Endodermal Cells Research Articles

Immunocytochemical Analysis of Bifid Trichomes in Aldrovanda vesiculosa L. Traps.

The two-armed bifids (bifid trichomes) occur on the external (abaxial) trap surface, petiole, and stem of the aquatic carnivorous plant Aldrovanda vesiculosa (Droseracee). These trichomes play the role of mucilage trichomes. This study aimed to fill the gap in the literature concerning the immunocytochemistry of the bifid trichomes and compare them with digestive trichomes. Light and electron microscopy was used to show the trichome structure. Fluorescence microscopy revealed the localization of carbohydrate epitopes associated with the major cell wall polysaccharides and glycoproteins. The stalk cells and the basal cells of the trichomes were differentiated as endodermal cells. Cell wall ingrowths occurred in all cell types of the bifid trichomes. Trichome cells differed in the composition of their cell walls. The cell walls of the head cells and stalk cells were enriched with arabinogalactan proteins (AGPs); however, they were generally poor in both low- and highly-esterified homogalacturonans (HGs). The cell walls in the trichome cells were rich in hemicelluloses: xyloglucan and galactoxyloglucan. The cell wall ingrowths in the basal cells were significantly enriched with hemicelluloses. The presence of endodermal cells and transfer cells supports the idea that bifid trichomes actively transport solutes, which are polysaccharide in nature. The presence of AGPs (which are considered plant signaling molecules) in the cell walls in these trichome cells indicates the active and important role of these trichomes in plant function. Future research should focus on the question of how the molecular architecture of trap cell walls changes in cells during trap development and prey capture and digestion in A. vesiculosa and other carnivorous plants.

The Impact of Different Implantation Sites and Sex on the Differentiation of Human Pancreatic Endoderm Cells Into Insulin-Secreting Cells InVivo.

Few studies have directly compared the differentiation of human embryonic stem cell-derived progenitors in different implantation sites in male and female recipients. We investigated whether the site of implantation and/or the sex of the recipient influenced the differentiation of pancreatic progenitors invivo in mice. Mice implanted with cells in macroencapsulation devices contained fewer off-target structures and developed stimulated insulin release faster than other implant sites, while females implanted with cells under the kidney capsule developed stimulated insulin release before males. Macroencapsulation devices reduced the formation of off-target cells from human embryonic stem cell-derived progenitors, a useful characteristic for clinical applications.

Quantifying endodermal strains during heart tube formation in the developing chicken embryo

In the early avian embryo, the developing heart forms when bilateral fields of cardiac progenitor cells, which reside in the lateral plate mesoderm, move toward the embryonic midline, and fuse above the anterior intestinal portal (AIP) to form a straight, muscle-wrapped tube. During this process, the precardiac mesoderm remains in close contact with the underlying endoderm. Previous work has shown that the endoderm around the AIP actively contracts to pull the cardiac progenitors toward the midline. The morphogenetic deformations associated with this endodermal convergence, however, remain unclear, as do the signaling pathways that might regulate this process. Here, we fluorescently labeled populations of endodermal cells in early chicken embryos and tracked their motion during heart tube formation to compute time-varying strains along the anterior endoderm. We then determined how the computed endodermal strain distributions are affected by the pharmacological inhibition of either myosin II or fibroblast growth factor (FGF) signaling. Our data indicate that a mediolateral gradient in endodermal shortening is present around the AIP, as well as substantial convergence and extension movements both anterior and lateral to the AIP. These active endodermal deformations are disrupted if either actomyosin contractility or FGF signaling are inhibited pharmacologically. Taken together, these results demonstrate how active deformations along the anterior endoderm contribute to heart tube formation within the developing embryo.

T-REX17 is a transiently expressed non-coding RNA essential for human endoderm formation.

