A CUL-2 ubiquitin ligase containing three FEM proteins degrades TRA-1 to regulate C. elegans sex determination

Noncanonical inheritance of phenotypic information by protein amyloids

All known heritable phenotypic information in animals is transmitted by direct inheritance of nucleic acids, their covalent modifications or histone modifications that modulate expression of associated genomic regions. Nonetheless, numerous familial traits and disorders cannot be attributed to known heritable molecular factors. Here we identify amyloid-like protein structures that are stably inherited in wild-type animals and influence traits. Their perturbation by genetic, environmental or pharmacological treatments leads to developmental phenotypes that can be epigenetically passed onto progeny. Injection of amyloids isolated from different phenotypic backgrounds into naive animals recapitulates the associated phenotype in offspring. Genetic and proteomic analyses reveal that the 26S proteasome and its conserved regulators maintain heritable amyloids across generations, which enables proper germ cell sex differentiation. We propose that inheritance of a proteinaceous epigenetic memory coordinates developmental timing and patterning with the environment to confer adaptive fitness.

Hominini-specific regulation of the cell cycle by stop codon readthrough of FEM1B

FEM1B is a substrate-recognition component of the CRL2 E3 ubiquitin-protein ligase. This multi-protein complex targets specific proteins for ubiquitylation, which leads to their degradation. Here, we demonstrate the regulation of FEM1B expression by stop codon readthrough (SCR). In this process, translating ribosomes readthrough the stop codon of FEM1B to generate a C-terminally extended isoform that is highly unstable. A total of 81 nucleotides in the proximal 3'UTR of FEM1B constitute the necessary and sufficient cis-signal for SCR. Also, they encode the amino acid sequence responsible for the degradation of the SCR product. CRISPR-edited cells lacking this region, and therefore SCR of FEM1B, showed increased FEM1B expression. This in turn resulted in reduced expression of SLBP (a target of FEM1B-mediated degradation) and replication-dependent histones (target of SLBP for mRNA stability), causing cell cycle delay. Evolutionary analysis revealed that this phenomenon is specific to the genus Pan and Homo (Hominini). Overall, we show a relatively recently evolved SCR process that relieves the cell cycle from the negative regulation by FEM1B.

Rewiring the Sex-Determination Pathway During the Evolution of Self-Fertility

Although evolution is driven by changes in how regulatory pathways control development, we know little about the molecular details underlying these transitions. The TRA-2 domain that mediates contact with TRA-1 is conserved in Caenorhabditis. By comparing the interaction of these proteins in two species, we identified a striking change in how sexual development is controlled. Identical mutations in this domain promote oogenesis in Caenorhabditis elegans but promote spermatogenesis in Caenorhabditis briggsae. Furthermore, the effects of these mutations involve the male-promoting gene fem-3 in C. elegans but are independent of fem-3 in C. briggsae. Finally, reciprocal mutations in these genes show that C. briggsae TRA-2 binds TRA-1 to prevent expression of spermatogenesis regulators. By contrast, in C. elegans TRA-1 sequesters TRA-2 in the germ line, allowing FEM-3 to initiate spermatogenesis. Thus, we propose that the flow of information within the sex determination pathway has switched directions during evolution. This result has important implications for how evolutionary change can occur.

COP9 signalosome component CSN-5 stabilizes PUF proteins FBF-1 and FBF-2 in Caenorhabditis elegans germline stem and progenitor cells

RNA-binding proteins FBF-1 and FBF-2 (FBFs) are required for germline stem cell maintenance and the sperm/oocyte switch in Caenorhabditis elegans, although the mechanisms controlling FBF protein levels remain unknown. We identified an interaction between both FBFs and CSN-5), a component of the constitutive photomorphogenesis 9 (COP9) signalosome best known for its role in regulating protein degradation. Here, we find that the Mpr1/Pad1 N-terminal metalloprotease domain of CSN-5 interacts with the Pumilio and FBF RNA-binding domain of FBFs and the interaction is conserved for human homologs CSN5 and PUM1. The interaction between FBF-2 and CSN-5 can be detected in vivo by proximity ligation. csn-5 mutation results in the destabilization of FBF proteins, which may explain previously observed decrease in the numbers of germline stem and progenitor cells, and disruption of oogenesis. The loss of csn-5 does not decrease the levels of a related PUF protein PUF-3, and csn-5(lf) phenotype is not enhanced by fbf-1/2 knockdown, suggesting that the effect is specific to FBFs. The effect of csn-5 on oogenesis is largely independent of the COP9 signalosome and is cell autonomous. Surprisingly, the regulation of FBF protein levels involves a combination of COP9-dependent and COP9-independent mechanisms differentially affecting FBF-1 and FBF-2. This work supports a previously unappreciated role for CSN-5 in the stabilization of germline stem cell regulatory proteins FBF-1 and FBF-2.

Structural insights into the ubiquitylation strategy of the oligomeric CRL2FEM1B E3 ubiquitin ligase

Cullin-RING E3 ubiquitin ligase (CRL) family members play critical roles in numerous biological processes and diseases including cancer and Alzheimer's disease. Oligomerization of CRLs has been reported to be crucial for the regulation of their activities. However, the structural basis for its regulation and mechanism of its oligomerization are not fully known. Here, we present cryo-EM structures of oligomeric CRL2FEM1B in its unneddylated state, neddylated state in complex with BEX2 as well as neddylated state in complex with FNIP1/FLCN. These structures reveal that asymmetric dimerization of N8-CRL2FEM1B is critical for the ubiquitylation of BEX2 while FNIP1/FLCN is ubiquitylated by monomeric CRL2FEM1B. Our data present an example of the asymmetric homo-dimerization of CRL. Taken together, this study sheds light on the ubiquitylation strategy of oligomeric CRL2FEM1B according to substrates with different scales.

Let's talk about sex: Mechanisms of neural sexual differentiation in Bilateria

In multicellular organisms, sexed gonads have evolved that facilitate release of sperm versus eggs, and bilaterian animals purposefully combine their gametes via mating behaviors. Distinct neural circuits have evolved that control these physically different mating events for animals producing eggs from ovaries versus sperm from testis. In this review, we will describe the developmental mechanisms that sexually differentiate neural circuits across three major clades of bilaterian animals-Ecdysozoa, Deuterosomia, and Lophotrochozoa. While many of the mechanisms inducing somatic and neuronal sex differentiation across these diverse organisms are clade-specific rather than evolutionarily conserved, we develop a common framework for considering the developmental logic of these events and the types of neuronal differences that produce sex-differentiated behaviors. This article is categorized under: Congenital Diseases > Stem Cells and Development Neurological Diseases > Stem Cells and Development.

CaMKII mediates sexually dimorphic synaptic transmission at neuromuscular junctions in C. elegans

Sexually dimorphic behaviors are ubiquitous throughout the animal kingdom. Although both sex-specific and sex-shared neurons have been functionally implicated in these diverse behaviors, less is known about the roles of sex-shared neurons. Here, we discovered sexually dimorphic cholinergic synaptic transmission in C. elegans occurring at neuromuscular junctions (NMJs), with males exhibiting increased release frequencies, which result in sexually dimorphic locomotion behaviors. Scanning electron microscopy revealed that males have significantly more synaptic vesicles (SVs) at their cholinergic synapses than hermaphrodites. Analysis of previously published transcriptome identified the male-enriched transcripts and focused our attention on UNC-43/CaMKII. We ultimately show that differential accumulation of UNC-43 at cholinergic neurons controls axonal SV abundance and synaptic transmission. Finally, we demonstrate that sex reversal of all neurons in hermaphrodites generates male-like cholinergic transmission and locomotion behaviors. Thus, beyond demonstrating UNC-43/CaMKII as an essential mediator of sex-specific synaptic transmission, our study provides molecular and cellular insights into how sex-shared neurons can generate sexually dimorphic locomotion behaviors.

