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The positioning of the nucleus, the central organelle of the cell, is an active and regulated process crucially linked to cell cycle, differentiation, migration, and polarity. Alterations in positioning have been correlated with cell and tissue function deficiency and genetic or chemical manipulation of nuclear position is embryonic lethal. Nuclear positioning is a precursor for symmetric or asymmetric cell division which is accompanied by fate determination of the daughter cells. Nuclear positioning also plays a key role during early embryonic developmental stages in insects, such as Drosophila, where hundreds of nuclei divide without cytokinesis and are distributed within the large syncytial embryo at roughly regular spacing. While the cytoskeletal elements and the linker proteins to the nucleus are fairly well characterised, including some of the force generating elements driving nuclear movement, there is considerable uncertainty about the biophysical mechanism of nuclear positioning, while the field is debating different force models. In this review, we highlight the current body of knowledge, discuss cell context dependent models of nuclear positioning, and outline open questions.

Zygotic genome activation (ZGA) initiates regionalized transcription underlying distinct cellular identities. ZGA is dependent upon dynamic chromatin architecture sculpted by conserved DNA-binding proteins. However, the direct mechanistic link between the onset of ZGA and the tissue-specific transcription remains unclear. Here, we have addressed the involvement of chromatin organizer Satb2 in orchestrating both processes during zebrafish embryogenesis. Integrative analysis of transcriptome, genome-wide occupancy and chromatin accessibility reveals contrasting molecular activities of maternally deposited and zygotically synthesized Satb2. Maternal Satb2 prevents premature transcription of zygotic genes by influencing the interplay between the pluripotency factors. By contrast, zygotic Satb2 activates transcription of the same group of genes during neural crest development and organogenesis. Thus, our comparative analysis of maternal versus zygotic function of Satb2 underscores how these antithetical activities are temporally coordinated and functionally implemented highlighting the evolutionary implications of the biphasic and bimodal regulation of landmark developmental transitions by a single determinant., Activation of the zygotic genome is a critical transition during development, though the link to tissue-specific gene regulation remains unclear. Here the authors demonstrate distinct functions for Satb2 before and after zygotic genome activation, highlighting the temporal coordination of these roles.

The early insect embryo develops as a multinucleated cell distributing the genome uniformly to the cell cortex. Mechanistic insight for nuclear positioning beyond cytoskeletal requirements is missing. Contemporary hypotheses propose actomyosin driven cytoplasmic movement transporting nuclei, or repulsion of neighbor nuclei driven by microtubule motors. Here, we show that microtubule crosslinking by Feo and Klp3A is essential for nuclear distribution and internuclear distance maintenance in Drosophila. Germline knockdown causes irregular, less dense nuclear delivery to the cell cortex and smaller distribution in ex vivo embryo explants. A minimal internuclear distance is maintained in explants from control embryos but not from Feo inhibited embryos, following micromanipulation assisted repositioning. A dimerization deficient Feo abolishes nuclear separation in embryo explants while the full-length protein rescues the genetic knockdown. We conclude that Feo and Klp3A crosslinking of antiparallel microtubule overlap generates a length-regulated mechanical link between neighboring microtubule asters. Enabled by a novel experimental approach, our study illuminates an essential process of embryonic multicellularity.

