PLoS Genetics最新文献

[This corrects the article DOI: 10.1371/journal.pgen.1011799.].

Reproduction and immunity are energy intensive processes that often compete for resources, leading to trade-offs across species. Lipid metabolism integrates these processes, particularly during stressful conditions such as pathogenic infections, yet the underlying molecular mechanisms remain poorly understood. TCER-1, the C. elegans homolog of mammalian TCERG1, suppresses immunity and promotes fertility, especially upon maternal infection. Here, we show that TCER-1 coordinates this balance by regulating two conserved lysosomal lipases, lipl-1 and lipl-2. Using transcriptomic, lipidomic, and molecular-genetic analyses, we demonstrate that both lipases mediate infection-induced lipid remodeling but with distinct outcomes: lipl-1 promotes immunity, whereas, lipl-2 does not. LIPL-1 catalyzes the accumulation of specific ceramide species, including Cer 17:1;O2/24:0, whose supplementation rescues the immunity phenotypes of tcer-1;lipl-1 mutants and enhances post-infection survival of wild-type animals. Both lipases influence fertility with lipl-2 playing a key role in maintaining embryonic-eggshell integrity during maternal infection and aging. Remarkably, expression of human lysosomal acid lipase (hLAL/LIPA), the ortholog of 'lipl' genes, restores immunity defects triggered by lipl-1 loss and enhances immune resilience but does not significantly ameliorate the fertility defects. Together, these findings reveal distinct roles for lipl-1 and lipl-2 in modulating lipid species that link immune defense, reproductive fitness and healthspan through a potentially conserved mechanism.

The cryptochrome-photolyase family, a highly conserved set of flavoproteins, mediates many direct and indirect responses to sunlight. While the photolyases are light-dependent enzymes which catalyze photoreactivation repair of UV-induced DNA damage, the cryptochromes serve as circadian clock components and photoreceptors. Do DNA repair and circadian clock functions overlap in these flavoproteins? While 6-4 photolyase (6-4phr) is well-documented to repair UV-induced 6-4 photoproducts, we demonstrate that loss of 6-4phr function in fish cells and fin clips significantly attenuates circadian rhythms of period gene expression. Importantly, 6-4phr represses, as well as activates transcription directed by E-box and D-box enhancer elements respectively. Furthermore, we document physical interaction between 6-4phr and Clock1/Bmal1 at multiple domains which interferes with Clock1-Bmal1 heterodimerization. In addition, 6-4phr interacts with the D-box binding transcription factor, Tef. Thus, we reveal significant overlap between DNA repair and circadian clock functions in 6-4phr.

Enteroendocrine cells (EECs) of the intestinal epithelium are major regulators of metabolism and energy homeostasis. This is mainly due to their expression and secretion of enteroendocrine peptides (EEPs). These peptides serve as hormones that control many aspects of metabolic homeostasis including feeding behavior, intestinal contractions, and utilization of energy stores. Regulation of EEP production and release depends largely on EEC-exclusive G protein-coupled receptors (GPCRs) that sense nutrient levels. Here we report the characterization of a GPCR expressed principally in EECs, which we have named GulpR due to its role in the response to nutrient stress. We show that GulpR regulates transcription of the EEP Tachykinin (Tk) and that both GulpR and Tk are essential for the transcriptional response that promotes survival of nutrient limitation. Oral infection with V. cholerae also activates expression of GulpR, Tk, and lipid mobilization genes. However, Tk does not play a role in regulation of lipid mobilization genes during infection and does not impact survival. Our findings identify a role for GulpR and Tk in survival during starvation and suggest that, although starvation and infection result in significant mobilization of energy stores, the signal transduction systems that regulate the metabolic response to each are distinct.

