SEARCH · bioRxiv Science

Results for “Developmental Biology”

Search indexed bioRxiv preprints in genomics, neuroscience, cell biology and bioinformatics. Read source abstracts and check manuscript versions; preprints are not peer reviewed.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,405 records · Page 78Linked to original sources

bioRxiv2019

Dynamics of Sox2 expression during rat germ cell development and its relationship with emergence of spermatogonia

1.The gonocytes represent a specific phase of male gem cell development that precedes spermatogonial stem cell differentiation. Here, we describe the expression of Sox2, an OCT4 partner, during rat germ cell development. Our hypothesis is that SOX2 has a cytoplasmic role during gonocyte-to-spermatogonia transition. Male rat embryos and testes were submitted to the analysis of Sox2 expression. Sox2 was detected in germ cells from 14 days post-conception (dpc) to 8dpp. SOX2 was present in 14dpc and 15dpc embryos and absent at 17 and 19dpc; however, it did not show direct correlation with mRNA. SOX2 labelling was detected after birth and its expression increased from 1dpp to 5dpp. SOX2 was localized in the cytoplasm and showed a granulated pattern similar to P-bodies. Indeed, GW182/SOX2 and LIN28/SOX2 double-labelling showed that SOX2 partially co-localized with the P-bodies components GW182 and LIN28. At 8dpp SOX2 was detected in the nucleus and/or in the cytoplasm of spermatogonia, whereas at 25dpp it was detected in the nucleus of rare spermatogonia. This suggests that SOX2 localization changes during gonocytes to spermatogonia transition.

developmental biology↗

bioRxiv2019

Evolutionary conserved canonical BMP activity controls cortical neurogenesis

The growth and evolutionary expansion of the cerebral cortex are defined by the spatial-temporal production of neurons, which itself depends on the decision of radial glial cells (RGCs) to self-amplify or to switch to neurogenic divisions. The mechanisms regulating these RGC fate decisions are still incompletely understood. Here we describe a novel and evolutionarily conserved role of the canonical BMP transcription factors SMAD1/5 in controlling neurogenesis and growth during corticogenesis. Reducing the expression of both SMAD1 and SMAD5 in neural progenitors at early mouse cortical development caused microcephaly and an increased production of early-born cortical neurons at the expense of late-born ones, which correlated with the premature differentiation and depletion of the pool of cortical progenitors. Gain- and loss-of-function experiments performed during early cortical neurogenesis in the chick revealed that SMAD1/5 activity supports self-amplifying RGC divisions and restrain the neurogenic ones. Furthermore, we demonstrate that SMAD1/5 stimulate RGC self-amplification through the positive post-transcriptional regulation of the Hippo signaling effector YAP. We anticipate this SMAD1/5-YAP signaling module to be fundamental in controlling growth and evolution of the amniote cerebral cortex.

developmental biology↗

bioRxiv2019

Cell-type specific mechanical response and actomyosin dynamics in the developing Drosophila retina

During organogenesis, different cell types need to work together to induce functional multicellular structures. To study this process, we made use of the genetically tractable fly retina, with a focus on the mechanisms that coordinate morphogenesis between the different epithelial cell types that make up the optical lens. Our work shows that these epithelial cells present contractile apical-medial MyosinII meshworks, which control the apical area and junctional geometry of these cells during lens development. Our study also suggests that MyosinII meshworks drive cell shape changes in response to external forces, and thus they mediate part of the biomechanical coupling that takes place between these cells. Importantly, our work, including mathematical modelling of forces and material stiffness during lens development, raises the possibility that increased cell stiffness acts as a mechanism for limiting this mechanical coupling. We propose this might be required in complex tissues, where different cell types undergo concurrent morphogenesis and where averaging out of forces across cells could compromise individual cell apical geometry and thereby organ function.

developmental biology↗

bioRxiv2019

YAP is involved in replenishment of granule cell progenitors following injury to the neonatal cerebellum

