Early Cell Division Research Articles

Immunohistochemical Changes of Polycystic Ovaries in rats Treated with Asparagus Officinalis L. Roots Extract

Abstract Background: Polycystic ovary syndrome (PCOS) which a series reproductive, metabolic and psychological condition that is characterized by abnormal gonadotropin secretion or hyperandrogenism and associated with insulin resistance and most commonly found in the reproductive age female. Objectives: This research paper were conducted to examine the effects of Asparagus officinalis L. roots extract on letrozole induced PCOS where the effect of 400 mg/kg A. officinalis L. root extract on the PCOS was studied for 28 days in female rats. Materials and Methods: Thirty-five female Albino rats were randomly divided into five groups, including control negative group, positive control, PCOS, treatment and preventive group. During 28 days, the positive control group got an extract of the A. officinalis roots. Letrozole 1 mg/kg dissolve in 0.5% carboxymethyl cellulose solution was used to cause PCOS for 28 days. Following the induction of PCOS, the treatment group received extract A. officinalis roots for 28 days. The preventative group received an extract of asparagus roots during PCOS induction. Results: Immunohistochemical results are shown Ovary slices from of the therapeutic and preventative groups next to the asparagus group were immunostained for Ki 67, which showed high positive statistically (P <0.05) immunological activity in the granulosa nuclei and less in the theca cells. When compared to the PCOS group, both the granulosa and theca layers had very weak positive immunostaining (P <0.05). According to the morphological findings, granulosa cells from the Control group and asparagus group proliferated much more than granulosa cells from the PCOS group statistically significant (P <0.05). Conclusion: The findings show that theca and granulosa cells are quickly stimulated to proliferate by asparagus root extract. Moreover, it therefore speeds up oogenesis and early cell divisions.

A cytokinetic ring-driven cell rotation achieves Hertwig’s rule in early development

Hertwig's rule states that cells divide along their longest axis, usually driven by forces acting on the mitotic spindle. Here, we show that in contrast to this rule, microtubule-based pulling forces in early Caenorhabditis elegans embryos align the spindle with the short axis of the cell. We combine theory with experiments to reveal that in order to correct this misalignment, inward forces generated by the constricting cytokinetic ring rotate the entire cell until the spindle is aligned with the cell's long axis. Experiments with slightly compressed mouse zygotes indicate that this cytokinetic ring-driven mechanism of ensuring Hertwig's rule is general for cells capable of rotating inside a confining shell, a scenario that applies to early cell divisions of many systems.

The two tether system regulates early stage cell division progression in Escherichia coli

The two tether system regulates early stage cell division progression in Escherichia coli

Enhancing Protoplast Isolation and Early Cell Division from Cannabis sativa Callus Cultures via Phenylpropanoid Inhibition.

De novo regeneration of Cannabis sativa L. (cannabis) using tissue culture techniques remains unreliable and infrequent. Conventional methods for the regeneration and transformation of cannabis have not achieved the reliability and replicability that need to be integrated into research and breeding programs. Protoplast systems are effective for gene expression studies and transformation and genome-editing technologies and open the possibility of somatic hybridization to create interspecific hybrids. To date, leaf-derived protoplasts have been isolated for transient gene expression studies, but protoplast-to-plant regeneration has not been reported. The present study aims to evaluate the efficacy of using a callus culture system as an abundant tissue source for protoplast isolation and lays the groundwork for a protoplast-to-plant regeneration system. Using hypocotyl-derived callus cultures, which are known to have relatively greater regenerative potential, the efficacy of protoplast isolation and initial cell division were assessed. In this study, the effect of 2-aminoindane-2-phosphonic acid (AIP), a competitive inhibitor of phenylalanine ammonia lyase (PAL), in callus culture media and the effect of subculture frequency on protoplast yield were assessed. This study found that inclusion of AIP at 1 mM resulted in a 334% increase in protoplast yield compared with AIP-free medium, representing the first known use of AIP in cannabis tissue culture. Inclusion of AIP led to a 28% decrease in total soluble phenolics and 52% decrease in tissue browning compared with the control medium. Lastly, a two-phase culture system for protoplast regeneration was tested. At a concentration of 2.0 × 105 protoplasts per mL, cell wall reconstitution and cell division were observed, providing one of the first know reports of cell division from cannabis protoplasts and setting the stage for the future development of a protoplast-to-plant regeneration system.