DNA:RNA hybrids are unusual structures found throughout the genomes of many species, including yeast and mammals. While DNA:RNA hybrids may promote various cellular functions, persistent hybrids lead to double strand breaks, resulting in genomic instability. DNA:RNA hybrid formation and removal are therefore highly regulated, including by enzymes that either degrade or unwind RNA from the hybrid. Meiosis is the specialized cell division that creates haploid gametes for sexual reproduction. Previous work in yeast and mammals showed that elimination of DNA:RNA hybrids by RNase H facilitates meiotic recombination. This work demonstrates that the conserved Sen1 DNA/RNA helicase functions during three temporally distinct processes during yeast meiosis. First, SEN1 allows meiosis-specific genes to be expressed at the proper time to allow entry into meiosis. Second, SEN1 prevents the accumulation of hybrids during premeiotic DNA replication. Third, SEN1 promotes the repair of programmed meiotic double strand breaks that are necessary to form crossovers between homologous chromosomes to allow their proper segregation at the first meiotic division. Given the evolutionary conservation of Sen1 with its mammalian counterpart, Senataxin, studies of Sen1 function in yeast are likely to be informative about the regulation of DNA:RNA hybrids during human meiosis as well.

Elucidation of the complex mechanisms of action of antimicrobial peptides (AMPs) is critical for improving their efficacy. A major challenge in AMP research is distinguishing AMP effects resulting from various protein interactions from those caused by membrane disruption. Moreover, since AMPs often act in multiple cellular compartments, it is challenging to pinpoint where their distinct activities occur. Nodule-specific cysteine-rich (NCR) peptides secreted by some legumes, including NCR247, have evolved from AMPs to regulate differentiation of their nitrogen-fixing bacterial partner during symbiosis as well as to exert antimicrobial actions. At sub-lethal concentrations, NCR247 exhibits strikingly pleiotropic effects on Sinorhizobium meliloti. We used the L- and D-enantiomeric forms of NCR247 to distinguish between phenotypes resulting from stereospecific, protein-targeted interactions and those caused by non-specific interactions such as membrane disruption. In addition, we utilized an S. meliloti strain lacking BacA, a transporter that imports NCR peptides into the cytoplasm. The bacterial protein BacA, plays critical symbiotic roles by possibly reducing periplasmic peptide accumulation and fine-tuning symbiotic signaling. Use of the BacA-deficient strain made it possible to distinguish between phenotypes resulting from peptide interactions in the periplasm and those occurring in the cytoplasm. At high concentrations, both L- and D-NCR247 permeabilize bacterial membranes, consistent with nonspecific cationic AMP activity. In the cytoplasm, both NCR247 enantiomers sequester heme and trigger iron starvation in a chirality-independent but BacA-dependent manner. However, only L-NCR247 activates bacterial two-component systems via stereospecific periplasmic interactions. By combining stereochemistry and genetics, this work disentangles the spatial and molecular complexity of NCR247 action. This approach provides critical mechanistic insights into how host peptides with pleiotropic functions modulate bacterial physiology.

The cohesin complex is composed of core ring proteins (Smc1, Smc3 and Mcd1) and associated factors (Pds5, Scc3, and Rad61) that bind via Mcd1. Extrusion (looping from within a single DNA molecule) and cohesion (the tethering together of two different DNA molecules) underlie the many roles that cohesins play in chromosome segregation, gene transcription, DNA repair, chromosome condensation, replication fork progression, and genome organization. While cohesin functions flank the activities of critical cell checkpoints (including spindle assembly and DNA damage checkpoints), the extent to which checkpoints directly target cohesins, in response to aberrant cohesin function, remains unknown. Based on prior evidence that cells mutated for cohesin contain reduced Mcd1 protein, we tested whether loss of Mcd1 is based simply on cohesin instability or integrity. The results show that Mcd1 loss persists even in rad61 cells, which contain elevated levels of stable chromosome-bound cohesins, and also in scc2-4, which do not affect cohesin complex integrity. In fact, re-elevating Mcd1 levels suppresses the temperature-sensitive growth defects of all cohesin alleles tested, revealing that Mcd1 loss is a fundamental mechanism through which cohesins are inactivated to promote cell lethality. Our findings further reveal that cells that exhibit aberrant cohesin function employ E3 ligases (such as San1) to target Mcd1 for degradation. This mechanism of degradation appears unique in that Mcd1 is reduced during S phase, when Mcd1 levels typically peak and despite a dramatic upregulation in MCD1 transcription. We infer from these latter findings that cells contain a negative feedback mechanism used to maintain Mcd1 homeostasis.