The cerebellum (CB) undergoes major rapid growth during the third trimester and early neonatal stage in humans, making it vulnerable to injuries in pre-term babies. Experiments in mice have revealed a remarkable ability of the neonatal CB to recover from injuries around birth. In particular, recovery following irradiation-induced ablation of granule cell precursors (GCPs) involves adaptive reprogramming of Nestin-expressing glial progenitors (NEPs). Sonic hedgehog signaling is required for the initial step in NEP reprogramming; however, the full spectrum of developmental signaling pathways that promote NEP-driven regeneration is not known. Since the growth regulatory Hippo pathway has been implicated in the repair of several tissue types, we tested whether Hippo signaling is involved in regeneration of the CB. Using mouse models, we found that the Hippo pathway transcriptional co-activator YAP (Yes-associated protein) but not TAZ (transcriptional coactivator with PDZ binding motif) is required in NEPs for full recovery of the CB following irradiation one day after birth. The size of the adult CB, and in particular the internal granule cell layer produced by GCPs, is significantly reduced in mutants, and the organization of Purkinje cells and Bergmann glial fibers is disrupted. Surprisingly, the initial proliferative response of Yap mutant NEPs to irradiation is normal and the cells migrate to the GCP niche, but then undergo increased cell death. Loss of Yap in NEPs or GCPs during normal development leads to only mild defects in differentiation. Moreover, loss of Taz does not abrogate regeneration of GCPs by Yap mutant NEPs or alter development of the cerebellum. Our study provides new insights into the molecular signaling underlying postnatal cerebellar development and regeneration.

developmental biology↗

bioRxiv2019

Loss of function mutation of mouse Snap29 on a mixed genetic background phenocopy abnormalities found in CEDNIK and 22q11.2 Deletion Syndrome patients

Synaptosomal-associated protein 29 (SNAP29) is a member of the SNARE family of proteins involved in maintenance of various intracellular protein trafficking pathways. SNAP29 maps to the 22q11.2 region and is deleted in 90% of patients with 22q11.2 deletion syndrome (22q11.2DS). However, the contribution of hemizygosity of SNAP29 to developmental abnormalities in 22q11.2DS remains to be determined. Mutations in SNAP29 are responsible for the developmental syndrome called CEDNIK (cerebral dysgenesis, neuropathy, ichthyosis, and keratoderma). On an inbred C57Bl/6J genetic background, only the ichthyotic skin defect associated with CEDNIK was reported. In this study, we show that loss of function mutation of Snap29 on a mixed genetic background not only models skin abnormalities found in CEDNIK, but also phenocopy ophthalmological, neurological, and motor defects found in these patients and a subset of 22q11.2DS patients. Thus, our findings indicate that mouse models of human syndromes should be analyzed on a mixed genetic background. Our work also reveals an unanticipated requirement for Snap29 in male fertility, and support contribution of hemizygosity for SNAP29 to the phenotypic spectrum of abnormalities found in 22q11.2DS patients.

developmental biology↗

bioRxiv2019

Basal protrusions mediate spatiotemporal patterns of spinal neuron differentiation

During early spinal cord development, neurons of particular subtypes differentiate with a sparse periodic pattern while later neurons differentiate in the intervening space to eventually produce continuous columns of similar neurons. The mechanisms that regulate this spatiotemporal pattern are unknown. In vivo imaging of zebrafish reveals differentiating spinal neurons transiently extend two long protrusions along the basal surface of the spinal cord prior to axon initiation. These protrusions express Delta protein consistent with the possibility they influence Notch signalling at a distance of several cell diameters. Experimental reduction of laminin expression leads to smaller protrusions and shorter distances between differentiating neurons. The experimental data and a theoretical model support the proposal that the pattern of neuronal differentiation is regulated by transient basal protrusions that deliver temporally controlled lateral inhibition mediated at a distance. This work uncovers novel, stereotyped protrusive activity of new-born neurons that organizes long distance spatiotemporal patterning of differentiation.