Testing effects of vapor pressure deficit on fruit growth: a comparative approach using peach, mango, olive, orange, and loquat.

Determining the influence of vapor pressure deficit (VPD) on fruit growth is a key issue under a changing climate scenario. Using a comparative approach across different fruit tree species may provide solid indications of common or contrasting plant responses to environmental factors. Knowing fruit growth responses to VPD may also be useful to optimize horticultural management practices under specific atmospheric conditions. Climate data to calculate VPD and fruit relative growth rates (RGR) by fruit gauges were monitored in peach at cell division, pit hardening and cell expansion stages; in two mango cultivars at cell division, cell expansion and maturation stages; in two olive cultivars, either full irrigated or rainfed, at early and late cell expansion stages; in 'Valencia' orange at early and late cell division stage, before and after mature fruit harvest; in loquat at cell expansion and maturation stages. At the fruit cell division stage, sensitivity of fruit growth to VPD seems to vary with species, time, and probably soil and atmospheric water deficit. 'Keitt' mango and 'Valencia' orange fruit growth responded to VPD in opposite ways, and this could be due to very different time of the year and VPD levels in the monitoring periods of the two species. At pit hardening stage of peach fruit growth, a relatively weak relationship was observed between VPD and RGR, and this is not surprising as fruit growth in size at this stage slows down significantly. A consistent and marked negative relationship between VPD and RGR was observed at cell expansion stage, when fruit growth is directly depending on water intake driving cell turgor. Another behavior common to all observed species was the gradual loss of relationship between VPD and RGR at the onset of fruit maturation, when fruit growth in size is generally programmed to stop. Finally, regardless of fruit type, VPD may have a significant effect on fruit growth and could be a useful parameter to be monitored for tree water management mainly when the cell expansion process prevails during fruit growth.

Laser Capture Microdissection Transcriptome Reveals Spatiotemporal Tissue Gene Expression Patterns of Medicago truncatula Roots Responding to Rhizobia.

We report a public resource for examining the spatiotemporal RNA expression of 54,893 Medicago truncatula genes during the first 72 h of response to rhizobial inoculation. Using a methodology that allows synchronous inoculation and growth of more than 100 plants in a single media container, we harvested the same segment of each root responding to rhizobia in the initial inoculation over a time course, collected individual tissues from these segments with laser capture microdissection, and created and sequenced RNA libraries generated from these tissues. We demonstrate the utility of the resource by examining the expression patterns of a set of genes induced very early in nodule signaling, as well as two gene families (CLE peptides and nodule specific PLAT-domain proteins) and show that despite similar whole-root expression patterns, there are tissue differences in expression between the genes. Using a rhizobial response dataset generated from transcriptomics on intact root segments, we also examined differential temporal expression patterns and determined that, after nodule tissue, the epidermis and cortical cells contained the most temporally patterned genes. We circumscribed gene lists for each time and tissue examined and developed an expression pattern visualization tool. Finally, we explored transcriptomic differences between the inner cortical cells that become nodules and those that do not, confirming that the expression of 1-aminocyclopropane-1-carboxylate synthases distinguishes inner cortical cells that become nodules and provide and describe potential downstream genes involved in early nodule cell division. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

#25 : The Prediction Value of EEVA in the Timelapse GERI Incubator for the Blastocyst Morphology

