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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.[5][6][7] Hence it has been assumed that variants have a role in brain development,[8][9] but in normal individuals no effect on mental ability or behavior has yet been demonstrated in either this or another similarly studied microcephaly gene, ASPM.[10][11] 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) and common genetic variants within both the MCPH1 gene and another similarly studied microcephaly gene, CDK5RAP2.[12]

MCPH1
Available structures
PDBOrtholog search: PDBe RCSB
Identifiers
AliasesMCPH1, BRIT1, MCT, microcephalin 1
External IDsOMIM: 607117 MGI: 2443308 HomoloGene: 32586 GeneCards: MCPH1
Gene location (Human)
Chromosome 8 (human)
Chr.Chromosome 8 (human)[1]
Chromosome 8 (human)
Genomic location for MCPH1
Genomic location for MCPH1
Band8p23.1Start6,406,596 bp[1]
End6,648,508 bp[1]
Orthologs
SpeciesHumanMouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_173189

RefSeq (protein)

NP_775281

Location (UCSC)Chr 8: 6.41 – 6.65 MbChr 8: 18.6 – 18.8 Mb
PubMed search[3][4]
Wikidata
View/Edit HumanView/Edit Mouse
Microcephalin protein
Identifiers
SymbolMicrocephalin
PfamPF12258
InterProIPR022047

StructureEdit

Microcephalin proteins contain the following three domains:

Expression in the brainEdit

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.

EvolutionEdit

A derived form of MCPH1 called haplogroup D 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.[13][14] However, scientists have not identified the evolutionary pressures that may have caused the spread of these mutations.[15] This variant of the gene is thought to contribute to increased brain volume.[16] Modern distributions of chromosomes bearing the ancestral forms of MCPH1 and ASPM are correlated with the incidence of tonal languages, but the nature of this relationship is far from clear.[17]

Haplogroup D 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.[14] 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.[18][19]

ControversyEdit

The research results[clarification needed] began to attract considerable controversy 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."[20] 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.[21][22]

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".[23] However, a later study by Rimol et al.[12] 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 regions, and allowed for separate effects for males and females.

Model organismsEdit

Model organisms have been used in the study of MCPH1 function. A conditional knockout mouse line, called Mcph1tm1a(EUCOMM)Wtsi[30][31] was generated as part of the International Knockout Mouse Consortium program — a high-throughput mutagenesis project to generate and distribute animal models of disease to interested scientists.[32][33][34]

Male and female animals underwent a standardized phenotypic screen to determine the effects of deletion.[28][35] Twenty four tests were carried out on mutant mice and six significant abnormalities were observed.[28] Homozygous mutant animals were infertile, did not have a pinna reflex, had a moderate degree of hearing impairment, abnormal cornea morphology, lens morphology and cataracts, and displayed chromosomal instability in a micronucleus test.[28]

Family membersEdit

In addition to MCPH1 the other five family members are: MCPH2, CDK5RAP2, MCPH4, ASPM and CENPJ.