The Caenorhabditis elegans cullin-RING ubiquitin ligase CRL4DCAF-1 is required for proper germline nucleolus morphology and male development

Cullin-RING ubiquitin ligases (CRLs) are the largest class of ubiquitin ligases with diverse functions encompassing hundreds of cellular processes. Inactivation of core components of the CRL4 ubiquitin ligase produces a germ cell defect in Caenorhabditis elegans that is marked by abnormal globular morphology of the nucleolus and fewer germ cells. We identified DDB1 Cullin4 associated factor (DCAF)-1 as the CRL4 substrate receptor that ensures proper germ cell nucleolus morphology. We demonstrate that the dcaf-1 gene is the ncl-2 (abnormal nucleoli) gene, whose molecular identity was not previously known. We also observed that CRL4DCAF-1 is required for male tail development. Additionally, the inactivation of CRL4DCAF-1 results in a male-specific lethality in which a percentage of male progeny arrest as embryos or larvae. Analysis of the germ cell nucleolus defect using transmission electron microscopy revealed that dcaf-1 mutant germ cells possess significantly fewer ribosomes, suggesting a defect in ribosome biogenesis. We discovered that inactivation of the sperm-fate specification gene fog-1 (feminization of the germ line-1) or its protein-interacting partner, fog-3, rescues the dcaf-1 nucleolus morphology defect. Epitope-tagged versions of both FOG-1 and FOG-3 proteins are aberrantly present in adult dcaf-1(RNAi) animals, suggesting that DCAF-1 negatively regulates FOG-1 and FOG-3 expression. Murine CRL4DCAF-1 targets the degradation of the ribosome assembly factor periodic trptophan protein 1 (PWP1). We observed that the inactivation of Caenorhabditis elegansDCAF-1 increases the nucleolar levels of PWP1 in the germ line, intestine, and hypodermis. Reducing the level of PWP-1 rescues the dcaf-1 mutant defects of fewer germ cell numbers and abnormal nucleolus morphology, suggesting that the increase in PWP-1 levels contributes to the dcaf-1 germline defect. Our results suggest that CRL4DCAF-1 has an evolutionarily ancient role in regulating ribosome biogenesis including a conserved target in PWP1.

Temporal transitions in the postembryonic nervous system of the nematode Caenorhabditis elegans: Recent insights and open questions

After the generation, differentiation and integration into functional circuitry, post-mitotic neurons continue to change certain phenotypic properties throughout postnatal juvenile stages until an animal has reached a fully mature state in adulthood. We will discuss such changes in the context of the nervous system of the nematode C. elegans, focusing on recent descriptions of anatomical and molecular changes that accompany postembryonic maturation of neurons. We summarize the characterization of genetic timer mechanisms that control these temporal transitions or maturational changes, and discuss that many but not all of these transitions relate to sexual maturation of the animal. We describe how temporal, spatial and sex-determination pathways are intertwined to sculpt the emergence of cell-type specific maturation events. Finally, we lay out several unresolved questions that should be addressed to move the field forward, both in C. elegans and in vertebrates.

Eriocheir sinensis feminization-1c (Fem-1c) and Its Predicted miRNAs Involved in Sexual Development and Regulation

Feminization-1c (Fem-1c) is important for sex differentiation in the model organism Caenorhabditis elegans. In our previous study, the basic molecular characteristics of the Fem-1c gene (EsFem-1c) in Eriocheir sinensis (Henri Milne Edwards, 1854) were cloned to determine the relationship with sex differentiation. In this study, the genomic sequence of EsFem-1c contained five exons and four introns, with an exceptionally long 3'UTR sequence. The qRT-PCR results of EsFem-1c demonstrated lower tissue expression in the androgenic gland of the intersex crab than the normal male crab, implying that EsFem-1c plays a role in crab AG development. RNA interference experiments and morphological observations of juvenile and mature crabs indicated that EsFem-1c influences sexual development in E. sinensis. A dual-luciferase reporter assay disclosed that tcf-miR-315-5p effectively inhibits the translation of the EsFem-1c gene, influencing male development. An intriguing finding was that miRNA tcf-miR-307 could increase EsFem-1c expression by binding to the alternative splicing region with a length of 248 bp (ASR-248) in the 3'UTR sequence. The present research contributes to a better understanding of the molecular regulation mechanism of EsFem-1c and provides a resource for future studies of the miRNA-mediated regulation of sexual development and regulation in E. sinensis.

Mutations, sex, and genetic diversity: New arguments for partially directed evolution

A review of the theories of the existence of sexes, genetic diversity, and the distribution of mutations among organisms shows that all these concepts are not a product of random evolution and cannot be explained within the framework of Darwinism. Most mutations are the result of the genome acting on itself. This is an organized process that is implemented very differently in different species, in different places in the genome. Because of the fact that it is not random, this process must be directed and regulated, albeit with complex and not fully understood laws. This means that an additional reason must be included in order to model such mutations during evolution. The assumption of directionality must not only be explicitly included in evolutionary theory but must also occupy a central place in it. In this study an updated model of partially directed evolution is constructed, which is capable of qualitatively explaining the indicated features of evolution. Experiments are described that can confirm or disprove the proposed model.

Sexually dimorphic architecture and function of a mechanosensory circuit in C. elegans

How sensory perception is processed by the two sexes of an organism is still only partially understood. Despite some evidence for sexual dimorphism in auditory and olfactory perception, whether touch is sensed in a dimorphic manner has not been addressed. Here we find that the neuronal circuit for tail mechanosensation in C. elegans is wired differently in the two sexes and employs a different combination of sex-shared sensory neurons and interneurons in each sex. Reverse genetic screens uncovered cell- and sex-specific functions of the alpha-tubulin mec-12 and the sodium channel tmc-1 in sensory neurons, and of the glutamate receptors nmr-1 and glr-1 in interneurons, revealing the underlying molecular mechanisms that mediate tail mechanosensation. Moreover, we show that only in males, the sex-shared interneuron AVG is strongly activated by tail mechanical stimulation, and accordingly is crucial for their behavioral response. Importantly, sex reversal experiments demonstrate that the sexual identity of AVG determines both the behavioral output of the mechanosensory response and the molecular pathways controlling it. Our results present extensive sexual dimorphism in a mechanosensory circuit at both the cellular and molecular levels.

