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Chunk of protein explains our big brains, study proposes

Chunk of protein explains our big brains, study proposes

Re­search­ers have found what they think is the key to un­der­stand­ing why the hu­man brain is larg­er and more com­plex than that of oth­er an­i­mals.

The hu­man brain, with its un­equaled cog­ni­tive ca­pa­city, has evolved rap­idly and dra­mat­ic­ally. “We wanted to know why,” said James Sike­la of the Uni­vers­ity of Col­o­rad­o School of Med­i­cine, who head­ed the team of sci­en­tists in the new stu­dy. “The size and cog­ni­tive ca­pa­city of the hu­man brain sets us apart. But how did that hap­pen?”

“This re­search in­di­cates that what drove the ev­o­lu­tion­ary ex­pan­sion of the hu­man brain may well be a spe­cif­ic un­it with­in a pro­tein - called a pro­tein do­main - that is far more nu­mer­ous in hu­mans than oth­er spe­cies.”

A pro­tein do­main is a part of a pro­tein that can re­ap­pear in iden­ti­cal form in many dif­fer­ent pro­teins. Pro­teins are the mo­le­cules that do much of the work that keep us func­tion­ing, and they are pro­duced in the body us­ing a blue­print set by genes.

The pro­tein do­main in ques­tion is called DUF1220. Hu­mans have more than 270 cop­ies of DUF1220 en­cod­ed in the ge­nome, far more than oth­er spe­cies. The clos­er a spe­cies is to hu­mans, the more cop­ies of DUF1220 show up. Chimps have the next high­est num­ber, 125. Go­ril­las have 99, mar­mosets 30 and mice just one.

“The one over-rid­ing theme that we saw re­peat­edly was that the more cop­ies of DUF1220 in the ge­nome, the big­ger the brain. And this held true wheth­er we looked at dif­fer­ent spe­cies or with­in the hu­man popula­t­ion,” Sikela said.

Sikela and his team al­so linked DUF1220 to brain dis­or­ders. They as­so­ci­at­ed low­er num­bers of DUF1220 with mi­cro­ceph­a­ly, in which the brain is too small; larg­er num­bers of the pro­tein do­main were as­so­ci­at­ed with mac­ro­ceph­a­ly, in which the brain is too large.

The find­ings were re­ported Aug. 16 in the on­line edi­tion of The Amer­i­can Jour­nal of Hu­man Ge­net­ics. The re­search­ers drew their con­clu­sions by com­par­ing ge­nome se­quences from hu­mans and oth­er an­i­mals as well as check­ing the DNA of peo­ple with mi­cro­cephaly and macro­cephaly and of a healthy group.

“The take-home mes­sage was that brain size may be to a large de­gree a mat­ter of pro­tein do­main dosage,” Sikela said. “This dis­cov­ery opens many new doors. It pro­vides new tools to di­ag­nose dis­eases re­lat­ed to brain size. And more broad­ly, it points to a new way to study the hu­man brain and its dra­mat­ic in­crease in size and abil­ity over what, in ev­o­lu­tion­ary terms, is a short amount of time.”


Source : http://www.world-science.net

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