Biology subjects

Pendas, A. M.

Publications and source records attributed to Pendas, A. M..

8 recordsLinked to original sources

bioRxiv2026

Set mediates chromosome alignment and Cohesin cleavage independently of direct PP2A-B56-binding in oocyte meiosis

Set promotes cohesion removal in mitosis by evicting phosphorylated Histone H1 and counteracting Sgo1. In addition, Set promotes chromosome alignment by counteracting Aurora B activation. The underlying molecular mechanisms through which Set performs these activities remain insufficiently characterized, but roles of Set as a Histone chaperone and PP2A inhibitor have been proposed. Building on our previous observations that Set promotes pericentromeric Cohesin removal in oocyte meiosis II, we generated an oocyte-specific conditional knock-out of Set to address its functions in meiosis. Similar to mitosis, Set depletion caused chromosome alignment and cohesion defects. We found that Set is required for accurate error correction by localizing Aurora B/C, and for efficient cleavage of the meiosis-specific Cohesin subunit Rec8 by Separase. Paired chromosomes and sister chromatids were often incompletely separated, likely a primary cause of missegregation. Set performed both its roles in a Sgo2-dependent manner, but, unexpectedly, independently of interaction with PP2A-B56. In line with a role of Set as a Histone chaperone, accumulation of phosphorylated Histone H1 in Set knock-out oocytes occurs concomitantly with reduction of oocyte-specific H1foo on chromosome arms, indicating that Set is required to create the optimal chromatin environment for efficient Rec8 cleavage by Separase in meiosis.

cell biology↗

bioRxiv2024

BEND2 is a crucial player in oogenesis and reproductive aging

Infertility affects up to 12% of couples globally, with genetic factors contributing to nearly half of the cases. Advances in genomic technologies have led to the discovery of genes like Bend2, which plays a crucial role in gametogenesis. In the testis, Bend2 expresses two protein isoforms: full-length and a smaller one. Ablation of both proteins results in an arrested spermatogenesis. Because the Bend2 locus is on the X chromosome, and the Bend2-/y mutants are sterile, BEND2s role in oogenesis remained elusive. In this study, we employed a novel Bend2 mutation that blocks the expression of the full-length BEND2 protein but allows the expression of the smaller BEND2 isoform. Interestingly, this mutation does not confer male sterility and mildly affects spermatogenesis. Thus, it allowed us to study the role of BEND2 in oogenesis. Our findings demonstrate that full-length BEND2 is dispensable for male fertility, and its ablation leads to a reduced establishment of the ovarian reserve. These results reveal a critical role for full-length BEND2 in oogenesis and provide insights into the mechanisms underlying the establishment of the ovarian reserve. Furthermore, these findings hold relevance for the diagnostic landscape of human infertility.

cell biology↗

bioRxiv2024

Genome-wide transcriptional silencing and mRNA stabilization allow the coordinated expression of the meiotic program in mice

The transcriptional dynamic of mammalian cells when these transit from the ubiquitous mitotic to a meiotic specific program is key to understand this switch central to sexual reproduction. By quantifying active RNA polymerase II and nascent transcripts using single cell dataset and ethynyl-uridine pool-down with sorted cells from synchronised testes, we detailed the transcriptional activity of murine male germ cells. When spermatogonia differentiate, transcription slows down, reaching minimal activity at meiotic entry and resumes during pachytene stage. This event, we termed EMLT (for early meiotic low transcription), is distinct from the silencing of sex chromosomes as it is independent of Setdb1 though it is accompanied by the same chromatin mark, H3K9me3. EMLT is delayed in Stra8KO but occurs in mutants altering meiotic chromosome structure or DSB formation or repair. By comparing transcript abundance and neotranscription we unveil a massive event of mRNA stabilization that parallels EMLT. Altogether our data indicate that meiosis is initiated with a nearly silent genome and we propose that the stabilization of transcripts at that time facilitates the meiotic entry by synchronising the expression of several meiotic sub-programs.

cell biology↗

bioRxiv2020

A cryptic BRCA2 repeated motif binds to HSF2BP oligomers with no impact on meiotic recombination

BRCA2 plays a prominent role in meiotic homologous recombination (HR). Loss of BRCA2 or several of its meiotic partners causes fertility defects. One of these partners, HSF2BP, was recently discovered as expressed physiologically in germline and ectopically produced in cancer cells. It has an N-terminal coiled coil motif involved in direct binding to the protein BRME1, and both HSF2BP and BRME1 are essential for meiotic HR during spermatogenesis. It also interacts through its C-terminal Armadillo (ARM) domain with a conserved region of BRCA2 of unknown function. We analyzed the structural properties and functional consequences of the BRCA2-HSF2BP interaction and tested the emerging model of its involvement in meiosis. We solved the crystal structure of the complex between the BRCA2 fragment that is disordered in solution and the HSF2BP dimeric ARM domain. This revealed two previously unrecognized BRCA2 repeats that each interact with one ARM monomer from two different dimers. BRCA2 binding triggers ARM tetramerization, resulting in a complex containing two BRCA2 fragments connecting two ARM dimers. The 3D structures of the BRCA2 repeats are superimposable, revealing conserved contacts between the BRCA2 residues defining the repeats and the HSF2BP residues lining the groove of the ARM. This large interface is responsible for the nanomolar affinity of the interaction, significantly stronger than any other measured interaction involving BRCA2. Deleting exon 12 from Brca2, encoding the first repeat, disrupted BRCA2 binding to HSF2BP in vitro and in cells. However, Brca2{Delta}12/{Delta}12 mice with the same deletion were fertile and did not show any meiotic defects, contrary to the prediction from the model positing that HSF2BP acts as a meiotic localizer of BRCA2. We conclude that the high-affinity interaction between BRCA2 and HSF2BP and the resulting HSF2BP oligomerization are not required for RAD51 and DMC1 recombinase localization to meiotic double strand breaks and for productive meiotic HR.

