Genetique Reproduction and Developpement

Abstract. Explosive volcanic eruptions generate large amounts of volcanic ash that release essential and nonessential trace metals upon deposition in seawater, modifying its chemical composition. Tropical scleractinian corals, known for accumulating trace metals, are susceptible to these changes, making them valuable biomonitors for increased metal concentrations. In this study, we investigated how volcanic ash leaching influences trace metal partitioning within the hermatypic branching coral Stylophora pistillata through six-week coral culture experiments. Coral nubbins were reared under control and ash exposed conditions, with 2.5 g ash added three times a week (averaging 250 mg L−1 per week). We quantified trace metals (V, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) in the ash-seawater leachate, and in three distinct coral compartments (skeleton, tissue and symbionts). 24 hour ash leaching experiments at a ratio of 1 : 100 (g ash : mL seawater) demonstrated that ash from La Soufrière (St. Vincent) released trace metals in the order Mn, Zn, Co, Cu, Cd, Fe, and Ni into seawater, while Pb and V were scavenged. Trace metal concentrations in coral compartments correlated with seawater concentrations, with most significant changes observed in the skeletal metal content. Ash exposure enriched skeletal concentrations of V, Mn, Fe, Ni, and Zn while depleting Cu and Pb. Ash leaching also shifted the metal distribution in coral skeletons, affecting relationships between transition and alkaline earth/alkali metals. Apparent skeletal distribution coefficients (KEl) for labgrown corals showed most trace metals were less abundant in skeletons than seawater (KEl < 1), except for Pb, Cd and Co (KEl > 1). Metal concentrations varied between tissues and symbionts, with Mn and Fe significantly enriched in ash exposed tissues. Volcanic ash releases a range of trace metals, altering the coral metallome by affecting bioaccumulation and metal redistribution across coral compartments. These findings not only advance our understanding of coral trace metal dynamics at the organismal level, but also provide a basis for estimating environmental metal fluxes during future eruptive scenarios and help interpret geochemical coral archives of past eruptions.

Crop breeding relies on the creation of high-performance varieties that possess a genotype containing numerous agronomical traits of interest. The specific combination of traits is generated in the parents by meiotic recombination, a highly conserved and controlled cellular process. Improvement of recombination, both in terms of quantity of crossovers and control of their localisation, would enhance the breeding capacities for all crops. This includes allopolyploid wheats, particularly tetraploid durum wheat (Triticum turgidum ssp. durum, AABB genome) and hexaploid bread wheat (Triticum aestivum, AABBDD), two of the most important cultivated species on the planet. As allopolyploid species, recombination in wheat is subjected to two levels of control: (1) recombination between homologous chromosomes that is biologically favoured but has low frequency and uneven distribution; (2) recombination between homoeologous chromosomes that is prevented, although this is the process that allows the introduction of diversity from related species. During the last ten years, a lot of effort has been focused on identifying and studying genes involved in controlling the rate and distribution of homologous and homoeologous recombination in wheat. In this review, we focus on recent results and propose a model for the control of these two processes.

What is the optimal stage (immature vs mature) and most efficient vitrification technique (semi-automated vs manual) to ensure the safety of the rescue-IVM (r-IVM) procedure for oocyte cryopreservation? Human oocytes should be cryopreserved after r-IVM at the mature stage (r-MII oocytes) by semi-automated or manual vitrification. r-IVM of immature oocytes may increase the number of oocytes cryopreserved for fertility preservation. However, the best stage and vitrification system (semi-automated or manual) for cryopreserving oocytes with the least possible impact on nuclear quality is unclear. From January 2020 to June 2024, a prospective study was conducted on patients undergoing ICSI, including cases with at least one immature germinal vesicle (GV) stage oocyte on the day of oocyte collection, resulting in a total of 414 oocytes. The study included 175 patients under 37 years old with no ovulatory disorder and undergoing ICSI. A total of 414 immature oocytes were collected and divided into five groups. The control group included fresh in vitro-matured oocytes (IVM, n = 81). After r-IVM, oocytes were vitrified by a semi-automated technique (IVM+VITg group, n = 63) or a closed manual procedure (IVM+VITm group, n = 66). Before r-IVM, oocytes were vitrified using both techniques (VITg+IVM group, n = 113 and VITm+IVM group, n = 91). The fresh IVM group combined IVM, IVM+VITg, and IVM+VITm groups.Survival rates of oocytes were evaluated 2-h post-warming. r-IVM was performed in a time-lapse incubator , allowing the assessment of r-IVM rates and maturation kinetics, including GV breakdown (GVBD) and first polar body extrusion timings. We assessed the quality of oocyte nuclear maturation through the evaluation of meiotic spindle polarity and chromosomes alignment by 3D analysis of confocal microscopy images and aneuploidy rate by array-CGH (a-CGH). The oocyte post-warming survival rate was lower when semi-automated vitrification was performed before r-IVM (50% for VITg+IVM group) compared with the three other groups (88% for IVM+VITg, 93% for IVM+VITm, and 80% for VITm+IVM, adjusted P-value < 0.001). IVM rates were not different between the three groups (fresh IVM: 80%, VITg+IVM: 80% and VITm+IVM: 69%, Pa = 0.131). Longer GVBD timings were observed when semi-automated vitrification was performed before r-IVM (VITg+IVM: 10.4 h) compared with Fresh IVM (7.9 h, Pa = 0.003). The percentages of oocytes with bipolar spindles or/and aligned chromosomes were not different between the five groups. Similarly, there was no difference in aneuploidy rates (monosomy or trisomy) between the five study groups (Pa = 0.847). Shorter GVBD timings were observed for oocytes with a bipolar spindle or aligned chromosomes (7.8 h) than for oocytes with a non-bipolar spindle or misaligned chromosomes (10.1 h, Pa = 0.011). The results are limited to the type of biological samples (GV-stage immature oocytes from stimulated ovaries) and the defined study population (patients < 37 years old without ovulatory disorders) used in this study. Furthermore, additional research is required to evaluate the ability of oocytes to undergo successful fertilization and embryo development, as well as their capacity to result in a live birth. Our findings provide reassurance regarding the use of semi-automated technique after r-IVM in clinics to optimize and standardize oocyte vitrification. The emerging field of r-IVM combined with cryopreservation by vitrification represents a promising option for fertility preservation, particularly for patients with a poor response to ovarian stimulation. Moreover, our study has revealed a previously unidentified correlation between extended GVBD timing and aberrant spindle morphology and chromosome misalignment. This provides a promising new non-invasive marker of nuclear oocyte quality for use in clinical practice. This study was funded by the French Biomedicine Agency (grant number: ABM 20AMP004) and the University Hospital of Clermont-Ferrand (France, Bourse Innovation). There are no conflicts of interest to be declared for any of the authors. There are no patents, products in development, or marketed products to declare. ClinicalTrials.gov ID NCT03680937.