Ubiquitin ligases and a processive proteasome facilitate protein clearance during the oocyte-to-embryo transition in Caenorhabditis elegans

The ubiquitin-mediated degradation of oocyte translational regulatory proteins is a conserved feature of the oocyte-to-embryo transition. In the nematode Caenorhabditis elegans, multiple translational regulatory proteins, including the TRIM-NHL RNA-binding protein LIN-41/Trim71 and the Pumilio-family RNA-binding proteins PUF-3 and PUF-11, are degraded during the oocyte-to-embryo transition. Degradation of each protein requires activation of the M-phase cyclin-dependent kinase CDK-1, is largely complete by the end of the first meiotic division and does not require the anaphase-promoting complex. However, only LIN-41 degradation requires the F-box protein SEL-10/FBW7/Cdc4p, the substrate recognition subunit of an SCF-type E3 ubiquitin ligase. This finding suggests that PUF-3 and PUF-11, which localize to LIN-41-containing ribonucleoprotein particles, are independently degraded through the action of other factors and that the oocyte ribonucleoprotein particles are disassembled in a concerted fashion during the oocyte-to-embryo transition. We develop and test the hypothesis that PUF-3 and PUF-11 are targeted for degradation by the proteasome-associated HECT-type ubiquitin ligase ETC-1/UBE3C/Hul5, which is broadly expressed in C. elegans. We find that several GFP-tagged fusion proteins that are degraded during the oocyte-to-embryo transition, including fusions with PUF-3, PUF-11, LIN-41, IFY-1/Securin, and CYB-1/Cyclin B, are incompletely degraded when ETC-1 function is compromised. However, it is the fused GFP moiety that appears to be the critical determinant of this proteolysis defect. These findings are consistent with a conserved role for ETC-1 in promoting proteasome processivity and suggest that proteasomal processivity is an important element of the oocyte-to-embryo transition during which many key oocyte regulatory proteins are rapidly targeted for degradation.

Sex Determination in Nematode Germ Cells

BACKGROUND

Animal germ cells differentiate as sperm or as oocytes. These sexual fates are controlled by complex regulatory pathways to ensure that the proper gametes are made at the appropriate times.

SUMMARY

Nematodes like Caenorhabditis elegans and its close relatives are ideal models for studying how this regulation works, because the XX animals are self-fertile hermaphrodites that produce both sperm and oocytes. In these worms, germ cells use the same signal transduction pathway that functions in somatic cells. This pathway determines the activity of the transcription factor TRA-1, a Gli protein that can repress male genes. However, the pathway is extensively modified in germ cells, largely by the action of translational regulators like the PUF proteins. Many of these modifications play critical roles in allowing the XX hermaphrodites to make sperm in an otherwise female body. Finally, TRA-1 cooperates with chromatin regulators in the germ line to control the activity of fog-1 and fog-3, which are essential for spermatogenesis. FOG-1 and FOG-3 work together to determine germ cell fates by blocking the translation of oogenic transcripts. Key Messages: Although there is great diversity in how germ cell fates are controlled in other animals, many of the key nematode genes are conserved, and the critical role of translational regulators may be universal.

Sulforaphane Targets TRA-1/GLI Upstream of DAF-16/FOXO to Promote C. elegans Longevity and Healthspan

Broccoli-derived isothiocyanate sulforaphane inhibits inflammation and cancer. Sulforaphane may support healthy aging, but the underlying detailed mechanisms are unclear. We used the C. elegans nematode model to address this question. Wild-type and 4 mutant C. elegans worm strains were fed in the presence or absence of sulforaphane and E. coli food bacteria transfected with RNA interference gene constructs. Kaplan-Meier survival analysis, live imaging of mobility and pharyngeal pumping, fluorescence microscopy, RT-qPCR, and Western blotting were performed. In the wild type, sulforaphane prolonged lifespan and increased mobility and food intake because of sulforaphane-induced upregulation of the sex-determination transcription factor TRA-1, which is the ortholog of the human GLI mediator of sonic hedgehog signaling. In turn, the tra-1 target gene daf-16, which is the ortholog of human FOXO and the major mediator of insulin/IGF-1 and aging signaling, was induced. By contrast, sulforaphane did not prolong lifespan and healthspan when tra-1 or daf-16 was inhibited by RNA interference or when worms with a loss-of-function mutation of the tra-1 or daf-16 genes were used. Conversely, the average lifespan of C. elegans with hyperactive TRA-1 increased by 8.9%, but this longer survival was abolished by RNAi-mediated inhibition of daf-16. Our data suggest the involvement of sulforaphane in regulating healthy aging and prolonging lifespan by inducing the expression and nuclear translocation of TRA-1/GLI and its downstream target DAF-16/FOXO.

Downregulation of FEM1C enhances metastasis and proliferation in colorectal cancer

Background

Feminization-1 (FEM-1) is considered a substrate recognition subunit of CUL2-RING E3 ubiquitin ligase complexes, which refers to sex determination by modulating TRA-1 stability in C. elegans. The function of mammalian orthologous gene of FEM-1 remains to be elucidated.

Methods

The expression of FEM1C in colorectal cancer (CRC) cells was interfered by small interference RNA (siRNA) transfection, and Cell counting kit-8 (CCK-8) assay, colony formation assay and transwell assay were performed. In order to estimate the function on metastasis, stable knockdown FEM1C cells were used to established liver and lung metastasis models. In addition, the expression of FEM1C in normal tissues, adenomas and tumor tissues were analyzed, and the relationship between FEM1C expression level and prognosis was analyzed by Kaplan-Meier method.

Results

Here, we report that the elimination of FEM1C, one of the members of FEM-1, significantly promoted the migration and invasion of colorectal cancer (CRC) cells in vitro and promoted liver and lung metastases in vivo. It also showed that the removal of FEM1C improved the proliferation ability of CRC cells. In particular, the cell shape changed from epithelial to fibroblast-like morphology. The tight cell monolayer was transformed into a dispersed distribution. Furthermore, it was demonstrated that FEM1C is down-regulated in tissues of CRC compared to normal tissues, and the high expression of FEM1C positively correlates with a good prognosis in patients with CRC. GSEA analysis showed that EMT signatures was enriched in FEM1C knockdown groups.

Conclusions

Down-regulation of FEM1C promotes proliferation and metastasis, and FEM1C may be a tumor suppressor in the development of CRC.

Identification and Functional Analysis of the Sex-Determiner Transformer-2 Homologue in the Freshwater Pearl Mussel, Hyriopsis cumingii

Transformer-2 (Tra-2) is an upstream regulatory element of the sex regulation mechanism in insects and plays a critical role in sex formation. To understand the role of tra-2 in Hyriopsis cumingii, the full-length Hctra-2 (1867 bp) was obtained from the gonads, and sequence alignment with other species showed that HCTRA-2 protein had a highly conserved RRM domain. Phylogenetic analysis showed that the HCTRA-2 protein was a close relative to of the mollusks TRA-2 protein. The qRT-PCR of tissue-specific expression pattern showed that the Hctra-2 was abundant in gonads, and the expression in testes was higher than that in ovaries (p < 0.01). It suggests that Hctra-2 may play a potential regulatory role in gonadal development of H. cumingii. In the early gonadal development, the Hctra-2 expression was the highest on the third day after fertilization and increased slightly from 4 months to 5 months, which may be related to the embryonic sex determination and early gonadal development. In situ hybridization showed that Hctra-2 mRNA signals were present in both male and female gonads. After silencing Hctra-2 by RNAi, the expression levels of Hcfem-1b and Hcdmrt were changed. It is speculated that there may be a certain relationship between them, which plays an important role in the sex regulation of H. cumingii. Our research will help to deepen our understanding of the shellfish sex determination mechanisms.

