RNF212B E3 ligase is essential for crossover designation and maturation during male and female meiosis in the mouse.

Meiosis, a reductional cell division, relies on precise initiation, maturation, and resolution of crossovers (COs) during prophase I to ensure the accurate segregation of homologous chromosomes during metaphase I. This process is regulated by the interplay of RING-E3 ligases such as RNF212 and HEI10 in mammals. In this study, we functionally characterized a recently identified RING-E3 ligase, RNF212B. RNF212B colocalizes and interacts with RNF212, forming foci along chromosomes from zygonema onward in a synapsis-dependent and DSB-independent manner. These consolidate into larger foci at maturing COs, colocalizing with HEI10, CNTD1, and MLH1 by late pachynema. Genetically, RNF212B foci formation depends on Rnf212 but not on Msh4, Hei10, and Cntd1, while the unloading of RNF212B at the end of pachynema is dependent on Hei10 and Cntd1. Mice lacking RNF212B, or expressing an inactive RNF212B protein, exhibit modest synapsis defects, a reduction in the localization of pro-CO factors (MSH4, TEX11, RPA, MZIP2) and absence of late CO-intermediates (MLH1). This loss of most COs by diakinesis results in mostly univalent chromosomes. Double mutants for Rnf212b and Rnf212 exhibit an identical phenotype to that of Rnf212b single mutants, while double heterozygous demonstrate a dosage-dependent reduction in CO number, indicating a functional interplay between paralogs. SUMOylome analysis of testes from Rnf212b mutants and pull-down analysis of Sumo- and Ubiquitin-tagged HeLa cells, suggest that RNF212B is an E3-ligase with Ubiquitin activity, serving as a crucial factor for CO maturation. Thus, RNF212 and RNF212B play vital, yet overlapping roles, in ensuring CO homeostasis through their distinct E3 ligase activities.

Synaptonemal Complex in Human Biology and Disease.

The synaptonemal complex (SC) is a meiosis-specific multiprotein complex that forms between homologous chromosomes during prophase of meiosis I. Upon assembly, the SC mediates the synapses of the homologous chromosomes, leading to the formation of bivalents, and physically supports the formation of programmed double-strand breaks (DSBs) and their subsequent repair and maturation into crossovers (COs), which are essential for genome haploidization. Defects in the assembly of the SC or in the function of the associated meiotic recombination machinery can lead to meiotic arrest and human infertility. The majority of proteins and complexes involved in these processes are exclusively expressed during meiosis or harbor meiosis-specific subunits, although some have dual functions in somatic DNA repair and meiosis. Consistent with their functions, aberrant expression and malfunctioning of these genes have been associated with cancer development. In this review, we focus on the significance of the SC and their meiotic-associated proteins in human fertility, as well as how human genetic variants encoding for these proteins affect the meiotic process and contribute to infertility and cancer development.

The Oncogenic FOXL2 C134W Mutation Is a Key Driver of Granulosa Cell Tumors.

Adult-type granulosa cell tumors (AGCT) are the most common type of malignant ovarian sex cord-stromal tumors. Most AGCTs carry the somatic variant c.402C>G (p.C134W) affecting the transcription factor FOXL2. Germline dominant variants in FOXL2 are responsible for blepharophimosis syndrome, which is characterized by underdevelopment of the eyelid. In this work, we generated a mouse model harboring the C134W variant of FOXL2 to evaluate in vivo the poorly understood oncogenic role of FOXL2. The mutation was dominant regarding eyelid hypoplasia, reminiscent of blepharophimosis syndrome. Interestingly, Foxl2+/C134W female mice had reduced fertility and developed AGCTs through a progression from abnormal ovaries with aberrant granulosa cells to ovaries with stromal hyperplasia and atypia and on to tumors in adut mice. The genes dysregulated in mouse AGCTs exhibited the hallmarks of cancer and were consistent with a gain-of-function of the mutated allele affecting TGFß signaling. A comparison of these data with previous results on human AGCTs indicated similar deregulated pathways. Finally, a mutational analysis of mouse AGCT transcriptomic data suggested the absence of additional driver mutations apart from FOXL2-C134W. These results provide a clear in vivo example in which a single mutational hit triggers tumor development associated with profound transcriptomic alterations. SIGNIFICANCE: A newly generated mouse model carrying a FOXL2 mutation characteristic of adult-type granulosa cell tumors shows that FOXL2 C134W shifts the transcriptome towards a signature of granulosa cell cancer and drives tumorigenesis.

