Epigenetic modifications to DNA and its associated proteins affect cell plasticity and cell fate restrictions throughout embryonic development. Development of the vertebrate pancreas is characterized by initial is an over-lapping expression of a set of transcriptional regulators in a defined region of the posterior foregut endoderm that collectively promote pancreas progenitor specification and proliferation. As development progresses, these transcription factors segregate into distinct pancreatic lineages, with some being maintained in specific subsets of terminally differentiated pancreas cell types throughout adulthood. Here we describe the progressive stages and cell fate restrictions that occur during pancreas development and the relevant known epigenetic regulatory events that drive the dynamic expression patterns of transcription factors that regulate pancreas development. In addition, we highlight how changes in epigenetic marks can affect susceptibility to pancreas diseases (such as diabetes), adult pancreas cell plasticity, and the ability to derive replacement insulin-producing β cells for the treatment of diabetes.
A fundamental question in developmental biology is how a single genome gives rise to the diversity of cell fates. In essence, each cell fate in the human body is a unique but stable output state of the genome, maintained by positive and negative feedbacks from both inside and outside the cell (a stable cell state). Traditionally, defining a cell fate means identifying a unique combination of transcriptional factors expressed by the specific cell type. The hundreds of transcriptional factors in the genome, however, have complicated the task of simplifying cell fate representation and obtaining insights into its regulation. Moreover, results from this approach provides only a mostly static picture, with each cell fate/state disconnected from one another. An alternative approach instead defines cell fates by determining their relationship to each other, through identifying the signaling pathways that control each step of their lineage transition from a common progenitor during development. Decades of studies have shown only a handful of signaling pathways are sufficient to specify all cell fates in the body, simplifying the execution of such a strategy. In this review, I will argue this alternative approach is not only feasible but also has the potential of simplifying the cell fate landscape as well as facilitating the engineering of different cell fates for regenerative medicine.
Fertilization in mammals is initiated by species-restricted binding of free-swimming sperm to the unfertilized egg's thick extracellular matrix, the zona pellucida (ZP). Both acrosome-intact and acrosome-reacted sperm can bind to the ZP, but only the latter can penetrate the ZP, reach the egg's plasma membrane, and fuse with plasma membrane (fertilization) to produce a zygote. Following fertilization, the ZP is modified by cortical granule components such that acrosome-intact and acrosome-reacted sperm are unable to bind to fertilized eggs. Here we review some of the evidence that bears directly on the involvement of two mouse ZP proteins, mZP2 and mZP3, as receptors for binding of mouse sperm to unfertilized eggs and address some contentious issues surrounding this important initial step in the process of mammalian fertilization.
According to the Developmental Origins of Health and Disease (DOHaD) hypothesis, the intrauterine environment influences fetal programming and development, affecting offspring disease susceptibility in adulthood. In recent years, therapeutic use of the Type 2 diabetes drug metformin has expanded to the treatment of pre-diabetes, polycystic ovarian syndrome, and gestational diabetes. Because metformin both undergoes renal excretion and binds to receptors on the placenta, the fetus receives equivalent maternal dosing. Although no teratogenic nor short-term harmful fetal impact of metformin is known to occur, the effects of metformin exposure on longer-range offspring development have not yet been fully elucidated. This review encapsulates the (albeit limited) existing knowledge regarding the potential longer-term impact of intrauterine metformin exposure on the development of key organs including the liver, central nervous system, heart, gut, and endocrine pancreas in animal models and humans. We discuss molecular and cellular mechanisms that would be altered in response to treatment and describe the potential consequences of these developmental changes on postnatal health. Further studies regarding the influence of metformin exposure on fetal programming and adult metabolic health will provide necessary insight to its long-term risks, benefits, and limitations in order to guide decisions for use of metformin during pregnancy.
