Caenorhabditis elegans p97/CDC-48 is crucial for progression of meiosis I

Transitions to asexuality and evolution of gene expression in Artemia brine shrimp

While sexual reproduction is widespread among many taxa, asexual lineages have repeatedly evolved from sexual ancestors. Despite extensive research on the evolution of sex, it is still unclear whether this switch represents a major transition requiring major molecular reorganization, and how convergent the changes involved are. In this study, we investigated the phylogenetic relationship and patterns of gene expression of sexual and asexual lineages of Eurasian Artemia brine shrimp, to assess how gene expression patterns are affected by the transition to asexuality. We find only a few genes that are consistently associated with the evolution of asexuality, suggesting that this shift may not require an extensive overhauling of the meiotic machinery. While genes with sex-biased expression have high rates of expression divergence within Eurasian Artemia, neither female- nor male-biased genes appear to show unusual evolutionary patterns after sexuality is lost, contrary to theoretical expectations.

Disruption of p97/VCP induces autophagosome accumulation, cell cycle arrest and apoptosis in human choriocarcinoma cells

Gestational choriocarcinoma is aggressive trophoblastic disease. The development, progression and the cure of this disease is not well-established. p97/Valosin containing protein has been shown to play critical roles in many cellular processes. In various cancers, higher expression of p97/VCP has been reported and targeting of p97/VCP with its spesific inhibitors or siRNA's (siVCP) in cancer therapy was suggested. However, no study is avaible about the expression and function of p97/VCP in gestational choriocarcinoma. Hence, the aim of the study was to evaluate effects of p97/VCP inhibitor, DBeQ and siVCP on choriocarcinoma cells. We use human placental choriocarcinoma cell line (Jeg3) as model to find out the effects of DBeQ and VCP siRNA's (siVCP) on apoptotic and autophagic pathway by immunflouroscence staining, Western blotting, qPCR and flow-cytometry. p97/VCP siRNA's and DBeQ induced accumulation of autophagic proteins, LC3II and p62 in the cytoplasm of Jeg3 cells detected. Concurrently, Jeg3 cells treated with DBeQ and siVCP demonstrated G0/G1 cell cycle arrest, accompanied by accumulation of poly-ubiquitinated proteins. Moreover, disruption of p97/VCP by siRNA and DBeQ inhibited cancer cell growth managing the caspases-3 and -7. Our results show that inhibition of p97/VCP activity with DBeQ and depletion of p97/VCP expression with siRNA in Jeg3 cells induce caspase activation, inhibits cell proliferation and leads to a defect in autophagosome maturation, thus providing potential target for the prevention and treatment of choriocarcinoma.

Inhibition of p97/VCP function leads to defective autophagosome maturation, cell cycle arrest and apoptosis in mouse Sertoli cells

p97/valosin-containing protein (VCP) is expressed in many cells and plays critical functions in a broad range of diverse cellular processes. Because it is expressed in the mouse testes, predominantly in Sertoli cells, and is known to play a critical role in autophagy and apoptosis in different cell types, we set out to investigate its function in autophagosome maturation, apoptosis and cell cycle arrest in a mouse Sertoli cell line. To study the mechanism of p97/VCP action, p97/VCP siRNA and a specific p97/VCP inhibitor, N²,N⁴-dibenzylquinazoline-2,4-diamine (DBeQ), were used in the mouse 15P1 Sertoli cell line. Loss of p97/VCP activity due to DBeQ exposure and silencing of p97/VCP (siVCP) expression results in autophagosome (LC3 and p62) accumulation in the cytoplasm of Sertoli cells. The coexpression of autophagosomal and lysosomal markers (LAMP1 and LAMP2) was reduced in cells in which p97/VCP expression had been inactivated. To better understand in which step of autophagy p97/VCP functions, the interaction between autophagosomal and autolysosomal markers was studied by coimmunoprecipitation and colocalization experiments. The interaction between autophagosomal markers and lysosomal markers decreased in siVCP-expressing and DBeQ-exposed cells. Moreover, the expression of siVCP and DBeQ exposure caused cytoplasmic vacuolation, induced caspase 3-7-mediated cell death and decreased cell cycle progression in mouse Sertoli cells. Taken together, the results show that p97/VCP is essential for autophagosome maturation and cell survival in mouse Sertoli cells. When these functions are prevented, impaired autophagy and apoptosis may have a detrimental effect on germ cells and cause male infertility.