Background and Aims: Time-lapse monitoring of embryo development may represent a superior way to culture and select embryos in vitro. The EEVA Test records the development of each embryo with a cell-tracking system and predicts the potential (High, Medium or Low) that an embryo will form a blastocyst based on automated detection and analysis of time-lapse imaging information of early cell division stage. The blastocyst grade will help clinicians in selecting the best embryos for transfer to increase pregnancy rates and reduce multiple pregnancies. The aim of this study is to determine the correlation between EEVA score and some blastocyst morphological parameters. Methods: Retrospective analysis study on 2522 embryos with indication for prolonging embryo culture to the blastocyst stage in time-lapse GERI incubator from January 2020 to June 2022. Results: Embryos with E1 and E2 score had significant higher morphological ratios of ICM A, ICM B, TE A, TE B, blastocoele expansion ratios of BL5,6 and lower morphological ratios of ICM D, TE D,compared with embryos having E3, E4, E5 score, p<0.01. Embryos with E3 score had significant higher morphological ratios of ICM A, ICM B, TE A, TE B, blastocoele expansion ratios of BL5,6 and lower morphological ratios of ICM D, TE D, compared with embryos having E4, E5 score, p<0.01. Conclusions: The blastocyst morphological parameters were associcated with the EEVA score. The rate of blastocyst with the ICM A, ICM B, TE A, TE B, BL 5,6 tended to decrease and the rate of blastocyst with ICM D; TE D tended to increase for embryos with low EEVA score. In other words, the good quality blastocyst rate tended to decrease, and the bad quality blastocyst rate tended to increase for embryos with low EEVA score.

Single-cell RNA sequencing analysis of the embryogenic callus clarifies the spatiotemporal developmental trajectories of the early somatic embryo in Dimocarpus longan.

Plant embryogenic calli (ECs) can undergo somatic embryogenesis to regenerate plants. This process is mediated by regulatory factors, such as transcription factors and specifically expressed genes, but the precise molecular mechanisms underlying somatic embryogenesis at the single-cell level remain unclear. In this study, we performed high-resolution single-cell RNA sequencing analysis to determine the cellular changes in the EC of the woody plant species Dimocarpus longan (longan) and clarify the continuous cell differentiation trajectories at the transcriptome level. The highly heterogeneous cells in the EC were divided into 12 putative clusters (e.g., proliferating, meristematic, vascular, and epidermal cell clusters). We determined cluster-enriched expression marker genes and found that overexpression of the epidermal cell marker gene GDSL ESTERASE/LIPASE-1 inhibited the hydrolysis of triacylglycerol. In addition, the stability of autophagy was critical for the somatic embryogenesis of longan. The pseudo-timeline analysis elucidated the continuous cell differentiation trajectories from early embryonic cell division to vascular and epidermal cell differentiation during the somatic embryogenesis of longan. Moreover, key transcriptional regulators associated with cell fates were revealed. We found that ETHYLENE RESPONSIVE FACTOR 6 was characterized as a heat-sensitive factor that negatively regulates longan somatic embryogenesis under high-temperature stress conditions. The results of this study provide new spatiotemporal insights into cell division and differentiation during longan somatic embryogenesis at single-cell resolution.

Rhizome architecture, development and vascularization in the water lily Nymphaea alba.

Water lilies are of particular interest with regard to the evolution of angiosperms. They live in an aquatic environment and have been regarded as links to the monocots by some authors. Vascular bundles are sometimes described as scattered or atactostelar as in monocots. However, this view needs to be clarified as the morphology and vascularization of Nymphaea rhizomes remain to be understood. The rhizome of Nymphaea alba was re-investigated morphologically and histologically. Developmental studies were conducted using scanning electron microscopy. Comprehensive histological analyses, including hand and microtome sections and a variety of specific staining procedures, were conducted to re-evaluate the composition of longitudinal and transverse tissue. The rhizome is covered by parenchymatous nodal cushions each bearing a leaf and several adventitious roots. Internodes are extremely short. The apex is flat and early overtopped by developing leaf primordia and cushions. The phyllotaxis is spiral and passes alternately through vegetative and reproductive phases. Flowers appear in the leaf spiral, and lack a subtending bract and a cushion below the peduncle. The reproductive phase includes two or three flowers which alternate with a single leaf. The rhizome is histologically subdivided into a central core, an aerenchymatic cortex, and a parenchymatic exocortex formed to a great extent by the nodal cushions. The core contains strands of vascular bundles united to a complex vascular plexus. Vascular elements continuously anastomose and change shape and direction. Provascular strands originating from leaf primordia merge with the outer core vascular tissue whereas the flower strands run into the centre of the core. Roots originating from the parenchymatous cushions show the characteristic actinostelic pattern, which changes into a collateral pattern inside the rhizome. Several root traces merge and form one strand leading to the central core. Early cell divisions below the apical meristem dislocate leaf, flower and root primordia and their provascular strands outwards. Consequently, fully developed vascular strands insert horizontally into the vascular plexus at advanced rhizome stages. The absence of bracts and cushions below the flowers, the alternate leaf-flower sequence and the course of the peduncle strand suggest that the rhizome is sympodially instead of monopodially organized. The spiral phyllotaxis extends in this case over several shoot orders, masking the branching pattern. The vascular strands in the central plexus differ considerably from vascular bundles in monocots, confirming the unique vascularization in Nymphaea. Sclerenchymatic bundle sheaths are lacking, and vascular bundles continuously split and anastomose throughout the rhizome. Though vascular bundles in petioles and peduncles of N. alba show similarities with some Alismatales, the vascular system of N. alba in general has little in common with that of monocots.