Long non-coding RNAs (lncRNAs) have emerged as fundamental regulators in various biological processes, including embryonic development and cellular differentiation. Despite much progress over the past decade, the genome-wide annotation of lncRNAs remains incomplete and many known non-coding loci are still poorly characterized. Here, we report the discovery of a previously unannotated lncRNA that is transcribed 230 kb upstream of the SOX17 gene and located within the same topologically associating domain. We termed it T-REX17 (Transcript Regulating Endoderm and activated by soX17) and show that it is induced following SOX17 activation but its expression is more tightly restricted to early definitive endoderm. Loss of T-REX17 affects crucial functions independent of SOX17 and leads to an aberrant endodermal transcriptome, signaling pathway deregulation and epithelial to mesenchymal transition defects. Consequently, cells lacking the lncRNA cannot further differentiate into more mature endodermal cell types. Taken together, our study identified and characterized T-REX17 as a transiently expressed and essential non-coding regulator in early human endoderm differentiation.

Ascidian gastrulation and blebbing activity of isolated endoderm blastomeres

Gastrulation is the first dynamic cell movement during embryogenesis. Endoderm and mesoderm cells are internalized into embryos during this process. Ascidian embryos provide a simple system for studying gastrulation in chordates. Gastrulation starts in spherical late 64-cell embryos with 10 endoderm blastomeres. The mechanisms of gastrulation in ascidians have been investigated, and a two-step model has been proposed. The first step involves apical constriction of endoderm cells, followed by apicobasal shortening in the second step. In this study, isolated ascidian endoderm progenitor cells displayed dynamic blebbing activity at the gastrula stage, although such a dynamic cell-shape change was not recognized in toto. Blebbing is often observed in migrating animal cells. In ascidians, endoderm cells displayed blebbing activity, while mesoderm and ectoderm cells did not. The timing of blebbing of isolated endoderm cells coincided with that of cell invagination. The constriction rate of apical surfaces correlated with the intensity of blebbing activity in each endoderm-lineage cell. Fibroblast growth factor (FGF) signaling was both necessary and sufficient for inducing blebbing activity, independent of cell fate specification. In contrast, the timing of initiation of blebbing and intensity of blebbing response to FGF signaling were controlled by intrinsic cellular factors. It is likely that the difference in intensity of blebbing activity between the anterior A-line and posterior B-line cells could account for the anteroposterior difference in the steepness of the archenteron wall. Inhibition of zygotic transcription, FGF signaling, and Rho kinase, all of which suppressed blebbing activity, resulted in incomplete apical constriction and failure of the eventual formation of cup-shaped gastrulae. Blebbing activity was involved in the progression and maintenance of apical constriction, but not in apicobasal shortening in whole embryos. Apical constriction is mediated by distinct blebbing-dependent and blebbing-independent mechanisms. Surface tension and consequent membrane contraction may not be the sole mechanical force for apical constriction and formation of cup-shaped gastrulae. The present study reveals the hidden cellular potential of endodermal cells during gastrulation and discusses the possible roles of blebbing in the invagination process.

Sudden unexpected death caused by a colloid cyst in the third ventricle: case report

BackgroundColloid cysts arise from congenital abnormalities of the endodermis and are characteristically comprised of an external fibrous layer, with a lining of cuboidal and columnar epithelial cells and endodermal ciliated cells. They contain a gelatinous matrix, produced by mucus-producing epithelial cells.Case presentationAn 8-year-old Saudi girl died in Dammam Central Hospital, to which she was admitted by her parents following her complaints of intense headaches. When the body was examined externally, it was noted that she had bilateral eye congestion, evidence of needle marks on all four limbs and in the region of the femoral triangle and bruising in the central chest and left shoulder areas. No other evidence of injury was noted. A cyst in the third ventricle of the brain was identified at post mortem. Investigations for alcohol, toxins and illicit substances were negative.ConclusionIt was surmised that the child had died as a result of a cerebral colloid cyst and its clinical sequelae.

