[asa] Gene Mutation Linked to Cognition is Found Only In Humans

From: Rich Blinne <rich.blinne@gmail.com>
Date: Tue May 08 2007 - 08:24:52 EDT

Gene mutation linked to cognition is found only in
humans<http://www.eurekalert.org/pub_releases/2007-05/jws-gml050107.php>

The human and chimpanzee genomes vary by just 1.2 percent, yet there is a
considerable difference in the mental and linguistic capabilities between
the two species. A new study showed that a certain form of neuropsin, a
protein that plays a role in learning and memory, is expressed only in the
central nervous systems of humans and that it originated less than 5 million
years ago. The study, which also demonstrated the molecular mechanism that
creates this novel protein, will be published online in Human Mutation, the
official journal of the Human Genome Variation Society. The journal is
available online via Wiley InterScience at
http://www.interscience.wiley.com/journal/humanmutation.

Led by Dr. Bing Su of the Chinese Academy of Sciences in Kunming, China,
researchers analyzed the DNA of humans and several species of apes and
monkeys. Their previous work had shown that type II neuropsin, a longer form
of the protein, is not expressed in the prefrontal cortex (PFC) of lesser
apes and Old World monkeys. In the current study, they tested the expression
of type II in the PFC of two great ape species, chimpanzees and orangutans,
and found that it was not present. Since these two species diverged most
recently from human ancestors (about 5 and 14 million years ago
respectively), this finding demonstrates that type II is a human-specific
form that originated relatively recently, less than 5 million years ago.

Gene sequencing revealed a mutation specific to humans that triggers a
change in the splicing pattern of the neuropsin gene, creating a new
splicing site and a longer protein. Introducing this mutation into
chimpanzee DNA resulted in the creation of type II neuropsin. "Hence, the
human-specific mutation is not only necessary but also sufficient in
creating the novel splice form," the authors state.

The results also showed a weakening effect of a different, type I-specific
splicing site and a significant reduction in type I neuropsin expression in
human and chimpanzee when compared with the rhesus macaque, an Old World
monkey. This pattern suggests that before the emergence of the type II
splice form in human, the weakening of the type I splicing site already
existed in the common ancestor of humans and chimpanzees, implying a
multi-step process that led to the dramatic change of splicing pattern in
humans, the authors note. They identified a region of the chimpanzee
sequence that has a weakening effect on the splicing site that also probably
applies to humans. "It is likely that both the creation of novel splice form
and the weakening of the constitutive splicing contribute to the splicing
pattern changes during primate evolution, suggesting a multi-step process
eventually leading to the origin of the type II form in human," the authors
state.

They note that further studies should probe the biological function of type
II neuropsin in humans, as the extra 45 amino acids in this form may cause
protein structural and functional changes. They note that in order to
understand the genetic basis that underlies the traits that set humans apart
from nonhuman primates, recent studies have focused on identifying genes
that have been positively selected during human evolution. They conclude,
"The present results underscore the potential importance of the creation of
novel splicing forms in the central nervous system in the emergence of human
cognition."
###

Article: "A Human-Specific Mutation Leads to the Origin of a Novel Splice
Form of Neuropsin (KLK8), a Gene Involved in Learning and Memory," Zhi-xiang
Lu, Jia Peng, Bing Su, Human Mutation; May 2007; (DOI: 10.1002/humu.20547).

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Received on Tue May 8 08:25:37 2007

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