The effect of early irregular cell division of human embryos on blastocyst euploidy: considerations from the subsequent development of the blastomeres by direct or reverse cleavage

To investigate whether blastocysts that divide irregularly reduce subsequent blastocyst euploidy. Retrospective study. Private clinic. A total of 122 blastocysts for which consent for disposal and research use was obtained. None. Results of next-generation sequencing analysis of the blastocysts and whether blastomeres by normal or irregular divisions subsequently participated in blastocyst formation or not. The embryos were classified according to their dynamics until the second cleavage. The blastocyst euploidy rates were 33.3% (19/57) in the normal cleavage (NC) group, 38.3% (18/47) in the direct cleavage (embryos with one cell dividing into 3 cells) (DC) group, and 72.2% (13/18) in the reverse cleavage (RC) (embryos with fused cells once divided) group. The rate of the RC group was significantly higher than that of the NC group. The blastocyst participation rate of the blastomeres were 95.6% in the NC group and 56.5% in that derived from DC of the first cleavage, and 91.7% in that of blastomeres derived from normal division of the second cleavage and 53.6% in that derived from DC of the second cleavage, both of which were significantly lower in the latter. In the RC group, the rates of fused and nonfused blastomeres were 62.1% and 87.5%, respectively, with no significant difference. The blastomeres generated by DC were often excluded from blastocyst formation, and we speculate that this is one reason why their division does not reduce blastocyst euploidy. The association between RC and euploidy of blastocysts merits further study.

FtsK, a DNA Motor Protein, Coordinates the Genome Segregation and Early Cell Division Processes in Deinococcus radiodurans.

Filament temperature-sensitive mutant K (FtsK)/SpoIIIE family proteins are DNA translocases known as the fastest DNA motor proteins that use ATP for their movement on DNA. Most of the studies in single chromosome-containing bacteria have established the role of FtsK in chromosome dimer resolution (CDR), connecting the bacterial chromosome segregation process with cell division. Only limited reports, however, are available on the interdependent regulation of genome segregation and cell division in multipartite genome harboring (MGH) bacteria. In this study, for the first time, we report the characterization of FtsK from the radioresistant MGH bacterium Deinococcus radiodurans R1 (drFtsK). drFtsK shows the activity characteristics of a typical FtsK/SpoIIIE/Tra family. It stimulates the site-specific recombination catalyzed by Escherichia coli tyrosine recombinases. drFtsK interacts with various cell division and genome segregation proteins of D. radiodurans. Microscopic examination of different domain deletion mutants of this protein reveals alterations in cellular membrane architecture and nucleoid morphology. In vivo localization studies of drFtsK-RFP show that it forms multiple foci on nucleoid as well as on the membrane with maximum density on the septum. drFtsK coordinates its movement with nucleoid separation. The alignment of its foci shifts from old to new septum indicating its cellular dynamics with the FtsZ ring during the cell division process. Nearly, similar positional dynamicity of FtsK was observed in cells recovering from gamma radiation exposure. These results suggest that FtsK forms a part of chromosome segregation, cell envelope, and cell division machinery in D. radiodurans. IMPORTANCE Deinococcus radiodurans show extraordinary resistance to gamma radiation. It is polyploid and harbors a multipartite genome comprised of 2 chromosomes and 2 plasmids, packaged in a doughnut-shaped toroidal nucleoid. Very little is known about how the tightly packed genome is accurately segregated and the next divisional plane is determined. Filament temperature-sensitive mutant K (FtsK), a multifunctional protein, helps in pumping the septum-trapped DNA in several bacteria. Here, we characterized FtsK of D. radiodurans R1 (drFtsK) for the first time and showed it to be an active protein. The absence of drFtsK causes many defects in morphology at both cellular and nucleoid levels. The compact packaging of the deinococcal genome and cell membrane formation is hindered in ftsK mutants. In vivo drFtsK is dynamic, forms foci on both nucleoid and septum, and coordinates with FtsZ for the next cell division. Thus, drFtsK role in maintaining the normal genome phenotype and cell division in D. radiodurans is suggested.