A gestation length of normal duration and natural delivery at term are considered to be important indicators of a healthy pregnancy, especially given the potentially adverse consequences for neonates of being born premature. While many have assessed the factors influencing gestation length in humans, and there has been considerable interest in the pregnancy duration of domesticated farm animals, this topic has not been re-assessed recently in rhesus monkeys, the most commonly used primate in biomedical research. In older articles, it's gestation length was typically reported to be 165 days, although most authors acknowledged that viable pregnancies could occur out to 180 days. Predicting the normal range of acceptable due dates has important veterinary implications for when to intervene in a prolonged pregnancy. Using archival records from a large, established breeding program, gestation lengths and infant birthweights were analyzed for 408 pregnancies across a 25-year period. The potential influence of maternal factors, including age and parity, was assessed. Familial concordance in gestation length within mother-daughter matrilines was examined, as well as similarity in length across repeat pregnancies for 84 multiparous females. Mean duration from mating to delivery was 168.8 days, longer than reported in most but not all previous articles. Many females birthed successfully at a longer duration that might have prompted consideration of a caesarian delivery. Gestation length for an individual female was fairly stable and significantly correlated across multiple pregnancies. There was not a pronounced transgenerational influence on gestation length even though familial propensities for birthing small and large infants were evident in the female descendants. Typical pregnancy lengths and birthweights are provided as reference norms to assist other breeding programs and to enhance our understanding of the natural reproduction of rhesus macaques that still live in many forested and urban locations across South Asia.
Ligand-based screening of large molecular databases can help reduce costs with experiments by filtering and ranking promising compounds in an initial stage of the drug developing process. However, some ligand-based methods can be ineffective when presented with a high-dimensional number of attributes extracted from an extensive dataset of compounds. Herein, we propose a drugmining algorithm that can be used to screen ligands and repurpose known drugs, from any dataset for any target. The Milk-Way algorithm combines mathematical and regression methods to select promising compounds from a high-dimensional dataset without the use of massive computational power. We carried out a prospective screening targeting cyclin-dependent kinase two (CDK2), an attractive target for therapeutics designed to arrest or recover control of the cell cycle. The combined use of the algorithm metrics and molecular docking suggested five promising drugs to be repositioned (Pramocaine, Prochlorperazine, Trifluoperazine, Methionine, and Pergolide), in which three were already mentioned as possible inhibitors of related diseases in the literature.
All mammalian oocytes and eggs are surrounded by a relatively thick extracellular matrix (ECM), the zona pellucida (ZP), that plays vital roles during oogenesis, fertilization, and preimplantation development. Unlike ECM surrounding somatic cells, the ZP is composed of only a few glycosylated proteins, ZP1–4, that are unique to oocytes and eggs. ZP1–4 have a large region of polypeptide, the ZP domain (ZPD), consisting of two subdomains, ZP-N and ZP-C, separated by a short linker region, that plays an essential role in polymerization of nascent ZP proteins into crosslinked fibrils. Both subdomains adopt immunoglobulin (Ig)-like folds for their 3-dimensional structure. Mouse and human ZP genes are encoded by single-copy genes located on different chromosomes and are highly expressed in the ovary by growing oocytes during late stages of oogenesis. Genes encoding ZP proteins are conserved among mammals, and their expression is regulated by cis-acting sequences located close to the transcription start-site and by the same/similar trans-acting factors. Nascent ZP proteins are synthesized, packaged into vesicles, secreted into the extracellular space, and assembled into long, crosslinked fibrils that have a structural repeat, a ZP2-ZP3 dimer, and constitute the ZP matrix. Fibrils are oriented differently with respect to the oolemma in the inner and outer layers of the ZP. Sequence elements in the ZPD and the carboxy-terminal propeptide of ZP1–4 regulate secretion and assembly of nascent ZP proteins. The presence of both ZP2 and ZP3 is required to assemble ZP fibrils and ZP1 and ZP4 are used to crosslink the fibrils. Inactivation of mouse ZP genes by gene targeting has a detrimental effect on ZP formation around growing oocytes and female fertility. Gene sequence variations in human ZP genes due to point, missense, or frameshift mutations also have a detrimental effect on ZP formation and female fertility. The latter mutations provide additional support for the role of ZPD subdomains and other regions of ZP polypeptide in polymerization of human ZP proteins into fibrils and matrix.
