Dynamin 2-dependent endocytosis is essential for mouse oocyte development and fertility

During folliculogenesis, oocytes are dependent on metabolic and molecular support from surrounding somatic cells. Here, we examined the role of the dynamin (DNM) family of mechanoenzymes in mediating endocytotic uptake into growing follicular oocytes. We found DNM1 and DNM2 to be highly expressed in growing follicular oocytes as well as in mature germinal vesicle (GV) and metaphase II (MII) stage oocytes. Moreover, oocyte-specific conditional knockout (cKO) of DNM2 (DNM2Δ) led to complete sterility, with follicles arresting at the preantral stage of development. In addition, DNM2Δ ovaries were characterized by disrupted follicular growth as well as oocyte and follicle apoptosis. Further, the loss of DNM activity, either through DNM2 cKO or through pharmacological inhibition (Dyngo 6a) led to the impairment of endocytotic pathways in preantral oocytes as well as in mature GV and MII oocytes, respectively. Loss of DNM activity resulted in the redistribution of endosomes and the misslocalization of clathrin and actin, suggesting dysfunctional endocytosis. Notably, there was no observable effect on the fertility of DNM1Δ females. Our study has provided new insight into the complex and dynamic nature of oocyte growth during folliculogenesis, suggesting a role for DNM2 in mediating the endocytotic events that are essential for oocyte development.

Inhibition of lysine-specific histone demethylase 1A results in meiotic aberration during oocyte maturation in vitro in goats

Histone methylation is associated with oocyte maturation in several species and is also expected in goat oocytes, while the mechanism is still unclear. Therefore, single-cell RNA sequencing (scRNA-seq) was performed on goat germinal vesicle (GV) and metaphase II (MII) oocytes, and the functions of lysine-specific histone demethylase 1A (LSD1), one of the differentially expressed genes (DEGs) were investigated during in vitro maturation (IVM) of goat oocytes. Through scRNA-seq, 4516 DEGs were identified from GV oocytes and MII oocytes in goats, among which there were 16 histone methyltransferase and demethylase DEGs (including LSD1). The functions of LSD1 during IVM of goat oocytes were investigated through its inhibitor, GSK-LSD1. We found that the first polar body extrusion rate of goat oocytes significantly reduced with an increase in GSK-LSD1 concentration supplemented into IVM medium (0 μM: 58.84 ± 0.95%; 2.5 μM: 52.14 ± 0.51%, P < 0.01; 50 μM: 41.22 ± 0.42%, P < 0.001; 100 μM: 29.78 ± 1.78%, P < 0.001). Moreover, compared with the control group, the level of H3K4me2 methylation and p-H2AX in goat oocytes significantly increased (P < 0.001 and P < 0.01, respectively) upon 50-μM GSK-LSD1 treatment for 12 h. Furthermore, abnormalities in spindle assembly (25.94 ± 1.02% vs. 71.15 ± 3.32%; P < 0.01) and chromosome alignment (22.93 ± 1.11% vs. 76.03 ± 3.25%; P < 0.01) were observed, and cytoskeletal organization (15.31 ± 1.60% vs. 67.50 ± 3.09%; P < 0.001) was disrupted upon treatment with 50-μM GSK-LSD1 for 12 h, which compared with that in the control group. Additionally, the ratio of BCL2:BAX significantly higher (P < 0.01) in oocytes with 50-μM GSK-LSD1 treatment than that in control group. Collectively, these results indicate the important role of LSD1 in meiotic maturation of goat oocytes. Our data not only clarify dynamic changes in mRNA during oocyte maturation but also provide a theoretical basis and technical means for further studies of meiotic maturation of goat oocytes.