De novo balanced reciprocal translocation mosaic t(1;3)(q42;q25) detected by prenatal genetic diagnosis: a fetus conceived using preimplantation genetic testing due to a t(12;14)(q22;q13) balanced paternal reciprocal translocation

IntroductionDe novo balanced reciprocal translocations mosaicism in fetus conceived using preimplantation genetic testing from a different balanced translocation carrier parent has been rarely reported.MethodsChromosomal microarray analysis, karyotype analysis and fluorescent in situ hybridization were performed to verify the type and heredity of the rearrangement. STR analysis was conducted to identify potential contamination and verify kinship. In addition, a local BLAST engine was performed to locate potentially homologous segments which might contribute to the translocation in breakpoints of chromosome.ResultsA rare de novo balanced reciprocal translocations mosaicism mos 46,XY,t(1;3)(q42;q25)[40]/46,XY[39] was diagnosed in a fetus conceived using preimplantation genetic testing due to a 46,XY,t(12;14)(q22;q13) balanced translocation carrier father through multiplatform genetic techniques. Two of the largest continuous high homology segments were identified in chromosomal band 1q42.12 and 3q25.2. At the 21-months follow up, infant has achieved all psychomotor development milestones as well as growth within the normal reference range.ConclusionWe present a prenatal diagnosis of a rare de novo balanced reciprocal translocations mosaicism in a fetus who conceived by preimplantation genetic testing. The most reasonable driving mechanism was that a de novo mitotic error caused by nonallelic homologous recombination between 1q42.12 and 3q25.2 in a zygote within the first or early cell divisions, which results in a mosaic embryo with the variant present in a half proportion of cells.

The human sperm basal body is a complex centrosome important for embryo preimplantation development.

The mechanism of conversion of the human sperm basal body to a centrosome after fertilization, and its role in supporting human early embryogenesis, has not been directly addressed so far. Using proteomics and immunofluorescence studies, we show here that the human zygote inherits a basal body enriched with centrosomal proteins from the sperm, establishing the first functional centrosome of the new organism. Injection of human sperm tails containing the basal body into human oocytes followed by parthenogenetic activation, showed that the centrosome contributes to the robustness of the early cell divisions, increasing the probability of parthenotes reaching the compaction stage. In the absence of the sperm-derived centrosome, pericentriolar material (PCM) components stored in the oocyte can form de novo structures after genome activation, suggesting a tight PCM expression control in zygotes. Our results reveal that the sperm basal body is a complex organelle which converts to a centrosome after fertilization, ensuring the early steps of embryogenesis and successful compaction. However, more experiments are needed to elucidate the exact molecular mechanisms of centrosome inheritance in humans.

Plant regeneration from root segments of Anthurium andraeanum and assessment of genetic fidelity of in vitro regenerates

