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 DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. These are usually treated separately as the ...

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 Human accelerated regions (HARs), first described in August 2006, are a set of 49 segments of the human genome that are conserved throughout vertebrate evolution but are strikingly different in humans. They are named according to their degree of dif ...

. 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 mi ...

genes, HAR1A (HAR1F) and HAR1B (HAR1R).supplement
/ref>

HAR1A

HAR1A is expressed in Cajal-Retzius cells, 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 impor ...

. 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. 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 * Dorsal c ...

telencephalon The cerebrum, 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 olfactory bulb. In ...

in fetuses. In adult humans, it is found throughout the cerebellum 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 (prosencephalon), the midbrain (mesencephalon), and hindbrain (rhombencephalon) are the three primary ...

; it is also found in the

testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...

. There is evidence that HAR1 is repressed by

REST Rest or REST may refer to: Relief from activity * Sleep ** Bed rest * Kneeling * Lying (position) * Sitting * Squatting position Structural support * Structural support ** Rest (cue sports) ** Armrest ** Headrest ** Footrest Arts and enter ...

in individuals with

Huntington's disease Huntington's disease (HD), also known as Huntington's chorea, is a neurodegenerative disease that is mostly inherited. The earliest symptoms are often subtle problems with mood or mental abilities. A general lack of coordination and an uns ...

, perhaps contributing to the neurodegeneration associated with the disease. Further work on the secondary structure 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 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 * Strand Street ...

of the

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

. 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