Single Germ Layer Research Articles

Cognizance of stem cells: A gist

Stem cells are undifferentiated cells which usually arises from one cell (clonal) and has the characteristic of self renewal i.e ability to proliferate and differentiate into various styles of cells (potent). Depending upon the potencies there are different sources of stem cells. Pluripotent cells have the flexibility to differentiate into tissues from the three germ layers. There are various sources of stem cells with varying potencies. Pluripotent cells have the ability to differentiate into tissue from all 3 germ layers (endoderm, mesoderm, and ectoderm). Multipotent stem cells may differentiate into tissue derived from a single germ layer like mesenchymal stem cells which form adipose tissue, bone, and cartilage thanks to the limited generation of most somatic cells, stem cells’ capacity to replenish damaged somatic cells and maintain a self-renewing reservoir of progenitors is crucial for homeostasis in many tissues of the many organisms. Thus, there is an immense interest in understanding the mechanisms for self-renewal and differentiation in stem cells, given their potential applications in regenerative medicine and studies of human development or aging. This review article emphasizes on stem cells and its various types.

Multi-scale imaging and analysis identify pan-embryo cell dynamics of germlayer formation in zebrafish

The coordination of cell movements across spatio-temporal scales ensures precise positioning of organs during vertebrate gastrulation. Mechanisms governing such morphogenetic movements have been studied only within a local region, a single germlayer or in whole embryos without cell identity. Scale-bridging imaging and automated analysis of cell dynamics are needed for a deeper understanding of tissue formation during gastrulation. Here, we report pan-embryo analyses of formation and dynamics of all three germlayers simultaneously within a developing zebrafish embryo. We show that a distinct distribution of cells in each germlayer is established during early gastrulation via cell movement characteristics that are predominantly determined by their position in the embryo. The differences in initial germlayer distributions are subsequently amplified by a global movement, which organizes the organ precursors along the embryonic body axis, giving rise to the blueprint of organ formation. The tools and data are available as a resource for the community.

A molecular atlas of the developing ectoderm defines neural, neural crest, placode, and nonneural progenitor identity in vertebrates.

During vertebrate neurulation, the embryonic ectoderm is patterned into lineage progenitors for neural plate, neural crest, placodes and epidermis. Here, we use Xenopus laevis embryos to analyze the spatial and temporal transcriptome of distinct ectodermal domains in the course of neurulation, during the establishment of cell lineages. In order to define the transcriptome of small groups of cells from a single germ layer and to retain spatial information, dorsal and ventral ectoderm was subdivided along the anterior-posterior and medial-lateral axes by microdissections. Principal component analysis on the transcriptomes of these ectoderm fragments primarily identifies embryonic axes and temporal dynamics. This provides a genetic code to define positional information of any ectoderm sample along the anterior-posterior and dorsal-ventral axes directly from its transcriptome. In parallel, we use nonnegative matrix factorization to predict enhanced gene expression maps onto early and mid-neurula embryos, and specific signatures for each ectoderm area. The clustering of spatial and temporal datasets allowed detection of multiple biologically relevant groups (e.g., Wnt signaling, neural crest development, sensory placode specification, ciliogenesis, germ layer specification). We provide an interactive network interface, EctoMap, for exploring synexpression relationships among genes expressed in the neurula, and suggest several strategies to use this comprehensive dataset to address questions in developmental biology as well as stem cell or cancer research.

Mesenchymal stem cells in the treatment of chronic lung disease.

Mesenchymal stem cells (MSCs) are a populace of non-haematopoietic multipotent stromal cells, which have the ability to differentiate into tissue derived from a single germ layer. MSCs have been isolated from various sites, including adipose tissue, skeletal muscle, synovium, spleen, thymus, lung and amniotic fluid, but are most often isolated from bone marrow. MSCs have several valuable functions that make them a promising therapeutic option in the field of regenerative medicine, including the secretion of anti-inflammatory cytokines and growth factors, the migration of cells to the site of injury when administered and the ability to 'rescue' cells through the transfer of functional mitochondria. They also offer the possibility of autologous cell transplantation, circumventing immune rejection. These properties, among others, make MSCs a promising potential therapeutic agent in the treatment of chronic lung diseases with high rates of morbidity and mortality, such as idiopathic pulmonary fibrosis (IPF), COPD and obstructive bronchiolitis (OB). Numerous animal models have shown the protective and reparative effects of MSCs in models of experimental lung injury. There are currently several clinical trials underway to evaluate the safety and efficacy of MSCs in the treatment of IPF, COPD and OB. While early results are encouraging, a considerable amount of research must be done concerning the safety MSCs, as well as their optimal dosage, time and route of administration. In addition, much is still unknown about the pathogenesis of these chronic lung diseases, as well as the mechanisms MSCs utilize to assist in their repair.

