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چکیده
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Genomic imprinting is a phenomenon in which expression of a gene depends on whether it is inherited from the male or the female parent. Approximately one hundred imprinted genes have been identified in mice with many more predicted to be present. Imprinted genes found in mice are often used as candidates for investigating imprinted genes in other mammals. In mammals, most known imprinted genes are organized into clusters that share common ICRs to direct the parent specific regulation of multiple genes within the cluster. Epigenetic modifiers of gene expression such as DNA methylation, histone modification, non-RNA, and higher-order chromatin formation act within ICRs to establish and maintain the imprinted state. Just after fertilization, a global demethylation event occurs in the zygote, first in the paternal pronucleus, followed by the maternal pronucleus. Imprinting established during gametogenesis must resist this demethylation process. Remethylation of the diploid genome occurs post-implantation and sets secondary imprints that are maintained for the life of the individual. Imprinted regions are effectively haploid, which makes them vulnerable to recessive mutations and epigenetic changes. Many developmental disorders and human diseases are linked to imprinted genes. These genes are often involved in cancer pathogenesis such as neuroblastoma (maternal chromosome 1p36 and paternal chromosome 2), acute myeblastic leukemia (paternal chromosome 7), Wilms’ tumour (maternal chromosome 11p15.5).Some complex behavioral traits including maternal care ,reactivity to novel environments ,social dominance ,and memory consolidation also seem to have an imprinted component . Patients with Turner syndrome show differences in cognitive skills depending on the parental origin of the remaining X-chromosome.Neurological defects can have an influence on growth by changed hormone levels and on behavior. Prader–Willi syndrome / Angelman syndrome are related to neurological functions. Research on genomic imprinting help to develop better diagnostic tools and biomedical treatment of imprinting diseases and certainly contribute to our understanding of the impact of epigenetic mechanisms for human diseases in general.
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