Recent studies have linked compound heterozygous mutations in ASNA1 to progressive dilated cardiomyopathy and early infantile mortality in humans. However, the specific role of ASNA1 in cardiomyocytes and the molecular mechanisms underlying ASNA1-related cardiomyopathy remain poorly understood. Tail-anchored (TA) proteins, characterized by a single C-terminal transmembrane domain (TMD), require post-translational targeting to intracellular membranes, a process primarily mediated by the evolutionarily conserved Guided Entry of Tail-anchored proteins (GET) pathway in yeast and the Transmembrane Recognition Complex (TRC) pathway in mammals. ASNA1 (also known as TRC40 or GET3) serves as the central ATP-dependent chaperone delivering TA proteins to the endoplasmic reticulum (ER) membrane. To address ASNA1's role in the heart, we generated constitutive and inducible cardiomyocyte-specific Asna1 knockout mouse models. Constitutive Asna1 deletion during embryogenesis caused perinatal lethality with marked ventricular myocardial thinning by embryonic day 16.5, whereas inducible deletion in adult cardiomyocytes led to rapid ventricular dilation, impaired cardiac function, pathological remodeling, and early mortality. Mechanistically, ASNA1 deficiency destabilized the pre-targeting complex and reduced the expression of multiple TA protein substrates, impairing membrane trafficking and protein transport. Transcriptomic analyses revealed compensatory upregulation of genes involved in protein trafficking and Golgi-to-ER transport, reflecting maladaptive responses to disrupted vesicular transport. Collectively, our findings identify ASNA1 as a critical regulator of TA protein stability and vesicular trafficking in cardiomyocytes, whose loss disrupts cardiac proteostasis and contributes to the cardiomyopathy pathogenesis. Our work provides mechanistic insights into ASNA1-related cardiac disease and highlights potential therapeutic targets.

Competition between insects and their endosymbiotic bacteria for environmentally limited nutrients can compromise the fitness of both organisms. Tsetse flies, the vectors of pathogenic African trypanosomes, harbor a species and population-specific consortium of vertically transmitted endosymbiotic bacteria that range on the functional spectrum from mutualistic to parasitic. Tsetse's indigenous microbiota can include a member of the genus Spiroplasma, and infection with this bacterium causes fecundity-reducing phenotypes in the fly that include a prolonged gonotrophic cycle and a reduction in the motility of stored spermatozoa post-copulation. Herein we demonstrate that Spiroplasma and tsetse spermatozoa compete for fly-derived acylcarnitines, which in other bacteria and animals are used to maintain cell membranes and produce energy. The fat body of mated female flies increases acylcarnitine production in response to infection with Spiroplasma. Additionally, their spermathecae (sperm storage organs), and likely the sperm within, up-regulate expression of carnitine O-palmitoyltransferase-1, which is indicative of increased acylcarnitine metabolism and thus increased energy demand and energy production in this organ. These compensatory measures are insufficient to rescue the motility defect of spermatozoa stored in the spermathecae of Spiroplasma-infected females and thus results in reduced fly fecundity. Tsetse's taxonomically simple and highly tractable indigenous microbiota make the fly an efficient model system for studying the biological processes that facilitate the maintenance of bacterial endosymbioses, and how these relationships impact conserved mechanisms (mammalian spermatozoa also use acylcarnitines as an energy source) that regulated animal host fecundity. In the case of insect pests and vectors, a better understanding of the metabolic mechanisms that underlie these associations can lead to the development of novel control strategies.

The budding yeast Saccharomyces cerevisiae has 'point' centromeres, which are much smaller and simpler than centromeres of most other eukaryotes and have a defined DNA sequence. Other yeast taxa have different and highly diverse centromere structures, but a clear picture of how yeast centromeres have evolved is lacking. Here, we investigated nine yeast species in two taxonomic orders that are close outgroups to S. cerevisiae. We find that they have a wide diversity of centromere structures, indicating that multiple transitions of structure have occurred within the last 200 Myr. Some species have centromeres with defined sequence motifs (17 - 200 bp), others consist of Inverted Repeats (IRs), and others have Ty5-like retroelement clusters. Strikingly, the chromosomal locations of centromeres have largely been conserved across taxonomic orders, even as their structures have changed, which suggests that structure replacement occurs in situ. In some Barnettozyma species we find that a single genome can contain chromosomes with different centromere structures - some with IRs and some without - which suggests that a structural transition is underway in this genus. We identified only one example of a centromere moving by a long distance: a new centromere formed recently at the MAT locus of Barnettozyma californica, 250 kb from the previous centromere on that chromosome.