Schistosome W-linked genes inform temporal dynamics of sex chromosome evolution and suggest candidate for sex determination

Schistosomes, the human parasites responsible for snail fever, are female-heterogametic. Different parts of their ZW sex chromosomes have stopped recombining in distinct lineages, creating "evolutionary strata" of various ages. While the Z-chromosome is well characterized at the genomic and molecular level, the W-chromosome has remained largely unstudied from an evolutionary perspective, as only a few W-linked genes have been detected outside of the model species Schistosoma mansoni. Here, we characterize the gene content and evolution of the W-chromosomes of S. mansoni and of the divergent species S. japonicum. We use a combined RNA/DNA k-mer based pipeline to assemble around one hundred candidate W-specific transcripts in each of the species. About half of them map to known protein coding genes, the majority homologous to S. mansoni Z-linked genes. We perform an extended analysis of the evolutionary strata present in the two species (including characterizing a previously undetected young stratum in S. japonicum) to infer patterns of sequence and expression evolution of W-linked genes at different time points after recombination was lost. W-linked genes show evidence of degeneration, including high rates of protein evolution and reduced expression. Most are found in young lineage-specific strata, with only a few high expression ancestral W-genes remaining, consistent with the progressive erosion of non-recombining regions. Among these, the splicing factor U2AF2 stands out as a promising candidate for primary sex determination, opening new avenues for understanding the molecular basis of the reproductive biology of this group.

Sex Determination: TRA-1 Is a Non-binary Regulator of Sexual Identity

In nematodes, TRA-1 represses the transcription of genes involved in male differentiation, allowing XX animals to undergo normal hermaphrodite development. New reports show that this transcription factor also acts in XO males, to control the differentiation of many neurons.

Transcriptional profiles in Strongyloides stercoralis males reveal deviations from the Caenorhabditis sex determination model

The human and canine parasitic nematode Strongyloides stercoralis utilizes an XX/XO sex determination system, with parasitic females reproducing by mitotic parthenogenesis and free-living males and females reproducing sexually. However, the genes controlling S. stercoralis sex determination and male development are unknown. We observed precocious development of rhabditiform males in permissive hosts treated with corticosteroids, suggesting that steroid hormones can regulate male development. To examine differences in transcript abundance between free-living adult males and other developmental stages, we utilized RNA-Seq. We found two clusters of S. stercoralis-specific genes encoding predicted transmembrane proteins that are only expressed in free-living males. We additionally identified homologs of several genes important for sex determination in Caenorhabditis species, including mab-3, tra-1, fem-2, and sex-1, which may have similar functions. However, we identified three paralogs of gld-1; Ss-qki-1 transcripts were highly abundant in adult males, while Ss-qki-2 and Ss-qki-3 transcripts were highly abundant in adult females. We also identified paralogs of pumilio domain-containing proteins with sex-specific transcripts. Intriguingly, her-1 appears to have been lost in several parasite lineages, and we were unable to identify homologs of tra-2 outside of Caenorhabditis species. Together, our data suggest that different mechanisms control male development in S. stercoralis and Caenorhabditis species.

Molecular basis for ubiquitin ligase CRL2FEM1C-mediated recognition of C-degron

Proteome integrity depends on the ubiquitin-proteasome system to degrade unwanted or abnormal proteins. In addition to the N-degrons, C-terminal residues of proteins can also serve as degradation signals (C-degrons) that are recognized by specific cullin-RING ubiquitin ligases (CRLs) for proteasomal degradation. FEM1C is a CRL2 substrate receptor that targets the C-terminal arginine degron (Arg/C-degron), but the molecular mechanism of substrate recognition remains largely elusive. Here, we present crystal structures of FEM1C in complex with Arg/C-degron and show that FEM1C utilizes a semi-open binding pocket to capture the C-terminal arginine and that the extreme C-terminal arginine is the major structural determinant in recognition by FEM1C. Together with biochemical and mutagenesis studies, we provide a framework for understanding molecular recognition of the Arg/C-degron by the FEM family of proteins.

The development of sex differences in the nervous system and behavior of flies, worms, and rodents

Understanding how sex differences in innate animal behaviors arise has long fascinated biologists. As a general rule, the potential for sex differences in behavior is built by the developmental actions of sex-specific hormones or regulatory proteins that direct the sexual differentiation of the nervous system. In the last decade, studies in several animal systems have uncovered neural circuit mechanisms underlying discrete sexually dimorphic behaviors. Moreover, how certain hormones and regulatory proteins implement the sexual differentiation of these neural circuits has been illuminated in tremendous detail. Here, we discuss some of these mechanisms with three case-studies-mate recognition in flies, maturation of mating behavior in worms, and play-fighting behavior in young rodents. These studies illustrate general and unique developmental mechanisms to establish sex differences in neuroanatomy and behavior and highlight future challenges for the field.

BEX2 suppresses mitochondrial activity and is required for dormant cancer stem cell maintenance in intrahepatic cholangiocarcinoma

Cancer stem cells (CSCs) define a subpopulation of cancer cells that are resistant to therapy. However, little is known of how CSC characteristics are regulated. We previously showed that dormant cancer stem cells are enriched with a CD274^low fraction of cholangiocarcinoma cells. Here we found that BEX2 was highly expressed in CD274^low cells, and that BEX2 knockdown decreased the tumorigenicity and G₀ phase of cholangiocarcinoma cells. BEX2 was found to be expressed predominantly in G₀ phase and starvation induced the USF2 transcriptional factor, which induced BEX2 transcription. Comprehensive screening of BEX2 binding proteins identified E3 ubiquitin ligase complex proteins, FEM1B and CUL2, and a mitochondrial protein TUFM, and further demonstrated that knockdown of BEX2 or TUFM increased mitochondria-related oxygen consumption and decreased tumorigenicity in cholangiocarcinoma cells. These results suggest that BEX2 is essential for maintaining dormant cancer stem cells through the suppression of mitochondrial activity in cholangiocarcinoma.

A Cellular Mechanism to Detect and Alleviate Reductive Stress

Metazoan organisms rely on conserved stress response pathways to alleviate adverse conditions and preserve cellular integrity. Stress responses are particularly important in stem cells that provide lifetime support for tissue formation and repair, but how these protective systems are integrated into developmental programs is poorly understood. Here we used myoblast differentiation to identify the E3 ligase CUL2FEM1B and its substrate FNIP1 as core components of the reductive stress response. Reductive stress, as caused by prolonged antioxidant signaling or mitochondrial inactivity, reverts the oxidation of invariant Cys residues in FNIP1 and allows CUL2FEM1B to recognize its target. The ensuing proteasomal degradation of FNIP1 restores mitochondrial activity to preserve redox homeostasis and stem cell integrity. The reductive stress response is therefore built around a ubiquitin-dependent rheostat that tunes mitochondrial activity to redox needs and implicates metabolic control in coordination of stress and developmental signaling.

