Table 1 Summary of the location, function and expression patterns of the human genes in this study.
From: Origin and evolution of candidate mental retardation genes on the human X chromosome (MRX)
Locus symbol | Gene name | Human location | Proposed function | Expression in human and/or mouse | reference |
|---|---|---|---|---|---|
RSK2 (RPS6KA3) | ribosomal S6 kinase 2 | Xp22.2 (XAR) | Serine threonine protein kinase that phosphorylates CREB and regulates histone H3 acetyltransferase, to play a role in long term memory | Expressed widely, but only at low levels in foetal and adult tissues; is concentrated in the adult brain, skeletal muscle and heart | [24–26] |
ARX | Aristaless-related homeobox gene | Xp22 (XAR) | Transcription factor with a role in neuronal proliferation and differentiation | Restricted to embryonic brain in human, but also found in mouse testis. Widespread strong expression in the adult heart, skeletal muscle, kidney and liver, no expression in the brain. | [27–30] |
TSPAN7 (TM4SF2) | tetraspanin 7 | Xp11.4 (XAR) | Modulates integrin-mediated signalling, to play a role in neurite outgrowth and synapse formation | Ubiquitous in foetus and adult | [31] |
SREB3 (GPR173) | Super conserved receptor expressed in the brain | Xp11.22 (XCR) | G- protein coupled receptor, role in MRX unknown | Restricted to brain and ovary with low levels detectable in the small intestine | [32, 33] |
JARID1C (SMCX) | Jumonji AT-rich interactive domain 1C | Xp11.22 (XCR) | Role in chromatin remodelling by regulating transcription | Widely expressed at different levels in different tissues. Strongest in adult brain and skeletal muscle. | [34] |
OPHN1 | Oligophrenin 1 | Xq12 (XCR) | Negatively regulates Rho-GTPase activity to affect formation and dismantling of the actin cytoskeleton and control of neurite growth | Ubiquitous in foetus, restricted to central and peripheral neuronal tissues in the adult | [35–37] |
RSK4 (RPS6KA6) | ribosomal S6 kinase 4 | Xq21 (XCR) | Serine threonine kinase with very high homology to RSK2, suggesting a role in normal cell proliferation and neuron differentiation | Widespread weak expression in adult, concentrated in the adult brain and kidney | [24, 38, 39] |
AGTR2 | angiotensin II receptor, type 2 | Xq22 (XCR) | Receptor protein with a role in central nervous system or cardiovascular function | Highly expressed in all developing foetal tissues, but adult expression only in brain, adrenal medulla, and atretic ovary | [40, 41] |
ARHGEF6 | rho guanine nucleotide exchange factor 6 | Xq26 (XCR) | activates Rho-GTPase activity to affect formation and dismantling of the actin cytoskeleton and control of neurite growth | Ubiquitous | [35, 42, 43] |
FMR1 | fragile X mental retardation 1 gene | Xq27.3 (XCR) | RNA-binding protein with roles in synaptic maturation and function, and in germ cell proliferation | Widely expressed in most adult and foetal tissues, highest in brain and the testis | [44–46] |
FMR2 | fragile site mental retardation 2 gene | Xq28 (XCR) | Nuclear transcriptional regulator with a role in learning and memory | Restricted to placenta and adult brain. | [47, 48]. |