Neighbor-specific gene expression revealed from physically interacting cells during mouse embryonic development

Development of multicellular organisms is orchestrated by persistent cell-cell communication between neighboring partners. Direct interaction between different cell types can induce molecular signals that dictate lineage specification and cell fate decisions. Current single-cell RNA-seq technology cannot adequately analyze cell-cell contact-dependent gene expression, mainly due to the loss of spatial information. To overcome this obstacle and resolve cell-cell contact-specific gene expression during embryogenesis, we performed RNA sequencing of physically interacting cells (PIC-seq) and assessed them alongside similar single-cell transcriptomes derived from developing mouse embryos between embryonic day (E) 7.5 and E9.5. Analysis of the PIC-seq data identified gene expression signatures that were dependent on the presence of specific neighboring cell types. Our computational predictions, validated experimentally, demonstrated that neural progenitor (NP) cells upregulate Lhx5 and Nkx2-1 genes, when exclusively interacting with definitive endoderm (DE) cells. Moreover, there was a reciprocal impact on the transcriptome of DE cells, as they tend to upregulate Rax and Gsc when in contact with NP cells. Using individual cell transcriptome data, we formulated a means of computationally predicting the impact of one cell type on the transcriptome of its neighboring cell types. We have further developed a distinctive spatial-t-distributed stochastic neighboring embedding to display the pseudospatial distribution of cells in a 2-dimensional space. In summary, we describe an innovative approach to study contact-specific gene regulation during embryogenesis.

Whole-Mount In Situ Hybridization for Detection of Migrating Zebrafish Endodermal Cells.

One of the most important events in early vertebrate development is the formation and positioning of the endoderm, the embryonic progenitor cell population that gives rise to the internal organs. Recent years have seen renewed interest in the mechanisms underlying the specification and migration of endodermal progenitor cells. The zebrafish is a well-established, accessible, and powerful model to study this cell population. Zebrafish endodermal cells are specified around 4h after fertilization and subsequently migrate as evenly spaced single cells in a stereotypical manner in the next 6h. Given the large numbers of fertilized eggs that can be obtained from a single breeding pair and the ease of chemical and genetic perturbations, the zebrafish is an excellent model to study mechanisms underlying endoderm specification and migration. An easy approach to visualizing and quantitating endodermal cells and their migratory routes is by whole-mount in situ hybridization (WISH) on fixed embryos, collected in time series. This chapter provides basic information on the organization and staging of the embryos, with an emphasis on the migrating endodermal cell population. In addition, optimized protocols for the isolation and fixation of staged embryos are provided as well as detailed probe synthesis and WISH protocols, specific for migrating endoderm. Finally, details are provided on how to approach these experiments quantitatively, and some common pitfalls are discussed.

Behind the developing brains and beating hearts of stem cell-derived embryo models.

Studies over the past decade have shown how stem cells representing embryonic and extra-embryonic tissues of the mouse can self-assemble in the culture dish to recapitulate an astonishing part of early embryonic development. A systematic analysis has demonstrated how pluripotent embryonic stem cells can be induced to behave like the implanting epiblast; how they can interact with trophectoderm stem cells to form a patterned structure resembling the implanting embryo prior to gastrulation; and how the third stem cell type-extra-embryonic endoderm cells-can be incorporated to generate structures that undergo the cell movements and gene expression patterns of gastrulation. Moreover, such stem cell-derived embryo models can proceed to neurulation and establish progenitors for all parts of the brain and neural tube, somites, beating heart structures and gut tube. They develop within extra-embryonic yolk sacs that initiate haematopoiesis. Here we trace this journey of discovery.

Generation of Mouse Primitive Endoderm Stem Cells.

