Spatial and Temporal Scaling of Microtubules and Mitotic Spindles

During cell division, the mitotic spindle, a macromolecular structure primarily comprised of microtubules, drives chromosome alignment and partitioning between daughter cells. Mitotic spindles can sense cellular dimensions in order to adapt their length and mass to cell size. This scaling capacity is particularly remarkable during early embryo cleavage when cells divide rapidly in the absence of cell growth, thus leading to a reduction of cell volume at each division. Although mitotic spindle size scaling can occur over an order of magnitude in early embryos, in many species the duration of mitosis is relatively short, constant throughout early development and independent of cell size. Therefore, a key challenge for cells during embryo cleavage is not only to assemble a spindle of proper size, but also to do it in an appropriate time window which is compatible with embryo development. How spatial and temporal scaling of the mitotic spindle is achieved and coordinated with the duration of mitosis remains elusive. In this review, we will focus on the mechanisms that support mitotic spindle spatial and temporal scaling over a wide range of cell sizes and cellular contexts. We will present current models and propose alternative mechanisms allowing cells to spatially and temporally coordinate microtubule and mitotic spindle assembly.

Correlation between Pre-Ovulatory Follicle Diameter and Follicular Fluid Metabolome Profiles in Lactating Beef Cows

Induced ovulation of small pre-ovulatory follicles reduced pregnancy rates, embryo survival, day seven embryo quality, and successful embryo cleavage in beef cows undergoing fixed-time artificial insemination. RNA-sequencing of oocytes and associated cumulus cells collected from pre-ovulatory follicles 23 h after gonadotropin-releasing hormone (GnRH) administration to induce the pre-ovulatory gonadotropin surge suggested reduced capacity for glucose metabolism in cumulus cells of follicles ≤11.7 mm. We hypothesized that the follicular fluid metabolome influences metabolic capacity of the cumulus-oocyte complex and contributes to reduced embryo cleavage and quality grade observed following induced ovulation of small follicles. Therefore, we performed a study to determine the correlation between pre-ovulatory follicle diameter and follicular fluid metabolome profiles in lactating beef cows (Angus, n = 130). We synchronized the development of a pre-ovulatory follicle and collected the follicular contents approximately 20 h after GnRH administration. We then performed ultra-high performance liquid chromatography—high resolution mass spectrometry (UHPLC-HRMS) metabolomic studies on 43 follicular fluid samples and identified 38 metabolites within pre-ovulatory follicles of increasing size. We detected 18 metabolites with a significant, positive correlation to follicle diameter. Individual and pathway enrichment analysis of significantly correlated metabolites suggest that altered glucose and amino acid metabolism likely contribute to reduced developmental competence of oocytes when small pre-ovulatory follicles undergo induced ovulation.

Distribution of eggs and adults of alaska plaice Pleuronectes quadrituberculatus and flathead sole Hippoglossoides elassodon (Pleuronectidae) in the Pacific waters of Kamchatka

Distribution and biological parameters are considered for eggs and adults of two flatfish species on the data of annual surveys conducted on the shelf of southeastern Kamchatka in summer of 2011–2014 and 2016–2019. The eggs of Pleuronectes quadrituberculatus were sampled mostly at the stage of a germinal strip forming, whereas the eggs of Hippoglossoides elassodon were mostly at the stage of embryo cleavage. The main congestions of the eggs were found in the Kronotsky Bay and northern Avachinsky Bay. The adults of both species concentrated mainly in the northern Kronotsky Bay, at Cape Povorotny. Old age groups prevailed in aggregations of P. quadrituberculatus, but middle-age and young fish — in the aggregations of H. elassodon.

Stress Management during the Intracytoplasmic Sperm Injection Cycle May Slow Down First Embryo Cleavage and Accelerate Embryo Compaction: A Pilot Randomized Controlled Trial

<b><i>Introduction:</i></b> A firm consensus on the effectiveness of psychological interventions during infertility treatment has not been reached yet in terms of mental health and pregnancy rates. Moreover, the influence of these interventions on embryo cleavage kinetics has not been investigated. <b><i>Objective:</i></b> The aim of this work was to study whether stress management in couples undergoing an intracytoplasmic sperm injection (ICSI) cycle influences stress levels, mitochondrial DNA (mtDNA) levels in granulosa cells, and cleavage-stage embryos. <b><i>Methods:</i></b> Infertile couples were randomized into a treatment as usual (TAU) group (<i>n</i> = 30) and stress management program (SMP) group (<i>n</i> = 29) at the beginning of an ICSI cycle. Couples in the SMP group attended education and relaxation sessions at each visit to the clinic for folliculometry. The perceived stress scale (PSS) was used to assess stress levels at the beginning and end of the cycle. Moreover, mtDNA levels of granulosa cells and embryo morphokinetics were evaluated. <b><i>Results:</i></b> Post-intervention, women in the SMP group had significantly lower PSS scores than their initial PSS (<i>p</i> &#x3c; 0.001; effect size, ES = 0.5) and than the final PSS of the TAU group (<i>p</i> = 0.02; ES = 0.09). Additionally, mtDNA levels were significantly lower in luteal granulosa cells of the SMP group than the TAU group (<i>p</i> = 0.02). An earlier time of pronuclei appearance (<i>p</i> = 0.03) and time to 2 cells (<i>p</i> = 0.015) and a faster time to full compaction (<i>p</i> = 0.045) were detected in the embryos of the SMP group compared with the TAU group. <b><i>Conclusion(s):</i></b> The implemented program may reduce stress levels, retard first embryo cleavage, and accelerate embryo compaction. Further studies with an active control group are needed to confirm these results.

Par-1 controls the composition and growth of cortical actin caps during Drosophila embryo cleavage

Cell structure depends on the cortex, a thin network of actin polymers and additional proteins underlying the plasma membrane. The cell polarity kinase Par-1 is required for cells to form following syncytial Drosophila embryo development. This requirement stems from Par-1 promoting cortical actin caps that grow into dome-like metaphase compartments for dividing syncytial nuclei. We find the actin caps to be a composite material of Diaphanous (Dia)-based actin bundles interspersed with independently formed, Arp2/3-based actin puncta. Par-1 and Dia colocalize along extended regions of the bundles, and both are required for the bundles and for each other’s bundle-like localization, consistent with an actin-dependent self-reinforcement mechanism. Par-1 helps establish or maintain these bundles in a cortical domain with relatively low levels of the canonical formin activator Rho1-GTP. Arp2/3 is required for displacing the bundles away from each other and toward the cap circumference, suggesting interactions between these cytoskeletal components could contribute to the growth of the cap into a metaphase compartment.