Epigenetic Mechanisms Affecting Macronuclear Development in Paramecium and Tetrahymena

Abstract

Epigenetic inheritance includes all non-Mendelian inheritance, in fact any inheritance that does not arise from base changes. Ciliates, particularly Paramecium and Tetrahymena, undergo epigenetic changes to their macronuclei when they are formed at nuclear reorganization. Once set, however, they are reproduced in a constant fashion, except for allelic segregations, during vegetative fissions in Tetrahymena and certain life cycle changes in both Paramecium and Tetrahymena. This review is meant to be inclusive, discussing all the known cases of epigenetic changes in macronuclei. They involve virtually all traits. We find that these macronuclear changes are subject to a variety of modifications in the way that they are implemented. They constitute a major feature of ciliate genetics, probably because the separation of generative and vegetative functions to micronuclei and macronuclei makes such changes possible.

PAK Paradox: Paramecium Appears To Have More K + -Channel Genes than Humans

“…As reported in the Paramecium literature and in the two PAK genes previously analyzed (PAK1.1 and PAK1.2), IESs and introns have distinct features, and introns are retained during the development of the somatic nucleus (macronucleus) (28,30). Paramecium intron sequences that are spliced during mRNA maturation have a narrow size range (typically between 19 and 30 bp) and require the typical splicesome-type 5Ј-GT and AG-3Ј on the ends of the eliminated sequences (35).…”

Structure of the micronuclear α-tubulin gene in the phyllopharyngean ciliate Chilodonella uncinata : implications for the evolution of chromosomal processing

“…Although distinguishing between these hypotheses will require further fine-scale analyses of IESs at a variety of taxonomic levels, the second model is supported by increasing evidence that epigenetic phenomena underlie chromosomal rearrangements in ciliates (e.g. Preer, 2001;Fetzer et al, 2002;Mochizuki et al, 2002). If macronuclear development relies on epigenetic signals from the parental MAC, cisacting regulatory regions may evolve relatively quickly within and between ciliate classes.…”

Evolution of developmentally regulated genome rearrangements in eukaryotes

“…Consistent with this hypothesis is the demonstrated role of epigenetics in two of the three categories of DRGR. In the case of genomewide rearrangements, RNAi is involved in both chromosome fragmentation and IES excision in ciliates (Preer, 2000;Mochizuki et al, 2002). For example, in T. thermophila, both dicer homologs and small RNAs regulate the development of the macronuclear genome (Mochizuki et al, 2002).…”