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.

Metabolic strategy of macrophages under homeostasis or immune stress in Drosophila

Macrophages are well known for their phagocytic functions in innate immunity across species.In mammals,they rapidly consume a large amount of energy by shifting their metabolism from mitochondrial oxidative phosphorylation toward aerobic glycolysis,to perform the effective bactericidal function upon infection.Meanwhile,they strive for sufficient energy resources by restricting systemic metabolism.In contrast,under nutrient deprivation,the macrophage population is down-regulated to save energy for survival.Drosophila melanogaster possesses a highly conserved and comparatively simple innate immune system.Intriguingly,recent studies have shown that Drosophila plasmatocytes,the macrophage-like blood cells,adopt comparable metabolic remodeling and signaling pathways to achieve energy reassignment when challenged by pathogens,indicating the conservation of such metabolic strategies between insects and mammals.Here,focusing on Drosophila macrophages(plasmatocytes),we review recent advances regarding their comprehensive roles in local or systemic metabolism under homeostasis or stress,emphasizing macrophages as critical players in the crosstalk between the immune system and organic metabolism from a Drosophila perspective.