BRCA2 binding through a cryptic repeated motif to HSF2BP oligomers does not impact meiotic recombination.

BRCA2 and its interactors are required for meiotic homologous recombination (HR) and fertility. Loss of HSF2BP, a BRCA2 interactor, disrupts HR during spermatogenesis. We test the model postulating that HSF2BP localizes BRCA2 to meiotic HR sites, by solving the crystal structure of the BRCA2 fragment in complex with dimeric armadillo domain (ARM) of HSF2BP and disrupting this interaction in a mouse model. This reveals a repeated 23 amino acid motif in BRCA2, each binding the same conserved surface of one ARM domain. In the complex, two BRCA2 fragments hold together two ARM dimers, through a large interface responsible for the nanomolar affinity - the strongest interaction involving BRCA2 measured so far. Deleting exon 12, encoding the first repeat, from mBrca2 disrupts BRCA2 binding to HSF2BP, but does not phenocopy HSF2BP loss. Thus, results herein suggest that the high-affinity oligomerization-inducing BRCA2-HSF2BP interaction is not required for RAD51 and DMC1 recombinase localization in meiotic HR.

A missense in HSF2BP causing primary ovarian insufficiency affects meiotic recombination by its novel interactor C19ORF57/BRME1.

Primary Ovarian Insufficiency (POI) is a major cause of infertility, but its etiology remains poorly understood. Using whole-exome sequencing in a family with three cases of POI, we identified the candidate missense variant S167L in HSF2BP, an essential meiotic gene. Functional analysis of the HSF2BP-S167L variant in mouse showed that it behaves as a hypomorphic allele compared to a new loss-of-function (knock-out) mouse model. Hsf2bpS167L/S167L females show reduced fertility with smaller litter sizes. To obtain mechanistic insights, we identified C19ORF57/BRME1 as a strong interactor and stabilizer of HSF2BP and showed that the BRME1/HSF2BP protein complex co-immunoprecipitates with BRCA2, RAD51, RPA and PALB2. Meiocytes bearing the HSF2BP-S167L variant showed a strongly decreased staining of both HSF2BP and BRME1 at the recombination nodules and a reduced number of the foci formed by the recombinases RAD51/DMC1, thus leading to a lower frequency of crossovers. Our results provide insights into the molecular mechanism of HSF2BP-S167L in human ovarian insufficiency and sub(in)fertility.

Securin-independent regulation of separase by checkpoint-induced shugoshin-MAD2.

Separation of eukaryotic sister chromatids during the cell cycle is timed by the spindle assembly checkpoint (SAC) and ultimately triggered when separase cleaves cohesion-mediating cohesin1-3. Silencing of the SAC during metaphase activates the ubiquitin ligase APC/C (anaphase-promoting complex, also known as the cyclosome) and results in the proteasomal destruction of the separase inhibitor securin1. In the absence of securin, mammalian chromosomes still segregate on schedule, but it is unclear how separase is regulated under these conditions4,5. Here we show that human shugoshin 2 (SGO2), an essential protector of meiotic cohesin with unknown functions in the soma6,7, is turned into a separase inhibitor upon association with SAC-activated MAD2. SGO2-MAD2 can functionally replace securin and sequesters most separase in securin-knockout cells. Acute loss of securin and SGO2, but not of either protein individually, resulted in separase deregulation associated with premature cohesin cleavage and cytotoxicity. Similar to securin8,9, SGO2 is a competitive inhibitor that uses a pseudo-substrate sequence to block the active site of separase. APC/C-dependent ubiquitylation and action of the AAA-ATPase TRIP13 in conjunction with the MAD2-specific adaptor p31comet liberate separase from SGO2-MAD2 in vitro. The latter mechanism facilitates a considerable degree of sister chromatid separation in securin-knockout cells that lack APC/C activity. Thus, our results identify an unexpected function of SGO2 in mitotically dividing cells and a mechanism of separase regulation that is independent of securin but still supervised by the SAC.

Ubiquitin-specific protease 26 (USP26) is not essential for mouse gametogenesis and fertility.

