies called Gemini b ...

, and also interacts with several proteins known to be involved in the

biogenesis Spontaneous generation is a superseded scientific theory that held that living creatures could arise from nonliving matter and that such processes were commonplace and regular. It was hypothesized that certain forms, such as fleas, could arise ...

snRNP snRNPs (pronounced "snurps"), or small nuclear ribonucleoproteins, are RNA-protein complexes that combine with unmodified pre-mRNA and various other proteins to form a spliceosome, a large RNA-protein molecular complex upon which splicing of pre- ...

s, 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

s, 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 Advocates for Informed Choice, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex traits. The organizati ...

with: *

Bcl-2 Bcl-2 (B-cell lymphoma 2), encoded in humans by the ''BCL2'' gene, is the founding member of the Bcl-2 family of regulator proteins that regulate cell death (apoptosis), by either inhibiting (anti-apoptotic) or inducing (pro-apoptotic) apoptosi ...

, *

Coilin Coilin is a protein that in humans is encoded by the ''COIL'' gene. Coilin got its name from the coiled shape of the Cajal bodies in which it is found. It was first identified using human autoimmune serum. Function Coilin protein is one of the ...

, *

DDX20 Probable ATP-dependent RNA helicase DDX20, also known as DEAD-box helicase 20 and gem-associated protein 3 (GEMIN3), is an enzyme that in humans is encoded by the ''DDX20'' gene. Function DEAD box proteins, characterized by the conserved motif ...

, *

DHX9 ATP-dependent RNA helicase A (RHA; also known as DHX9, LKP, and NDHI) is an enzyme that in humans is encoded by the ''DHX9'' gene. Function DEAD/DEAH box helicases are proteins, and are putative RNA helicases. They are implicated in a number o ...

, * FBL, *

FUBP1 Far upstream element-binding protein 1 is a protein that in humans is encoded by the ''FUBP1'' gene. This gene encodes a ssDNA binding protein that activates the far upstream element (FUSE) of c-myc and stimulates expression of c-myc in undiffere ...

, * GAR1, * GEMIN2, *

, * GEMIN5, * GEMIN7, *

HNRNPR Heterogeneous nuclear ribonucleoprotein R is a protein that in humans is encoded by the ''HNRNPR'' gene. Function This gene belongs to the subfamily of ubiquitously expressed heterogeneous nuclear ribonucleoproteins (hnRNPs). The hnRNPs are R ...

, *

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. ...

, *

P53 p53, also known as Tumor protein P53, cellular tumor antigen p53 (UniProt name), or transformation-related protein 53 (TRP53) is a regulatory protein that is often mutated in human cancers. The p53 proteins (originally thought to be, and often s ...

, * SNRPD1, and * SNRPD2.

Evolutionary conservation

SMN is evolutionarily conserved including the

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

kingdom, though only fungal organisms with a great number of introns have the ''Smn'' gene (or the splicing factor spf30

paralogue Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a s ...

). Surprisingly, these are filamentous fungus which have

mycelia Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates ...

, so suggesting analogy to the neuronal axons.

References

External links