Invasion by exogenous RNA:cellular defense strategies and implications for RNA inference

Exogenous RNA poses a continuous threat to genome stability and integrity across various organisms.Accumulating evidence reveals complex mechanisms underlying the cellular response to exogenous RNA,including endo-lysosomal degradation,RNA-dependent repression and innate immune clearance.Across a variety of mechanisms,the natural anti-sense RNAdependent defensive strategy has been utilized both as a powerful gene manipulation tool and gene therapy strategy named RNA-interference(RNAi).To optimize the efficiency of RNAi silencing,a comprehensive understanding of the whole life cycle of exogenous RNA,from cellular entry to its decay,is vital.In this paper,we review recent progress in comprehending the recognition and elimination of foreign RNA by cells,focusing on cellular entrance,intracellular transportation,and immune-inflammatory responses.By leveraging these insights,we highlight the potential implications of these insights for advancing RNA interference efficiency,underscore the need for future studies to elucidate the pathways and fates of various exogenous RNA forms,and provide foundational information for more efficient RNA delivery methods in both genetic manipulation and therapy in different organisms.

Timing and characteristics of nuclear events during conjugation and genomic exclusion in Paramecium multimicronucleatum

Ciliated protists are ideal material for studying the origin and evolution of sex,because of their nuclear dimorphism(containing both germline micronucleus and somatic macronucleus in the same cytoplasm),special sexual processes(conjugation and autogamy),and high diversity of mating-type systems.However,the study of sexual process is limited to only a few species,due to the difficulties in inducing or observing conjugation.In the present study,we investigate the conjugation process in Paramecium multimicronucleatum:(1)of the three prezygotic divisions,all micronuclei undergo the first two divisions(meiosis I,II),while a variable number of nuclei undergo the third division(mitosis);(2)the synkaryon divides three times after fertilization,giving rise to eight products that differentiate into four macronuclear anlagen and four micronuclei;(3)cells restore the vegetative stage after two successive cell fissions during which the macronuclear anlagen are distributed into daughter cells without division,while micronuclei divide mitotically;(4)the parental macronucleus begins to fragment following the first meiotic division and finally degenerates completely;(5)the entire process takes about 110 h,of which about 85 h are required for macronuclear development.In addition,we describe for the first time the process of genomic exclusion occurring between amicronucleate and micronucleate cells of P.multimicronucleatum,during which the micronucleate cell contributes a pronucleus to the amicronucleate cell,resulting in both exconjugants being homozygotes.These results provide new insights into the diversity of sexual processes and lay an important cytological basis for future in-depth studies of mating systems in ciliates.