Gene Ontology (GO) is a database comprised of terms describing biological information that can be associated to gene products, categorized in "biological process", "molecular function" and "cellular component".These GO terms have been attributed to genes of diverse organisms from unicellular to plants and animals.Many terms have been annotated to several different species and can be looked upon through a comparative biology view.This allows us to inspect their taxonomic distribution, from which we can infer the clade of origin of the processes and functions described by these Gene Ontology terms.We studied the taxonomic distribution and inferred a putative ancestral clade for GO terms related to development, focusing on children of the term "developmental process" GO:0032502.We observed that while some biological processes are ancient, there are processes which have originated more recently in evolutionary history, some being restricted to placental mammals, or plants with flowers.Our approach was able to reveal the approximate period in evolution when the processes have risen.
Development of an organism depends on differential expression/regulation of genes in the genome to produce diverse cell types during the developmental processes. A typical animal/plant genome contains a certain/fixed number of genes, all of these are not expressed all the times. Depending on the differential expression of the genes under varying environmental conditions, the morphology/ physiology of the organism may vary. Epigenetic variations (DNA and histone modifications, and variation in small-RNA biogenesis) play important roles in the regulation of gene expression during the developmental process and environmental stresses. Genome editing helps unravelling the function(s) of a gene, and editing/correcting the gene of interest. Once we identify the epigenetic mark(s) associated with the trait of interest, we can use epigenome editing tools and techniques for manipulation of gene expression. Epigenome editing uses a fusion protein comprising a specific DNA recognition domain that recruits the attached enzymatic domain to the defined genomic site. Discovery of dCas9 provides a valuable tool for epigenome editing. However, gene expression is regulated depending on the dynamic and reversibly modifiable biological and chemical information in the epigenome/epitranscriptome. Recruitment of dCas9 fused with histone-acetyltransferase or Tet1 DNA-demethylase can be used to activate enhancers and thus gene expression. Even reversible recruitment of endogenous chromatin complexes to a genomic locus is possible in almost any cell type. Deploying heterochromatin complex (e.g. Hp1/Suv39h1) and chromatin-remodelling complex (e.g. BAF), there are possibilities of repression or activation of genes through epigenome. The recent developments with respect to baseand prime-editing promise to add precision in epigenome and epitranscriptome editing, respectively. This review provides newer insights into fine-tuning of gene expression through genome/epigenome editing, and thus might help unravelling some of the enigmas of developmental biology.
The development of the mammary gland encompasses four key periods.They are controlled by a set of gene products, either expressed at the period or acting in it, although they have already been expressed before.Conducting text-mining analysis, we collected 406 genes involved in the four periods of breast development: (i) embryonic development, (ii) puberty, (iii) pregnancy and lactation and (iv) regression after lactation.Comparative profiles of gene expression are available from several sources, and one of them is the Genotype-Tissue Expression (GTEx) project which comprises RNAseq data from 53 tissues.Here we analyzed the expression of the set of textmined mammary gland genes with a novel criterion which indicates if they are highly differentially expressed as outliers in the different tissues contained in the GTEx dataset.This approach aims to reveal in which tissues they are either "overactive" or "tissue-specific" and concomitantly being implicated in breast development.Data showed that, in most of the cases, genes of the mammary gland development, which are GOAT (Gene OverActive or Tissue-specific) in a subset of tissues, are not GOAT in breast.Thus, development of different tissues might require GOATs that will likewise act as controllers of breast development without being highly differentially expressed to play their role.Our analyses contribute to the understanding of the scenario of developmental control by gene expression, while providing a simple way to point out highly differentially expressed genes in different tissues.