A highly efficient regeneration system of Anthurium andraeanum Linden was established using root segments as explants of four genotypes, Arizona, SWD, OYH, and Mississippi. The root explants were firstly incubated on callus induction media containing NH4NO3 level of 206 mg L−1 or 825 mg L−1, and the calluses were formed from both ends of the root segments after 1 mo of culture. Root-derived calluses were then transferred to shoot regeneration media with NH4NO3 level of 412 mg L−1 or 1650 mg L−1, and numbers of shoot were successfully produced from the surface of calluses after 2 mo of culture. Medium containing 206 mg L−1 NH4NO3 induced more callus compared to 825 mg L−1. In contrast, the number of shoots per callus was the same between the above two shoot regeneration media indicating that NH4NO3 level had little effect on shoot regeneration. Long-termin vitro maintenance of the callus-bearing shoot initials was possible without compromising shoot regeneration and subsequent rooting. Histological analysis showed that early cell division was initiated from the inner cortical parenchyma cells near the vascular tissue and from the vascular parenchyma cells adjacent to the xylem vessel. The primary callus mainly comprised inner parenchyma cells with scattered procambial-like cells and xylem elements and two different meristematic zones beneath epidermal layers. Transfer of callus to the regenerative medium caused meristemoid formation and subsequent shoot primordia production. Calcium oxalate crystals and tannin-like deposits were visible on the outer callus layer or within the cotyledon-like structure of shoot primordium throughout callus development. Starch grains were abundant in root explants, but disappeared in the profusely growing primary callus, and were mobilized in the shoot primordium, indicating energy requirements of these two developmental stages. Flow cytometry analysis demonstrated that ploidy levels were maintained during in vitro cultures, including long-term regenerated plants. The inter-simple sequence repeat analysis indicated genomic DNA stability of Arizona and OYH but occasional genetic variation in primary regenerates of SWD and Mississippi.

SAC during early cell divisions: Sacrificing fidelity over timely division, regulated differently across organisms: Chromosome alignment and segregation are left unsupervised from the onset of development until checkpoint activity is acquired, varying from species to species.

Early embryogenesis is marked by a frail Spindle Assembly Checkpoint (SAC). The time of SAC acquisition varies depending on the species, cell size or a yet to be uncovered developmental timer. This means that for a specific number of divisions, biorientation of sister chromatids occurs unsupervised. When error-prone segregation is an issue, an aneuploidy-selective apoptosis system can come into play to eliminate chromosomally unbalanced cells resulting in healthy newborns. However, aneuploidy content can be too great to overcome, endangering viability. SAC generates a diffusible signal to lengthen time spent in mitosis if needed, ensuring correct chromosome segregation, a fundamental factor in the generation of euploid cells. Thus, it remains puzzling what benefit could come from delaying SAC acquisition till later in the development. In this review, we describe what is known on SAC acquisition in distinct species and highlight pending research as well as potential applications for such knowledge.

Three neuroparsin genes from oriental river prawn, Macrobrachium nipponense, involved in ovary maturation.

In this study, we identified three neuroparsin (NP) genes in Macrobrachium nipponense: Mn-NP1, Mn-NP2, and Mn-NP3, encoding 99, 100, and 101 amino acid proteins, respectively. Multiple sequence alignments showed that these genes contained 12 cysteine residues, of which 11 were at conserved positions. The total sequence identity between the genes was 47.5%, and they showed a high degree of sequence identity (> 54% similarity) with other crustacean genes. Phylogenetic tree analysis showed that Mn-NPs were clustered at different branches, indicating that Mn-NPs may have different functions. Tissue distribution data revealed that the three genes were present in males and females during the breeding and nonbreeding season, but their expression patterns differed. Mn-NP1 was highly expressed in the breeding season, in the male testis, and highly expressed in the nonbreeding season, in the female ovary. Mn-NP3 exhibited biased female expression in the breeding and nonbreeding season, with dominant expression in the ovary. All Mn-NPs were detected during embryo development, but with different expression patterns. These data indicated that Mn-NP1 may function during embryonic development, and that Mn-NP2 may be expressed during early embryo cell division, and late larval development. Mn-NP3 expression patterns reflected maternal inheritance, and may be associated with ovarian maturation. These expression data suggested that Mn-NP1 and Mn-NP2 are negatively correlated with ovarian development, with inhibition roles during this development. Mn-NP3 may be involved in vitellogenesis.

Wwc2 Is a Novel Cell Division Regulator During Preimplantation Mouse Embryo Lineage Formation and Oogenesis.