Characterization, expression and localization of valosin-containing protein in ovaries of the giant tiger shrimp Penaeus monodon

Valosin-containing protein (VCP), a member of the ATPase-associated with diverse cellular activity (AAA) family, was identified from the giant tiger shrimp (Penaeus monodon). The full-length cDNA of the PmVCP mRNA consisted of 2,724 bp containing an ORF of 2,367 bp corresponding to a deduced polypeptide of 788 amino acids. The deduced PmVCP protein contained two putative Cdc48 domains (positions 17-103, E-value=2.00e-36 and 120-186, E-value=3.60e-11) and two putative AAA domains (positions 232-368, E-value=3.67e-24 and 505-644, E-value=3.73e-25). PmVCP mRNA expression in ovaries was greater than that in testes in both juveniles and broodstock. PmVCP was significantly up-regulated in stages II and IV ovaries in intact wild broodstock (P<0.05) but it was not differentially expressed during ovarian development in eyestalk-ablated broodstock (P>0.05). The expression level of PmVCP mRNA in ovaries of 14-month-old shrimp was not affected by progesterone injection (0.1μg/g body weight, P>0.05). In contrast, exogenous 5-HT administration (50μg/g body weight) resulted in an increase of PmVCP mRNA in ovaries of 18-month-old shrimp at 6 and 24h post-injection (hpi) (P<0.05). The rPmCdc48-VCP protein and its polyclonal antibody were successfully produced. Cellular localization revealed that PmVCP was localized in the ooplasm of previtellogenic oocytes. Subsequently, it was translocated into the germinal vesicle of vitellogenic oocytes. Interestingly, PmVCP was found in nucleo-cytoplasmic compartments, in the cytoskeletal architecture and in the plasma membrane of mature oocytes in both intact and eyestalk-ablated broodstock.

The UBXN-2/p37/p47 adaptors of CDC-48/p97 regulate mitosis by limiting the centrosomal recruitment of Aurora A

UBXN-2, a substrate adaptor of the AAA ATPase CDC-48/p97, is required to coordinate centrosome maturation timing with mitosis.

Coordination of cell cycle events in space and time is crucial to achieve a successful cell division. Here, we demonstrate that UBXN-2, a substrate adaptor of the AAA ATPase Cdc48/p97, is required to coordinate centrosome maturation timing with mitosis. In UBXN-2–depleted Caenorhabditis elegans embryos, centrosomes recruited more AIR-1 (Aurora A), matured precociously, and alignment of the mitotic spindle with the axis of polarity was impaired. UBXN-2 and CDC-48 coimmunoprecipitated with AIR-1 and the spindle alignment defect was partially rescued by co-depleting AIR-1, indicating that UBXN-2 controls these processes via AIR-1. Similarly, depletion in human cells of the UBXN-2 orthologues p37/p47 resulted in an accumulation of Aurora A at centrosomes and a delay in centrosome separation. The latter defect was also rescued by inhibiting Aurora A. We therefore postulate that the role of this adaptor in cell cycle regulation is conserved.