developmental biology↗

bioRxiv2019

Positive feedback loop of regulating ERK phosphorylation in mESCs mediated by Etv5-Tet2-Fgfr2 axis

Dynamic equilibrium of extracellular signal-regulated kinase (ERK) activity is regulated elaborately by multiple feedback loops to ensure the normal self-renewal of mouse embryonic stem cells (mESCs). Previous studies on mESCs have demonstrated that the negative feedback loops are engaged to prevent the overactivated ERK phosphorylation (pERK). It is not clear whether there is any positive feedback loop involved to maintain a minimum of pERK in mESCs. Here, we found that blocking fibroblast growth factor (FGF)-ERK pathway by chemical PD0325901 downregulated the transcription of E26 transformation-specific (ETS) family transcription factor Etv5 in mESCs. In turn, knockout (KO) of Etv5 by CRISPR/Cas9 decreased pERK. Moreover, Etv5 KO enhanced the DNA methylation at promoter of fibroblast growth factor receptor 2 (Fgfr2) by downregulating DNA hydroxylase Tet2, which further decreased the expression of Fgfr2 in mESCs. Collectively, a positive feedback loop of regulating pERK was revealed in mESCs, which was mediated by Etv5-Tet2-Fgfr2 axis. Our findings provide a new paradigm for pERK regulation in mESCs and will be useful to understand the cell fate determination during early embryo development.

developmental biology↗

bioRxiv2019

STOCHASTIC SINGLE CELL BEHAVIOUR LEADS TO ROBUST HORIZONTAL CELL LAYER FORMATION IN THE VERTEBRATE RETINA

Developmental programs that arrange cells and tissues into patterned organs are remarkably robust. In the developing vertebrate retina for example, neurons reproducibly assemble into distinct layers giving the mature organ its overall structured appearance. This stereotypic neuronal arrangement, termed lamination, is important for efficient neuronal connectivity. While retinal lamination is conserved in many vertebrates including humans, how it emerges from single cell behaviour is not fully understood. To shed light on this question, we here investigated the formation of the retinal horizontal cell layer. Using in vivo light sheet imaging of the developing zebrafish retina, we generated a comprehensive quantitative analysis of horizontal single cell behaviour from birth to final positioning. Interestingly, we find that all parameters analyzed including cell cycle dynamics, migration paths and kinetics as well as sister cell dispersal are very heterogeneous. Thus, horizontal cells show individual non-stereotypic behaviour before final positioning. Yet, these initially stochastic cell dynamics always generate the correct laminar pattern. Consequently, our data shows that lamination of the vertebrate retina contains a yet underexplored extent of single cell stochasticity.

developmental biology↗

bioRxiv2019

Thyroid hormone coordinates developmental trajectories but does not underlie developmental truncation in Danionins

BackgroundChanges in post-embryonic developmental trajectories can profoundly alter adult phenotypes and life history transitions. In vertebrate clades with complex, biphasic life cycles, thyroid hormone (TH) regulates metamorphosis, and alterations to TH metabolism underlie famous cases of paedomorphosis. We tested the requirement for TH in multiple post-embryonic developmental processes in the zebrafish, and asked if TH loss was associated with paedomorphosis in miniaturized Danionellas. ResultsWe found that TH regulates the relative growth of different body parts in zebrafish, inhibiting head growth at juvenile stages. The lateral line also showed sensitivity to the hormone: head neuromasts were inhibited by TH, while trunk neuromasts required TH for their proliferation. While several aspects of Danionella morphology resembled that of larval zebrafish, these species did not resemble hypothyroid zebrafish in their shape or lateral line, and these fish showed functional thyroid follicles. ConclusionsAlthough zebrafish do not undergo a discrete ecological transformation, we found that multiple tissues go through a protracted metamorphosis, and that TH ushers in growth patterns and processes typical of juveniles. We found no evidence that compromised TH metabolism is responsible for paedomorphosis in Danionellas. Nonetheless, modulations to TH-sensitive pathways affect evolutionarily-relevant traits, and are likely important targets for adaptation. Bullet PointsO_LIThyroid hormone regulates shifts in relative growth trajectories in different zebrafish tissues C_LIO_LIThyroid hormone inhibits head growth in juvenile zebrafish, and regulates juvenile growth patterns C_LIO_LIThyroid hormone stimulates formation of neuromast canals in the head and stitches on the trunk of zebrafish C_LIO_LIDanionella, the miniaturized sister group to Danio morphologically resemble larval zebrafish and do not form neuromast canals C_LIO_LIHypothyroidism is not the cause of paedomorphosis in Danionella C_LI Grant SponsorsNIH R00GM105874 NIH R03HD091634 Burroughs Wellcome Collaborative Research Travel Grant 1017439