Ubiquitin-specific protease 26 (USP26) is a deubiquitylating enzyme belonging to the USPs family with a transcription pattern restricted to the male germline. Since protein ubiquitination is an essential regulatory mechanism during meiosis, many efforts have been focused on elucidating the function of USP26 and its relationship with fertility. During the last decade, several studies have reported the presence of different polymorphisms in USP26 in patients with non-obstructive azoospermia (NOA) or severe oligozoospermia suggesting that this gene may be associated with human infertility. However, other studies have revealed the presence of these and novel polymorphisms, including nonsense mutations, in men with normal spermatogenesis as well. Thus, the results remain controversial and its function is unknown. In the present study, we describe the in vivo functional analysis of mice lacking USP26. The phenotypic analysis of two different Usp26-null mutants showed no overt-phenotype with both males and females being fertile. Cytological analysis of spermatocytes showed no defects in synapsis, chromosome dynamics, DNA repair, or recombination. Histopathological analysis revealed a normal distribution and number of the different cell types in both male and female mice. Finally, normal counts were observed in fertility assessments. These results represent the first in vivo evidence showing that USP26 is not essential for mouse gametogenesis.

Local activation of mammalian separase in interphase promotes double-strand break repair and prevents oncogenic transformation.

Separase halves eukaryotic chromosomes in M-phase by cleaving cohesin complexes holding sister chromatids together. Whether this essential protease functions also in interphase and/or impacts carcinogenesis remains largely unknown. Here, we show that mammalian separase is recruited to DNA double-strand breaks (DSBs) where it is activated to locally cleave cohesin and facilitate homology-directed repair (HDR). Inactivating phosphorylation of its NES, arginine methylation of its RG-repeats, and sumoylation redirect separase from the cytosol to DSBs. In vitro assays suggest that DNA damage response-relevant ATM, PRMT1, and Mms21 represent the corresponding kinase, methyltransferase, and SUMO ligase, respectively. SEPARASE heterozygosity not only debilitates HDR but also predisposes primary embryonic fibroblasts to neoplasia and mice to chemically induced skin cancer. Thus, tethering of separase to DSBs and confined cohesin cleavage promote DSB repair in G2 cells. Importantly, this conserved interphase function of separase protects mammalian cells from oncogenic transformation.

Meikin is a conserved regulator of meiosis-I-specific kinetochore function.

The kinetochore is the crucial apparatus regulating chromosome segregation in mitosis and meiosis. Particularly in meiosis I, unlike in mitosis, sister kinetochores are captured by microtubules emanating from the same spindle pole (mono-orientation) and centromeric cohesion mediated by cohesin is protected in the following anaphase. Although meiotic kinetochore factors have been identified only in budding and fission yeasts, these molecules and their functions are thought to have diverged earlier. Therefore, a conserved mechanism for meiotic kinetochore regulation remains elusive. Here we have identified in mouse a meiosis-specific kinetochore factor that we termed MEIKIN, which functions in meiosis I but not in meiosis II or mitosis. MEIKIN plays a crucial role in both mono-orientation and centromeric cohesion protection, partly by stabilizing the localization of the cohesin protector shugoshin. These functions are mediated mainly by the activity of Polo-like kinase PLK1, which is enriched to kinetochores in a MEIKIN-dependent manner. Our integrative analysis indicates that the long-awaited key regulator of meiotic kinetochore function is Meikin, which is conserved from yeasts to humans.

Cohesin removal precedes topoisomerase IIα-dependent decatenation at centromeres in male mammalian meiosis II.

Sister chromatid cohesion is regulated by cohesin complexes and topoisomerase IIα. Although relevant studies have shed some light on the relationship between these two mechanisms of cohesion during mammalian mitosis, their interplay during mammalian meiosis remains unknown. In the present study, we have studied the dynamics of topoisomerase IIα in relation to that of the cohesin subunits RAD21 and REC8, the shugoshin-like 2 (Schizosaccharomyces pombe) (SGOL2) and the polo-like kinase 1-interacting checkpoint helicase (PICH), during both male mouse meiotic divisions. Our results strikingly show that topoisomerase IIα appears at stretched strands connecting the sister kinetochores of segregating early anaphase II chromatids, once the cohesin complexes have been removed from the centromeres. Moreover, the number and length of these topoisomerase IIα-connecting strands increase between lagging chromatids at anaphase II after the chemical inhibition of the enzymatic activity of topoisomerase IIα by etoposide. Our results also show that the etoposide-induced inhibition of topoisomerase IIα is not able to rescue the loss of centromere cohesion promoted by the absence of the shugoshin SGOL2 during anaphase I. Taking into account our results, we propose a two-step model for the sequential release of centromeric cohesion during male mammalian meiosis II. We suggest that the cohesin removal is a prerequisite for the posterior topoisomerase IIα-mediated resolution of persisting catenations between segregating chromatids during anaphase II.

