Biology subjects

Lopez-Jimenez, P.

Publications and source records attributed to Lopez-Jimenez, P..

7 recordsLinked to original sources

bioRxiv2025

The dynamics of ciliogenesis in prepubertal mouse meiosis reveal new clues about testicular maturation during puberty

The primary cilium, a solitary and non-motile extension of the plasma membrane, has recently been identified in adult male mouse spermatocytes. However, very little is known about when these cilia emerge during testicular maturation and what their function is. In the context of fertility establishment during puberty, this study investigates the dynamics of ciliogenesis in prepubertal mouse spermatocytes. Our findings reveal that primary cilia are not an intrinsic feature of spermatocytes during the first wave of meiosis, which initiates at 8 days post-partum (dpp). Instead, cilia begin polymerizing at 20 dpp, after first meiotic wave has been completed, and are present in spermatocytes across all stages of prophase I. Thus, no direct correlation between cilia polymerization and the initiation of synapsis or desynapsis was found, although chemical ablation of cilia may delay DNA repair during prophase I. Typical adult cilia features, which are shorter and restricted to zygotene spermatocytes, are settled upon acquisition of sexual maturity. This study also highlights that the emergence of ciliated spermatocytes in prepuberal mice coincides with the onset of flagellogenesis, hinting at a potential link between the regulation of the formation of both types of axonemes within the tissue developing environment. Proteomic analyses further identify temporal regulators of axoneme assembly, providing valuable targets for future research to unravel the molecular pathways underlying ciliogenesis, flagellogenesis, and their roles in spermatogenesis. We explored distinct regulatory mechanisms of ciliogenesis during the first meiotic wave and found that Aurora kinase A (AURKA) is a critical regulator of cilia disassembly during late diplotene, with evidence suggesting that centrosome migration and cilia depolymerization are mutually exclusive events during meiosis. In summary, this study provides the first detailed characterization of primary cilia dynamics during early testicular maturation in mice, revealing their spatiotemporal regulation, candidate molecular mediators, and potential roles during meiosis. These findings lay the groundwork for understanding the physiological relevance of meiotic cilia in spermatogenesis and testicular development.

cell biology↗

bioRxiv2023

Divergent patterns of meiotic double strand breaks and synapsis initiation dynamics suggest an evolutionary shift in the meiosis program between American and Australian marsupials

In eutherian mammals, hundreds of programmed DNA double-strand breaks (DSBs) are generated at the onset of meiosis. The DNA damage response is then triggered. Although the dynamics of this response is well studied in eutherian mammals, recent findings have revealed different patterns of DNA damage signaling and repair in marsupial mammals. To better characterize these differences, here we analyzed synapsis and the chromosomal distribution of meiotic DSBs markers in three different marsupial species (Thylamys elegans, Dromiciops gliorides, and Macropus eugenii) that represent South American and Australian Orders. Our results revealed inter-specific differences in the chromosomal distribution of DNA damage and repair proteins, which were associated with differing synapsis patterns. In the American species T. elegans and D. gliroides, synapsis progressed exclusively from the chromosomal ends towards interstitial regions. This was accompanied by sparse H2AX phosphorylation, mainly accumulating at chromosomal ends, which appeared conspicuously polarized in a bouquet configuration at early stages of prophase I. Accordingly, RAD51 and RPA were mainly localized at chromosomal ends throughout prophaseI in both American marsupials, likely resulting in reduced recombination rates at interstitial positions. In sharp contrast, synapsis initiated at both interstitial and distal chromosomal regions in the Australian representative M. eugenii, {gamma}H2AX had a broad nuclear distribution, and RAD51 and RPA foci displayed an even chromosomal distribution. Given the basal evolutionary position of T. elegans, it is likely that the meiotic features reported in this species represent an ancestral pattern in marsupials and that a shift in the meiotic program occurred after the split of D. gliroides and the Australian marsupial clade. Our results open intriguing questions about the regulation and homeostasis of meiotic DSBs in marsupials. The low recombination rates observed at the interstitial chromosomal regions in American marsupials can result in the formation of large linkage groups, thus having an impact in the evolution of their genomes.

