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Science 9 September 2005:
Vol. 309. no. 5741, p. 1693
DOI: 10.1126/science.1114321
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Brevia

A Human-Specific Gene in Microglia

Toshiyuki Hayakawa,1,2* Takashi Angata,1,2*{dagger} Amanda L. Lewis,1,3 Tarjei S. Mikkelsen,6 Nissi M. Varki,1,4 Ajit Varki1,2,5{ddagger}

Recent studies have shown multiple differences between humans and apes in sialic acid (Sia) biology, including Siglecs (Sia-recognizing-Ig-superfamily lectins). Comparisons with the chimpanzee genome indicate that human SIGLEC11 emerged through human-specific gene conversion by an adjacent pseudogene. Conversion involved 5¢ untranslated sequences and the Sia-recognition domain. This human protein shows reduced binding relative to the ancestral form but recognizes oligosialic acids, which are enriched in the brain. SIGLEC11 is expressed in human but not in chimpanzee brain microglia. Further studies will determine if this event was related to the evolution of Homo.

1 Glycobiology Research and Training Center, University of California at San Diego, La Jolla, CA 92093, USA.
2 Department of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, CA 92093, USA.
3 Department of Biological Sciences, University of California at San Diego, La Jolla, CA 92093, USA.
4 Department of Pathology, University of California at San Diego, La Jolla, CA 92093, USA.
5 Department of Medicine, University of California at San Diego, La Jolla, CA 92093, USA.
6 Broad Institute of the Massachusetts Institute of Technology and Harvard University, Cambridge, MA 02141, USA.

* These authors contributed equally to this work.

{dagger} Present Address: Research Center for Glycoscience, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan.

{ddagger} To whom correspondence should be addressed. E-mail: a1varki{at}ucsd.edu

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Comparing the human and chimpanzee genomes: Searching for needles in a haystack.
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