developmental biology↗

bioRxiv2019

A critical but divergent role of PRDM14 in human primordial germ cell fate revealed by inducible degrons

PRDM14 is a crucial regulator of mouse primordial germ cells (mPGC), epigenetic reprogramming and pluripotency, but its role in the evolutionarily divergent regulatory network of human PGCs (hPGCs) remains unclear. Besides, a previous knockdown study indicated that PRDM14 might be dispensable for human germ cell fate. Here, we decided to use inducible degrons for a more rapid and comprehensive PRDM14 depletion. We show that PRDM14 loss results in significantly reduced specification efficiency and an aberrant transcriptome of human PGC-like cells (hPGCLCs) obtained in vitro from human embryonic stem cells (hESCs). Chromatin immunoprecipitation and transcriptomic analyses suggest that PRDM14 cooperates with TFAP2C and BLIMP1 to upregulate germ cell and pluripotency genes, while repressing WNT signalling and somatic markers. Notably, PRDM14 targets are not conserved between mouse and human, emphasising the divergent molecular mechanisms of PGC specification. The effectiveness of degrons for acute protein depletion is widely applicable in various developmental contexts.

developmental biology↗

bioRxiv2019

A conserved requirement for Fbxo7 during male germ cell cytoplasmic remodelling

Summary statementFbxo7 is the substrate-recognition subunit of an SCF-type ubiquitin E3 ligase complex. It has physiologically important functions in regulating mitophagy, proteasome activity and the cell cycle in multiple cell types, like neurons, lymphocytes and erythrocytes. Here we show that in addition to the previously-known Parkinsonian and haematopoietic phenotypes, Fbxo7-deficient male mice are completely sterile. In these males, despite successful meiosis, nuclear elongation and eviction of histones from chromatin, the developing spermatids are phagocytosed by Sertoli cells during late spermiogenesis, as the cells undergo cytoplasmic remodelling. Surprisingly, despite the loss of all germ cells, there was no evidence of the symplast formation and cell sloughing that is typically associated with spermatid death in other mouse sterility models, suggesting that novel cell death and/or cell disposal mechanisms may be engaged in Fbxo7-deficient males. Mutation of the Drosophila Fbxo7 orthologue, nutcracker (ntc) was previously shown to cause sterility at a similar stage of germ cell development, indicating that the requirement for Fbxo7 is conserved. The ntc phenotype was attributed to proteasome mis-regulation via an interaction with the proteasome regulator, DmPI31. Our data suggest rather that in mice, the requirement for Fbxo7 is either independent of its interaction with PI31, or relates specifically to cytoplasmic proteasome activity during spermiogenesis.

developmental biology↗

bioRxiv2019

Sex differences in gene expression and proliferation are dependent on the epigenetic modifier HP1γ