A Giant Mature Cystic Teratoma Mimicking a Pleural Effusion.

The vast majority of teratomas originating from more than a single germ layer are benign. Often, such teratomas are initially asymptomatic. Later symptoms are caused by the weight per se of the teratoma and include chest pain, cough, dyspnea, and/or recurrent attacks of pneumonia. A mediastinal teratoma is treated by total surgical resection of the mass. Here, we report a case of giant mature cystic teratoma mimicking a pleural effusion in the thorax at the 7-month-old female patient with a symptom of persistent pulmonary infection and tachypnea.

Introduction to Stem Cells and Regenerative Medicine

Stem cells are a population of undifferentiated cells characterized by the ability to extensively proliferate (self-renewal), usually arise from a single cell (clonal), and differentiate into different types of cells and tissue (potent). There are several sources of stem cells with varying potencies. Pluripotent cells are embryonic stem cells derived from the inner cell mass of the embryo and induced pluripotent cells are formed following reprogramming of somatic cells. Pluripotent cells can differentiate into tissue from all 3 germ layers (endoderm, mesoderm, and ectoderm). Multipotent stem cells may differentiate into tissue derived from a single germ layer such as mesenchymal stem cells which form adipose tissue, bone, and cartilage. Tissue-resident stem cells are oligopotent since they can form terminally differentiated cells of a specific tissue. Stem cells can be used in cellular therapy to replace damaged cells or to regenerate organs. In addition, stem cells have expanded our understanding of development as well as the pathogenesis of disease. Disease-specific cell lines can also be propagated and used in drug development. Despite the significant advances in stem cell biology, issues such as ethical controversies with embryonic stem cells, tumor formation, and rejection limit their utility. However, many of these limitations are being bypassed and this could lead to major advances in the management of disease. This review is an introduction to the world of stem cells and discusses their definition, origin, and classification, as well as applications of these cells in regenerative medicine.

Evolutionary Origins of the Neural Crest and Neural Crest Cells

I evaluate the lines of evidence—cell types, genes, gene pathways, fossils—in putative chordate ancestors—cephalochordates and ascidians—pertaining to the evolutionary origin of the vertebrate neural crest. Given the intimate relationship between the neural crest and the dorsal nervous system during development, I discuss the dorsal nervous system in living (extant) members of the two groups, especially the nature, and genes, and gene regulatory networks of the brain to determine whether any cellular and/or molecular precursors (latent homologues) of the neural may have been present in ancestral cephalochordates or urochordates. I then examine those fossils that have been interpreted as basal chordates or cephalochordates to determine whether they shed any light on the origins of neural crest cell (NCC) derivatives. Do they have, for example, elements of a head skeleton or pharyngeal arches, two fundamental vertebrate characters (synapomorphies)? The third topic recognizes that the origin of the neural crest in the first vertebrates accompanied the evolution of a brain, a muscular pharynx, and paired sensory organs. In a paradigm-breaking hypothesis—often known as the ‘new head hypothesis’—Carl Gans and Glen Northcutt linked these evolutionary innovations to the evolution of the neural crest and ectodermal placodes (Gans and Northcutt Science 220:268-274, 1983. doi:10.1126/science.220.4594.268; Northcutt and Gans The Quarterly Review of Biology 58:1–28, 1983. doi:10.1086/413055). I outline the rationale behind the new head hypothesis before turning to an examination of the pivotal role played by NCCs in the evolution of pharyngeal arches, in the context of the craniofacial skeleton. Integrations between the evolving vertebrate brain, muscular pharynx and paired sensory organs may have necessitated that the pharyngeal arch skeletal system—and subsequently, the skeleton of the jaws and much of the skull (the first vertebrates being jawless)—evolved from NCCs whose developmental connections were to neural ectoderm and neurons rather than to mesoderm and connective tissue; mesoderm produces much of the vertebrate skeleton, including virtually all the skeleton outside the head. The origination of the pharyngeal arch skeleton raises the issue of the group of organisms in which and how cartilage arose as a skeletal tissue. Did cartilage arise in the basal proto-vertebrate from a single germ layer, cell layer or tissue, or were cells and/or genes co-opted from several layers or tissues? Two recent studies utilizing comparative genomics, bioinformatics, molecular fingerprinting, genetic labeling/cell selection, and GeneChip Microarray technologies are introduced as powerful ways to approach the questions that are central to this review.