The blastocysts consist of dozens of cells of three distinct lineages: epiblast (Epi), trophoblast (TB), and primitive endoderm (PrE). All embryonic and extraembryonic tissues are derived from Epi, TB, and PrE. Stem cell lines representing preimplantation Epi and TB have been established and are known as embryonic stem cells (ESCs) and trophoblast stem cells (TSCs). Extraembryonic endoderm cells (XENCs) constitute a cell line that has been established from PrE. Although in vivo, PrE gives rise to visceral endoderm (VE), parietal endoderm (PE), and marginal zone endoderm (MZE); XENCs, on blastocyst injection into chimeras, primarily contribute to the distal region of PE. Here, we provide a comprehensive protocol for the establishment of fully potent primitive endoderm stem cell (PrESC) lines. PrESCs are established and maintained on mouse embryonic fibroblast (MEF) feeder cells in a serum-free medium supplemented with fibroblast growth factor 4 (FGF4), heparin, CHIR99021, and platelet-derived growth factor-AA (PDGF-AA). PrESCs co-express markers indicative of pluripotency and endoderm lineage commitment, exhibiting characteristics akin to those of PrE. On transplantation of PrESCs into blastocysts, they demonstrate a high efficiency in contributing to VE, PE, and MZE. PrESCs serve as a valuable model for studying PrE, sharing similarities in gene expression profiles and differentiation potential. PrESCs constitute a pivotal cornerstone for in vitro analysis of early developmental mechanisms and for studies of embryo reconstitution in vitro, particularly in conjunction with ESCs and TSCs. Key features • Establishment and maintenance of primitive endoderm stem cell (PrESCs) capable of recapitulating the developmental prowess inherent to PrE. • Offering a source of PrE lineage for embryo-like organoid reconstitution studies.

Frozen mountain pine needles: The endodermis discriminates between the ice-containing central tissue and the ice-free fully functional mesophyll.

Conifer (Pinaceae) needles are the most frost-hardy leaves. During needle freezing, the exceptional leaf anatomy, where an endodermis separates the mesophyll from the vascular tissue, could have consequences for ice management and photosynthesis. The eco-physiological importance of needle freezing behaviour was evaluated based on the measured natural freezing strain at the alpine treeline. Ice localization and cellular responses to ice were investigated in mountain pine needles by cryo-microscopic techniques. Their consequences for photosynthetic activity were assessed by gas exchange measurements. The freezing response was related to the microchemistry of cell walls investigated by Raman microscopy. In frozen needles, ice was confined to the central vascular cylinder bordered by the endodermis. The endodermal cell walls were lignified. In the ice-free mesophyll, cells showed no freeze-dehydration and were found photosynthetically active. Mesophyll cells had lignified tangential cell walls, which adds rigidity. Ice barriers in mountain pine needles seem to be realised by a specific lignification patterning of cell walls. This, additionally, impedes freeze-dehydration of mesophyll cells and enables gas exchange of frozen needles. At the treeline, where freezing is a dominant environmental factor, the elaborate needle freezing pattern appears of ecological importance. This article is protected by copyright. All rights reserved.

Chromatin modifier developmental pluripotency associated factor 4 (DPPA4) is a candidate gene for alcohol-induced developmental disorders

BackgroundPrenatal alcohol exposure (PAE) affects embryonic development, causing a variable fetal alcohol spectrum disorder (FASD) phenotype with neuronal disorders and birth defects. We hypothesize that early alcohol-induced epigenetic changes disrupt the accurate developmental programming of embryo and consequently cause the complex phenotype of developmental disorders. To explore the etiology of FASD, we collected unique biological samples of 80 severely alcohol-exposed and 100 control newborns at birth.MethodsWe performed genome-wide DNA methylation (DNAm) and gene expression analyses of placentas by using microarrays (EPIC, Illumina) and mRNA sequencing, respectively. To test the manifestation of observed PAE-associated DNAm changes in embryonic tissues as well as potential biomarkers for PAE, we examined if the changes can be detected also in white blood cells or buccal epithelial cells of the same newborns by EpiTYPER. To explore the early effects of alcohol on extraembryonic placental tissue, we selected 27 newborns whose mothers had consumed alcohol up to gestational week 7 at maximum to the separate analyses. Furthermore, to explore the effects of early alcohol exposure on embryonic cells, human embryonic stem cells (hESCs) as well as hESCs during differentiation into endodermal, mesodermal, and ectodermal cells were exposed to alcohol in vitro.ResultsDPPA4, FOXP2, and TACR3 with significantly decreased DNAm were discovered—particularly the regulatory region of DPPA4 in the early alcohol-exposed placentas. When hESCs were exposed to alcohol in vitro, significantly altered regulation of DPPA2, a closely linked heterodimer of DPPA4, was observed. While the regulatory region of DPPA4 was unmethylated in both control and alcohol-exposed hESCs, alcohol-induced decreased DNAm similar to placenta was seen in in vitro differentiated mesodermal and ectodermal cells. Furthermore, common genes with alcohol-associated DNAm changes in placenta and hESCs were linked exclusively to the neurodevelopmental pathways in the enrichment analysis, which emphasizes the value of placental tissue when analyzing the effects of prenatal environment on human development.ConclusionsOur study shows the effects of early alcohol exposure on human embryonic and extraembryonic cells, introduces candidate genes for alcohol-induced developmental disorders, and reveals potential biomarkers for prenatal alcohol exposure.