Create and preserve: proteostasis in development and aging is governed by Cdc48/p97/VCP

The AAA-ATPase Cdc48 (also called p97 or VCP) acts as a key regulator in proteolytic pathways, coordinating recruitment and targeting of substrate proteins to the 26S proteasome or lysosomal degradation. However, in contrast to the well-known function in ubiquitin-dependent cellular processes, the physiological relevance of Cdc48 in organismic development and maintenance of protein homeostasis is less understood. Therefore, studies on multicellular model organisms help to decipher how Cdc48-dependent proteolysis is regulated in time and space to meet developmental requirements. Given the importance of developmental regulation and tissue maintenance, defects in Cdc48 activity have been linked to several human pathologies including protein aggregation diseases. Thus, addressing the underlying disease mechanisms not only contributes to our understanding on the organism-wide function of Cdc48 but also facilitates the design of specific medical therapies. In this review, we will portray the role of Cdc48 in the context of multicellular organisms, pointing out its importance for developmental processes, tissue surveillance, and disease prevention. This article is part of a Special Issue entitled: Ubiquitin-Proteasome System. Guest Editors: Thomas Sommer and Dieter H. Wolf.

A pro-cathepsin L mutant is a luminal substrate for endoplasmic-reticulum-associated degradation in C. elegans

Endoplasmic-reticulum associated degradation (ERAD) is a major cellular misfolded protein disposal pathway that is well conserved from yeast to mammals. In yeast, a mutant of carboxypeptidase Y (CPY*) was found to be a luminal ER substrate and has served as a useful marker to help identify modifiers of the ERAD pathway. Due to its ease of genetic manipulation and the ability to conduct a genome wide screen for modifiers of molecular pathways, C. elegans has become one of the preferred metazoans for studying cell biological processes, such as ERAD. However, a marker of ERAD activity comparable to CPY* has not been developed for this model system. We describe a mutant of pro-cathepsin L fused to YFP that no longer targets to the lysosome, but is efficiently eliminated by the ERAD pathway. Using this mutant pro-cathepsin L, we found that components of the mammalian ERAD system that participate in the degradation of ER luminal substrates were conserved in C. elegans. This transgenic line will facilitate high-throughput genetic or pharmacological screens for ERAD modifiers using widefield epifluorescence microscopy.

CDC-48/p97 is required for proper meiotic chromosome segregation via controlling AIR-2/Aurora B kinase localization in Caenorhabditis elegans

CDC-48/p97 is a AAA (ATPases associated with diverse cellular activities) chaperone involved in protein conformational changes such as the disassembly of protein complexes. We previously reported that Caenorhabditis elegans CDC-48.1 and CDC-48.2 (CDC-48s) are essential for the progression of meiosis I metaphase. Here, we report that CDC-48s are required for proper chromosome segregation during meiosis in C. elegans. In wild-type worms, at the diakinesis phase, phosphorylation of histone H3, one of the known substrates of aurora B kinase (AIR-2), on meiosis I chromatids correlated with AIR-2 localization at the cohesion sites of homologous chromatids. Conversely, depletion of CDC-48s resulted in a significant expansion of signals for AIR-2 and phosphorylated histone H3 over the entire length of meiotic chromosomes, leading to defective chromosome segregation, while the total amount of AIR-2 in lysates was not changed by the depletion of CDC-48s. The defective segregation of meiotic chromosomes caused by the depletion of CDC-48s was suppressed by the simultaneous depletion of AIR-2 and is similar to that observed following the depletion of protein phosphatase 1 (PP1) phosphatases. However, the amount and localization of PP1 were not changed by the depletion of CDC-48s. These results suggest that CDC-48s control the restricted localization of AIR-2 to the cohesion sites of homologous chromatids in meiosis I.