Melatonin promotes human oocyte maturation and early embryo development by enhancing clathrin-mediated endocytosis

Embryo development potential and reproductive clinical outcomes are all deeply rooted in oocyte maturation. Melatonin has been reported to promote oocyte maturation as an antioxidant in nonprimate species. Its antioxidative functions also help reduce plasma membrane rigidity, which facilitates clathrin-mediated endocytosis (CME). Whether melatonin has effects on human oocyte maturation by regulating CME is worthy of exploration. In this study, we found that the optimal melatonin concentration for human oocyte maturation was 10^-11  M, and the maturation rate of this group was 71.9% (P = .03). The metaphase II (MII) stage oocytes obtained by in vitro maturation with 10^-11  M melatonin had a significantly higher fertilization rate (81.4% vs 61.4%, respectively, P = .017) and blastocyst rate (32.2% vs 15.8%, respectively, P = .039) compared to controls. During maturation, antioxidative melatonin greatly enhanced CME and decreased intra-oocyte cAMP level. The former was evidenced by the increasing numbers of coated pits and vesicles, and the upregulated expression of two major CME markers-clathrin and adaptor protein-2 (AP2). CME inhibitor dynasore increased intra-oocyte cAMP level and blocked oocyte maturation, and melatonin could partly rescue oocyte maturation and significantly elevate the expression of clathrin and AP2 in the presence of dynasore. Therefore, we conclude that melatonin could promote human oocyte maturation and early embryo development through enhancing CME.

Modulation of dynamin function by small molecules

Dynamins are essential as membrane remodelers in various cellular processes, like receptor-mediated endocytosis, synaptic vesicle recycling and spermatogenesis. Moreover, dynamin is involved in the internalization of numerous viruses and in the motility of several cancer cell lines. As tools for dissecting the underlying mechanisms of these important biological processes and as potential future therapeutics, small molecules have been developed in the last two decades that modulate the functions of dynamin. In this review we give an overview of the compound classes that are currently in use and describe how they affect dynamin function.

Dynein promotes porcine oocyte meiotic progression by maintaining cytoskeletal structures and cortical granule arrangement

Cytoplasmic dynein is a family of cytoskeletal motor proteins that move towards the minus-end of the microtubules to perform functions in a variety of mitotic processes such as cargo transport, organelle positioning, chromosome movement and centrosome assembly. However, its specific roles during mammalian oocyte meiosis have not been fully defined. Herein, we investigated the critical events during porcine oocyte meiotic maturation after inhibition of dynein by Ciliobrevin D treatment. We found that oocyte meiotic progression was arrested when inhibited of dynein by showing the poor expansion of cumulus cells and decreased rate of polar body extrusion. Meanwhile, the spindle assembly and chromosome alignment were disrupted, accompanied by the reduced level of acetylated α-tubulin, indicative of weakened microtubule stability. Defective actin polymerization on the plasma membrane was also observed in dynein-inhibited oocytes. In addition, inhibition of dynein caused the abnormal distribution of cortical granules and precocious exocytosis of ovastacin, a cortical granule component, which predicts that ZP2, the sperm binding site in the zona pellucida, might be prematurely cleaved in the unfertilized dynein-inhibited oocytes, potentially leading to the fertilization failure. Collectively, our findings reveal that dynein plays a part in porcine oocyte meiotic progression by regulating the cytoskeleton dynamics including microtubule stability, spindle assembly, chromosome alignment and actin polymerization. We also find that dynein mediates the normal cortical granule distribution and exocytosis timing of ovastacin in unfertilized eggs which are the essential for the successful fertilization.

The Dynamin 2 inhibitor Dynasore affects the actin filament distribution during mouse early embryo development

Dynamin 2 is a large GTPase notably involved in clathrin-mediated endocytosis, cell migration and cytokinesis in mitosis. Our previous study identified that Dynamin 2 regulated polar body extrusion in mammalian oocytes, but its roles in early embryo development, remain elusive. Here, we report the critical roles of Dynamin 2 in mouse early embryo development. Dynamin 2 accumulated at the periphery of the blastomere during embryonic development. When Dynamin 2 activity was inhibited by Dynasore, embryos failed to cleave to the 2-cell or 4-cell stage. Moreover, the actin filament distribution and relative amount were aberrant in the treatment group. Similar results were observed when embryos were cultured with Dynasore at the 8-cell stage; the embryos failed to undergo compaction and develop to the morula stage, indicating a role of Dynamin 2 in embryo cytokinesis. Therefore, our data indicate that Dynamin 2 might participate in the early embryonic development through an actin-based cytokinesis.