Sex differences in growth rate in very early embryos have been recognized in a variety of mammals and attributed to sex-chromosome complement effects as they occur before overt sexual differentiation. We previously found that sex-chromosome complement, rather than sex hormones regulates heterochromatin-mediated silencing of a transgene and autosomal gene expression in mice. Here, sex dimorphism in proliferation was investigated. We confirm that male embryonic fibroblasts proliferate faster than female fibroblasts and show that this proliferation advantage is completely dependent upon heterochromatin protein 1 gamma (HP1{gamma}). To determine whether this sex-regulatory effect of HP1{gamma} was a more general phenomenon, we performed RNA sequencing on MEFs derived from males and females, with or without HP1{gamma}. Strikingly, HP1{gamma} was found to be crucial for regulating nearly all sexually dimorphic autosomal gene expression because deletion of the HP1{gamma} gene in males abolished sex differences in autosomal gene expression. The identification of a key epigenetic modifier as central in defining gene expression differences between males and females has important implications for understanding physiological sex differences and sex bias in disease.

developmental biology↗

bioRxiv2019

Pluripotency factors regulate the onset of Hox cluster activation in the early embryo

Pluripotent cells are a transient population present in the early mammalian embryo dependent on transcription factors, such as OCT4 and NANOG, which maintain pluripotency while simultaneously suppressing lineage specification. Interestingly, these factors are not exclusive to uncommitted cells, but are also expressed during early phases of differentiation. However, their role in the transition from pluripotency to lineage specification is largely unknown. Using genetic models for controlled Oct4 or Nanog expression during postimplantation stages, we found that pluripotency factors play a dual role in regulating key lineage specifiers, initially repressing their expression and later being required for their proper activation. We show that the HoxB cluster is coordinately regulated in this way by OCT4 binding sites located at the 3 end of the cluster. Our results show that core pluripotency factors are not limited to maintaining the pre-committed epiblast, but are also necessary for the proper deployment of subsequent developmental programs.

developmental biology↗

bioRxiv2019

In vivo study of gene expression with an enhanced dual-color fluorescent transcriptional timer

Fluorescent transcriptional reporters are widely used as signaling reporters and biomarkers to monitor pathway activities and determine cell type identities. However, a large amount of dynamic information is lost due to the long half-life of the fluorescent proteins. To better detect dynamics, fluorescent transcriptional reporters can be destabilized to shorten their half-lives. However, applications of this approach in vivo are limited due to significant reduction of signal intensities. To overcome this limitation, we enhanced translation of a destabilized fluorescent protein and demonstrate the advantages of this approach by characterizing spatio-temporal changes of transcriptional activities in Drosophila. In addition, by combining a fast-folding destabilized fluorescent protein and a slow-folding long-lived fluorescent protein, we generated a dual-color transcriptional timer that provides spatio-temporal information about signaling pathway activities. Finally, we demonstrate the use of this transcriptional timer to identify new genes with dynamic expression patterns.

developmental biology↗

bioRxiv2019

Neph/Nephrin-like adhesion and tissue level pulling forces regulate cell intercalation during Drosophila retina development.

Intercalation between neighboring cells contributes to shaping epithelial tissues and is regulated by the contractile actomyosin cytoskeleton. While intercalation typically occurs over minutes, instances of much slower cell intercalation have been reported during organogenesis. This is observed, for example, for the four glial-like cone cells (CC) that intercalate during Drosophila retinal patterning. Here we show that Myosin-II activity in the CCs is largely dispensable for their intercalation. Instead, we find that differential activity of the Notch-signaling pathway within the CC quartet regulates intercalation, which also depends on the cell adhesion proteins Roughest and Hibris. In addition, mathematical modeling predicts that forces external to the intercalating CC quartet are necessary for intercalation. Consistent with this prediction we show that the surrounding primary pigment cells are under significant contractile tension. Altogether, our work elucidates a novel mode of cell intercalation that relies on Neph/Nephrin-like adhesion and forces external to the intercalating cells.