Cdc48p/p97-mediated regulation of mitochondrial morphology is Vms1p-independent

Cdc48p/p97 is a cytosolic essential AAA chaperone, which regulates multiple cellular reactions in a ubiquitin-dependent manner. We have recently shown that Cdc48p exhibits positively cooperative ATPase activity and loss of the positive cooperativity results in yeast cell death. Here we show that loss of the positive cooperativity of the yeast Cdc48p ATPase activity led to severe mitochondrial aggregation. The actin cytoskeleton and distribution of the ER-mitochondria tethering complex (ERMES) were eliminated from the cause of the mitochondrial aggregation. Instead, a mitochondrial outer membrane protein Fzo1p, which is required for mitochondrial fusion, and components of ERMES, which is involved in mitochondrial morphology, were remarkably stabilized in the Cdc48p mutants. In the last couple of years, it was shown that Vms1p functions as a cofactor of Cdc48p for the function of protein degradation of mitochondrial outer membrane proteins. Nevertheless, we found that Vms1p was not involved in the Cdc48p-dependent mitochondrial aggregation and loss of Vms1p did not significantly affect degradation rates of proteins anchored to the mitochondrial outer membrane. These results suggest that Cdc48p controls mitochondrial morphology by regulating turnover of proteins involved in mitochondrial morphology in a Vms1p-independent manner.

Emerging functions of the VCP/p97 AAA-ATPase in the ubiquitin system

The ATP-driven chaperone valosin-containing protein (VCP)/p97 governs critical steps in ubiquitin-dependent protein quality control and intracellular signalling pathways. It cooperates with diverse partner proteins to help process ubiquitin-labelled proteins for recycling or degradation by the proteasome in many cellular contexts. Recent studies have uncovered unexpected cellular functions for p97 in autophagy, endosomal sorting and regulating protein degradation at the outer mitochondrial membrane, and elucidated a role for p97 in key chromatin-associated processes. These findings extend the functional relevance of p97 to lysosomal degradation and reveal a surprising dual role in protecting cells from protein stress and ensuring genome stability during proliferation.

CDC-48/p97 coordinates CDT-1 degradation with GINS chromatin dissociation to ensure faithful DNA replication

Faithful transmission of genomic information requires tight spatiotemporal regulation of DNA replication factors. In the licensing step of DNA replication, CDT-1 is loaded onto chromatin to subsequently promote the recruitment of additional replication factors, including CDC-45 and GINS. During the elongation step, the CDC-45/GINS complex moves with the replication fork; however, it is largely unknown how its chromatin association is regulated. Here, we show that the chaperone-like ATPase CDC-48/p97 coordinates degradation of CDT-1 with release of the CDC-45/GINS complex. C. elegans embryos lacking CDC-48 or its cofactors UFD-1/NPL-4 accumulate CDT-1 on mitotic chromatin, indicating a critical role of CDC-48 in CDT-1 turnover. Strikingly, CDC-48(UFD-1/NPL-4)-deficient embryos show persistent chromatin association of CDC-45/GINS, which is a consequence of CDT-1 stabilization. Moreover, our data confirmed a similar regulation in Xenopus egg extracts, emphasizing a conserved coordination of licensing and elongation events during eukaryotic DNA replication by CDC-48/p97.

Recent advances in p97/VCP/Cdc48 cellular functions

p97/VCP/Cdc48 is one of the best-characterized type II AAA (ATPases associated with diverse cellular activities) ATPases. p97 is suggested to be a ubiquitin-selective chaperone and its key function is to disassemble protein complexes. p97 is involved in a wide variety of cellular activities. Recently, novel functions, namely autophagy and mitochondrial quality control, for p97 have been uncovered. p97 was identified as a causative factor for inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia (IBMPFD) and more recently as a causative factor for amyotrophic lateral sclerosis (ALS). In this review, we will summarize and discuss recent progress and topics in p97 functions and the relationship to its associated diseases.

Positive cooperativity of the p97 AAA ATPase is critical for essential functions

p97 is composed of two conserved AAA (ATPases associated with diverse cellular activities) domains, which form a tandem hexameric ring. We characterized the ATP hydrolysis mechanism of CDC-48.1, a p97 homolog of Caenorhabditis elegans. The ATPase activity of the N-terminal AAA domain was very low at physiological temperature, whereas the C-terminal AAA domain showed high ATPase activity in a coordinated fashion with positive cooperativity. The cooperativity and coordination are generated by different mechanisms because a noncooperative mutant still showed the coordination. Interestingly, the growth speed of yeast cells strongly related to the positive cooperativity rather than the ATPase activity itself, suggesting that the positive cooperativity is critical for the essential functions of p97.