Stellate Trichomes in Dionaea muscipula Ellis (Venus Flytrap) Traps, Structure and Functions

The digestive organs of carnivorous plants have external (abaxial) glands and trichomes, which perform various functions. Dionaea muscipula Ellis (the Venus flytrap) is a model carnivorous plant species whose traps are covered by external trichomes. The aim of the study was to fill in the gap regarding the structure of the stellate outer trichomes and their immunocytochemistry and to determine whether these data support the suggestions of other authors about the roles of these trichomes. Light and electron microscopy was used to show the trichomes' structure. Fluorescence microscopy was used to locate the carbohydrate epitopes that are associated with the major cell wall polysaccharides and glycoproteins. The endodermal cells and internal head cells of the trichomes were differentiated as transfer cells, and this supports the idea that stellate trichomes transport solutes and are not only tomentose-like trichomes. Trichome cells differ in the composition of their cell walls, e.g., the cell walls of the internal head cells are enriched with arabinogalactan proteins (AGPs). The cell walls of the outer head cells are poor in both low and highly homogalacturonans (HGs), but the immature trichomes are rich in the pectic polysaccharide (1-4)-β-D-galactan. In the immature traps, young stellate trichomes produce mucilage which may protect the trap surface, and in particular, the trap entrance. However, the role of these trichomes is different when the outer head cells collapse. In the internal head cells, a thick secondary wall cell was deposited, which together with the thick cell walls of the outer head cells played the role of a large apoplastic space. This may suggest that mature stellate trichomes might function as hydathodes, but this should be experimentally proven.

Self-organization principles in stem-cell-derived synthetic embryo models

As embryos, we were extremely lucky to survive implantation, when we transitioned from a simple ball of undifferentiated cells to a complex structure of distinct lineages. During development, fertilization generates a totipotent zygote that ultimately gives rise to the myriad cell types of the whole organism. In mouse embryos, the first cell fate decision leads to trophectoderm (TE) progenitors on the outside of the early embryo, surrounding the inner cell mass. Epiblast (EPI) and primitive endoderm (PE) cells then arise from the inner cell mass and are initially intermingled (embryonic day 3.5).

Pea root responses under naproxen stress: changes in the formation of structural barriers in the primary root in context with changes of auxin and abscisic acid levels.

Pharmaceuticals belong to pseudo-persistent pollutants because of constant entry into the environment and hazardous potential for non-target organisms, including plants, in which they can influence biochemical and physiological processes. Detailed analysis of results obtained by microscopic observations using fluorescent dyes (berberine hemisulphate, Fluorol Yellow 088), detection of phytohormone levels (radioimmunoassay, enzyme-linked immune sorbent assay) and thermogravimetric analysis of lignin content proved that the drug naproxen (NPX) can stimulate the formation of root structural barriers. In the primary root of plants treated with 0.5, 1, and 10 mg/L NPX, earlier Casparian strip formation and development of the whole endodermis circle closer to its apex were found after five days of cultivation (by 9-20% as compared to control) and after ten days from 0.1 mg/L NPX (by 8-63%). Suberin lamellae (SL) were deposited in endodermal cells significantly closer to the apex under 10 mg/L NPX by up to 75%. Structural barrier formation under NPX treatment can be influenced indirectly by auxin-supported cell division and differentiation caused by its eight-times higher level under 10 mg/L NPX and directly by stimulated SL deposition induced by abscisic acid (higher from 0.5 mg/L NPX), as proved by the higher proportion of cells with SL in the primary root base (by 8-44%). The earlier modification of endodermis in plant roots can help to limit the drug transfer and maintain the homeostasis of the plant.