See alsoEdit

ReferencesEdit

  1. ^ a b c ENSG00000285262 GRCh38: Ensembl release 89: ENSG00000147316, ENSG00000285262 - Ensembl, May 2017
  2. ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000039842 - Ensembl, May 2017
  3. ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. ^ Jackson AP, Eastwood H, Bell SM, Adu J, Toomes C, Carr IM, et al. (July 2002). "Identification of microcephalin, a protein implicated in determining the size of the human brain". American Journal of Human Genetics. 71 (1): 136–42. doi:10.1086/341283. PMC 419993. PMID 12046007.
  6. ^ Online Mendelian Inheritance in Man (OMIM) 251200
  7. ^ Jackson AP, McHale DP, Campbell DA, Jafri H, Rashid Y, Mannan J, et al. (August 1998). "Primary autosomal recessive microcephaly (MCPH1) maps to chromosome 8p22-pter". American Journal of Human Genetics. 63 (2): 541–6. doi:10.1086/301966. PMC 1377307. PMID 9683597.
  8. ^ Wang YQ, Su B (June 2004). "Molecular evolution of microcephalin, a gene determining human brain size". Human Molecular Genetics. 13 (11): 1131–7. doi:10.1093/hmg/ddh127. PMID 15056608.
  9. ^ Evans PD, Anderson JR, Vallender EJ, Choi SS, Lahn BT (June 2004). "Reconstructing the evolutionary history of microcephalin, a gene controlling human brain size". Human Molecular Genetics. 13 (11): 1139–45. doi:10.1093/hmg/ddh126. PMID 15056607.
  10. ^ Woods RP, Freimer NB, De Young JA, Fears SC, Sicotte NL, Service SK, Valentino DJ, Toga AW, Mazziotta JC (June 2006). "Normal variants of Microcephalin and ASPM do not account for brain size variability". Human Molecular Genetics. 15 (12): 2025–9. doi:10.1093/hmg/ddl126. PMID 16687438.
  11. ^ Rushton JP, Vernon PA, Bons TA (April 2007). "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. doi:10.1098/rsbl.2006.0586. PMC 2104484. PMID 17251122.
  12. ^ a b Rimol LM, Agartz I, Djurovic S, Brown AA, Roddey JC, Kähler AK, Mattingsdal M, Athanasiu L, Joyner AH, Schork NJ, Halgren E, Sundet K, Melle I, Dale AM, Andreassen OA (January 2010). "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. Bibcode:2010PNAS..107..384R. doi:10.1073/pnas.0908454107. JSTOR 40536283. PMC 2806758. PMID 20080800.
  13. ^ Evans PD, Gilbert SL, Mekel-Bobrov N, Vallender EJ, Anderson JR, Vaez-Azizi LM, Tishkoff SA, Hudson RR, Lahn BT (September 2005). "Microcephalin, a gene regulating brain size, continues to evolve adaptively in humans". Science. 309 (5741): 1717–20. Bibcode:2005Sci...309.1717E. doi:10.1126/science.1113722. PMID 16151009. Lay summaryThe New York Times (September 8, 2005).
  14. ^ a b Evans PD, Mekel-Bobrov N, Vallender EJ, Hudson RR, Lahn BT (November 2006). "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. Bibcode:2006PNAS..10318178E. doi:10.1073/pnas.0606966103. JSTOR 30051829. PMC 1635020. PMID 17090677.
  15. ^ Mekel-Bobrov N, Posthuma D, Gilbert SL, Lind P, Gosso MF, Luciano M, et al. (March 2007). "The ongoing adaptive evolution of ASPM and Microcephalin is not explained by increased intelligence". Human Molecular Genetics. 16 (6): 600–8. doi:10.1093/hmg/ddl487. PMID 17220170.
  16. ^ Lari M, Rizzi E, Milani L, Corti G, Balsamo C, Vai S, Catalano G, Pilli E, Longo L, Condemi S, Giunti P, Hänni C, De Bellis G, Orlando L, Barbujani G, Caramelli D (May 2010). "The microcephalin ancestral allele in a Neanderthal individual". PLOS ONE. 5 (5): e10648. Bibcode:2010PLoSO...510648L. doi:10.1371/journal.pone.0010648. PMC 2871044. PMID 20498832.
  17. ^ Dediu D, Ladd DR (June 2007). "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. Bibcode:2007PNAS..10410944D. doi:10.1073/pnas.0610848104. JSTOR 25436044. PMC 1904158. PMID 17537923.