Oxysterol-induced soluble endoglin release and its involvement in hypertension.

BACKGROUND: Ischemia in the placenta is considered the base of the pathogenesis of preeclampsia, a pregnancy-specific syndrome in which soluble endoglin (sEng) is a prognostic marker and plays a pathogenic role. Here, we investigated the effects of hypoxia and the downstream pathways in the release of sEng. METHODS AND RESULTS: Under hypoxic conditions, the trophoblast-like cell line JAR showed an increase in sEng parallel to an elevated formation of reactive oxygen species. Because reactive oxygen species are related to the formation of oxysterols, we assessed the effect of 22-(R)-hydroxycholesterol, a natural ligand of the liver X receptor (LXR), and the LXR synthetic agonist T0901317. Treatment of JAR cells or human placental explants with 22-(R)-hydroxycholesterol or T0901317 resulted in a clear increase in sEng that was dependent on LXR. These LXR agonists induced an increased matrix metalloproteinase-14 expression and activity and a significant reduction of its endogenous inhibitor, tissue inhibitor of metalloproteinase-3. In addition, mice treated with LXR agonists underwent an increase in the plasma sEng levels, concomitant with an increase in arterial pressure. Moreover, transgenic mice overexpressing sEng displayed high blood pressure. Finally, administration of an endoglin peptide containing the consensus matrix metalloproteinase-14 cleavage site G-L prevented the oxysterol-dependent increase in arterial pressure and sEng levels in mice. CONCLUSIONS: These studies provide a clue to the involvement of the LXR pathway in sEng release and its pathogenic role in vascular disorders such as preeclampsia.

Metalloproteinase MT5-MMP is an essential modulator of neuro-immune interactions in thermal pain stimulation.

Peripheral interactions between nociceptive fibers and mast cells contribute to inflammatory pain, but little is known about mechanisms mediating neuro-immune communication. Here we show that metalloproteinase MT5-MMP (MMP-24) is an essential mediator of peripheral thermal nociception and inflammatory hyperalgesia. We report that MT5-MMP is expressed by CGRP-containing peptidergic nociceptors in dorsal root ganglia and that Mmp24-deficient mice display enhanced sensitivity to noxious thermal stimuli under basal conditions. Consistently, mutant peptidergic sensory neurons hyperinnervate the skin, a phenotype that correlates with changes in the regulated cleavage of the cell-cell adhesion molecule N-cadherin. In contrast to basal nociception, Mmp24(-/-) mice do not develop thermal hyperalgesia during inflammation, a phenotype that appears associated with alterations in N-cadherin-mediated cell-cell interactions between mast cells and sensory fibers. Collectively, our findings demonstrate an essential role of MT5-MMP in the development of dermal neuro-immune synapses and suggest that this metalloproteinase may be a target for pain control.

Membrane-bound serine protease matriptase-2 (Tmprss6) is an essential regulator of iron homeostasis.

Proteolytic events at the cell surface are essential in the regulation of signal transduction pathways. During the past years, the family of type II transmembrane serine proteases (TTSPs) has acquired an increasing relevance because of their privileged localization at the cell surface, although our current understanding of the biologic function of most TTSPs is limited. Here we show that matriptase-2 (Tmprss6), a recently described member of the TTSP family, is an essential regulator of iron homeostasis. Thus, Tmprss6(-/-) mice display an overt phenotype of alopecia and a severe iron deficiency anemia. These hematologic alterations found in Tmprss6(-/-) mice are accompanied by a marked up-regulation of hepcidin, a negative regulator of iron export into plasma. Likewise, Tmprss6(-/-) mice have reduced ferroportin expression in the basolateral membrane of enterocytes and accumulate iron in these cells. Iron-dextran therapy rescues both alopecia and hematologic alterations of Tmprss6(-/-) mice, providing causal evidence that the anemic phenotype of these mutant mice results from the blockade of intestinal iron export into plasma after dietary absorption. On the basis of these findings, we conclude that matriptase-2 activity represents a novel and relevant step in hepcidin regulation and iron homeostasis.