Birth weight (BW) at delivery is an important developmental milestone indicative of prenatal conditions and portends of the postnatal growth trajectory that will occur during infancy and childhood. Previous research has documented that there are also many physiological and health consequences of being born either small-for-gestational age (SGA) or large-for-gestational age (LGA). Analyses of breeding animals have demonstrated further that a gravid female exerts a strong influence on the size of her infant by term, and this permissiveness or constraint over fetal growth can be transmitted from mothers to their daughters. The following research tested additional hypotheses about matrilineal effects on BW by examining records from a large breeding colony of rhesus monkeys across multiple generations. The analyses utilized BW of 1710 infant monkeys obtained over 4 decades. In addition to determining the association between the birth weight (BW) of a female and her own infants birthed later as a mother, the multi-generational transmission of birth size from a grandmother through her daughters to the next generation was examined. Other maternal influences were evident, including a progressive increase in infant BW with parity, which synergized with matrilineal effects across a female's reproductive life. In addition, our modeling indicated that if an infant's BW was discordant-a SGA female birthing a larger daughter-the discrepant fetal growth pattern could be accentuated in the next generation. Overall, the findings confirm that the size of an infant at term is significantly influenced by a type of gestational imprinting on daughters during the prenatal period, which then continues to shape birth outcomes in subsequent generations.
Mutations in cytochrome P450 1B1 (CYP1B1) gene are reported in patients with primary congenital glaucoma. Cyp1b1-deficient (Cyp1b1-/-) mice show dysgenesis of the trabecular meshwork (TM) tissue and attenuation of retinal neovascularization during oxygen-induced ischemic retinopathy (OIR). Although retinal vascular cells, including endothelial cells (EC), pericytes (PC), astrocytes (AC), and TM endothelial cells express CYP1B1, the cell autonomous contribution of CYP1B1 to attenuation of retinal neovascularization and TM tissue dysgenesis remains unknown. Here we determined the impact lack of CYP1B1 expression in EC, PC or AC has on retinal neovascularization and TM tissue integrity. We generated Cyp1b1-transgenic mice with vascular cell-specific targeted Cre+-deletion in EC (Cyp1b1EC), in PC (Cyp1b1PC) and in AC (Cyp1b1AC). Pathologic retinal neovascularization during OIR was evaluated by collagen IV staining of retinal wholemounts. Structural morphology of TM tissue was examined by transmission electron microscopy (TEM). The assessment of retinal neovascularization indicated a significant decrease in retinal neovascular tufts only in Cyp1b1PC mice compared with control mice. TEM evaluation demonstrated Cyp1b1PC mice also exhibited a defect in TM tissue morphology and integrity similar to that reported in Cyp1b1-/- mice. Thus, Cyp1b1 expression in PC plays a significant role in retinal neovascularization and the integrity of TM tissue.
The process of taking a piece of tissue and transplanting it into a novel location has been of paramount importance for life sciences. The technique of transplantation has served an important role in providing a basic understanding of all facets of biology ranging from cancer and evolutionary biology to developmental biology. First employed by early embryologists, transplantation has played a particularly critical role in elucidating virtually every aspect of embryonic development including cell specification, commitment, cell fate determination, embryonic induction, and plasticity. This review will detail the essential role cell transplantation experiments have played in uncovering fundamental developmental and cell biological processes as well as their valuable contribution to contemporary developmental biology. Finally, it will suggest fruitful directions that this technique, in conjunction with current molecular and sequencing technologies, could play in future work.