Formation of the hatching mouse blastocyst marks the end of preimplantation development, whereby previous cell cleavages culminate in the formation of three distinct cell lineages (trophectoderm, primitive endoderm and epiblast). We report that dysregulated expression of Wwc2, a genetic paralog of Kibra/Wwc1 (a known activator of Hippo-signaling, a key pathway during preimplantation development), is specifically associated with cell autonomous deficits in embryo cell number and cell division abnormalities. Division phenotypes are also observed during mouse oocyte meiotic maturation, as Wwc2 dysregulation blocks progression to the stage of meiosis II metaphase (MII) arrest and is associated with spindle defects and failed Aurora-A kinase (AURKA) activation. Oocyte and embryo cell division defects, each occurring in the absence of centrosomes, are fully reversible by expression of recombinant HA-epitope tagged WWC2, restoring activated oocyte AURKA levels. Additionally, clonal embryonic dysregulation implicates Wwc2 in maintaining the pluripotent epiblast lineage. Thus, Wwc2 is a novel regulator of meiotic and early mitotic cell divisions, and mouse blastocyst cell fate.

Dynamic optima in cell sizes during early development enable normal gastrulation in zebrafish embryos

Cell migration is the main driver of the evolutionarily conserved process of gastrulation, which shapes metazoan embryo morphology. The molecular and cellular mechanisms of cell migration during gastrulation though well researched lacks an understanding of the contribution of cell sizes to collective cell migration. This is especially important during the early phase of metazoan development, which is dominated by constantly changing cell sizes in the background of which cells migrate en mass to shape the embryo. Here we investigate this phenomenon in zebrafish embryos, a model system in which early cell divisions causes cell sizes to decrease naturally over time as cells migrate collectively to sculpt the embryonic body plan. Because mutations that can perturb cell sizes so early in development do not exist, we generate haploid and tetraploid zebrafish embryos and show that cell sizes in such embryos are smaller and larger than the diploid norm, respectively. Cells in embryos made of smaller or larger than normal cells migrate sub-optimally, leading to gastrulation defects. Gene expression analysis suggests that the observed defects originate from altered cell size, and not from pleiotropic effects of altered ploidy. This interpretation is strengthened when gastrulation defects are rescued by increasing cell sizes in embryos wherein cell sizes are smaller than normal. We show that the migration defects are cell-autonomous by live imaging migrating haploid and tetraploid cells during gastrulation in chimeric diploid embryos. Analysis of membrane protrusion dynamics in single cells shows that cells normally extend protrusions non-uniformly during migration, a phenomenon which is perturbed when cell sizes deviate from the norm. Thus, an optimal range of developmental stage-specific cell sizes appears necessary for collective cell migration to correctly position cells in space and time to shape an amorphous ball of blastoderm into an embryo.

Kinesin-7 CENP-E regulates cell division, gastrulation and organogenesis in development

Kinesin-7 CENP-E motor protein is essential for chromosome alignment and kinetochore-microtubule attachment in cell division. Human CENP-E has recently identified to be linked with the microcephalic primordial dwarfism syndromes associated with a smaller head, brain malformations and a prominent nose. However, the roles of CENP-E in embryonic development remain largely unknown. In this study, we find that zebrafish CENP-E inhibition results in defects in early zygote cleavage, including asymmetric cell division, cell cycle arrest and the developmental abnormalities. We also demonstrate that CENP-E ablation in cultured cells leads to chromosome misalignment, spindle abnormalities and interruptions of the cell cycle. These observations suggest that CENP-E plays a key role in early cell division and cell cycle progression. Furthermore, we also find that CENP-E inhibition results in the defects in the epiboly, the developmental arrest, the smaller head and the abnormal embryo during zebrafish embryogenesis. Our data demonstrate new functions of CENP-E in development and provide insights into its essential roles in organogenesis.

Chromosome dynamics and spindle microtubule establishment in mouse embryos.

Chromosome segregation errors in mammalian embryos are common and jeopardize embryo health. Here, we perform for the first time 4-Dimensional imaging and tracking of chromosomes and centromeres through each preimplantation mitotic cell division in mouse embryos to define the normal dynamics of chromosome segregation. We show that a microtubule (MT)-dependent inward movement of chromosomes occurs at the time of nuclear envelope breakdown (NEBD), particularly in the earliest cell divisions, to position chromosomes prior to spindle assembly. Establishment of a rudimentary metaphase plate occurs immediately after NEBD, and is followed by a progressive alignment and biorientation of mitotic chromosomes. Stable end-on kinetochore-MT attachments form rapidly and attachment errors are uncommon. Altogether our data describe a rapid and efficient spindle assembly pathway that apparently minimizes the need for canonical MT attachment error correction in normally dividing embryos.