Biology:Microcephalin

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Short description: Protein-coding gene in the species Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example
Microcephalin protein
Microcephalin (MCPH1) is a gene that is expressed during fetal brain development
Microcephalin.png
Identifiers
SymbolMicrocephalin
PfamPF12258
InterProIPR022047

Microcephalin (MCPH1) is a gene that is expressed during fetal brain development. Certain mutations in MCPH1, when homozygous, cause primary microcephaly—a severely diminished brain.[1][2][3] Hence, it has been assumed that variants have a role in brain development.[4][5] However, in normal individuals no effect on mental ability or behavior has yet been demonstrated in either this or another similarly studied microcephaly gene, ASPM.[6][7] However, an association has been established between normal variation in brain structure, as measured with MRI (i.e., primarily cortical surface area and total brain volume) but only in females, and common genetic variants within both the MCPH1 gene and another similarly studied microcephaly gene, CDK5RAP2.[8]

Structure

Microcephalin proteins contain the following three domains:

Expression in the brain

MCPH1 is expressed in the fetal brain, in the developing forebrain, and on the walls of the lateral ventricles. Cells of this area divide, producing neurons that migrate to eventually form the cerebral cortex.

Evolution

A derived form of MCPH1 appeared about 37,000 years ago (any time between 14,000 and 60,000 years ago) and has spread to become the most common form of microcephalin throughout the world except Sub-Saharan Africa; this rapid spread suggests a selective sweep.[9][10] However, scientists have not identified the evolutionary pressures that may have caused the spread of these mutations.[11] This variant of the gene is thought to contribute to increased brain volume[12] and may correlate with the incidence of tonal languages,[13] though modern distributions of chromosomes bearing the ancestral forms of MCPH1 and ASPM showed neither microcephalin or ASPM had any significant effect on IQ.[11]

The derived form of MCPH1 may have originated from a lineage separated from modern humans approximately 1.1 million years ago and later introgressed into humans. This finding supports the possibility of admixture between modern humans and extinct Homo spp.[10] While Neanderthals have been suggested as the possible source of this haplotype, the haplotype was not found in the individuals used to prepare the first draft of the Neanderthal genome.[14][15]

Controversy

The research results[clarification needed] began to attract considerable controversy[when?] in the science world. John Derbyshire wrote that as a result of the findings, "our cherished national dream of a well-mixed and harmonious meritocracy [...] may be unattainable."[16] Richard Lewontin considers the two published papers as "egregious examples of going well beyond the data to try to make a splash." Bruce Lahn maintains that the science of the studies is sound, and freely admits that a direct link between these particular genes and either cognition or intelligence has not been clearly established. Lahn is now engaging himself with other areas of study.[17][18] Later studies have not found those gene variants to be associated with mental ability or cognition.[19][11][7]

Later genetic association studies by Mekel-Bobrov et al. and Evans et al. also reported that the genotype for MCPH1 was under positive selection. An analysis by Timpson et al., found "no meaningful associations with brain size and various cognitive measures".[19] A later 2010 study by Rimol et al.[8] demonstrated a link between brain size and structure and two microcephaly genes, MCPH1 (only in females) and CDK5RAP2 (only in males). In contrast to previous studies, which only considered small numbers of exonic single nucleotide polymorphisms (SNPs) and did not investigate sex-specific effects, this study used microarray technology to genotype a range of SNPs associated with all four MCPH genes, including upstream and downstream regulatory elements, and allowed for separate effects for males and females.

Other MCPH genes

In addition to MCPH1, other genes have been designated MCPH genes based on their role in brain size. These include WDR62 (MCPH2), CDK5RAP2 (MCPH3), KNL1 (MCPH4), ASPM (MCPH5), CENPJ (MCPH6), STIL (MCPH7), CEP135 (MCPH8), CEP152 (MCPH9), ZNF335 (MCPH10), PHC1 (MCPH11) and CDK6 (MCPH12).[20]

Research studies

In March 2019, Chinese scientists reported inserting the human brain-related MCPH1 gene into laboratory rhesus monkeys, resulting in the transgenic monkeys performing better and answering faster on "short-term memory tests involving matching colors and shapes", compared to control non-transgenic monkeys, according to the researchers.[21][22]