Nuclear envelope defects cause stem cell dysfunction in premature-aging mice.

Nuclear lamina alterations occur in physiological aging and in premature aging syndromes. Because aging is also associated with abnormal stem cell homeostasis, we hypothesize that nuclear envelope alterations could have an important impact on stem cell compartments. To evaluate this hypothesis, we examined the number and functional competence of stem cells in Zmpste24-null progeroid mice, which exhibit nuclear lamina defects. We show that Zmpste24 deficiency causes an alteration in the number and proliferative capacity of epidermal stem cells. These changes are associated with an aberrant nuclear architecture of bulge cells and an increase in apoptosis of their supporting cells in the hair bulb region. These alterations are rescued in Zmpste24(-/-)Lmna(+/-) mutant mice, which do not manifest progeroid symptoms. We also report that molecular signaling pathways implicated in the regulation of stem cell behavior, such as Wnt and microphthalmia transcription factor, are altered in Zmpste24(-/-) mice. These findings establish a link between age-related nuclear envelope defects and stem cell dysfunction.

Earlier onset of tumoral angiogenesis in matrix metalloproteinase-19-deficient mice.

Among matrix metalloproteinases (MMP), MMP-19 displays unique structural features and tissue distribution. In contrast to most MMPs, MMP-19 is expressed in normal human epidermis and down-regulated during malignant transformation and dedifferentiation. The contribution of MMP-19 during tumor angiogenesis is presently unknown. In an attempt to give new insights into MMP-19 in vivo functions, angiogenic response of mutant mice lacking MMP-19 was analyzed after transplantation of murine malignant PDVA keratinocytes and after injection of Matrigel supplemented with basic fibroblast growth factor. In situ hybridization and immunohistochemical analysis revealed that MMP-19 is produced by host mesenchymal cells but not by endothelial capillary cells or CD11b-positive inflammatory cells. Based on a new computer-assisted method of quantification, we provide evidence that host MMP-19 deficiency was associated with an increased early angiogenic response. In addition, increased tumor invasion was observed in MMP-19-/- mice. We conclude that, in contrast to most MMPs that promote tumor progression, MMP-19 is a negative regulator of early steps of tumor angiogenesis and invasion. These data highlight the requirement to understand the individual functions of each MMP to improve anticancer strategies.

Accelerated ageing in mice deficient in Zmpste24 protease is linked to p53 signalling activation.

Zmpste24 (also called FACE-1) is a metalloproteinase involved in the maturation of lamin A (Lmna), an essential component of the nuclear envelope. Both Zmpste24- and Lmna-deficient mice exhibit profound nuclear architecture abnormalities and multiple histopathological defects that phenocopy an accelerated ageing process. Similarly, diverse human progeroid syndromes are caused by mutations in ZMPSTE24 or LMNA genes. To elucidate the molecular mechanisms underlying these devastating diseases, we have analysed the transcriptional alterations occurring in tissues from Zmpste24-deficient mice. We demonstrate that Zmpste24 deficiency elicits a stress signalling pathway that is evidenced by a marked upregulation of p53 target genes, and accompanied by a senescence phenotype at the cellular level and accelerated ageing at the organismal level. These phenotypes are largely rescued in Zmpste24-/-Lmna+/- mice and partially reversed in Zmpste24-/-p53-/- mice. These findings provide evidence for the existence of a checkpoint response activated by the nuclear abnormalities caused by prelamin A accumulation, and support the concept that hyperactivation of the tumour suppressor p53 may cause accelerated ageing.

Genomic instability in laminopathy-based premature aging.