genetics↗

bioRxiv2023

The organotypic culture of mouse seminiferous tubules as a reliable methodology for the study of meiosis in vitro

Male mouse meiosis has been traditionally studied using descriptive methods like histological sections, spreading or squashing techniques, which allow the observation of fixed meiocytes in either wildtype or genetically modified mice. For these studies, the sacrifice of the males and the extraction of the testicles are required to obtain the material of study. Other functional in vivo studies include the administration of intravenous or intraperitoneal drugs, or the exposure to mutagenic agents or generators of DNA damage, in order to study their impact on meiosis progression. However, in these studies, the exposure times or drug concentration are important limitations to consider when acknowledging animal welfare. Recently, several approaches have been proposed to offer alternative methodologies that allow the in vitro study of spermatocytes with a considerable reduction in the use of animals. Here we revisit and validate an optimal technique of organotypic culture of fragments of seminiferous tubules for meiotic studies. This technique is a trustable methodology to develop functional studies that preserve the histological configuration of the seminiferous tubule, aim homogeneity of the procedures (the use of the same animal for different study conditions), and allow procedures that would compromise the animal welfare. Therefore, this methodology is highly recommendable for the study of meiosis and spermatogenesis, while it supports the principle of 3R's for animal research.

cell biology↗

bioRxiv2022

The male mouse meiotic cilium emanates from the mother centriole at zygotene prior to centrosome duplication

Cilia are hair-like projections of the plasma membrane with an inner microtubule skeleton known as axoneme. Motile cilia and flagella beat to displace extracellular fluids, playing important roles in the airways and reproductive system, among others. Instead, primary cilia function as cell type-dependent sensory organelles, detecting chemical, mechanical or optical signals from the extracellular environment. Cilia dysfunction is associated with genetic diseases called ciliopathies, and with some types of cancer. Cilia have been recently identified in zebrafish gametogenesis as an important regulator of the bouquet conformation and recombination. However, there is very little information about the structure and functions of cilia in mammalian meiosis. Here we describe the presence of cilia in male mouse meiotic cells. These solitary cilia form transiently in 20% of zygotene spermatocytes and reach considerable lengths (up to 15 m). CEP164 and CETN3 localization studies indicate that these cilia emanate from the mother centriole, prior to centrosome duplication. In addition, the study of telomeric TFR2 suggests that these cilia are not directly related to the bouquet conformation during early male mouse meiosis. Instead, based on TEX14 labeling of intercellular bridges in spermatocyte cysts, we suggest that mouse meiotic cilia may have sensory roles affecting cyst function during prophase I.

cell biology↗

bioRxiv2022

The kleisin subunit controls the function of meiotic cohesins by determining the mode of DNA binding and differential regulation by SCC-2 and WAPL-1

The cohesin complex plays essential roles in chromosome segregation, 3D genome organisation, and DNA damage repair through its ability to modify DNA topology. In higher eukaryotes, meiotic chromosome function, and therefore fertility, requires cohesin complexes containing meiosis-specific kleisin subunits: REC8 and RAD21L in mammals and REC-8 and COH-3/4 in C. elegans. How these complexes perform the multiple functions of cohesin during meiosis and whether this involves different modes of DNA binding or dynamic association with chromosomes is poorly understood. Combining time-resolved methods of protein removal with live imaging and exploiting the temporospatial organisation of the C. elegans germline, we show that REC-8 complexes provide sister chromatid cohesion (SCC) and DNA repair, while COH-3/4 complexes control higher-order chromosome structure. High-abundance COH-3/4 complexes associate dynamically with individual chromatids in a manner dependent on cohesin loading (SCC-2) and removal (WAPL-1) factors. In contrast, low-abundance REC-8 complexes associate stably with chromosomes, tethering sister chromatids from S-phase until the meiotic divisions. Our results reveal that kleisin identity determines the function of meiotic cohesin by controlling the mode and regulation of cohesin-DNA association, and are consistent with a model in which SCC and DNA looping are performed by variant cohesin complexes that coexist on chromosomes.

