SIGLEC11 (sialic acid binding Ig-like lectin 11)

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The gene encoding Siglec-11 underwent a human specific gene conversion event involving an adjacent pseudogene, resulting in a new amino-terminal sequence and promoter region. This resulted in the first reported "human-specific" protein. A consequence of this event was a significant change in the binding properties of the molecule, along with new expression in the microglia of the brain. The gene conversion event involved a small part of the 5' untranslated sequences of SIGLEC11. Studies are underway to determine if this could explain the new expression in microglia seen only in humans. The significance of this event for human brain evolution is unknown at this time. It is also of interest that microglia are prominent apparently human-specific diseases such as Alzheimer's diesease and AIDS associated dementia.  In this regard, it is interesting that SIglec-11 is capable of suppressing inflammatory responses in microglia.  The recent discovery of a paired activating receptor (Siglec-16) present only in some humans further complicates the picture.

Timing

Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Possible Appearance (Lineage Separation Event): 
Probable Appearance (Lineage Separation Event): 
Definite Appearance (Lineage Separation Event): 
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Genetics Topic Attributes
Gene symbols follow the HUGO Gene Nomenclature Committee standard.
Gene Symbol Type of Human-Specific Changes
SIGLEC11 Amino Acid Change, Gene Conversion, Expression Pattern Change

References

  1. Evolution of siglec-11 and siglec-16 genes in hominins, Wang, X., Mitra N., Cruz P., Deng L., Program Nisc Comparativ, Varki N., Angata T., Green E. D., Mullikin J., Hayakawa T., et al. , Mol Biol Evol, Aug, Volume 29, Number 8, p.2073-86, (2012)
  2. A human-specific gene in microglia., Hayakawa, Toshiyuki, Angata Takashi, Lewis Amanda L., Mikkelsen Tarjei S., Varki Nissi M., and Varki Ajit , Science, 2005 Sep 9, Volume 309, Issue 5741, p.1693, (2005)