Caenorhabditis elegans UBX cofactors for CDC-48/p97 control spermatogenesis

UBX (ubiquitin regulatory X) domain-containing proteins act as cofactors for CDC-48/p97. CDC-48/p97 is essential for various cellular processes including retro-translocation in endoplasmic reticulum-associated degradation, homotypic membrane fusion, nuclear envelope assembly, degradation of ubiquitylated proteins, and cell cycle progression. CDC-48/p97-dependent processes are determined by differential binding of cofactors including UBX proteins, but the cellular functions of UBX proteins have not yet been elucidated, especially in multicellular organisms. Therefore, we investigated the functions of UBX family members using Caenorhabditis elegans, which expresses six UBX proteins, UBXN-1 to UBXN-6. All six UBXN proteins directly interacted with CDC-48.1 and CDC-48.2, and simultaneous knockdown of the expression of three genes, ubxn-1, ubxn-2 and ubxn-3, induced embryonic lethal and sterile phenotypes, but knockdown of either one or two did not. The sterile worms had a feminized germ-line phenotype, producing oocytes but no sperm. UBXN-1, UBXN-2 and UBXN-3 colocalized with CDC-48 in spermatocytes but not mature sperm. TRA-1A, which is a key factor in the sex determination pathway and inhibits spermatogenesis, accumulated in worms in which UBXN-1, UBXN-2 and UBXN-3 had been simultaneously knocked down. Taken together, these results suggest that UBXN-1, UBXN-2 and UBXN-3 are redundant cofactors for CDC-48/p97 and control spermatogenesis via the degradation of TRA-1A.

WldS can delay Wallerian degeneration in mice when interaction with valosin-containing protein is weakened

Axon degeneration is an early event in many neurodegenerative disorders. In some, the mechanism is related to injury-induced Wallerian degeneration, a proactive death program that can be strongly delayed by the neuroprotective slow Wallerian degeneration protein (Wld(S)) protein. Thus, it is important to understand the Wallerian degeneration mechanism and how Wld(S) blocks it. Wld(S) location is influenced by binding to valosin-containing protein (VCP), an essential protein for many cellular processes including membrane fusion and endoplasmic reticulum-associated degradation. In mice, the N-terminal 16 amino acids (N16), which mediate VCP binding, are essential for Wld(S) to protect axons, a role which another VCP binding sequence can substitute. In Drosophila, the Wld(S) phenotype is weakened by a similar N-terminal truncation and by knocking down the VCP homologue ter94. Neither null nor floxed VCP mice are viable so it is difficult to confirm the requirement for VCP binding in mammals in vivo. However, the hypothesis can be tested further by introducing a Wld(S) missense mutation, altering its affinity for VCP but minimizing the risk of disturbing other aspects of its structure or function. We introduced the R10A mutation, which weakens VCP binding in vitro, and expressed it in transgenic mice. R10AWld(S) fails to co-immunoprecipitate VCP from mouse brain, and only occasionally and faintly accumulates in nuclear foci for which VCP binding is necessary but not sufficient. Surprisingly however, axon protection remains robust and indistinguishable from that in spontaneous Wld(S) mice. We suggest that either N16 has an additional, VCP-independent function in mammals, or that the phenotype requires only weak VCP binding which may be driven forwards in vivo by the high VCP concentration.