cell biology↗

bioRxiv2020

BAP1/ASXL complex modulation regulates Epithelial-Mesenchymal Transition during trophoblast differentiation and invasion

Normal function of the placenta depends on the earliest developmental stages when trophoblast cells differentiate and invade into the endometrium to establish the definitive maternal-fetal interface. Previously, we identified the ubiquitously expressed tumour suppressor BRCA1-associated protein 1 (BAP1) as a central factor of a novel molecular node controlling early mouse placentation. However, functional insights into how BAP1 regulates trophoblast biology are still missing. Using CRISPR/Cas9 knockout and overexpression technology, here we demonstrate that the downregulation of BAP1 protein is essential to trigger epithelial-mesenchymal transition (EMT) during trophoblast differentiation associated with a gain of invasiveness. This function, which is conserved in mouse and humans, is dependent on the binding of BAP1 binding to Additional sex comb-like (ASXL1/2/3) proteins to form the Polycomb repressive deubiquitinase (PR-DUB) complex. Our results reveal that the physiological modulation of BAP1 determines the invasive properties of trophoblast, delineating a new role of the BAP1 PR-DUB complex in regulating early placentation.

developmental biology↗

bioRxiv2020

Meiosis reveals the early steps in the evolution of a neo-XY sex chromosome pair in the African pygmy mouse Mus minutoides

Sex chromosomes of eutherian mammals are highly different in size and gene content, and share only a small region of homology (pseudoautosomal region, PAR). They are thought to have evolved through an addition-attrition cycle involving the addition of autosomal segments to sex chromosomes and their subsequent differentiation. The events that drive this process are difficult to investigate because sex chromosomes in most mammals are at a very advanced stage of differentiation. Here, we have taken advantage of a recent translocation of an autosome to both sex chromosomes in the African pygmy mouse Mus minutoides, which has restored a large segment of homology (neo-PAR). By studying meiotic sex chromosome behavior and identifying fully sex-linked genetic markers in the neo-PAR, we demonstrate that this region shows unequivocal signs of early sex-differentiation. First, synapsis and resolution of DNA damage intermediates are delayed in the neo-PAR during meiosis. Second, recombination is suppressed in a large portion of the neo-PAR. However, the inactivation process that characterizes sex chromosomes during meiosis does not extend to this region. Finally, the sex chromosomes show a dual mechanism of association at metaphase-I that involves the formation of a chiasma in the neo-PAR and the preservation of an ancestral achiasmate mode of association in the non-homologous segments. We show that the study of meiosis is crucial to apprehend the onset of sex chromosome differentiation, as it introduces structural and functional constrains to sex chromosome evolution. Synapsis and DNA repair dynamics are the first processes affected in the incipient differentiation of X and Y chromosomes, and they may be involved in accelerating their evolution. This provides one of the very first reports of early steps in neo-sex chromosome differentiation in mammals, and for the first time a cellular framework for the addition-attrition model of sex chromosome evolution. AUTHOR SUMMARYThe early steps in the evolution of sex chromosomes are particularly difficult to study. Cessation of recombination around the sex-determining locus is thought to initiate the differentiation of sex chromosomes. Several studies have investigated this process from a genetic point of view. However, the cellular context in which recombination arrest occurs has not been considered as an important factor. In this report, we show that meiosis, the cellular division in which pairing and recombination between chromosomes takes place, can affect the incipient differentiation of X and Y chromosomes. Combining cytogenetic and genomic approaches, we found that in the African pygmy mouse Mus minutoides, which has recently undergone a sex chromosome-autosome fusion, synapsis and DNA repair dynamics are altered along the newly added region of the sex chromosomes, likely interfering with recombination and thus contributing to the genetic isolation of a large segment of the Y chromosome. Therefore, the cellular events that occur during meiosis are crucial to understand the very early stages of sex chromosome differentiation. This can help to explain why sex chromosomes evolve very fast in some organisms while in others they have barely changed for million years.

genetics↗