Canine induced pluripotent stem cells efficiently differentiate into definitive endoderm in 3D cell culture conditions using high-dose activin A.

Endoderm-derived organs support indispensable functions in the body. Pluripotent stem cells can generate endoderm-derived cells or tissues and have excellent therapeutic potential to replace the functions of endodermal tissues. However, there is no viable method to induce endodermal precursor cells, definitive endoderm (DE), from canine induced pluripotent stem cells (ciPSCs). A ciPSC line was used in this study. In order to induce DE, ciPSCs were cultured with high dose activin A and fetal bovine serum. We considered the optimal differentiation period and starting cell density. Next, to reduce the remaining undifferentiated cells and improve the DE induction efficiency, DE was induced from 3D cell aggregates with knockout serum replacement instead of fetal bovine serum. Finally, hepatic and pancreatic induction were performed to investigate whether DE could differentiate into downstream lineages. After differentiation, some cells expressed the DE markers FOXA2 and SOX17. DE induction period and starting cell density were found to be important for efficient DE induction. However, some cells remained undifferentiated even after optimization of cell density and culture period. Cell differentiation under 3D culture conditions reduced undifferentiated cells and the replacement of fetal bovine serum with knockout serum replacement improved the DE induction efficiency. After hepatic and pancreatic induction, cells expressed some early hepatic and pancreatic markers. A ciPSC line was successfully differentiated to DE efficiently using a high dose of activin A with knockout serum replacement under 3D cell culture conditions. We believe that this study will be fundamental to achieving the generation of canine endodermal tissues from ciPSCs.

Integration of Transcriptome and Metabolome Analyses Reveals the Mechanistic Basis for Cadmium Accumulation in Maize.

Cadmium (Cd) pollution in soil has become a major environmental issue worldwide. However, the underlying molecular mechanism of low grain-Cd accumulation (GCA) in maize is still largely unknown. Herein, we report the mechanistic basis for low GCA in maize by a multiomics approach. The low GCA genotype L63 showed normal vacuolar formation and a lower capacity of xylem loading of Cd than the high-accumulator L42 under Cd stress. Transcriptomic sequencing identified 84 low-GCA-associated genes which are mainly involved in the S-adenosylmethionine (SAM) cycle, metal transport, and vacuolar sequestration. A metabolome analysis revealed that L63 plants had a more active SAM cycle and a greater capacity for terpenoid synthesis and phenylalanine metabolism than L42. Combining the analysis of transcriptome and metabolome characterized several genes as key genes involved in the determination of Cd accumulation. Our study identifies a mechanistic basis for low Cd accumulation in maize grains and provides candidate genes for genetic improvement of crops.

Regionally specific levels and patterns of keratin 8 expression in the mouse embryo visceral endoderm emerge upon anterior-posterior axis determination.

The mechanical properties of the different germ layers of the early mammalian embryo are likely to be critical for morphogenesis. Cytoskeleton components (actin and myosin, microtubules, intermediate filaments) are major determinants of epithelial plasticity and resilience to stress. Here, we take advantage of a mouse reporter for Keratin 8 to record the pattern of the keratin intermediate filaments network in the first epithelia of the developing mouse embryo. At the blastocyst stage, Keratin 8 is strongly expressed in the trophectoderm, and undetectable in the inner cell mass and its derivatives, the epiblast and primitive endoderm. Visceral endoderm cells that differentiate from the primitive endoderm at the egg cylinder stage display apical Keratin 8 filaments. Upon migration of the Anterior Visceral Endoderm and determination of the anterior-posterior axis, Keratin 8 becomes regionally distributed, with a stronger expression in embryonic, compared to extra-embryonic, visceral endoderm. This pattern emerges concomitantly to a modification of the distribution of Filamentous (F)-actin, from a cortical ring to a dense apical shroud, in extra-embryonic visceral endoderm only. Those regional characteristics are maintained across gastrulation. Interestingly, for each stage and region of the embryo, adjacent germ layers display contrasted levels of keratin filaments, which may play a role in their adaptation to growth and morphological changes.