The mRNA expression pattern of tet family of methyl cytosine dioxygenase enzymes (ten-eleven translocation, tet1, tet2, and tet3), which catalyze the conversion of 5-methylcytosine (5mC) to 5hydroxymethylcytosine (5hmC) and initiate 5mC remodeling through active demethylation, was investigated in brain, ovary, and liver of Japanese rice fish (Oryzias latipes) adults, and in whole embryos after fertilization to hatching. Moreover, fertilized eggs were exposed to ethanol or 5azacytidine (5-azaC), 0-2 day post fertilization (dpf), and tet mRNAs on 2 and 6 dpf were analyzed. Our data indicated that all three tet mRNAs were expressed in brain, liver, and ovary of adult fish with substantial variations. In embryos, all three tet mRNAs showed rhythmic expression, high copies in 1-3 dpf followed by down regulation until hatching. Embryonic exposure either to ethanol or 5-azaC was unable to alter the expression of any of these tet mRNAs in 2 dpf; in 6 dpf, there was an increase in tet expression in response to high levels of ethanol (400-500 mM) and 5-azaC (2 mM). Although we have previously documented that both ethanol and 5-azaC was able to induce fetal alcohol spectrum disorder (FASD)-like phenotypic features in Japanese rice fish, the present study indicates that the DNA demethylation by tet may differ between these two compounds.
The Developmental Origins of Health and Disease (DOHaD) Hypothesis postulates that the in utero environment influences postnatal health and plays a role in disease etiology. Studies in both humans and animal models have shown that exposure to either under- or overnutrition in utero results in an increased risk of metabolic disease later in life. In addition, offspring born to overweight or obese mothers are more likely to be obese as children and into early adulthood and to have impaired glucose tolerance as adults. The Centers for Disease Control and Prevention estimates that over 70% of adults over the age of 20 are either overweight or obese and that nearly half of women are either overweight or obese at the time they become pregnant. Thus, the consequences of maternal overnutrition on the developing fetus are likely to be realized in greater numbers in the coming decades. This review will focus specifically on the effects of in utero overnutrition on pancreatic islet development and function and how the resulting morphological and functional changes influence the offspring's risk of developing metabolic disease. We will discuss the advantages and challenges of different animal models, the effects of exposure to overnutrition during distinct periods of development, the similarities and differences between and within model systems, and potential mechanisms and future directions in understanding how developmental alterations due to maternal diet exposure influence islet health and function later in life.
A satellite symposium to the Canadian Developmental Biology Conference 2016 was held on March 16-17, 2016 in Banff, Alberta, Canada, entitled Forebrain Neurogenesis: From embryo to adult. The Forebrain Neurogenesis symposium was a focused, high-intensity meeting, bringing together the top Canadian and international researchers in the field. This symposium reported the latest breaking news, along with 'state of the art' techniques to answer fundamental questions in developmental neurobiology. Topics covered ranged from stem cell regulation to neurocircuitry development, culminating with a session focused on neuropsychiatric disorders. Understanding the underlying causes of neurodevelopmental disorders such as autism spectrum disorder (ASD) and attention deficit/hyperactivity disorder (ADHD) is of great interest as diagnoses of these conditions are climbing at alarming rates. For instance, in 2012, the Centers for Disease Control reported that the prevalence rate of ASD in the U.S. was 1 in 88; while more recent data indicate that the number is as high as 1 in 68 (Centers for Disease Control and Prevention MMWR Surveillance Summaries. Vol. 63. No. 2). Similarly, the incidence of ASD is on the rise in Canada, increasing from 1 in 150 in 2000 to 1 in 63 in 2012 in southeastern Ontario (Centers for Disease Control and Prevention). Currently very little is known regarding the deficits underlying these neurodevelopmental conditions. Moreover, the development of effective therapies is further limited by major gaps in our understanding of the fundamental processes that regulate forebrain development and adult neurogenesis. The Forebrain Neurogenesis satellite symposium was thus timely, and it played a key role in advancing research in this important field, while also fostering collaborations between international leaders, and inspiring young researchers.