Premature aging syndromes often result from mutations in nuclear proteins involved in the maintenance of genomic integrity. Lamin A is a major component of the nuclear lamina and nuclear skeleton. Truncation in lamin A causes Hutchinson-Gilford progerial syndrome (HGPS), a severe form of early-onset premature aging. Lack of functional Zmpste24, a metalloproteinase responsible for the maturation of prelamin A, also results in progeroid phenotypes in mice and humans. We found that Zmpste24-deficient mouse embryonic fibroblasts (MEFs) show increased DNA damage and chromosome aberrations and are more sensitive to DNA-damaging agents. Bone marrow cells isolated from Zmpste24-/- mice show increased aneuploidy and the mice are more sensitive to DNA-damaging agents. Recruitment of p53 binding protein 1 (53BP1) and Rad51 to sites of DNA lesion is impaired in Zmpste24-/- MEFs and in HGPS fibroblasts, resulting in delayed checkpoint response and defective DNA repair. Wild-type MEFs ectopically expressing unprocessible prelamin A show similar defects in checkpoint response and DNA repair. Our results indicate that unprocessed prelamin A and truncated lamin A act dominant negatively to perturb DNA damage response and repair, resulting in genomic instability which might contribute to laminopathy-based premature aging.

Matrix metalloproteinases in cancer: from new functions to improved inhibition strategies.

Over the last years, the relevance of the matrix metalloproteinase (MMP) family in cancer research has grown considerably. These enzymes were initially associated with the invasive properties of tumour cells, owing to their ability to degrade all major protein components of the extracellular matrix (ECM) and basement membranes. However, further studies have demonstrated the implication of MMPs in early steps of tumour evolution, including stimulation of cell proliferation and modulation of angiogenesis. The establishment of causal relationships between MMP overproduction in tumour or stromal cells and cancer progression has prompted the development of clinical trials with a series of inhibitors designed to block the proteolytic activity of these enzymes. Unfortunately, the results derived from using broad-spectrum MMP inhibitors (MMPIs) for treating patients with advanced cancer have been disappointing in most cases. There are several putative explanations for the lack of success of these MMPIs including the recent finding that some MMPs may play a paradoxical protective role in tumour progression. These observations together with the identification of novel functions for MMPs in early stages of cancer have made necessary a reformulation of MMP inhibition strategies. A better understanding of the functional complexity of this proteolytic system and global approaches to identify the relevant MMPs which must be targeted in each individual cancer patient, will be necessary to clarify whether MMP inhibition may be part of future therapies against cancer.

Diet-induced obesity and reduced skin cancer susceptibility in matrix metalloproteinase 19-deficient mice.

Matrix metalloproteinase 19 (MMP-19) is a member of the MMP family of endopeptidases that, in contrast to most MMPs, is widely expressed in human tissues under normal quiescent conditions. MMP-19 has been found to be associated with ovulation and angiogenic processes and is deregulated in diverse pathological conditions such as rheumatoid arthritis and cancer. To gain further insights into the in vivo functions of this protease, we have generated mutant mice deficient in Mmp19. These mice are viable and fertile and do not display any obvious abnormalities. However, Mmp19-null mice develop a diet-induced obesity due to adipocyte hypertrophy and exhibit decreased susceptibility to skin tumors induced by chemical carcinogens. Based on these results, we suggest that this enzyme plays an in vivo role in some of the tissue remodeling events associated with adipogenesis, as well as in pathological processes such as tumor progression.

Loss of collagenase-2 confers increased skin tumor susceptibility to male mice.

Matrix metalloproteinases (MMPs) have fundamental roles in tumor progression, but most clinical trials with MMP inhibitors have not shown improvements in individuals with cancer. This may be partly because broad-range inhibitors also reduce host-protective antitumor properties of individual MMPs. We generated mice deficient in collagenase-2 (Mmp8), an MMP mainly produced by neutrophils in inflammatory reactions and detected in some malignant tumors. Loss of Mmp8 did not cause abnormalities during embryonic development or in adult mice. Contrary to previous studies with MMP-deficient mice, however, the absence of Mmp8 strongly increased the incidence of skin tumors in male Mmp8(-/-)mice. Female Mmp8(-/-)mice whose ovaries were removed or were treated with tamoxifen were also more susceptible to tumors compared with wild-type mice. Bone marrow transplantation experiments confirmed that Mmp8 supplied by neutrophils was sufficient to restore the natural protection against tumor development mediated by this protease in male mice. Histopathological analysis showed that mutant mice had abnormalities in the inflammatory response induced by carcinogens. Our study identifies a paradoxical protective role for Mmp8 in cancer and provides a genetic model to evaluate the molecular basis of gender differences in cancer susceptibility.