T-box transcription factor TBX1 also known as T-box protein 1 and testis-specific T-box protein 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 TBX1
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 ...
.
Genes in the
T-box
T-box refers to a group of transcription factors involved in embryonic limb and heart development. Every T-box protein has a relatively large DNA-binding domain, generally comprising about a third of the entire protein that is both necessary a ...
family are transcription factors that play important roles in the formation of tissues and organs during embryonic development.
To carry out these roles, proteins made by this gene family bind to specific areas of
DNA called T-box binding element (TBE)
to control the expression of target genes.
Gene
The TBX1 gene is located on the long (q) arm of
chromosome 22
Chromosome 22 is one of the 23 pairs of chromosomes in human cells. Humans normally have two copies of chromosome 22 in each cell. Chromosome 22 is the second smallest human chromosome, spanning about 49 million DNA base pairs and representing b ...
at position 11.21, from
base pair 18,118,779 to base pair 18,145,669.
Function
The T-box 1 protein appears to be necessary for the normal development of large arteries that carry blood out of the
heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...
,
muscles and
bone
A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
s of the face and neck, and glands such as the
thymus
The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...
and
parathyroid
Parathyroid glands are small endocrine glands in the neck of humans and other tetrapods. Humans usually have four parathyroid glands, located on the back of the thyroid gland in variable locations. The parathyroid gland produces and secretes pa ...
. Although the T-box 1 protein acts as a transcription factor, it is not yet known which genes are regulated by the protein.
Clinical significance
Most cases of
22q11.2 deletion syndrome are caused by the deletion of a small piece of
chromosome 22
Chromosome 22 is one of the 23 pairs of chromosomes in human cells. Humans normally have two copies of chromosome 22 in each cell. Chromosome 22 is the second smallest human chromosome, spanning about 49 million DNA base pairs and representing b ...
. This region of the chromosome contains about 30
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, including the TBX1 gene. In a small number of affected individuals without a chromosome 22 deletion,
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 the TBX1 gene are thought to be responsible for the characteristic signs and symptoms of the syndrome. Of the three known mutations, two mutations change one
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
(a building block of proteins) in the T-box 1 protein. The third mutation deletes a single amino acid from the protein. These mutations likely disrupt the ability of the T-box 1 protein to bind to DNA and regulate the activity of other genes.
Loss of the TBX1 gene, due to either a mutation in the gene or a deletion of part of chromosome 22, is responsible for many of the features of 22q11.2 deletion syndrome. Specifically, a loss of the TBX1 gene is associated with heart defects, an opening in the roof of the mouth (a
cleft palate
A cleft lip contains an opening in the upper lip that may extend into the nose. The opening may be on one side, both sides, or in the middle. A cleft palate occurs when the palate (the roof of the mouth) contains an opening into the nose. The ...
), distinctive facial features, and low calcium levels, but does not appear to cause learning disabilities.
Mutation in TBX1 causes predisposition to
hernia
A hernia is the abnormal exit of tissue or an organ, such as the bowel, through the wall of the cavity in which it normally resides. Various types of hernias can occur, most commonly involving the abdomen, and specifically the groin. Groin herni ...
s.
References
Further reading
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External links
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{{NLM content
Transcription factors