Making Meaningful Decisions for Life: Epigenetic Monoallelic Gene Expression in Mammals

Monoallelic gene expression or allelic exclusion, once known to be restricted to random X chromosome inactivation in female mammals, seems to be more common than thought with crucial effects in embryonic development, apparently as a way to increase the repertoire of variations in gene expression patterns. Monoallelic expression of immunoglubin genes and T-cell receptors is responsible for huge diversity of antibody production and antigen recognition, respectively, through DNA rearrangements. However, other patterns of monoallecic gene expression all come in effect via epigenetic mechanisms employ on similar genetic backgrounds. Among these phenomena, mammalian X chromosome inactivation in female tissues and the parent-specific genomic imprinting considered as classic paradigms for epigenetic gene regulation. While Xchromosome inactivation occurs via “random choice”, however, genomic imprinting exhibits a deterministic choice for the expression/repression of the respective genes through a parent- of- origin specific pattern during gametogenesis. Interestingly, X chromosome inactivation shows both patterns of random choice in mammalian somatic tissues, the paternally imprinted form of X chromosome inactivation occurs in marsupials, and also in rodents and human placentas. The last category encompasses stochastic allelic exclusion of a plethora of different autosomal genes, including genes for odor sensing in olfactory sensory neurons, as it seems the rule of one neuron-one receptor gene is essential for odor perception. All kind of epigenetic monollelic gene expression share similar epigenetic signatures, including the expression of long noncoding RNAs, DNA methylation and extensive chromatin modifications, polycomb protein bindings, etc. Also, their organization along the genome and mechanisms involved show considerable parallels. In current lecture, along with a brief introduction of various instances of epigenetic allelic exclusion, its various roles in growth and development ofembryos and its some evolutionary implications are discussed.

کلیدواژه ها:

Allelic exclusion ، Monoallelic gene expression ، X-chromosome inactivation ، Genomic imprinting ، olfactory receptor genes