Bilateral Obstructing Laryngeal Epithelial Adenomatous Hamartomas

n 1991, the World Health Organization defined hamartomas as anomalies characterized by the formation of a tumorlike mass composed of identical mature cellular tissue elements that are normally present where the mass is found but that occur in abnormal proportions or patterns. 1 A hamartoma does not have the capability of continuous growth or recurrence and is composed of a single germ layer, distinguishing it from a true neoplasm and a teratoma, respectively. It is also distinct from a choristoma because it is composed of tissue elements that are normally found in the region. Finally, because this type of focal overgrowth does not produce the normal architecture of the surrounding tissues, hamartomas should be further differentiated from hyperplasia.

Functional evidence for a single endodermal origin for the thymic epithelium

T cell development depends critically on several distinct thymic epithelial cell types that are organized into two main compartments: cortex and medulla. The prevailing hypothesis suggests that these derive from ectoderm and endoderm, respectively. Here we show that lineage analysis provides no evidence for an ectodermal contribution to the thymic rudiment. We further demonstrate, via ectopic transplantation, that isolated pharyngeal endoderm can generate a functional thymus containing organized cortical and medullary regions and that this capacity is not potentiated by the presence of pharyngeal ectoderm. These data establish that the cortical and medullary thymic epithelial compartments derive from a single germ layer, the endoderm, thus refuting the 'dual-origin' model of thymic epithelial ontogeny.

Cell lineage analysis of the amphipod crustacean Parhyale hawaiensis reveals an early restriction of cell fates.

In the amphipod crustacean, Parhyale hawaiensis, the first few embryonic cleavages are total and generate a stereotypical arrangement of cells. In particular, at the eight-cell stage there are four macromeres and four micromeres, and each of these cells is uniquely identifiable. We describe our studies of the cell fate pattern of these eight blastomeres, and find that the eight clones resulting from these cells set up distinct cell lineages that differ in terms of proliferation, migration and cell fate. Remarkably, the cell fate of each blastomere is restricted to a single germ layer. The ectoderm originates from three of the macromeres, while the remaining macromere generates the visceral mesoderm. Two of the micromeres generate the somatic mesoderm, a third micromere generates the endoderm and the fourth micromere generates the germline. These findings demonstrate for the first time a total cleavage pattern in an arthropod which results in an invariant cell fate of the blastomeres, but notably, the cell lineage pattern of Parhyale reported shows no clear resemblance to those found in spiralians, nematodes or deuterostomes. Finally, the techniques we have developed for the analysis of Parhyale development suggest that this arthropod may be particularly useful for future functional analyses of crustacean development.

Allocation of epiblast cells to germ layer derivatives during mouse gastrulation as studied with a retroviral vector.

The embryonic ectoderm, or epiblast, is the source of the three primary germ layers that form during gastrulation in the mouse embryo. Previous studies have investigated the fate of epiblast cells in early gastrulation stages using clonal analysis of cell lineage and in late gastrulation stages using transplantation of labeled grafts. In this study, we studied the fate of late gastrulation stage epiblast using a clonal analysis based on a retroviral vector encoding the Escherichia coli lacZ gene. We found that by reducing the volume of viral suspension injected into each embryo, it was possible to achieve single infectious events. Our analysis of 20 embryos singly infected at the late streak stage and 21 at the head fold stage revealed clonal descendants in only a single germ layer in each embryo. These results indicate that allocation of epiblast progenitors to a single germ layer fate has occurred by late gastrulation in mouse embryos.

Clonal analysis of epiblast fate during germ layer formation in the mouse embryo

The fate of cells in the epiblast at prestreak and early primitive streak stages has been studied by injecting horseradish peroxidase (HRP) into single cells in situ of 6.7-day mouse embryos and identifying the labelled descendants at midstreak to neural plate stages after one day of culture. Ectoderm was composed of descendants of epiblast progenitors that had been located in the embryonic axis anterior to the primitive streak. Embryonic mesoderm was derived from all areas of the epiblast except the distal tip and the adjacent region anterior to it: the most anterior mesoderm cells originated posteriorly, traversing the primitive streak early; labelled cells in the posterior part of the streak at the neural plate stage were derived from extreme anterior axial and paraxial epiblast progenitors; head process cells were derived from epiblast at or near the anterior end of the primitive streak. Endoderm descendants were most frequently derived from a region that included, but extended beyond, the region producing the head process: descendants of epiblast were present in endoderm by the midstreak stage, as well as at later stages. Yolk sac and amnion mesoderm developed from posterolateral and posterior epiblast. The resulting fate map is essentially the same as those of the chick and urodele and indicates that, despite geometrical differences, topological fate relationships are conserved among these vertebrates. Clonal descendants were not necessarily confined to a single germ layer or to extraembryonic mesoderm, indicating that these lineages are not separated at the beginning of gastrulation. The embryonic axis lengthened up to the neural plate stage by (1) elongation of the primitive streak through progressive incorporation of the expanding lateral and initially more anterior regions of epiblast and, (2) expansion of the region of epiblast immediately cranial to the anterior end of the primitive streak. The population doubling time of labelled cells was 7.5 h; a calculated 43% were in, or had completed, a 4th cell cycle, and no statistically significant regional differences in the number of descendants were found. This clonal analysis also showed that (1) growth in the epiblast was noncoherent and in most regions anisotropic and directed towards the primitive streak and (2) the midline did not act as a barrier to clonal spread, either in the epiblast in the anterior half of the axis or in the primitive streak. These results taken together with the fate map indicate that, while individual cells in the epiblast sheet behave independently with respect to their neighbours, morphogenetic movement during germ layer formation is coordinated in the population as a whole.

