Like “Joe the Plumber” (whose real name is Samuel), CNTNAP2 (whose real name is CASPR2) has achieved a bit of fame lately. While recently appearing almost everywhere (here, here, here) except FOX News, CNTNAP2 (not Joe the Plumber) is apparently a transcriptional target of the infamous FOXP2 “language gene” – so says Sonja C. Vernes & colleagues [doi: 10.1056/NEJMoa0802828] who precipitated DNA-protein complexes using anti-FOXP2 antibodies from a cell line transiently expressing FOXP2. The team later evaluated measures of expressive and receptive language abilities and nonsense-word repetition and found that a series of snps – most significantly rs17236239 – were associated with performance of children from a consortium of families at risk for language impairment. This adds to several previous reports of CNTNAP2 and risk for autism, a disorder where language ability is severely impaired.
So what’s all the fuss ? How can something so insignificant (rs17236239 not Joe the Plumber) stir up so much trouble ? Well, as reported in a previous post, the expression of CNTNAP2 in the developing superior temporal cortex may be a relevant clue since this brain region is activated by language tasks. Also, this gene encodes a rather massive protein which (as reported by Coman et al.,) seems to participate in the establishment of myelination and “nodes” that permit rapid neural transmission and long-range coordination across neural structures in the brain. Interestingly, this gene shows evidence for recent positive selection in humans (as posted on here and here) although the newly derived G-allele at rs17236239 seems to be the allele that is causing the language difficulties. My own 23andMe profile shows a middling A/G here which makes it slightly hard to recall and repeat “Samuel Wurzelbacher”.
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Image via Wikipedia The evolution of language sometimes seems like a sort of jewel in the evolutionary crown of homo sapiens. Evidence of positive selection in the verbal dyspraxia FOXP2 gene, is often discussed with amazement and a reverential tone befitting this special evolutionary achievement. Enter the humble zebra finch – who’s songs and language articulation could teach Sinatra a thing or two. Haesler and colleagues use short-hairpin RNAs to interfere with the zebra finch homolog of FOXP2 in a brain area known as ‘area x’ (functionally equivalent to the human striatum) where the gene is upregulated during the late summer when males must belt out their best version of Strangers in the Night to woo the females. In their paper, “Incomplete and Inaccurate Vocal Imitation after Knockdown of FoxP2 in Songbird Basal Ganglia Nucleus Area X“, (DOI) the research team finds that young zebra finches with lower expression of FOXP2 have difficulty learning new songs and are less able to articulate specific sounds and lyrical blurbs. These difficulties are much like the difficulties experienced by human children who carry mutations in FOXP2.
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Image by wallyg via Flickr Can you say this 5 times quickly, “secreted sushi containing SRPX2 as a source of sylvian seizures seems like a spandrel” ? Well, if you can, you might say thanks to your FOXP2 gene (much ado recently), but of course its important to say thanks to so many other co-evolutionary substitutions. A recent article by Royer et al. (doi:10.1186/1471-2156-8-72) examines the recent evolution of the SRPX2 gene and found an R75K change that marks a human-primate split and also occurs in an important functional loop of the first sushi domain of SRPX2 (one that carries a mutation that is responsible for sylvian seizures involving oral and speech dyspraxia). Although they did not find evidence for positive selection, its easy to suspect that Lysine-75 plays an important supporting role in our tongue-twisting skills.
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