Dynamic, Non-binary Specification of Sexual State in the C. elegans Nervous System

Biological sex in animals is often considered a fixed, individual-level characteristic. However, not all sex-specific features are static: for example, C. elegans males (XO) can sometimes exhibit hermaphrodite (XX)-like feeding behavior [1, 2]. (C. elegans hermaphrodites are somatic females that transiently produce self-sperm.) Essentially all somatic sex differences in C. elegans are governed by the master regulator tra-1, whose activity is controlled by chromosomal sex and is necessary and sufficient to specify the hermaphrodite state [3]. One aspect of this state is high expression of the chemoreceptor odr-10. In hermaphrodites, high odr-10 expression promotes feeding, but in males, low odr-10 expression facilitates exploration [4]. However, males suppress this sex difference in two contexts: juvenile males exhibit high odr-10 expression and food deprivation activates odr-10 in adult males [4-6]. Remarkably, we find that both of these phenomena require tra-1. In juvenile (L3) males, tra-1 is expressed in numerous neurons; this expression diminishes as individuals mature into adulthood, a process that requires conserved regulators of sexual maturation. tra-1 remains expressed in a small number of neurons in adult males, where it likely has a permissive role in odr-10 activation. Thus, the neuronal functions of tra-1 are not limited to hermaphrodites; rather, tra-1 also acts in the male nervous system to transiently suppress a sexual dimorphism, developmentally and in response to nutritional stress. Our results show that the molecular and functional representation of sexual state in C. elegans is neither static nor homogeneous, challenging traditional notions about the nature of biological sex.

Molecular characterization of ovary-specific gene Mrfem-1 and siRNA-mediated regulation on targeting Mrfem-1 in the giant freshwater prawn, Macrobrachium rosenbergii

Characterized by ankyrin repeat motifs, the feminization-1 (fem-1) gene plays an essential role in sex determination/differentiation in Caenorhabditis elegans. However, there are only a few reports on fem-1 in crustaceans. In this study, a fem-1 gene (Mrfem-1) was first isolated from the giant freshwater prawn Macrobrachium rosenbergii. The full-length cDNA of Mrfem-1 was 2607 bp long, containing an open reading frame encoding 615 amino acids, and presenting eight ankyrin repeats. The full-length cDNA has been submitted to GenBank with the accession no. MT160093. According to the RT-PCR results, Mrfem-1 was exclusively expressed in the ovary. The expression level of Mrfem-1 had increased with ovarian maturation and reached the highest peak at vitellogenic stage. In situ hybridization results showed that positive signals were concentrated in the cytoplasm of previtellogenic stage, and scattered in the cytoplasm and follicular cells at vitellogenic stage, suggesting that Mrfem-1 might be associated with ovarian maturation. Moreover, two effective siRNAs targeting Mrfem-1 were found and their effectiveness verified in vitro. These results on Mrfem-1 will help us to better understand the fem family and provide a new resource for subsequent investigations of siRNA-mediated regulation on ovarian development in M. rosenbergii.

Distinct roles of two eIF4E isoforms in the germline of Caenorhabditis elegans

Germ cells use both positive and negative mRNA translational control to regulate gene expression that drives their differentiation into gametes. mRNA translational control is mediated by RNA-binding proteins, miRNAs and translation initiation factors. We have uncovered the discrete roles of two translation initiation factor eIF4E isoforms (IFE-1, IFE-3) that bind 7-methylguanosine (m7G) mRNA caps during Caenorhabditiselegans germline development. IFE-3 plays important roles in germline sex determination (GSD), where it promotes oocyte cell fate and is dispensable for spermatogenesis. IFE-3 is expressed throughout the germline and localizes to germ granules, but is distinct from IFE-1 and PGL-1, and facilitates oocyte growth and viability. This contrasts with the robust expression in spermatocytes of IFE-1, the isoform that resides within P granules in spermatocytes and oocytes, and promotes late spermatogenesis. Each eIF4E is localized by its cognate eIF4E-binding protein (IFE-1:PGL-1 and IFE-3:IFET-1). IFE-3 and IFET-1 regulate translation of several GSD mRNAs, but not those under control of IFE-1. Distinct mutant phenotypes, in vivo localization and differential mRNA translation suggest independent dormant and active periods for each eIF4E isoform in the germline.

Insights into the Involvement of Spliceosomal Mutations in Myelodysplastic Disorders from Analysis of SACY-1/DDX41 in Caenorhabditis elegans

Mutations affecting spliceosomal proteins are frequently found in hematological malignancies, including myelodysplastic syndromes and acute myeloid leukemia (AML). DDX41/Abstrakt is a metazoan-specific spliceosomal DEAD-box RNA helicase that is recurrently mutated in inherited myelodysplastic syndromes and in relapsing cases of AML. The genetic properties and genomic impacts of disease-causing missense mutations in DDX41 and other spliceosomal proteins have been uncertain. Here, we conduct a comprehensive analysis of the Caenorhabditis elegans DDX41 ortholog, SACY-1 Biochemical analyses defined SACY-1 as a component of the C. elegans spliceosome, and genetic analyses revealed synthetic lethal interactions with spliceosomal components. We used the auxin-inducible degradation system to analyze the consequence of SACY-1 depletion on the transcriptome using RNA sequencing. SACY-1 depletion impacts the transcriptome through splicing-dependent and splicing-independent mechanisms. Altered 3' splice site usage represents the predominant splicing defect observed upon SACY-1 depletion, consistent with a role for SACY-1 in the second step of splicing. Missplicing events appear more prevalent in the soma than the germline, suggesting that surveillance mechanisms protect the germline from aberrant splicing. The transcriptome changes observed after SACY-1 depletion suggest that disruption of the spliceosome induces a stress response, which could contribute to the cellular phenotypes conferred by sacy-1 mutant alleles. Multiple sacy-1 /ddx41 missense mutations, including the R525H human oncogenic variant, confer antimorphic activity, suggesting that their incorporation into the spliceosome is detrimental. Antagonistic variants that perturb the function of the spliceosome may be relevant to the disease-causing mutations, including DDX41, affecting highly conserved components of the spliceosome in humans.

Caenorhabditis elegans phosphatase complexes in UniProtKB and Complex Portal

Phosphatases play an essential role in the regulation of protein phosphorylation. Less abundant than kinases, many phosphatases are components of one or more macromolecular complexes with different substrate specificities and specific functionalities. The expert scientific curation of phosphatase complexes for the UniProt and Complex Portal databases supports the whole scientific community by collating and organising small- and large-scale experimental data from the scientific literature into context-specific central resources, where the data can be freely accessed and used to further academic and translational research. In this review, we discuss how the diverse biological functions of phosphatase complexes are presented in UniProt and the Complex Portal, and how understanding the biological significance of phosphatase complexes in Caenorhabditis elegans offers insight into the mechanisms of substrate diversity in a variety of cellular and molecular processes.

The Roles of Cullin-2 E3 Ubiquitin Ligase Complex in Cancer

Posttranslational protein modifications play an important role in regulating protein stability and cellular function. There are at least eight Cullin family members. Among them, Cullin-2 forms a functional E3 ligase complex with elongin B, elongin C, RING-box protein 1 (RBX1, also called ROC1), as well as the substrate recognition subunit (SRS) to promote the substrate ubiquitination and degradation. In this book chapter, we will review Cullin-2 E3 ligase complexes that include various SRS proteins, including von Hippel Lindau (pVHL), leucine-rich repeat protein-1 (LRR-1), preferentially expressed antigen of melanoma (PRAME), sex-determining protein FEM-1 and early embryogenesis protein ZYG-11. We will focus on the VHL signaling pathway in clear cell renal cell carcinoma (ccRCC), which may reveal various therapeutic avenues in treating this lethal cancer.