Immunohistochemical characterization of pulmonary blastoma.

The immunohistochemical staining patterns of three pulmonary blastomas (PBs) were studied for markers of mesenchymal (vimentin, muscle-specific actin) and epithelial (cytokeratin, epithelial membrane antigen) differentiation to clarify their phenotypic nature and, possibly, their histogenesis. Epithelial markers were confined to the tubular component of the tumors, and the mesenchymal markers were confined to the stromal component, demonstrating that PBs are true mixed tumors. These findings are consistent with origin from a primitive pluripotential stem cell but do not rule out derivation from a single germ layer with subsequent metaplastic transformation.

Early epochal maps of two different cell adhesion molecules.

N-CAM, the neural cell-adhesion molecule, has previously been found to be expressed during several epochs of development and function, first as an early marker in embryo-genesis, later during organogenesis, and finally in adult life. L-CAM, the liver cell-adhesion molecule, has now been localized in embryonic and adult tissues of the chicken by fluorescent antibody techniques. In the early embryonic epoch, L-CAM and N-CAM appeared in epiblastic and hypoblastic tissues. L-CAM was distributed thereafter across all three germ layers. By the onset of neurulation, however, L-CAM disappeared in the region of the neural plate and N-CAM increased in amount in that region. L-CAM appeared strongly on all budding endodermal structures (liver, pancreas, lung, thyroid, parathyroid, thymus, and bursa of Fabricius) whereas N-CAM appeared most strongly in the neural plate, neural tube, and in cardiac mesoderm but was not found in endodermal derivatives. In placodes, both L-CAM and N-CAM were present until the formation of definitive neural structures, at which time L-CAM disappeared. In kidney precursors, the two CAMs followed a complex reciprocal pattern of appearance and disappearance. For the most part, however, the distributions of the two molecules did not overlap during organogenesis. Like N-CAM, L-CAM persisted in a distinctive pattern of expression in adult tissues. During embryonic development, the two different CAMs were distributed on tissues derived from more than two-thirds of the early embryonic surface. Interpretation of maps summarizing CAM distributions over a defined developmental epoch suggested a key role for both L-CAM and N-CAM in embryonic induction. Consistent with this interpretation and with the fact that the continuity of germ layers is lost when organ rudiments are formed, neither of the CAMs was limited in distribution to a single germ layer. The regions of the early epochal maps that lacked both L-CAM and N-CAM comprised some portions of the splanchnopleure and somatopleure. Certain adult tissues that derive from this lateral plate mesoderm such as smooth muscle also lacked L-CAM and N-CAM. Such observations suggest that at least one more CAM may exist in these and similarly derived tissues.

Solid Teratoid Tumors of the Anterior Mediastinum: Report of Two Cases

Because of the comparative rarity of tumors of the mediastinum, and the incompleteness of the data in many of the published cases, Haagensen (1) has recently emphasized the desirability of adequately reporting additional instances. The gravity of exploratory procedures in this region makes necessary a basis upon which to arrive at a reasonable preoperative clinical evaluation of such cases. In this paper, two teratoid tumors are reported in some detail, both from the clinical and the pathological standpoint. The term “teratoma” is commonly used to describe tumors including derivatives from all three germ layers. There is, however, a large group of tumors of presumably the same etiology but which include demonstrable multiple elements derived from but two or even a single germ layer. In many of these instances the failure to demonstrate additional elements is attributable (1) to the taking of insufficient sections for microscopic study, (2) to extensive necrosis of tissue, the actual nature of which is obviously impossible to determine, or (3) to an early overgrowth of a single germ layer. In order to include these essentially similar tumors, whether complete or incomplete, under a single heading, the term “teratoid” has been used. Although not the most common of the mediastinal tumors, these teratoid growths are among the most interesting from the pathological standpoint, since they apparently arise from totipotential cells, and may exhibit any combination of tissues, benign or malignant.