developmental biology↗

bioRxiv2019

A smooth muscle-like niche facilitates lung epithelial regeneration

The mammalian lung is a highly complex organ due to its branched, tree-like structure and diverse cellular composition. Recent efforts using state-of-the-art genetic lineage tracing and single-cell transcriptomics have helped reduce this complexity and delineate the ancestry and fate of various cell subpopulations during organogenesis, homeostasis and repair after injury. However, mesenchymal cell heterogeneity and function in development and disease remain a longstanding issue in the lung field. In this study, we break down smooth muscle heterogeneity into the constituent subpopulations by combining in vivo lineage tracing, single-cell RNA sequencing and in vitro organoid cultures. We identify a repair-supportive mesenchymal cell (RSMC) population that is distinct from pre-existing airway smooth muscle cells (ASMC) and is critical for regenerating the conducting airway epithelium. Progenitors of RSMCs are intertwined with airway smooth muscle, undergo active WNT signaling, transiently acquire the expression of the smooth muscle marker ACTA2 in response to epithelial injury and are marked by PDGFR expression. Our data simplify the cellular complexity of the peribronchiolar domain of the adult lung and represent a forward step towards unraveling the role of mesenchymal cell subpopulations in instructing epithelial behavior during repair processes.

developmental biology↗

bioRxiv2019

A pleiotropic role for FGF signaling in mammary gland stromal fibroblasts

Fibroblast growth factor (FGF) signaling is crucial for mammary gland development. While multiple roles for FGF signaling in the epithelium were described, the function of FGF signaling in mammary stroma has not been elucidated. In this study, we investigated FGF signaling in mammary fibroblasts. We found that mammary fibroblasts express FGF receptors 1 and 2 and respond to FGF ligands. In particular, FGF2 and FGF9 induce sustained ERK1/2 signaling and promote fibroblast proliferation and migration in 2D. Intriguingly, only FGF2 induces fibroblast migration in 3D extracellular matrix (ECM) through regulation of actomyosin cytoskeleton and promotes force-mediated collagen remodeling by mammary fibroblasts. Moreover, FGF2 regulates production of ECM proteins by mammary fibroblasts, including collagens, fibronectin, osteopontin, and matrix metalloproteinases. Finally, we show that FGF2 signaling in mammary fibroblasts enhances fibroblast-induced branching of mammary epithelium. Our results demonstrate a pleiotropic role for FGF signaling in mammary fibroblasts with implications for regulation of mammary stromal functions and epithelial branching morphogenesis. Summary statementFGF signaling in mammary fibroblasts regulates fibroblast proliferation, migration, extracellular matrix production and remodeling, and fibroblast-mediated mammary epithelial branching morphogenesis.

developmental biology↗

bioRxiv2019

The Marginal Cells of the Caenorhabditis elegans Pharynx Scavenge Cholesterol and Other Hydrophobic Small Molecules

The nematode worm Caenorhabditis elegans is a bacterivore filter feeder. Through the contraction of the worms pharynx, a bacterial suspension is sucked into the pharynxs lumen. Excess liquid is then shunted out of the buccal cavity through ancillary channels that are made from specialized pharyngeal cells called marginal cells. Through the characterization of our library of worm-bioactive small molecules (a.k.a. wactives), we found that more than one third of wactives visibly accumulate inside of the marginal cells as crystals or globular spheres. Wactives that visibly accumulate are typically more hydrophobic than those that do not. To understand why wactives accumulate specifically in marginal cells, we performed a forward genetic screen for mutants that resist the lethality associated with one crystallizing wactive. We identified a presumptive sphingomyelin-synthesis pathway that is necessary for crystal and sphere accumulation. Sphingomyelin is a phospholipid that is enriched in the outer leaflet of the plasma membranes of most metazoans. We find that the predicted terminal enzyme of this pathway, sphingomyelin synthase 5 (SMS-5), is expressed in the pharynx, contributes to sphingomyelin abundance, and that its expression in marginal cells is sufficient for wactive accumulation. We also find that the expression of SMS-5 in the marginal cells is necessary for the proper absorption of exogenous cholesterol, without which C. elegans cannot develop. We conclude that the sphingomyelin-rich plasma membrane of the marginal cells acts as a sink to scavenge important hydrophobic nutrients from the filtered liquid that might otherwise be shunted back into the environment. One sentence summaryThe anterior pharynx of C. elegans is a Sink for Hydrophobic Small Molecules

developmental biology↗