La SUMOylation est un mécanisme post-traductionnel réversible qui élargit le répertoire fonctionnel des protéines nucléaires pour piloter les programmes génétiques de différenciation cellulaire tout au long de la vie. Des SUMOylations inappropriées ont été associées à des maladies ovariennes humaines telles que l’insuffisance ovarienne prématurée et les tumeurs ovariennes. Nous avons précédemment montré que l’hypo-SUMOylation chronique in vivo, entraînait une perte de la fonction ovarienne et une interruption du maintien de l’identité ovarienne chez la souris . Afin de préciser le rôle de la SUMOylation dans la physiologie ovarienne, nous avons développé un nouveau modèle murin (Senp2cKO) d’hyper-SUMOylation chronique ciblée dans les cellules somatiques ovariennes. Des analyses transcriptomiques et histologiques des ovaires Senp2cKO ont été réalisées pour mieux caractériser l’effet de cette hyper-SUMOylation. Ces souris mutantes développent une hypofertilité à l’âge de 8 semaines et une insuffisance ovarienne complète dès 3 mois associée à une absence de corps jaune et des niveaux de LH plasmatiques élevés. Les analyses comparatives en RNA-Seq révèlent une expression dérégulée pour 7157 gènes dans les ovaires Senp2cKO vs WT, confirment une fonction lutéale inopérante malgré la présence du récepteur LHCGR, et pointent des altérations du contrôle de la prolifération, des activités lytiques ovulatoires et des régulateurs clés de la lutéinisation des follicules pré-ovulatoires. Nos résultats montrent qu’une hypo-SUMOylation transitoire et contrôlée est nécessaire dans les cellules somatiques des follicules antraux pour la mise en route des programmes de lutéinisation folliculaire et d’ovulation.

Two fundamental cell types are found in multicellular organisms: somatic cells and germ cells. In somatic and in germ line cells, the mechanisms involved differ, although they both entail ancient and conserved mechanisms based on DNA, chromatin modification and small RNA (sRNA)-mediated silencing. This chapter updates the highly connected, dynamic set of mechanisms through which Transposable Element (TE) control is assured or sometimes lost in both types of cells. TE epigenetic silencing, independent of changes in DNA sequence, may be transmitted over multiple generations via the gametes as a transgenerational epigenetic inheritance. The environment experienced during lifetime may then impact the health of descendants after harmful TE mutations. Far more dramatic consequences on the progeny have been suggested when bursts of transpositions, due to relaxation of TE silencing, were associated with macroevolution and speciation.

Combining two or more related homoeologous genomes in a single nucleus, newly formed allopolyploids must rapidly adapt meiosis to restore balanced chromosome segregation, production of euploid gametes and fertility. The poor fertility of such neo-allopolyploids thus strongly selects for the limitation or avoidance of genetic crossover formation between homoeologous chromosomes. In this study, we have reproduced the interspecific hybridization between Arabidopsis thaliana and Arabidopsis arenosa leading to the allotetraploid Arabidopsis suecica and have characterized the first allopolyploid meioses. First-generation neo-allopolyploid siblings vary considerably in fertility, meiotic behavior and levels of homoeologous recombination. We show that centromere dynamics at early meiosis is altered in synthetic neo-allopolyploids compared with evolved A. suecica, with a significant increase in homoeologous centromere interactions at zygotene. At metaphase I, the presence of multivalents involving homoeologous chromosomes confirms that homoeologous recombination occurs in the first-generation synthetic allopolyploid plants and this is associated with a significant reduction in homologous recombination, compared to evolved A. suecica. Together, these data strongly suggest that the fidelity of recombination partner choice, likely during the DNA invasion step, is strongly impaired during the first meiosis of neo-allopolyploids and requires subsequent adaptation.