Advances in the development and function of plant root endodermis

<p indent="0mm">Root, an important underground vegetative organ of plants, plays diversified roles in plant lifecycle, including fixation and support, absorption and transportation, storage and reproduction. In meristem zone of root tip, the apical meristem is continuously divided to produce new cells, promoting the growth of root tip. Mature tissues formed through primary growth constituted the primary structure of plant roots. Water and mineral ions entered the epidermis of root, passed through the outer cortex, cortex, and endodermis in a radial direction, and reached the middle column, and were transported upward in xylem through transpiration, so as to meet the needs of aboveground part. The endodermis lies the innermost cortex surrounding the central vascular tissue system, as is constructed by only monolayer cells Endodermis is a cylindrical boundary separating the central vascular tissue from the outer cortex, and is an extracellular barrier for plant selective nutrient absorption. There were mainly two stages in differentiation of endodermis, of which in differentiation stage I, lignin was continuously deposited on lateral and radial walls of endodermis cells near the root tip, forming Casparian strips. The nature of Casparian strips was a local modification on the primary wall of endodermal layer, which was formed by the lignin polymer “impregnate” the primary wall. The complete Casparian strips show a continuous belt thickening structure, which blocked the apoplast transport pathway, prevented the diffusion of solutes between cell walls, and forced solutes to transport through the plasma membrane. In differentiation stage II, and based on the Casparian strips, hydrophobic suberin was deposited on six cell walls of endodermal cells, forming suberin lamellae structure, which inhibited the transmembrane transport of substances and was a protective barrier structure. Development of Casparian strips and suberin lamellae structure are regulated by their own growth and development mechanism and closely regulated by external environmental factors. The structure of endodermis could respond to the stress environment, and the lack of necessary mineral elements, including potassium, iron or sulfur, may cause changes in composition and structure of the Casparian strips and suberin lamellae. The above change was called plant phenotypic plasticity, whose most significant function was to support plants to adapt to the environment, integrate environmental information, optimize nutrient absorption, and maintain ion homeostasis in plants, so as to improve their survival under stressful environment. A complete suberin lamellae barrier was capable of preventing calcium ions from flowing in and potassium ions from seeping out, maintaining the balance of calcium/potassium ions in plants, supporting to regulate calcium signaling system, promoting plants photosynthesis, and improving stress resistance of crops. The paper comprehensively introduced the general development mode of plant endodermis, and the structure, concluded the composition and formation regulation mechanism of Casparian strips and suberin lamellae, and discussed the changing law of endodermis plasticity responding to abiotic stress and its importance for maintaining plant ion homeostasis, as well as prospected the future research direction, providing a new idea for cultivating new stress-resistant species.

Cdx1b protects intestinal cell fate by repressing signaling networks for liver specification

In mammals, the expression of the homeobox family member Cdx2/CDX2 is restricted within the intestine. Conditional ablation of the mouse Cdx2 in the endodermal cells causes a homeotic transformation of the intestine towards the esophagus or gastric fate. In this report, we show that null mutants of zebrafish cdx1b, encoding the counterpart of mammalian CDX2, could survive more than 10 days post fertilization, a stage when the zebrafish digestive system has been well developed. Through RNA sequencing (RNA-seq) and single-cell sequencing (scRNA-seq) of the dissected intestine from the mutant embryos, we demonstrate that the loss-of-function of the zebrafish cdx1b yields hepatocyte-like intestinal cells, a phenotype never observed in the mouse model. Further RNA-seq data analysis, and genetic double mutants and signaling inhibitor studies reveal that Cdx1b functions to guard the intestinal fate by repressing, directly or indirectly, a range of transcriptional factors and signaling pathways for liver specification. Finally, we demonstrate that heat shock-induced overexpression of cdx1b in a transgenic fish abolishes the liver formation. Therefore, we demonstrate that Cdx1b is a key repressor of hepatic fate during the intestine specification in zebrafish.