Interpreting rare variants remains a challenge in personal genomics, especially for disorders with several causal genes and for genes that cause multiple disorders. ZNF423 encodes a transcriptional regulatory protein that intersects several developmental pathways. ZNF423 has been implicated in rare neurodevelopmental disorders, consistent with midline brain defects in Zfp423-mutant mice, but pathogenic potential of most patient variants remains uncertain. We engineered ~50 patient-derived and small deletion variants into the highly-conserved mouse ortholog and examined neuroanatomical measures for 791 littermate pairs. Three substitutions previously asserted pathogenic appeared benign, while a fourth was effectively null. Heterozygous premature termination codon (PTC) variants showed mild haploabnormality, consistent with loss-of-function intolerance inferred from human population data. In-frame deletions of specific zinc fingers showed mild to moderate abnormalities, as did low-expression variants. These results affirm the need for functional validation of rare variants in biological context and demonstrate cost-effective modeling of neuroanatomical abnormalities in mice., Author summary Gene identification in rare disorders is typically supported by finding different mutations of the same gene in multiple families with the same disorder. However, causal evidence for any specific mutation found in one or a few related individuals is weaker, especially if the disorder can be caused by any of several genes and the functional effect of the mutation is not certain. Experimental models can be helpful in testing causal effects, but only to the extent that the model is validated to recapitulate one or more aspects of the disorder. We used CRISPR/Cas9-based genome engineering to create a wide range of mutations in mouse Zfp423, whose human cognate is implicated in neurodevelopmental disorders, especially cerebellar vermis hypoplasia and Joubert syndrome. This large collection of animal models shows that both reduced Zfp423 expression, including heterozygosity for loss-of-function mutations, and normally-expressed domain deletions, including specific zinc finger domains, produce measureable abnormalities in midline development. Despite this high level of validation, most patient-derived amino acid substitution variants tested did not produce measureable effects. The single exception is a substitution, H1277Y, that destroys a structural element in the last zinc finger domain and results in dramatic loss of steady-state Zfp423 protein level.

7033 Background: Shared decision making to confront choices with clinical equipoise, has been the privilege of those patients with access to time intensive consults with oncologists. We conducted a randomized controlled trial for breast cancer patients to use an online, self-administered, out-of-the-medical-encounter decision aid (DA) to choose between breast conserving surgery (BCS) and mastectomy. Methods: Navya Patient Preference Tool (Navya PPT) is a multilingual DA based on adaptive conjoint analysis of tradeoffs between cost, adverse effects of radiation, and breast conservation. Prior analysis established high internal reliability and external validity of the Navya PPT. Eligible cT1/2, cN0 breast cancer patients planned for surgery were block randomized, in 1:1:1 ratio, to receive the research questionnaire (RQ) to measure decisional conflict on choice of surgery (control, arm 1), Navya PPT followed by RQ (experimental, arm 2) or Navya PPT followed by RQ administered with key male family member (experimental, arm 3). Groups were stratified with respect to age, socio-economic status (SES) and educational level. The study was powered to detect a decrease in Decisional Conflict Index (DCI) by 0.25 (β-0.8, two sided α- 0.01). Results: Between June 2017 and December 2019, 247/255 patients were randomized to arm 1 (83), arm 2 (84), and arm 3 (80). Median age was 48 years (IQR 23-76), and median pT size was .5 cm (0.5-6 cm). 59% of patients were middle or lower SES and 46.2% had ≤ 12th grade education. DCI was significantly reduced in arm 2 as compared with arm 1 (1.34 vs. 1.65, Cohen’s d 0.49 (± 0.31) p

The early insect embryo develops as multinucleated cell distributing genomes uniformly to the cell cortex. Mechanistic insight for nuclear positioning beyond cytoskeletal requirements is missing to date. Contemporary hypotheses propose actomyosin driven cytoplasmic movement transporting nuclei, or repulsion of neighbor nuclei driven by microtubule motors. Here, we show that microtubule crosslinking by Feo and Klp3A is essential for nuclear distribution and internuclear distance maintenance in Drosophila. RNAi knockdown in the germline causes irregular, less dense nuclear delivery to the embryo cortex and smaller distribution in ex vivo embryo explants. A minimal internuclear distance is maintained in explants from control embryos but not from Feo depleted embryos, following micromanipulation assisted repositioning. A dominant-negative Feo protein abolishes nuclear separation in embryo explants while the full-length protein rescues the genetic knockdown. We conclude that antiparallel microtubule overlap crosslinking by Feo and Klp3A generates a length-regulated mechanical link between neighboring microtubule asters. Enabled by a novel experimental approach, our study illuminates an essential process of embryonic multicellularity.

