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Transgenerational Sterility of Piwi Mutants Represents a Dynamic Form of Adult Reproductive Diapause.

ABSTRACT: Environmental stress can induce adult reproductive diapause, a state of developmental arrest that temporarily suspends reproduction. Deficiency for C. elegans Piwi protein PRG-1 results in strains that reproduce for many generations but then become sterile. We found that sterile-generation prg-1/Piwi mutants typically displayed pronounced germ cell atrophy as L4 larvae matured into 1-day-old adults. Atrophied germlines spontaneously reproliferated across the first days of adulthood, and this was accompanied by fertility for day 2-4 adults. Sterile day 5 prg-1 mutant adults remained sterile indefinitely, but providing an alternative food source could restore their fertility. Our data imply that late-generation prg-1 mutants experience a dynamic form of adult reproductive diapause, promoted by stress response, cell death, and RNAi pathways, where delayed fertility and reproductive quiescence represent parallel adaptive developmental outcomes. This may occur in response to a form of "heritable stress" that is transmitted by gametes and epigenetic in nature.

SUBMITTER: Heestand B

PROVIDER: S-EPMC5918633 | biostudies-literature | 2018 Apr

REPOSITORIES: biostudies-literature

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Transgenerational Sterility of Piwi Mutants Represents a Dynamic Form of Adult Reproductive Diapause.

Heestand Bree B Simon Matt M Frenk Stephen S Titov Denis D Ahmed Shawn S

Cell reports 20180401 1

Environmental stress can induce adult reproductive diapause, a state of developmental arrest that temporarily suspends reproduction. Deficiency for C. elegans Piwi protein PRG-1 results in strains that reproduce for many generations but then become sterile. We found that sterile-generation prg-1/Piwi mutants typically displayed pronounced germ cell atrophy as L4 larvae matured into 1-day-old adults. Atrophied germlines spontaneously reproliferated across the first days of adulthood, and this was ...[more]

PMID: 29617657

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Project description:Fluctuating environments threaten fertility and viability. To better match the immediate, local environment, many organisms adopt alternative phenotypic states, a phenomenon called "phenotypic plasticity." Natural populations that predictably encounter fluctuating environments tend to be more plastic than conspecific populations that encounter a constant environment, suggesting that phenotypic plasticity can be adaptive. Despite pervasive evidence of such "adaptive phenotypic plasticity," gene regulatory mechanisms underlying plasticity remains poorly understood. Here we test the hypothesis that environment-dependent phenotypic plasticity is mediated by epigenetic factors. To test this hypothesis, we exploit the adaptive reproductive arrest of Drosophila melanogaster females, called diapause. Using an inbred line from a natural population with high diapause plasticity, we demonstrate that diapause is determined epigenetically: only a subset of genetically identical individuals enter diapause and this diapause plasticity is epigenetically transmitted for at least three generations. Upon screening a suite of epigenetic marks, we discovered that the active histone marks H3K4me3 and H3K36me1 are depleted in diapausing ovaries. Using ovary-specific knockdown of histone mark writers and erasers, we demonstrate that H3K4me3 and H3K36me1 depletion promotes diapause. Given that diapause is highly polygenic, that is, distinct suites of alleles mediate diapause plasticity across distinct genotypes, we also investigated the potential for genetic variation in diapause-determining epigenetic marks. Specifically, we asked if these histone marks were similarly depleted in diapause of a genotypically distinct line. We found evidence of divergence in both the gene expression program and histone mark abundance. This study reveals chromatin determinants of phenotypic plasticity and suggests that these determinants may be genotype-dependent, offering new insight into how organisms may exploit and evolve epigenetic mechanisms to persist in fluctuating environments.

Project description:For many insects, diapause is the primary mechanism for surviving unfavorable seasons. Some aspects of diapause regulation are well known, but we still lack a mechanistic understanding of molecular mechanisms that control the diapause pathway. Accumulating evidence suggests microRNAs regulate diapause in evolutionarily diverse insect species including flesh flies and moths, and, it is likely that microRNAs regulate multiple characteristics of diapause, including arrested egg follicle development and fat hypertrophy, in females of the Northern house mosquito, Culex pipiens. To investigate microRNA regulation of diapause in this species, we measured changes in egg follicle development and total lipid content over 22 days following adult emergence. We also evaluated changes in the abundance of candidate microRNAs associated with these physical changes during the same time frame. We found egg follicle size and lipid content were nearly the same in diapausing and nondiapausing females on the day of adult emergence, and then diverged over time such that by day 22 diapausing females had significantly smaller egg follicles and higher total lipids than their nondiapausing counterparts. Several microRNAs associated with lipid metabolism in insects, including miR-14-3p, miR-277-3p, and miR-305-5p, were underexpressed in diapausing females compared to nondiapausing females on the day of adult emergence, which suggests microRNA regulation occurs ahead of observed changes in these two features of the diapause phenotype. We also found miR-309-3p, miR-375-3p which stimulate ovarian development in other mosquito species, were underexpressed in diapausing females of Cx. pipiens at times after diapause is fully established and may be responsible for the arrest in ovarian development in this species. Taken together, our results demonstrate that changes in the abundance of some microRNAs is associated with phenotypic changes in diapause Cx. pipiens and suggests this epigenetic mechanism is part of the molecular toolkit regulating diapause.

Dataset Information

Transgenerational Sterility of Piwi Mutants Represents a Dynamic Form of Adult Reproductive Diapause.

Publications

Transgenerational Sterility of Piwi Mutants Represents a Dynamic Form of Adult Reproductive Diapause.

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