A natural antisense transcript of the fem-1 gene was found expressed in female gonads during the characterization, expression profile, and cellular localization of the fem-1 gene in Pacific white shrimp Penaeus vannamei

The fem-1 gene in Caenorhabditis elegans is involved in sex differentiation; it is specifically required for all aspects of male development. In this study, the full-length cDNA of the fem-1 (Pvfem-1) gene was isolated from the Pacific whiteleg shrimp Penaeus vannamei. The Pvfem-1 transcript is 3778 nt long and encodes a putative protein (PvFEM-1) of 638 amino acids that presented eight ankyrin repeats. The translated protein showed a significant (P < 0.05) structural similitude by superposition with C. elegans FEM-1 protein. Pvfem-1 expression was evaluated by qPCR and in situ hybridization (ISH) during embryogenesis, larval development, and gonads of both genders in subadult and adult life stages. Pvfem-1 was found expressed in brain, intestine, hepatopancreas, and in the gonads of both genders in subadults and adults when quantified by RT-qPCR. A significant finding was the discovery of a natural antisense transcript (NAT) of Pvfem-1 by ISH. It was present in the oocyte nucleus of subadult female shrimp gonads but was not seen within oocytes from adult females, although it was detected in follicular cells, suggesting a possible post-transcriptional regulation of Pvfem-1 in female gonad. Conversely, in males, no NAT was observed, and Pvfem-1 was found expressed in spermatogonia of both, subadult and adult shrimps indicating a function in male sexual differentiation and gametes generation. This study represents the first step for future functional analysis that is expected to contribute to clarifying the role of Pvfem-1 in sex differentiation and determination.

Timing mechanism of sexually dimorphic nervous system differentiation

The molecular mechanisms that control the timing of sexual differentiation in the brain are poorly understood. We found that the timing of sexually dimorphic differentiation of postmitotic, sex-shared neurons in the nervous system of the Caenorhabditis elegans male is controlled by the temporally regulated miRNA let-7 and its target lin-41, a translational regulator. lin-41 acts through lin-29a, an isoform of a conserved Zn finger transcription factor, expressed in a subset of sex-shared neurons only in the male. Ectopic lin-29a is sufficient to impose male-specific features at earlier stages of development and in the opposite sex. The temporal, sexual and spatial specificity of lin-29a expression is controlled intersectionally through the lin-28/let-7/lin-41 heterochronic pathway, sex chromosome configuration and neuron-type-specific terminal selector transcription factors. Two Doublesex-like transcription factors represent additional sex- and neuron-type specific targets of LIN-41 and are regulated in a similar intersectional manner.

Regulation of germ cell development by ARI1 family ubiquitin ligases in C. elegans

RING-between-RING (RBR) E3 ubiquitin ligases are implicated in various developmental processes, and mutations in genes encoding RBR proteins HHARI/ARIH1 and Parkin are associated with human diseases. Here we show by phylogenetic analysis that the ARI1 family has undergone a dramatic expansion within the Caenorhabditis clade in recent history, a characteristic shared by some genes involved in germline development. We then examined the effects of deleting all ARI1 family members in the nematode Caenorhabditis elegans, which to our knowledge represents the first complete knockout of ARI1 function in a metazoan. Hermaphrodites that lacked or had strongly reduced ARI1 activity had low fecundity and were partially defective in initiation of oocyte differentiation. We provide evidence that the C. elegans ARI1s likely function downstream or in parallel to FBF-1 and FBF-2, two closely related RNA-binding proteins that are required for the switch from spermatogenesis to oogenesis during late larval development. Previous studies have shown that the E2 enzymes UBC-18/UBCH7 and UBC-3/CDC34 can functionally collaborate with ARI1 family members. Our data indicated that UBC-18, but not UBC-3, specifically cooperates with the ARI1s in germline development. These findings provide new insights into the functions of RING-between-RING proteins and Ariadne E3s during development.

Novel Class of Viral Ankyrin Proteins Targeting the Host E3 Ubiquitin Ligase Cullin-2

Ankyrin repeat (ANK) domains are among the most abundant motifs in eukaryotic proteins. ANK proteins are rare amongst viruses, with the exception of poxviruses, which presumably acquired them from the host via horizontal gene transfer. The architecture of poxvirus ANK proteins is, however, different from that of their cellular counterparts, and this precludes a direct acquisition event. Here we combine bioinformatics analysis and quantitative proteomics to discover a new class of viral ANK proteins with a domain organization that relates to cellular ANK proteins. These noncanonical viral ANK proteins, termed ANK/BC, interact with host Cullin-2 via a C-terminal BC box resembling that of cellular Cullin-2 substrate adaptors such as the von Hippel-Lindau protein. Mutagenesis of the BC box-like sequence abrogates binding to Cullin-2, whereas fusion of this motif to an ANK-only protein confers Cullin-2 association. We demonstrated that these viral ANK/BC proteins are potent immunomodulatory proteins suppressing the activation of the proinflammatory transcription factors NF-κB and interferon (IFN)-responsive factor 3 (IRF-3) and the production of cytokines and chemokines, including interferon, and that association with Cullin-2 is required for optimal inhibitory activity. ANK/BC proteins exist in several orthopoxviruses and cluster into 2 closely related orthologue groups in a phylogenetic lineage that is separate from that of canonical ANK/F-box proteins. Given the existence of cellular proteins with similar architecture, viral ANK/BC proteins may be closely related to the original ANK gene acquired by an ancestral orthopoxvirus. These findings uncover a novel viral strategy to antagonize innate immunity and shed light on the origin of the poxviral ANK protein family.IMPORTANCE Viruses encode multiple proteins aimed at modulating cellular homeostasis and antagonizing the host antiviral response. Most of these genes were originally acquired from the host and subsequently adapted to benefit the virus. ANK proteins are common in eukaryotes but are unusual amongst viruses, with the exception of poxviruses, where they represent one of the largest protein families. We report here the existence of a new class of viral ANK proteins, termed ANK/BC, that provide new insights into the origin of poxvirus ANK proteins. ANK/BC proteins target the host E3 ubiquitin ligase Cullin-2 via a C-terminal BC box domain and are potent suppressors of the production of inflammatory cytokines, including interferon. The existence of cellular ANK proteins whose architecture is similar suggests the acquisition of a host ANK/BC gene by an ancestral orthopoxvirus and its subsequent duplication and adaptation to widen the repertoire of immune evasion strategies.

Molecular mechanisms underlying sexual differentiation of the nervous system

A long-standing goal in developmental neuroscience is to understand the mechanisms by which steroid sex hormones pattern the mammalian central nervous system along male or female pathways to enable subsequent displays of sexually dimorphic behaviors. In this article, we review recent advances in understanding the epigenetic and transcriptional mechanisms mediating sexual differentiation of the brain in mammals, flies, and worms. These studies suggest a model of sexual differentiation wherein master regulators of sex determination initiate a cascade of sexually dimorphic gene expression that controls development of neural pathways and behavioral displays in a strikingly modular manner. With these advances in molecular genetics, it is now feasible to disassemble different components of sexually dimorphic social behaviors without disrupting other behavioral interactions. Such experimental tractability promises rapid advances in this exciting field.

