Question

What are some unique characteristics of human brains, relative to other vertebrates? Identify three genetic changes in humans lead to these differences. What is the mechanism for each?

Answer 1

Human brain is extremely complex. There are innumerable changes and development occurring every moment which makes us different from other species. Some of such genes which leads to such differences are discussed below:

1. Human accelerated regions or HARs were identified as developmental enhancers in the brain .One of theHAR1 encodes a long noncoding RNA (lncRNA) . This RNA that is expressed specifically in the developing human neocortex(in Cajal-Retzius neurons) . Cajal-Retzius neurons produces reelin,it is a glycoprotein which is a large, secreted, extracellular matrix. The main function of reelin is to control processes of neuronal migration and positioning during the development of neocortex. Thus in short this unique expression pattern of this HAR plays an important role in regulating the shape or structure of cerebral cortex.

2. Human FOXP2 protein differs from other organism at some amino acid residue sites. When comparison is made between human and chimpanzees ,these amino acid changes are functionally important . Human and chimpanzee FOXP2 have different transcriptional targets, these targets are involved in the development of central nervous. Genes involved in branchial arch formation and craniofacial development, are also targets of Human-specific FOXP2, which required for spoken language. Thus the FOXP2 gene plays a key role in language and vocalization. This has allowed humans to understand and blend with the evolution of complex languages.

3. The SRGAP2 gene , i.e Slit-Robo Rho GTPase-activating protein 2 (SRGAP2) genes has an important role in gene duplication in brain evolution. This gene has different forms in different species, mice have only one form of the Srgap2 gene, but humans have four forms, one ancestral form (SRGAP2A), which is similar to mouse Srgap2, and three paralogs are human-specific (SRGAP2B, SRGAP2C, and SRGAP2D) . These are produced by incomplete segmental duplication.This gene is important for cerebral cortical development. The three human-specific paralogs are located in the human-lineage-specific loci 1q21.1 and 1p12, these loci contain a number of genes involved in neurodevelopment.

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