  18. ^ Pennisi E (February 2009). "Neandertal genomics. Tales of a prehistoric human genome". Science. 323 (5916): 866–71. doi:10.1126/science.323.5916.866. PMID 19213888.
  19. ^ Green RE, Krause J, Briggs AW, Maricic T, Stenzel U, Kircher M, et al. (May 2010). "A draft sequence of the Neandertal genome". Science. 328 (5979): 710–722. Bibcode:2010Sci...328..710G. doi:10.1126/science.1188021. PMC 5100745. PMID 20448178.
  20. ^ Derbyshire J (November 2005). "The specter of difference". National Review. Retrieved 2008-09-21.
  21. ^ Regalado A (June 2006). "Scientist's Study Of Brain Genes Sparks a Backlash". The Wall Street Journal.
  22. ^ Balter M (December 2006). "Bruce Lahn profile. Brain man makes waves with claims of recent human evolution". Science. 314 (5807): 1871–3. doi:10.1126/science.314.5807.1871. PMID 17185582.
  23. ^ Timpson N, Heron J, Smith GD, Enard W (August 2007). "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. Bibcode:2007Sci...317.1036T. doi:10.1126/science.1141705. PMID 17717170.
  24. ^ "Neurological assessment data for Mcph1". Wellcome Trust Sanger Institute.
  25. ^ "Eye morphology data for Mcph1". Wellcome Trust Sanger Institute.
  26. ^ "Salmonella infection data for Mcph1". Wellcome Trust Sanger Institute.
  27. ^ "Citrobacter infection data for Mcph1". Wellcome Trust Sanger Institute.
  28. ^ a b c d Gerdin, AK (2010). "The Sanger Mouse Genetics Programme: High throughput characterisation of knockout mice". Acta Ophthalmologica. 88: 0. doi:10.1111/j.1755-3768.2010.4142.x.
  29. ^ Mouse Resources Portal, Wellcome Trust Sanger Institute.
  30. ^ "International Knockout Mouse Consortium".
  31. ^ "Mouse Genome Informatics".
  32. ^ Skarnes WC, Rosen B, West AP, Koutsourakis M, Bushell W, Iyer V, Mujica AO, Thomas M, Harrow J, Cox T, Jackson D, Severin J, Biggs P, Fu J, Nefedov M, de Jong PJ, Stewart AF, Bradley A (June 2011). "A conditional knockout resource for the genome-wide study of mouse gene function". Nature. 474 (7351): 337–42. doi:10.1038/nature10163. PMC 3572410. PMID 21677750.
  33. ^ Dolgin E (June 2011). "Mouse library set to be knockout". Nature. 474 (7351): 262–3. doi:10.1038/474262a. PMID 21677718.
  34. ^ Collins FS, Rossant J, Wurst W (January 2007). "A mouse for all reasons". Cell. 128 (1): 9–13. doi:10.1016/j.cell.2006.12.018. PMID 17218247.
  35. ^ van der Weyden L, White JK, Adams DJ, Logan DW (June 2011). "The mouse genetics toolkit: revealing function and mechanism". Genome Biology. 12 (6): 224. doi:10.1186/gb-2011-12-6-224. PMC 3218837. PMID 21722353.

Further readingEdit

  • Xu X, Lee J, Stern DF (August 2004). "Microcephalin is a DNA damage response protein involved in regulation of CHK1 and BRCA1". The Journal of Biological Chemistry. 279 (33): 34091–4. doi:10.1074/jbc.C400139200. PMID 15220350.
  • Wang YQ, Su B (June 2004). "Molecular evolution of microcephalin, a gene determining human brain size". Human Molecular Genetics. 13 (11): 1131–7. doi:10.1093/hmg/ddh127. PMID 15056608.
  • Bates TC, Luciano M, Lind PA, Wright MJ, Montgomery GW, Martin NG (2008). "Recently-derived variants of brain-size genes ASPM, MCPH1, CDK5RAP and BRCA1 not associated with general cognition, reading or language". Intelligence. 36 (6): 689–93. doi:10.1016/j.intell.2008.04.001.
  • Passemard S, Kaindl AM, Titomanlio L, Gerard B, Gressens P, Verloes A (1993). "Primary Autosomal Recessive Microcephaly". In Pagon RA, Bird TD, Dolan CR, Stephens K, Adam MP (eds.). GeneReviews. PMID 20301772.

External linksEdit