In molecular biology, Human Accelerated Region 1 (Highly Accelerated Region 1, HAR1) is a segment of the

human genome The human genome is a complete set of nucleic acid sequences for humans, encoded as the DNA within each of the 23 distinct chromosomes in the cell nucleus. A small DNA molecule is found within individual Mitochondrial DNA, mitochondria. These ar ...

found on the long arm of

chromosome 20 Chromosome 20 is one of the 23 pairs of chromosomes in humans. Chromosome 20 spans around 66 million base pairs (the building material of DNA) and represents between 2 and 2.5 percent of the total DNA in cells. Chromosome 20 was fully sequenced i ...

. It is a human accelerated region. It is located within a pair of overlapping

long non-coding RNA Long non-coding RNAs (long ncRNAs, lncRNA) are a type of RNA, generally defined as transcripts more than 200 nucleotides that are not translated into protein. This arbitrary limit distinguishes long ncRNAs from small non-coding RNAs, such as mic ...

genes 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 ...

, HAR1A (HAR1F) and HAR1B (HAR1R).supplement
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HAR1A

HAR1A is expressed in

Cajal–Retzius cell Cajal–Retzius cells (CR cells) (also known as horizontal cells of Cajal) are a heterogeneous population of morphologically and molecularly distinct reelin-producing cells. They are found in the marginal zone/layer I of the developing cerebral c ...

s, contemporaneously with the protein

reelin Reelin, encoded by the ''RELN'' gene, is a large secreted extracellular matrix glycoprotein that helps regulate processes of neuronal migration and positioning in the developing brain by controlling cell–cell interactions. Besides this importa ...

. HAR1A was identified in August 2006 when human accelerated regions (HARs) were first investigated. These 49 regions represent parts of the human genome that differ significantly from highly conserved regions of our closest ancestors in terms of evolution. Many of the HARs are associated with genes known to play a role in

neurodevelopment The development of the nervous system in humans, or neural development, or neurodevelopment involves the studies of embryology, developmental biology, and neuroscience. These describe the cellular and molecular mechanisms by which the complex ...

. One particularly altered region, HAR1, was found in a stretch of genome with no known protein-coding RNA sequences. Two RNA genes, HAR1F and HAR1R, were identified partly within the region. The RNA structure of HAR1A has been shown to be stable, with a secondary structure unlike those previously described. HAR1A is active in the developing human brain between the 7th and 18th gestational weeks. It is found in the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

telencephalon The cerebrum (: cerebra), telencephalon or endbrain is the largest part of the brain, containing the cerebral cortex (of the two cerebral hemispheres) as well as several subcortical structures, including the hippocampus, basal ganglia, and olf ...

in fetuses. In adult humans, it is found throughout the

cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...

and

forebrain In the anatomy of the brain of vertebrates, the forebrain or prosencephalon is the rostral (forward-most) portion of the brain. The forebrain controls body temperature, reproductive functions, eating, sleeping, and the display of emotions. Ve ...

; it is also found in the

testes A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of androgens, primarily testosterone. The ...

. There is evidence that HAR1 is repressed by

REST REST (Representational State Transfer) is a software architectural style that was created to describe the design and guide the development of the architecture for the World Wide Web. REST defines a set of constraints for how the architecture of ...

in individuals with

Huntington's disease Huntington's disease (HD), also known as Huntington's chorea, is an incurable neurodegenerative disease that is mostly Genetic disorder#Autosomal dominant, inherited. It typically presents as a triad of progressive psychiatric, cognitive, and ...

, perhaps contributing to the

neurodegeneration A neurodegenerative disease is caused by the progressive loss of neurons, in the process known as neurodegeneration. Neuronal damage may also ultimately result in their cell death, death. Neurodegenerative diseases include amyotrophic lateral sc ...

associated with the disease. Further work on the

secondary structure Protein secondary structure is the local spatial conformation of the polypeptide backbone excluding the side chains. The two most common Protein structure#Secondary structure, secondary structural elements are alpha helix, alpha helices and beta ...

of HAR1A has suggested that the human form adopts a different fold to that of other mammals exemplified by the chimpanzee sequence.

HAR1B

The HAR1B gene overlaps HAR1A, and is located on the opposite

strand Strand or The Strand may refer to: Topography *The flat area of land bordering a body of water, a: ** Beach ** Shoreline * Strand swamp, a type of swamp habitat in Florida Places Africa * Strand, Western Cape, a seaside town in South Africa * ...

of the

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

. Its expression in the human brain is lower than that of HAR1A.

References

External links

* {{Rfam, id=RF00635, name=Human accelerated region 1F
UCSC genome browser page for Human accelerated region 1F
Non-coding RNA Molecular neuroscience Developmental neuroscience

HAR1A

HAR1B

See also

References

Further reading

External links