Mitosis, in a broader sense, is an intracellular mechanical process that is fueled by chemical reactions and regulated by a complex protein interaction network. Research aimed at understanding mitosis in all these aspects is often limited to pharmaceutical treatment or genetic manipulation of single cells or entire tissues. These experimental models entail physical boundaries imposed by the cell membrane, making it extremely challenging to apply mechanical perturbations, or to introduce larger molecules such as peptides, proteins, or genetic transcripts in an acute and specific manner. Here, we present a cell-free experimental assay that is exploiting the properties of a large, multinucleated embryo cell. Drosophila, like almost all insects, initially develops as a syncytial embryo, the task of which is to replicate and distribute the genetic material quickly and regularly. We describe an experimental procedure that allows the isolation of nucleocytoplasm from single embryos that retains the developmental processes, most importantly the native mitotic progression of nuclei.

Mitosis, in a broader sense, is an intracellular mechanical process that is fueled by chemical reactions and regulated by a complex protein interaction network. Research aimed at understanding mitosis in all these aspects is often limited to pharmaceutical treatment or genetic manipulation of single cells or entire tissues. These experimental models entail physical boundaries imposed by the cell membrane, making it extremely challenging to apply mechanical perturbations, or to introduce larger molecules such as peptides, proteins, or genetic transcripts in an acute and specific manner. Here, we present a cell-free experimental assay that is exploiting the properties of a large, multinucleated embryo cell. Drosophila, like almost all insects, initially develops as a syncytial embryo, the task of which is to replicate and distribute the genetic material quickly and regularly. We describe an experimental procedure that allows the isolation of nucleocytoplasm from single embryos that retains the developmental processes, most importantly the native mitotic progression of nuclei.

The epidermis is a stratified epithelium, which forms a barrier to maintain the internal milieu in metazoans. Being the outermost tissue, growth of the epidermis has to be strictly coordinated with the growth of the embryo. The key parameters that determine tissue growth are cell number and cell size. So far, it has remained unclear how the size of epidermal cells is maintained and whether it contributes towards epidermal homeostasis. We have used genetic analysis in combination with cellular imaging to show that zebrafish goosepimples/myosin Vb regulates plasma membrane homeostasis and is involved in maintenance of cell size in the periderm, the outermost epidermal layer. The decrease in peridermal cell size in Myosin Vb deficient embryos is compensated by an increase in cell number whereas decrease in cell number results in the expansion of peridermal cells, which requires myosin Vb (myoVb) function. Inhibition of cell proliferation as well as cell size expansion results in increased lethality in larval stages suggesting that this two-way compensatory mechanism is essential for growing larvae. Our analyses unravel the importance of Myosin Vb dependent cell size regulation in epidermal homeostasis and demonstrate that the epidermis has the ability to maintain a dynamic balance between cell size and cell number., Author Summary The epidermis is the outermost epithelial component of the vertebrate skin. It functions as an effective barrier against pathogens and prevents loss of body fluids to the surrounding environment. The factors involved in the maintenance of epidermal architecture have been under intense investigation since the last two decades. Here we report that zebrafish Myosin Vb, a molecular motor, which transports various cargoes inside epithelial cells, is involved in the maintenance of cell size in the outermost epidermal layer called periderm. We show that in the absence of myosin Vb function there is perturbed membrane transport and an increase in degradation of membrane components leading to cell shrinkage in the myosin Vb mutant. The epidermis compensates for this decrease in cell size, which may compromise epidermal integrity, by increasing the cell number. We also show that in the absence of cell proliferation, the cell size increases to compensate for the decrease in cell number. Simultaneous reduction in cell proliferation as well as cell size results in death of the embryos. Thus, our analyses unravel previously unknown compensatory mechanisms that exist in the epidermis to maintain the tissue integrity.