to the persisting repression of a necessary gene. This can then lead to the expression or suppression of an undesired phenotype which may affect the normal functionality of certain systems in the organism. Among the many silencer elements and proteins, REST/NSRF is an important silencer factor that has a variety of impacts, not only in neural aspects of development. In fact, in many cases, REST/NSRF acts in conjunction with RE-1/NRSE to repress and influence non-neuronal cells. Its effects range from frogs (Xenopus laevis) to humans, with innumerous effects in phenotype and also in development. In Xenopus laevis, REST/NRSF malfunction or damage has been associated to abnormal ectodermal patterning during development and significant consequences in neural tube, cranial ganglia, and eye development. In humans, a deficiency in the REST/NSRF silencer element has been correlated to Huntington's disease due to the decrease in the transcription of BDNF. Furthermore, ongoing studies indicate that NRSE is involved in the regulation of the ANP gene, which when over expressed, can lead to ventricular hypertrophy. Mutations in the Polycomb-group (PcG) complexes also presented significant modifications in physiological systems of organisms. Hence, modification in silencer elements and sequences can result in either devastating or unnoticeable changes. REST/NRSF in Xenopus laevis The effects and influences of RE1/NRSE and REST/NRSF are significant in non-neuronal cells that require the repression or silencing of neuronal genes. These silencer elements also regulate the expression of genes that do not induce neuron-specific proteins and studies have shown the extensive impact these factors have in cellular processes. In Xenopus laevis, RE1/NRSE and REST/NRSF dysfunction or mutation demonstrated significant impact on neural tube, cranial ganglia, and eye development. All of these alterations can be traced to an improper patterning of the ectoderm during Xenopus development. Thus, a mutation or alteration in either the silencing region RE1/NRSE or silencer REST/NRSF factor can disrupt the proper differentiation and specification of the neuroepithelial domain and also hinder the formation of skin or ectoderm. The lack of these factors result in a decreased production of bone morphogenetic protein (BMP), which translates into a deficient development of the neural crest. Hence, the effects of NRSE and NRSF are of fundamental importance for neurogenesis of the developing embryo, and also in the early stages of ectodermal patterning. Ultimately, inadequate functioning of these factors can result in aberrant neural tube, cranial ganglia, and eye development in Xenopus. REST/NSRF and Huntington's disease Huntington's