Caenorhabditis elegans p97 controls germline-specific sex determination by controlling the TRA-1 level in a CUL-2-dependent manner

p97 (CDC-48 in Caenorhabditis elegans) is a ubiquitin-selective AAA (ATPases associated with diverse cellular activities) chaperone and its key function is to disassemble protein complexes. p97 functions in diverse cellular processes including endoplasmic reticulum (ER)-associated degradation, membrane fusion, and meiotic and mitotic progression. However, its cellular functions in development have not yet been clarified. Here, we present data that p97 is involved in the switch from spermatogenesis to oogenesis in the germline of the C. elegans hermaphrodite. We found that the cdc-48.1 deletion mutant produced less sperm than the wild type and thus showed a decreased brood size. The cdc-48.1 mutation suppressed the sperm-overproducing phenotypes of fbf-1 and fem-3(gf) mutants. In addition, the p97/CDC-48-UFD-1-NPL-4 complex interacted with the E3 ubiquitin ligase CUL-2 complex via NPL-4 binding to Elongin C. Furthermore, TRA-1A, which is the terminal effector of the sex determination pathway and is regulated by CUL-2-mediated proteolysis, accumulated in the cdc-48.1 mutant. Proteasome activity was also required for the brood size determination and sperm-oocyte switch. Our results demonstrate that the C. elegans p97/CDC-48-UFD-1-NPL-4 complex controls the sperm-oocyte switch by regulating CUL-2-mediated TRA-1A proteasome degradation.

An Afg2/Spaf-related Cdc48-like AAA ATPase regulates the stability and activity of the C. elegans Aurora B kinase AIR-2

The Aurora B kinase is the enzymatic core of the chromosomal passenger complex, which is a critical regulator of mitosis. To identify novel regulators of Aurora B, we performed a genome-wide screen for suppressors of a temperature-sensitive lethal allele of the C. elegans Aurora B kinase AIR-2. This screen uncovered a member of the Afg2/Spaf subfamily of Cdc48-like AAA ATPases as an essential inhibitor of AIR-2 stability and activity. Depletion of CDC-48.3 restores viability to air-2 mutant embryos and leads to abnormally high AIR-2 levels at the late telophase/G1 transition. Furthermore, CDC-48.3 binds directly to AIR-2 and inhibits its kinase activity from metaphase through telophase. While canonical p97/Cdc48 proteins have been assigned contradictory roles in the regulation of Aurora B, our results identify a member of the Afg2/Spaf AAA ATPases as a critical in vivo inhibitor of this kinase during embryonic development.

Cell cycle progression requires the CDC-48UFD-1/NPL-4 complex for efficient DNA replication

Since cdc48 mutants were isolated by the first genetic screens for cell division cycle (cdc) mutants in yeast, the requirement of the chaperone-like ATPase Cdc48/p97 during cell division has remained unclear. Here, we discover an unanticipated function for Caenorhabditis elegans CDC-48 in DNA replication linked to cell cycle control. Our analysis of the CDC-48(UFD-1/NPL-4) complex identified a general role in S phase progression of mitotic cells essential for embryonic cell division and germline development of adult worms. These developmental defects result from activation of the DNA replication checkpoint caused by replication stress. Similar to loss of replication licensing factors, DNA content is strongly reduced in worms depleted for CDC-48, UFD-1, and NPL-4. In addition, these worms show decreased DNA synthesis and hypersensitivity toward replication blocking agents. Our findings identified a role for CDC-48(UFD-1/NPL-4) in DNA replication, which is important for cell cycle progression and genome stability.

p97 Homologs from Caenorhabditis elegans, CDC-48.1 and CDC-48.2, suppress the aggregate formation of huntingtin exon1 containing expanded polyQ repeat