See also

References

  1. ↑ "Identification of microcephalin, a protein implicated in determining the size of the human brain". American Journal of Human Genetics 71 (1): 136–42. July 2002. doi:10.1086/341283. PMID 12046007. 
  2. ↑ Online Mendelian Inheritance in Man (OMIM) 251200
  3. ↑ "Primary autosomal recessive microcephaly (MCPH1) maps to chromosome 8p22-pter". American Journal of Human Genetics 63 (2): 541–6. August 1998. doi:10.1086/301966. PMID 9683597. 
  4. ↑ "Molecular evolution of microcephalin, a gene determining human brain size". Human Molecular Genetics 13 (11): 1131–7. June 2004. doi:10.1093/hmg/ddh127. PMID 15056608. 
  5. ↑ "Reconstructing the evolutionary history of microcephalin, a gene controlling human brain size". Human Molecular Genetics 13 (11): 1139–45. June 2004. doi:10.1093/hmg/ddh126. PMID 15056607. 
  6. ↑ "Normal variants of Microcephalin and ASPM do not account for brain size variability". Human Molecular Genetics 15 (12): 2025–9. June 2006. doi:10.1093/hmg/ddl126. PMID 16687438. 
  7. ↑ 7.0 7.1 "No evidence that polymorphisms of brain regulator genes Microcephalin and ASPM are associated with general mental ability, head circumference or altruism". Biology Letters 3 (2): 157–60. April 2007. doi:10.1098/rsbl.2006.0586. PMID 17251122. 
  8. ↑ 8.0 8.1 "Sex-dependent association of common variants of microcephaly genes with brain structure". Proceedings of the National Academy of Sciences of the United States of America 107 (1): 384–8. January 2010. doi:10.1073/pnas.0908454107. PMID 20080800. Bibcode: 2010PNAS..107..384R. 
  9. ↑ "Microcephalin, a gene regulating brain size, continues to evolve adaptively in humans". Science 309 (5741): 1717–20. September 2005. doi:10.1126/science.1113722. PMID 16151009. Bibcode: 2005Sci...309.1717E. 
  10. ↑ 10.0 10.1 "Evidence that the adaptive allele of the brain size gene microcephalin introgressed into Homo sapiens from an archaic Homo lineage". Proceedings of the National Academy of Sciences of the United States of America 103 (48): 18178–83. November 2006. doi:10.1073/pnas.0606966103. PMID 17090677. Bibcode: 2006PNAS..10318178E. 
  11. ↑ 11.0 11.1 11.2 "The ongoing adaptive evolution of ASPM and Microcephalin is not explained by increased intelligence". Human Molecular Genetics 16 (6): 600–8. March 2007. doi:10.1093/hmg/ddl487. PMID 17220170. 
  12. ↑ "The microcephalin ancestral allele in a Neanderthal individual". PLOS ONE 5 (5): e10648. May 2010. doi:10.1371/journal.pone.0010648. PMID 20498832. Bibcode: 2010PLoSO...510648L. 
  13. ↑ "Linguistic tone is related to the population frequency of the adaptive haplogroups of two brain size genes, ASPM and Microcephalin". Proceedings of the National Academy of Sciences of the United States of America 104 (26): 10944–9. June 2007. doi:10.1073/pnas.0610848104. PMID 17537923. Bibcode: 2007PNAS..10410944D. 
  14. ↑ "Neandertal genomics. Tales of a prehistoric human genome". Science 323 (5916): 866–71. February 2009. doi:10.1126/science.323.5916.866. PMID 19213888. 
  15. ↑ "A draft sequence of the Neandertal genome". Science 328 (5979): 710–722. May 2010. doi:10.1126/science.1188021. PMID 20448178. Bibcode: 2010Sci...328..710G. 
  16. ↑ Derbyshire, John (November 2005). "The specter of difference". National Review. http://www.johnderbyshire.com/Opinions/HumanSciences/specterofdifference.html. 
  17. ↑ Regalado, Antonio (June 2006). "Scientist's Study Of Brain Genes Sparks a Backlash". The Wall Street Journal. https://www.wsj.com/articles/SB115040765329081636. 
  18. ↑ "Bruce Lahn profile. Brain man makes waves with claims of recent human evolution". Science 314 (5807): 1871–3. December 2006. doi:10.1126/science.314.5807.1871. PMID 17185582. 
  19. ↑ 19.0 19.1 "Comment on papers by Evans et al. and Mekel-Bobrov et al. on Evidence for Positive Selection of MCPH1 and ASPM". Science 317 (5841): 1036; author reply 1036. August 2007. doi:10.1126/science.1141705. PMID 17717170. Bibcode: 2007Sci...317.1036T. 
  20. ↑ "Molecular genetics of human primary microcephaly: an overview". BMC Medical Genomics 8 (Suppl 1): S4. 2015-01-15. doi:10.1186/1755-8794-8-S1-S4. PMID 25951892. 
  21. ↑ "Scientists Put a Human Intelligence Gene Into a Monkey. Other Scientists are Concerned.". Discover. 29 December 2019. https://www.discovermagazine.com/mind/scientists-put-a-human-intelligence-gene-into-a-monkey-other-scientists-are. 
  22. ↑ Shi, Lei (27 March 2019). "Transgenic rhesus monkeys carrying the human MCPH1 gene copies show human-like neoteny of brain development". Chinese National Science Review 6 (3): 480–493. doi:10.1093/nsr/nwz043. PMID 34691896. 

Further reading

External links



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