molecular biology↗

bioRxiv2020

A missense in HSF2BP causing Primary Ovarian Insufficiency affects meiotic recombination by its novel interactor C19ORF57/MIDAP

Primary Ovarian Insufficiency (POI) is a major cause of infertility, but its etiology remains poorly understood. Using whole-exome sequencing in a family with 3 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, compared to a new HSF2BP knock-out mouse showed that it behaves as a hypomorphic allele. HSF2BP-S167L females show reduced fertility with small litter sizes. To obtain mechanistic insights, we identified C19ORF57/MIDAP as a strong interactor and stabilizer of HSF2BP by forming a higher-order macromolecular structure involving BRCA2, RAD51, RPA and PALB2. Meiocytes bearing the HSF2BP-S167L mutation showed a strongly decreased expression of both MIDAP and HSF2BP at the recombination nodules. Although HSF2BP-S167L does not affect heterodimerization between HSF2BP and MIDAP, it promotes a lower expression of both proteins and a less proficient activity in replacing RPA by the recombinases RAD51/DMC1, thus leading to a lower frequency of cross-overs. Our results provide insights into the molecular mechanism of two novel actors of meiosis underlying non-syndromic ovarian insufficiency. SummaryFelipe-Medina et al. describe a missense variant in the meiotic gene HSF2BP in a consanguineous family with Premature Ovarian Insufficiency, and characterize it as an hypormorphic allele, that in vivo impairs its dimerization with a novel meiotic actor, MIDAP/ C19ORF57, and affect recombination at double-strand DNA breaks.

genetics↗

bioRxiv2020

Meiotic chromosome synapsis depends on multivalent SYCE1-SIX6OS1 interactions that are disrupted in cases of human infertility

Meiotic reductional division is dependent on the synaptonemal complex (SC), a supramolecular protein assembly that mediates homologous chromosomes synapsis and promotes crossover formation. The mammalian SC is formed of eight structural components, including SYCE1, the only central element protein with known causative mutations in human infertility. We combine mouse genetics, cellular and biochemical studies to reveal that SYCE1 undergoes multivalent interactions with SC component SIX6OS1. The N-terminus of SIX6OS1 binds and disrupts SYCE1s core dimeric structure to form a 1:1 complex, whilst their downstream sequences provide a distinct second interface. These interfaces are separately disrupted by SYCE1 mutations associated with non-obstructive azoospermia and premature ovarian failure, respectively. Mice harbouring SYCE1s POF mutation and a targeted deletion within SIX6OS1s N-terminus are infertile with failure of chromosome synapsis. We conclude that both SYCE1-SIX6OS1 binding interfaces are essential for SC assembly, thus explaining how SYCE1s reported clinical mutations give rise to human infertility.

biochemistry↗

bioRxiv2018

Spermatoproteasome-deficient mice are proficient in meiotic DNA repair but defective in meiotic exit

Meiotic recombination generates crossovers which are essential to ensure genome haploidization. The ubiquitin proteasome system regulates meiotic recombination through its association to the synaptonemal complex, a zipper-like structure that holds homologs and provides the structural framework for meiotic recombination. Here we show that the testis-specific 4s subunit (PSMA8) of the spermatoproteasome is located at the synaptonemal complex and is essential for the assembly of its activator PA200. Accordingly, synapsis-deficient mice show delocalization of PSMA8 from the synaptonemal complex. Genetic analysis of Psma8-deficient mice shows normal meiotic DNA repair, crossing over formation and an increase of spermatocytes at metaphase I and metaphase II which either enter into apoptosis or slip to give rise to an early spermatid arrest and infertility. Thus, spermatoproteasome-dependent histone degradation is dispensable for meiotic recombination. We show that PSMA8 deficiency alters the proteostasis of several key meiotic players such as acetylated histones, SYCP3, SYCP1, CDK1 and TRIP13 which in turn leads to an aberrant meiotic exit and early spermatid arrest prior to the histone displacement process that take place subsequently.

cell biology↗

bioRxiv2018

Shugoshin protects centromere pairing and promotes segregation of non-exchange partner chromosomes in meiosis

Faithful chromosome segregation during meiosis I depends upon the formation of connections between homologous chromosomes. Crossovers between homologs connect the partners allowing them to attach to the meiotic spindle as a unit, such that they migrate away from one another at anaphase I. Homologous partners also become connected by pairing of their centromeres in meiotic prophase. This centromere pairing can promote proper segregation at anaphase I of partners that have failed to become joined by a crossover. Centromere pairing is mediated by synaptonemal complex (SC) proteins that persist at the centromere when the SC disassembles. Here, using mouse spermatocyte and yeast model systems, we tested the role of shugoshin in promoting meiotic centromere pairing by protecting centromeric synaptonemal components from disassembly. The results show that shugoshin protects centromeric SC in meiotic prophase and, in anaphase, promotes the proper segregation of partner chromosomes that are not linked by a crossover. SIGNIFICANCEMeiotic crossovers form a connection between homologous chromosomes that allows them to attach to the spindle as a single unit in meiosis I. In humans, failures in this process are a leading cause of aneuploidy. A recently described process, called centromere pairing, can also help connect meiotic chromosome partners in meiosis. Homologous chromosomes become tightly joined by a structure called the synaptonemal complex (SC) in meiotic prophase. After the SC disassembles, persisting SC proteins at the centromeres mediate their pairing. Here, studies in mouse spermatocytes and yeast are used to show that the shugoshin protein helps SC components persist at centromeres and helps centromere pairing promote the proper segregation of yeast chromosomes that fail to become tethered by crossovers.

cell biology↗