Sunday, 27 May 2012

Programming Speech into the Human Genome


By Henry North (42935559)


The genes associated with speech – an ability exclusive to our species – are one of the great mysteries of the human genome. However, ten years ago a race to find a ‘language gene’ was sparked by an article published in Nature, looking at genes associated with chronic language-based disorders (Lai 2001). More significant findings have been made in recent years through research aimed at identifying this genetic factor (FOXP2), allowing geneticists to start looking into how evolution has programmed speech into our genome. The gene’s initial discovery paved the way for this new research.

In 1991, a genetic mutation that induced several severe speech disorders was identified in three generations of a London family referred to as KE.  This case was unusual; the disorders were the result of a mutation of just one gene (Macandrew 2003). The specific effects of the mutation were complex, affecting both facial muscle control and speech-associated neuronal processes (Cheuy 2003; Markus & Fisher 2003). Years later, brain scans of language-related cortical regions confirmed this (Copp et al. 2005). The effect on so many bodily functions associated with speech by the mutation of a single gene suggested that this gene was fundamental to our ability to communicate.

Using DNA samples taken from individuals with this specific disability (including the KE family), geneticists looked for re-occurring ‘markers’ –stretches of DNA that were common to all the affected individuals (Markus & Fisher 2003). On chromosome seven, locus 7q31, the FOXP2 gene was identified as the damaged gene (Cheuy 2007). The FOXP2 gene produces proteins that contain forkhead-box domains (or FOX proteins) through transcription and translation (Markus & Fisher 2003). FOX proteins are part of a group of transcription factors; regulatory proteins that bind to DNA and affect the transcription of specific genes (Reece et al. 2012).  Thus, the FOXP2 gene codes for a transcription factor that, in turn, affects the expression of many other genes involved with human speech. 




Fig. 1 (a) & (b) Geneticists looked at the KE family, using a QTL technique to identify 'markers', thus pinpointing the loci at which the mutation was occurring (Source: Marcus & Fisher, 2006). 



Fig. 2 An illustration of a generic transcription factor and its significance to the genome (source: Myers, 2006). 

Once the gene was identified, its evolutionary origins could be determined. FOXP2 is found in all animals and fungi - just two amino acids distinguish the human protein from the rodent version (Wade 2009). This is not to suggest that this difference is insignificant; two separate studies replaced gorilla and rodent FOXP2 genes with the human version, observing remarkable cellular and behavioural changes in test subjects (Markus & Fisher 2003; Genevive 2009).Genomic comparisons imply recent, rapid evolution of the human gene – likely because of the numerous advantages that speech provided early humans with (Enard et al. 2003). Interestingly, a mathematical analysis of the human and rodent versions of the FOXP2 gene suggests that the gene became fixed in the human genome around 200, 000 years ago – coinciding with estimates made by archaeologists regarding the first human languages (Markus & Fisher 2003).

Discovering the significance of the FOXP2 gene in a study of the KE family allowed further investigation into the genetics of human speech, though researchers insist that there is still much to learn (Trivedi 2004). It is important not to overestimate the role of FOXP2 as some journalists have done, deeming it ‘the language gene’; many undiscovered genes may play a role in providing the requirements for language (Enard 2001). Nonetheless, FOXP2 is clearly one of the most significant genes involved with speech, a behaviour that in many ways defines our species. 

Bibliography


Cheuy, D 2003, FOXP2, Department of Biology, Davidson College, viewed 18 March 2012 <http://www.bio.davidson.edu/courses/genomics/2003/cheuy/FOXP2.html>

Copp et al. 2005, ‘FOXP2 and the neuroanatomy of speech and language’, Nature Reviews neuroscience, vol. 6, no. 131-138, viewed 19 March 2012 <http://www.nature.com/nrn/journal/v6/n2/abs/nrn1605.html>

Enard, W et al. ‘Molecular evolution of FOXP2, a gene involved in speech and language’, Nature, vol. 418, no. 869-872, viewed 18 March <http://www.nature.com/nature/journal/v418/n6900/abs/nature01025.html>

Genevieve, K et al. 2009, ‘Human-specific transcriptional regulation of CNS development genes by FOXP2’, Nature, vol. 462, no. 213-217, viewed 18 march 2012 <http://www.nature.com/nature/journal/v462/n7270/abs/nature08549.html>

Lai, et al. 2001 A novel forkhead-domain gene is mutated in a severe speech and language disorder’, Nature, vol. 413, no. 519-523, viewed 18 March 2012 <http://eprints.ucl.ac.uk/4219/>

Macandrew, A 2003, FOXP2 and the Evolution of Language, viewed 18 March 2012 <http://www.evolutionpages.com/FOXP2_language.htm>

Markus, GF & Fisher, SE 2003, FOXP2 in focus: what can genes tell us about speech and language? Cell press, Massachusetts Institute of Technology, viewed 18 March 2012 <http://www.ai.mit.edu/projects/dm/foxp2.pdf>

Reece, JB et al. 2012, Campbell Biology, Pearson Australia, Sydney.

Trivedi, VP 2004, Scientists Identify a Language Gene, National Geographic, viewed 18 March 2012 <http://news.nationalgeographic.com/news/2001/10/1004_TVlanguagegene.html>

Wade, N 2009, Speech Gene Shows Its Bossy Nature, New York Times, viewed 18 March 2012 <http://www.nytimes.com/2009/11/12/science/12gene.html>

Images 

Myers, P, 2006, Transcription factors and morphogens, Pharyngula, viewed 20 March 2012. <http://scienceblogs.com/pharyngula/2006/07/transcription_factors_and_morp.php>

Markus, GF & Fisher, SE 2003, FOXP2 in focus: what can genes tell us about speech and language? Cell press, Massachusetts Institute of Technology, viewed 18 March 2012 <http://www.ai.mit.edu/projects/dm/foxp2.pdf>
 


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