Human Accelerated Region 1 (HAR1) is a fascinating piece of the human genome that has been a subject of intense research since its discovery in 2006. It's a segment of DNA located on chromosome 20, and it's been found to be remarkably different between humans and our closest relatives, the chimpanzees. What makes HAR1 so special is its rapid evolution. While most of the human genome is very similar to that of chimpanzees, HAR1 has undergone a significant number of mutations specifically in the human lineage. This rapid evolution suggests that HAR1 might play a crucial role in some of the unique characteristics that distinguish humans from other primates. One of the key findings about HAR1 is its association with a pair of overlapping genes called HAR1A and HAR1B. These genes are involved in the production of long non-coding RNA, which doesn't directly code for proteins but plays a vital role in regulating gene expression. Research has shown that HAR1A is particularly active in the developing human brain, specifically during the 7th to 18th weeks of gestation. It's found in a region of the brain called the dorsal telencephalon, which is crucial for the development of the cortex, the outer layer of the brain responsible for higher cognitive functions. Further studies have revealed that HAR1A's structure is different in humans compared to other mammals. This suggests that the changes in HAR1 might have contributed to the development of unique features of the human brain, possibly influencing cognitive abilities like language, memory, and social behavior. The rapid evolution of HAR1 and its association with brain development have led scientists to speculate about its potential role in the evolution of human intelligence. However, much remains to be understood about the precise function of HAR1 and its impact on human cognition. Further research is needed to unravel the mysteries of this intriguing region of our genome. Source:CARTA
In molecular biology, Human Accelerated Region 1 (Highly Accelerated Region 1, HAR1) is a segment of the human genome found on the long arm of chromosome 20. It is a human accelerated region. It is located within a pair of overlapping long non-coding RNA genes, HAR1A (HAR1F) and HAR1B (HAR1R).[1]
HAR1A is expressed in Cajal–Retzius cells, contemporaneously with the protein reelin.[1] [2] [3]
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 telencephalon in fetuses. In adult humans, it is found throughout the cerebellum and forebrain; it is also found in the testes. There is evidence that HAR1 is repressed by REST in individuals with Huntington's disease, perhaps contributing to the neurodegeneration associated with the disease.[4]
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.[5]
The HAR1B gene overlaps HAR1A, and is located on the opposite strand of the chromosome. Its expression in the human brain is lower than that of HAR1A.