RIO protein kinases (RIOKs) are a relatively conserved family of enzymes implicated in cell cycle control and ribosomal RNA processing. Despite their functional importance, they remain a poorly ...understood group of kinases in multicellular organisms. Here, we show that the C. elegans genome contains one member of each of the three RIOK sub-families and that each of the genes coding for them has a unique tissue expression pattern. Our analysis showed that the gene encoding RIOK-1 (riok-1) was broadly and strongly expressed. Interestingly, the intestinal expression of riok-1 was dependent upon two putative binding sites for the oxidative and xenobiotic stress response transcription factor SKN-1. RNA interference (RNAi)-mediated knock down of riok-1 resulted in germline defects, including defects in germ line stem cell proliferation, oocyte maturation and the production of endomitotic oocytes. Taken together, our findings indicate new functions for RIOK-1 in post mitotic tissues and in reproduction.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Interhomolog crossovers (COs) are a prerequisite for achieving accurate chromosome segregation during meiosis 1, 2. COs are not randomly positioned, occurring at distinct genomic intervals during ...meiosis in all species examined 3–10. The role of CO position as a major determinant of accurate chromosome segregation has not been previously directly analyzed in a metazoan. Here, we use spo-11 mutants, which lack endogenous DNA double-strand breaks (DSBs), to induce a single DSB by Mos1 transposon excision at defined chromosomal locations in the C. elegans germline and show that the position of the resulting CO directly affects the formation of distinct chromosome subdomains during meiotic chromosome remodeling. CO formation in the typically CO-deprived center region of autosomes leads to premature loss of sister chromatid cohesion and chromosome missegregation, whereas COs at an off-centered position, as in wild type, can result in normal remodeling and accurate segregation. Ionizing radiation (IR)-induced DSBs lead to the same outcomes, and modeling of IR dose-response reveals that the CO-unfavorable center region encompasses up to 6% of the total chromosome length. DSBs proximal to telomeres rarely form COs, likely because of formation of unstable recombination intermediates that cannot be sustained as chiasmata until late prophase. Our work supports a model in which regulation of CO position early in meiotic prophase is required for proper designation of chromosome subdomains and normal chromosome remodeling in late meiotic prophase I, resulting in accurate chromosome segregation and providing a mechanism to prevent aneuploid gamete formation.
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•CO position affects the formation of chromosome subdomains•COs at the center of autosomes lead to premature loss of sister chromatid cohesion•The CO-unfavorable center region encompasses up to 6% of the total chromosome length•CO formation close to telomeres is highly suppressed
Altendorfer et al. show that placing a crossover (CO) at a typically CO-deprived chromosome region results in a chromosome configuration susceptible to nondisjunction. Moreover, CO suppression at chromosome ends is a conserved feature of meiosis. This study proposes that CO placement is highly regulated to ensure productive chromosome remodeling.
DNA double-strand breaks (DSBs) are deleterious lesions, which must be repaired precisely to maintain genomic stability. During meiosis, programmed DSBs are repaired via homologous recombination (HR) ...while repair using the nonhomologous end joining (NHEJ) pathway is inhibited, thereby ensuring crossover formation and accurate chromosome segregation.1,2 How DSB repair pathway choice is implemented during meiosis is unknown. In C. elegans, meiotic DSB repair takes place in the context of the fully formed, highly dynamic zipper-like structure present between homologous chromosomes called the synaptonemal complex (SC).3,4,5,6,7,8,9 The SC consists of a pair of lateral elements bridged by a central region composed of the SYP proteins in C. elegans. How the structural components of the SC are regulated to maintain the architectural integrity of the assembled SC around DSB repair sites remained unclear. Here, we show that SYP-4, a central region component of the SC, is phosphorylated at Serine 447 in a manner dependent on DSBs and the ATM/ATR DNA damage response kinases. We show that this SYP-4 phosphorylation is critical for preserving the SC structure following exogenous (γ-IR-induced) DSB formation and for promoting normal DSB repair progression and crossover patterning following SPO-11-dependent and exogenous DSBs. We propose a model in which ATM/ATR-dependent phosphorylation of SYP-4 at the S447 site plays important roles both in maintaining the architectural integrity of the SC following DSB formation and in warding off repair via the NHEJ repair pathway, thereby preventing aneuploidy.
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•Phosphorylation at S447 on SC component SYP-4 is DSB and ATM/ATR dependent•SYP-4 phosphorylation at S447 regulates DSB repair and CO patterning•SC architectural integrity after exogenous DSBs requires SYP-4 phosphorylation•SYP-4 phosphorylation acts in DSB repair pathway choice by warding off NHEJ repair
Láscarez-Lagunas et al. show DSB- and ATM/ATR-dependent phosphorylation of the SC structural component SYP-4 at S447 during meiosis. SYP-4 phosphorylation is important for maintaining the architectural integrity of the SC following exogenous DSBs, regulating CO patterning, and warding off repair via the NHEJ repair pathway to prevent aneuploidy.