Sex-specific regulation of aging in Caenorhabditis elegans

A fascinating aspect of sexual dimorphism in various animal species is that the two sexes differ substantially in lifespan. In humans, for example, women's life expectancy exceeds that of men by 3-7 years. Whether this trait can be attributed to dissimilar lifestyles or genetic (regulatory) factors remains to be elucidated. Herein, we demonstrate that in the nematode Caenorhabditis elegans, the significantly longer lifespan of hermaphrodites-which are essentially females capable of sperm production-over males is established by TRA-1, the terminal effector of the sex-determination pathway. This transcription factor directly controls the expression of daf-16/FOXO, which functions as a major target of insulin/IGF-1 signaling (IIS) and key modulator of aging across diverse animal phyla. TRA-1 extends hermaphrodite lifespan through promoting daf-16 activity. Furthermore, TRA-1 also influences reproductive growth in a DAF-16-dependent manner. Thus, the sex-determination machinery is an important regulator of IIS in this organism. These findings provide a mechanistic insight into how longevity and development are specified unequally in the two genders. As TRA-1 is orthologous to mammalian GLI (glioma-associated) proteins, a similar sex-specific mechanism may also operate in humans to determine lifespan.

MAPK signaling couples SCF-mediated degradation of translational regulators to oocyte meiotic progression

RNA-binding proteins (RBPs) are important regulators of gene expression programs, especially during gametogenesis. How the abundance of particular RBPs is restricted to defined stages of meiosis remains largely elusive. Here, we report a molecular pathway that subjects two nonrelated but broadly evolutionarily conserved translational regulators (CPB-3/CPEB and GLD-1/STAR) to proteosomal degradation in Caenorhabditis elegans germ cells at the transition from pachytene to diplotene of meiotic prophase. Both RBPs are recognized by the same ubiquitin ligase complex, containing the molecular scaffold Cullin-1 and the tumor suppressor SEL-10/FBXW7 as its substrate recognition subunit. Destabilization of either RBP through this Skp, Cullin, F-box-containing complex (SCF) ubiquitin ligase appears to loosen its negative control over established target mRNAs, and presumably depends on a prior phosphorylation of CPB-3 and GLD-1 by MAPK (MPK-1), whose activity increases in mid- to late pachytene to promote meiotic progression and oocyte differentiation. Thus, we propose that the orchestrated degradation of RBPs via MAPK-signaling cascades during germ cell development may act to synchronize meiotic with sexual differentiation gene expression changes.

Sexually Dimorphic unc-6/Netrin Expression Controls Sex-Specific Maintenance of Synaptic Connectivity

Nervous systems display intriguing patterns of sexual dimorphisms across the animal kingdom, but the mechanisms that generate such dimorphisms remain poorly characterized. In the nematode Caenorhabditis elegans, a number of neurons present in both sexes are synaptically connected to one another in a sexually dimorphic manner as a result of sex-specific synaptic pruning and maintenance [1-3]. We define here a mechanism for the male-specific maintenance of the synaptic connections of the phasmid sensory neuron PHB and its male-specific target, the sex-shared AVG interneuron. We show that the C. elegans Netrin ortholog UNC-6, signaling through its cognate receptor UNC-40/DCC and the CED-5/DOCK180 guanine nucleotide exchange factor, is both required and sufficient for male-specific synaptic maintenance. The dimorphism of unc-6 activity is brought about by sex-specific regulation of unc-6 transcription. Although unc-6 is transcribed in the AVG neuron of males and hermaphrodites during juvenile stages, unc-6 expression is downregulated in AVG in hermaphrodites during sexual maturation but is maintained during sexual maturation of males. unc-6 downregulation in hermaphrodites is conferred by the master regulator of hermaphrodite sexual identity, the Gli/CI homolog TRA-1, which antagonizes the non-sex-specific function of the LIM homeobox gene lin-11, a terminal selector and activator of unc-6 in AVG. Preventing the downregulation of unc-6 in AVG of hermaphrodites through ectopic expression of unc-6 in transgenic animals results in the maintenance of the PHB>AVG synapses in hermaphrodites. Taken together, intersectional transcriptional regulation of unc-6/Netrin is required and sufficient to cell autonomously pattern sexually dimorphic synapses.

Atlas on substrate recognition subunits of CRL2 E3 ligases

The Cullin2-type ubiquitin ligases belong to the Cullin-Ring Ligase (CRL) family, which is a crucial determinant of proteasome-based degradation processes in eukaryotes. Because of the finding of von Hippel-Lindau tumor suppressor (VHL), the Cullin2-type ubiquitin ligases gain focusing in the research of many diseases, especially in tumors. These multisubunit enzymes are composed of the Ring finger protein, the Cullin2 scaffold protein, the Elongin B&C linker protein and the variant substrate recognition subunits (SRSs), among which the Cullin2 scaffold protein is the determining factor of the enzyme mechanism. Substrate recognition of Cullin2-type ubiquitin ligases depends on SRSs and results in the degradation of diseases associated substrates by intracellular signaling events. This review focuses on the diversity and the multifunctionality of SRSs in the Cullin2-type ubiquitin ligases, including VHL, LRR-1, FEM1b, PRAME and ZYG11. Recently, as more SRSs are being discovered and more aspects of substrate recognition have been illuminated, insight into the relationship between Cul2-dependent SRSs and substrates provides a new area for cancer research.

Fatty Acids Regulate Germline Sex Determination through ACS-4-Dependent Myristoylation

Fat metabolism has been linked to fertility and reproductive adaptation in animals and humans, and environmental sex determination potentially plays a role in the process. To investigate the impact of fatty acids (FA) on sex determination and reproductive development, we examined and observed an impact of FA synthesis and mobilization by lipolysis in somatic tissues on oocyte fate in Caenorhabditis elegans. The subsequent genetic analysis identified ACS-4, an acyl-CoA synthetase and its FA-CoA product, as key germline factors that mediate the role of FA in promoting oocyte fate through protein myristoylation. Further tests indicated that ACS-4-dependent protein myristoylation perceives and translates the FA level into regulatory cues that modulate the activities of MPK-1/MAPK and key factors in the germline sex-determination pathway. These findings, including a similar role of ACS-4 in a male/female species, uncover a likely conserved mechanism by which FA, an environmental factor, regulates sex determination and reproductive development.

FEM1 proteins are ancient regulators of SLBP degradation

FEM1A, FEM1B, and FEM1C are evolutionarily-conserved VHL-box proteins, the substrate recognition subunits of CUL2-RING E3 ubiquitin ligase complexes. Here, we report that FEM1 proteins are ancient regulators of Stem-Loop Binding Protein (SLBP), a conserved protein that interacts with the stem loop structure located in the 3' end of canonical histone mRNAs and functions in mRNA cleavage, translation and degradation. SLBP levels are highest during S-phase coinciding with histone synthesis. The ubiquitin ligase complex SCF^{cyclin F} targets SLBP for degradation in G2 phase; however, the regulation of SLBP during other stages of the cell cycle is poorly understood. We provide evidence that FEM1A, FEM1B, and FEM1C interact with and mediate the degradation of SLBP. Cyclin F, FEM1A, FEM1B and FEM1C all interact with a region in SLBP's N-terminus using distinct degrons. An SLBP mutant that is unable to interact with all 4 ligases is expressed at higher levels than wild type SLBP and does not oscillate during the cell cycle. We demonstrate that orthologues of SLBP and FEM1 proteins interact in C. elegans and D. melanogaster, suggesting that the pathway is evolutionarily conserved. Furthermore, we show that FEM1 depletion in C. elegans results in the upregulation of SLBP ortholog CDL-1 in oocytes. Notably, cyclin F is absent in flies and worms, suggesting that FEM1 proteins play an important role in SLBP targeting in lower eukaryotes.