Polyglutamine (polyQ)-expanded proteins are associated with cytotoxicity in some neurodegenerative disorders such as Huntington's disease. We have reported that the aggregation of the polyQ-expanded protein is partially suppressed by co-expression of either of two homologs of an AAA chaperone p97, CDC-48.1 or CDC-48.2, in Caenorhabditis elegans, but how p97 regulates the aggregation of polyQ-expanded proteins remains unclear. Here we present direct evidence that CDC-48.1 and CDC-48.2 suppress the aggregation of a huntingtin (Htt) exon1 fragment containing an expanded polyQ repeat in vitro. CDC-48.1 and CDC-48.2 bound the Htt exon1 fragment directly, and suppressed the formation of SDS-insoluble aggregates of Htt fragments containing 53 glutamine residues (HttQ53) independently of nucleotides. CDC-48.1 and CDC-48.2 also modulated the oligomeric states of HttQ53 during the aggregate formation. In the absence of CDC-48.1 and CDC-48.2, HttQ53 formed 70-150 kDa oligomers, whereas 300-500 kDa oligomers as well as 70-150 kDa oligomers accumulated in the presence of CDC-48.1 and CDC-48.2. Taken together, these results suggest that p97 plays a protective role in neurodegenerative disorders by directly suppressing the protein aggregation as a molecular chaperone.

C. elegans germ cells switch between distinct modes of double-strand break repair during meiotic prophase progression

Chromosome inheritance during sexual reproduction relies on deliberate induction of double-strand DNA breaks (DSBs) and repair of a subset of these breaks as interhomolog crossovers (COs). Here we provide a direct demonstration, based on our analysis of rad-50 mutants, that the meiotic program in Caenorhabditis elegans involves both acquisition and loss of a specialized mode of double-strand break repair (DSBR). In premeiotic germ cells, RAD-50 is not required to load strand-exchange protein RAD-51 at sites of spontaneous or ionizing radiation (IR)-induced DSBs. A specialized meiotic DSBR mode is engaged at the onset of meiotic prophase, coincident with assembly of meiotic chromosome axis structures. This meiotic DSBR mode is characterized both by dependence on RAD-50 for rapid accumulation of RAD-51 at DSB sites and by competence for converting DSBs into interhomolog COs. At the mid-pachytene to late pachytene transition, germ cells undergo an abrupt release from the meiotic DSBR mode, characterized by reversion to RAD-50-independent loading of RAD-51 and loss of competence to convert DSBs into interhomolog COs. This transition in DSBR mode is dependent on MAP kinase-triggered prophase progression and coincides temporally with a major remodeling of chromosome architecture. We propose that at least two developmentally programmed switches in DSBR mode, likely conferred by changes in chromosome architecture, operate in the C. elegans germ line to allow formation of meiotic crossovers without jeopardizing genomic integrity. Our data further suggest that meiotic cohesin component REC-8 may play a role in limiting the activity of SPO-11 in generating meiotic DSBs and that RAD-50 may function in counteracting this inhibition.

Faithful inheritance of chromosomes during sexual reproduction depends on the deliberate formation of double-strand DNA breaks (DSBs) and subsequent repair of a subset of these breaks by a mechanism that leads to crossovers between homologous chromosome pairs. The requirement for crossovers to ensure chromosome segregation poses a challenge for sexually reproducing organisms, as DSBs constitute a danger to genomic integrity in other contexts. This manuscript provides insight into the mechanisms that allow germ cells to generate recombination-based linkages that ensure chromosome inheritance while at the same time protecting the integrity of their genomes. Specifically, we provide a direct demonstration, based on our analysis of rad-50 mutants, that the meiotic program in C. elegans involves both acquisition and loss of a specialized meiotic mode of double-strand break repair (DSBR). We propose that the ability to revert to a less constrained DSBR environment at a late stage of meiotic prophase serves as a fail-safe mechanism for safeguarding the genome, as it provides an opportunity to repair any remaining DBSs and restore chromosome integrity prior to chromosome segregation.

Role(s) of Cdc48/p97 in mitosis

The ubiquitin-dependent chaperone Cdc48 (cell division cycle 48)/p97 is involved in a variety of degradative and regulatory processes during interphase that help to maintain cellular homoeostasis. The results available so far suggest that its basic activity is to mobilize ubiquitinated substrate proteins from cellular structures or segregate them from binding partners, and then hand them over for degradation or recycling. Several studies in different organisms show that Cdc48/p97 also has critical roles in mitosis. However, many important aspects of these functions and the general perspective have remained unclear.