Developmental processes are remarkably well conserved among species, and among the most highly conserved developmental regulators are transcription factor families. The Onecut transcription factor family consists of three members known for their single cut DNA-binding domain and an aberrant homeodomain. The three members of the Onecut family are highly conserved from Drosophila to humans and have significant roles in regulating the development of diverse tissues derived from the ectoderm or endoderm, where they activate a number of gene families. Of note, the genetic interaction between Onecut family members and Neurogenin genes appears to be essential in multiple tissues for proper specification and development of unique cell types. This review highlights the importance of the Onecut factors in cell fate specification and organogenesis, highlighting their role in vertebrates, and discusses their role in the maintenance of cell fate and prevention of disease. We cover the essential spatial and temporal control of Onecut factor expression and how this tight regulation is required for proper specification and subsequent terminal differentiation of multiple tissue types including those within the retina, central nervous system, liver and pancreas. Beyond development, Onecut factors perform necessary functions in mature cell types; their misregulation can contribute to diseases such as pancreatic cancer. Given the importance of this family of transcription factors in development and disease, their consideration in essential transcription factor networks is underappreciated.
The life-sustaining air-blood interface of the respiratory system requires the exquisite integration of the epithelial lining with the mesenchymal capillary network, all supported by elastic smooth muscle and rigid cartilage keeping the expandable airways open. These intimate tissue interactions originate in the early embryo, where bidirectional paracrine signaling between the endoderm epithelium and adjacent mesoderm orchestrates lung and trachea development and controls the stereotypical branching morphogenesis. Although much attention has focused on how these interactions impact the differentiation of the respiratory epithelium, relatively less is known about the patterning and differentiation of the mesenchyme. Endothelial cells, smooth muscle cells, and chondrocytes together with other types of mesenchymal cells are essential components of a functional respiratory system, and malformation of these cells can lead to various congenital defects. In this review, we summarize the current understanding of mesenchymal development in the fetal trachea and lung, focusing on recent findings from animal models that have begun to shed light on the poorly understood respiratory mesenchyme lineages.
All vertebrate eggs are surrounded by an extracellular coat that supports growth of oocytes, protects oocytes, eggs, and early embryos, and participates in the process of fertilization. In mammals (platypus to human beings) the coat is called a zona pellucida (ZP) and in non-mammals (molluscs to birds), a vitelline envelope (VE). The ZP and VE are composed of just a few proteins that are related to one another and possess a common motif, called the zona pellucida domain (ZPD). The ZPD arose more than ~600 million years ago, consists of ~260 amino acids, and has 8 conserved Cys residues that participate in 4 intramolecular disulfides. It is likely that egg-coat proteins are derived from a common ancestral gene. This gene duplicated several times during evolution and gave rise to 3-4 genes in fish, 5 genes in amphibians, 6 genes in birds, and 3-4 genes in mammals. Some highly divergent sequences, N- and C-terminal to the ZPD, have been identified in egg-coat proteins and some of these sequences may be under positive Darwinian selection that drives evolution of the proteins. These and other aspects of egg-coat proteins, including their structure and synthesis, are addressed in this review.
Pluripotent human embryonic stem (ES) cells provide a consistent developmental model for studying contaminant-induced changes in human cell fate and early developmental processes.Thus far, no studies have investigated the effects of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) exposure on the growth and differentiation of human ES cells.Here we show that the aryl hydrocarbon receptor (AhR) pathway is functional in human ES cells based on the ability of TCDD to induce the AhR/Arnt-dependent transcription of CYP1A1.No changes in colony morphology were observed in undifferentiated human ES cells following 8 days of treatment with TCDD.However, when human ES cells were allowed to replicate and spontaneously differentiate for 15 days in the presence of TCDD, colonies exhibited less morphological differentiation compared to control human ES cell cultures.This observation was confirmed on the molecular level by lower expression of markers of meso-and endodermal differentiation and higher expression of the pluripotency marker, Oct4, in TCDDtreated cultures.Additionally, TCDD inhibited the fibroblastic morphology resulting from the epithelial to mesenchymal transition (EMT) of spontaneously differentiating ES cells, preserving an undifferentiated cellular phenotype.Furthermore, lower expression of EMT markers as well as a lower incidence of the mesenchymal marker, N-cadherin, was observed around the edges of TCDD-treated cell colonies.These findings suggest that TCDD treatment inhibits human ES cell differentiation, potentially through the inhibition of an EMT-like process.