Sexually Dimorphic Differentiation of a C. elegans Hub Neuron Is Cell Autonomously Controlled by a Conserved Transcription Factor

Functional and anatomical sexual dimorphisms in the brain are either the result of cells that are generated only in one sex or a manifestation of sex-specific differentiation of neurons present in both sexes. The PHC neuron pair of the nematode C. elegans differentiates in a strikingly sex-specific manner. In hermaphrodites the PHC neurons display a canonical pattern of synaptic connectivity similar to that of other sensory neurons, but in males PHC differentiates into a densely connected hub sensory neuron/interneuron, integrating a large number of male-specific synaptic inputs and conveying them to both male-specific and sex-shared circuitry. We show that the differentiation into such a hub neuron involves the sex-specific scaling of several components of the synaptic vesicle machinery, including the vesicular glutamate transporter eat-4/VGLUT, induction of neuropeptide expression, changes in axonal projection morphology, and a switch in neuronal function. We demonstrate that these molecular and anatomical remodeling events are controlled cell autonomously by the phylogenetically conserved Doublesex homolog dmd-3, which is both required and sufficient for sex-specific PHC differentiation. Cellular specificity of dmd-3 action is ensured by its collaboration with non-sex-specific terminal selector-type transcription factors, whereas the sex specificity of dmd-3 action is ensured by the hermaphrodite-specific transcriptional master regulator of hermaphroditic cell identity tra-1, which represses the transcription of dmd-3 in hermaphrodite PHC. Taken together, our studies provide mechanistic insights into how neurons are specified in a sexually dimorphic manner.

Asymmetric Cell Division in the One-Cell C. elegans Embryo: Multiple Steps to Generate Cell Size Asymmetry

The first division of the one-cell C. elegans embryo has been a fundamental model in deciphering the mechanisms underlying asymmetric cell division. Polarization of the one-cell zygote is induced by a signal from the sperm centrosome and results in the asymmetric distribution of PAR proteins. Multiple mechanisms then maintain PAR polarity until the end of the first division. Once asymmetrically localized, PAR proteins control several essential aspects of asymmetric division, including the position of the mitotic spindle along the polarity axis. Coordination of the spindle and cytokinetic furrow positions is the next essential step to ensure proper asymmetric division. In this chapter, I review the different mechanisms underlying these successive steps of asymmetric division. Work from the last 30 years has revealed the existence of multiple and redundant regulatory pathways which ensure division robustness. Besides the essential role of PAR proteins, this work also emphasizes the importance of both microtubules and actomyosin throughout the different steps of asymmetric division.

The ubiquitin ligase CRL2ZYG11 targets cyclin B1 for degradation in a conserved pathway that facilitates mitotic slippage

Cells arrested in mitosis by inactivation of the APC/C complex sometimes manage to exit mitosis in a process called mitotic slippage, which helps cancer cells circumvent chemotherapy drugs. Balachandran et al. show that mitotic slippage occurs as a result of targeting of cyclin B1 for degradation by the ligase CRL2^ZYG11.

The anaphase-promoting complex/cyclosome (APC/C) ubiquitin ligase is known to target the degradation of cyclin B1, which is crucial for mitotic progression in animal cells. In this study, we show that the ubiquitin ligase CRL2^ZYG-11 redundantly targets the degradation of cyclin B1 in Caenorhabditis elegans and human cells. In C. elegans, both CRL2^ZYG-11 and APC/C are required for proper progression through meiotic divisions. In human cells, inactivation of CRL2^ZYG11A/B has minimal effects on mitotic progression when APC/C is active. However, when APC/C is inactivated or cyclin B1 is overexpressed, CRL2^ZYG11A/B-mediated degradation of cyclin B1 is required for normal progression through metaphase. Mitotic cells arrested by the spindle assembly checkpoint, which inactivates APC/C, often exit mitosis in a process termed “mitotic slippage,” which generates tetraploid cells and limits the effectiveness of antimitotic chemotherapy drugs. We show that ZYG11A/B subunit knockdown, or broad cullin–RING ubiquitin ligase inactivation with the small molecule MLN4924, inhibits mitotic slippage in human cells, suggesting the potential for antimitotic combination therapy.

Regulation of the MEI-1/MEI-2 Microtubule-Severing Katanin Complex in Early Caenorhabditis elegans Development

After fertilization, rapid changes of the Caenorhabditis elegans cytoskeleton occur in the transition from meiosis to mitosis, requiring precise regulation. The MEI-1/MEI-2 katanin microtubule-severing complex is essential for meiotic spindle formation but must be quickly inactivated to allow for proper formation of the mitotic spindle. MEI-1/MEI-2 inactivation is dependent on multiple redundant pathways. The primary pathway employs the MEL-26 substrate adaptor for the CUL-3/cullin-based E3 ubiquitin ligase, which targets MEI-1 for proteosomal degradation. Here, we used quantitative antibody staining to measure MEI-1 levels to determine how other genes implicated in MEI-1 regulation act relative to CUL-3/MEL-26. The anaphase-promoting complex/cyclosome, APC/C, the DYRK (Dual-specificity tyrosine-regulated kinase), MBK-2, and the CUL-2-based E3 ubiquitin ligase act together to degrade MEI-1, in parallel to MEL-26/CUL-3. CUL-2 is known to keep MEL-26 low during meiosis, so CUL-2 apparently changes its target from MEL-26 in meiosis to MEI-1 in mitosis. RFL-1, an activator of cullin E3 ubiquitin ligases, activates CUL-2 but not CUL-3 for MEI-1 elimination. HECD-1 (HECT/Homologous to the E6AP carboxyl terminus domain) E3 ligase acts as a MEI-1 activator in meiosis but functions as an inhibitor during mitosis, without affecting levels of MEI-1 or MEI-2. Our results highlight the multiple layers of MEI-1 regulation that are required during the switch from the meiotic to mitotic modes of cell division.

"The persistence of memory"-Hermaphroditism in nematodes

Self-fertility has evolved many times in nematodes. This transition often produces an androdioecious species, with XX hermaphrodites and XO males. Although these hermaphrodites resemble females in most respects, early germ cells differentiate as sperm, and late ones as oocytes. The sperm then receive an activation signal, populate the spermathecae, and are stored for later use in self-fertilization. These traits are controlled by complex modifications to the sex-determination and sperm activation pathways, which have arisen independently during the evolution of each hermaphroditic species. This transformation in reproductive strategy then promotes other major changes in the development, evolution, and population structure of these animals. Mol. Reprod. Dev. 84: 144-157, 2017. © 2016 Wiley Periodicals, Inc.