Parkinson's disease (PD) is the second most common neurodegenerative disease and is characterized by the formation of α-synuclein-containing protein aggregates called Lewy bodies within the brain. A ...crucial role for α-synuclein in the pathogenesis of PD is also suggested by the fact that point mutations, increased copy number, or polymorphisms in the α-synuclein gene SNCA all cause or contribute to the development of PD. In addition to SNCA, an increasing number of other genes have been implicated in PD. While mutations in at least some of these genes have been shown to cause the formation of Lewy bodies, the role of α-synuclein in these genetic forms of PD remains poorly defined. Since C. elegans do not have a homolog of α-synuclein, this organism provides the opportunity to identify synergism between α-synuclein and other genes implicated in PD. To do this, we generated a novel C. elegans model in which wild-type α-synuclein is ubiquitously expressed from a single copy transgene, and examined the resulting effect on phenotypic deficits in PD deletion mutants affecting PARK2/pdr-1, PINK1/pink-1, DJ-1/djr-1.1 and ATP13A2/catp-6. While the PD deletion mutants exhibit only mild phenotypic deficits in absence of α-synuclein, expression of wild-type α-synuclein caused increased sensitivity to multiple stresses, induced deficits in dopamine-dependent behavior, and accelerated loss of dopamine neurons. Overall, these results suggest that the recessive loss of function mutations act together with α-synuclein to cause PD, and that α-synuclein lowering strategies may be effective in genetic forms of PD.
Mitochondria are dynamic organelles that can change shape and size depending on the needs of the cell through the processes of mitochondrial fission and fusion. In this work, we investigated the role ...of mitochondrial dynamics in organismal stress response. By using C. elegans as a genetic model, we could visualize mitochondrial morphology in a live organism with well‐established stress assays and well‐characterized stress response pathways. We found that disrupting mitochondrial fission (DRP1/drp‐1) or fusion (OPA1/eat‐3, MFN/fzo‐1) genes caused alterations in mitochondrial morphology that impacted both mitochondrial function and physiologic rates. While both mitochondrial fission and mitochondrial fusion mutants showed increased sensitivity to osmotic stress and anoxia, surprisingly we found that the mitochondrial fusion mutants eat‐3 and fzo‐1 are more resistant to both heat stress and oxidative stress. In exploring the mechanism of increased stress resistance, we found that disruption of mitochondrial fusion genes resulted in the upregulation of multiple stress response pathways. Overall, this work demonstrates that disrupting mitochondrial dynamics can have opposite effects on resistance to different types of stress. Our results suggest that disruption of mitochondrial fusion activates multiple stress response pathways that enhance resistance to specific stresses.
Chromosome movements and licensing of synapsis must be tightly regulated during early meiosis to ensure accurate chromosome segregation and avoid aneuploidy, although how these steps are coordinated ...is not fully understood. Here we show that GRAS-1, the worm homolog of mammalian GRASP/Tamalin and CYTIP, coordinates early meiotic events with cytoskeletal forces outside the nucleus. GRAS-1 localizes close to the nuclear envelope (NE) in early prophase I and interacts with NE and cytoskeleton proteins. Delayed homologous chromosome pairing, synaptonemal complex (SC) assembly, and DNA double-strand break repair progression are partially rescued by the expression of human CYTIP in gras-1 mutants, supporting functional conservation. However, Tamalin, Cytip double knockout mice do not exhibit obvious fertility or meiotic defects, suggesting evolutionary differences between mammals. gras-1 mutants show accelerated chromosome movement during early prophase I, implicating GRAS-1 in regulating chromosome dynamics. GRAS-1-mediated regulation of chromosome movement is DHC-1-dependent, placing it acting within the LINC-controlled pathway, and depends on GRAS-1 phosphorylation at a C-terminal S/T cluster. We propose that GRAS-1 coordinates the early steps of homology search and licensing of SC assembly by regulating the pace of chromosome movement in early prophase I.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Proper growth and development of the female gamete, the oocyte, are critical for the propagation of sexually reproducing animals and plants. Oogenesis is a complex process, which requires precise ...coordination between oocyte growth and meiotic progression, to generate a competent oocyte that can support fertilization and embryogenesis. In C. elegans, a sperm-sensing mechanism regulates oocyte meiotic maturation and ovulation, tightly coordinating sperm availability and fertilization. Major sperm protein (MSP) released from sperm trigger meiotic resumption (meiotic maturation). In C. elegans, actomyosin-dependent cytoplasmic streaming through the cytoplasmic core of the gonad represents the major mechanism by which oocytes grow. During my thesis work, I found that the MSP hormone promotes the sustained actomyosin-dependent cytoplasmic streaming that drives oocyte growth. Further, I found that efficient oocyte production and cytoplasmic streaming require somatic Gαs-adenylate cyclase signaling, thereby providing a somatic mechanism that coordinates oocyte growth and meiotic maturation with sperm availability. MSP promotes cytoplasmic streaming in part by rapidly inducing the phosphorylation of the MLC-4 regulatory light chain (rMLC) of NMY-2 smooth muscle myosin throughout the germline. To elucidate the molecular mechanisms that regulate oocyte growth, I conducted a genetic analysis of the MSP-dependent oocyte growth process. Surprisingly, I found that GLP-1/Notch signaling functions in the germline to ensure proper oocyte growth when the MSP hormone is present. Loss-of-function mutations in glp-1/Notch cause oocytes to grow abnormally large in a manner that is dependent on the presence of MSP and somatic Gαs-adenylate cyclase signaling. By contrast, gain-of-function glp-1 mutations result in the production of small oocytes. In addition, MSP-dependent oocyte growth depends on DTC signaling involving the redundant function of GLP-1/Notch ligands LAG-2 and APX-1. Further, GLP-1/Notch signaling affects two cellular oocyte growth processes, actomyosin-dependent cytoplasmic streaming and oocyte cellularization. glp-1 loss-of-function mutants exhibit elevated rates of cytoplasmic streaming and delayed cellularization. My dissertation work suggests a model in which the two major signaling centers in the gonad, distal GLP-1/Notch signaling and proximal major sperm protein (MSP) signaling, coordinate the spatially and temporally distinct processes by which female germline stem cells grow and differentiate into functional oocytes in C. elegans.
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