Modern Developmental Biology Research Articles

Bioelectromagnetics in morphogenesis.

Understanding the factors that allow biological systems to reliably self-assemble consistent, highly complex, four dimensional patterns on many scales is crucial for the biomedicine of cancer, regeneration, and birth defects. The role of chemical signaling factors in controlling embryonic morphogenesis has been a central focus in modern developmental biology. While the role of tensile forces is also beginning to be appreciated, another major aspect of physics remains largely neglected by molecular embryology: electromagnetic fields and radiations. The continued progress of molecular approaches to understanding biological form and function in the post genome era now requires the merging of genetics with functional understanding of biophysics and physiology in vivo. The literature contains much data hinting at an important role for bioelectromagnetic phenomena as a mediator of morphogenetic information in many contexts relevant to embryonic development. This review attempts to highlight briefly some of the most promising (and often underappreciated) findings that are of high relevance for understanding the biophysical factors mediating morphogenetic signals in biological systems. These data originate from contexts including embryonic development, neoplasm, and regeneration.

Inverting the hourglass: quantitative evidence against the phylotypic stage in vertebrate development.

The concept of a phylotypic stage, when all vertebrate embryos show low phenotypic diversity, is an important cornerstone underlying modern developmental biology. Many theories involving patterns of development, developmental modules, mechanisms of development including developmental integration, and the action of natural selection on embryological stages have been proposed with reference to the phylotypic stage. However, the phylotypic stage has never been precisely defined, or conclusively supported or disproved by comparative quantitative data. We tested the predictions of the 'developmental hourglass' definition of the phylotypic stage quantitatively by looking at the pattern of developmental-timing variation across vertebrates as a whole and within mammals. For both datasets, the results using two different metrics were counter to the predictions of the definition: phenotypic variation between species was highest in the middle of the developmental sequence. This surprising degree of developmental character independence argues against the existence of a phylotypic stage in vertebrates. Instead, we hypothesize that numerous tightly delimited developmental modules exist during the mid-embryonic period. Further, the high level of timing changes (heterochrony) between these modules may be an important evolutionary mechanism giving rise to the diversity of vertebrates. The onus is now clearly on proponents of the phylotypic stage to present both a clear definition of it and quantitative data supporting its existence.

BEST: a novel computational approach for comparing gene expression patterns from early stages of Drosophila melanogaster development.

Embryonic gene expression patterns are an indispensable part of modern developmental biology. Currently, investigators must visually inspect numerous images containing embryonic expression patterns to identify spatially similar patterns for inferring potential genetic interactions. The lack of a computational approach to identify pattern similarities is an impediment to advancement in developmental biology research because of the rapidly increasing amount of available embryonic gene expression data. Therefore, we have developed computational approaches to automate the comparison of gene expression patterns contained in images of early stage Drosophila melanogaster embryos (prior to the beginning of germ-band elongation); similarities and differences in gene expression patterns in these early stages have extensive developmental effects. Here we describe a basic expression search tool (BEST) to retrieve best matching expression patterns for a given query expression pattern and a computational device for gene interaction inference using gene expression pattern images and information on the associated genotypes and probes. Analysis of a prototype collection of Drosophila gene expression pattern images is presented to demonstrate the utility of these methods in identifying biologically meaningful matches and inferring gene interactions by direct image content analysis. In particular, the use of BEST searches for gene expression patterns is akin to that of BLAST searches for finding similar sequences. These computational developmental biology methodologies are likely to make the great wealth of embryonic gene expression pattern data easily accessible and to accelerate the discovery of developmental networks.

Characterization of cis-regulatory elements of the homeobox gene Xanf-1

Investigation of molecular mechanisms underlying early patterning of the nervous system is an important task of modern developmental biology. Previously, we identified a novel homeobox gene, Anf, that is expressed in the most anterior zone at the beginning of neuroectoderm specification. The expression pattern of Anf corresponds to primordia of the telencephalon and the rostral part of the diencephalon. In the present work, we investigated cis-regulation of expression of the Xenopus laevis Anf, Xanf-1. Two elements, highly conserved in Xenopus, chick and human, were identified within the Xanf-1 promoter region. The first element, located near position −500, is necessary for overall enhancement of the Xanf-1 expression. The second element, near position −200, is crucial for maintenance of the Xanf-1 expression at moderate levels and also for specific localization of the expression in the anterior neuroectoderm. Thus, the distal part of this element is responsible for suppression of Xanf-1 posterior to the normal expression domain of this gene. The data obtained corroborate with the Nieuwkoop two-signal model of neural induction. This model states that at the first step of induction, all neuroectoderm acquires potencies to develop toward forebrain structures, but later these potencies are suppressed in posterior regions.

Advances in phylogenetic studies of Nematoda

Nematoda is a metazoan group with extremely high diversity only next to Insecta. Caenorhabditis elegans is now a favorable experimental model animal in modern developmental biology, genetics and genomics studies. However, the phylogeny of Nematoda and the phylogenetic position of the phylum within animal kingdom have long been in debate. Recent molecular phylogenetic studies gave great challenges to the traditional nematode classification. The new phylogenies not only placed the Nematoda in the Ecdysozoan and divided the phylum into five clades, but also provided new insights into animal molecular identification and phylogenetic biodiversity studies. The present paper reviews major progress and remaining problems in the current molecular phylogenetic studies of Nematoda, and prospects the developmental tendencies of this field.

Wyburn-Mason or Bonnet-Dechaume-Blanc as Cerebrofacial Arteriovenous Metameric Syndromes (CAMS)

The diagnosis of Bonnet-Dechaume-Blanc or Wyburn-Mason syndrome encompasses a spectrum of phenotypic expression. Features of the syndrome as originally described, and common to all, include arteriovenous malformations of the brain and orbit (with retinal and/or retrobulbar lesions). A portion of these patients manifest the complete expression of the disease with additional high-flow arteriovenous malformations of the maxillofacial or mandibular regions. These present the distinct and additional risks of lifethreatening epistaxis or gingival haemorrhage. We suggest new diagnostic criteria for the syndrome. Applying insights from modern developmental biology to our series of 15 patients (the largest to date), together with a review of the literature, we have recognised metameric patterns of involvement in what we believe to be a disease of the neural crest or adjacent cephalic mesoderm. This allows us to propose a new rational classification reflecting the putative, underlying disorder and to suggest a new name: Cerebrofacial Arteriovenous Metameric Syndrome (CAMS).

The D P Wilson Lecture. Research on settlement and metamorphosis of marine invertebrate larvae: Past, present and future

In 1952, D P Wilson remarked that invertebrate larvae, “... are indeed not helpless, for they are endowed with the power of choice,...”; at settlement. Subsequent efforts have greatly enhanced understanding of the conditions under which larvae metamorphose, altering the conceptual view of this process from “larval choice”; to “developmental induction,”; and aligning studies of invertebrate metamorphosis with those of modern developmental biology. While the precise chemical nature of most metamorphic inducers evades us, elucidation of the phenomena of reception and transduction appears imminent for many larvae. The evidence for receptor cells and molecules specific for inducer substances is convincing for larvae in several phyla, and a generalized picture of stimulation of electrically excitable cells has emerged; larvae from at least eight invertebrate phyla metamorphose in response to augmented K + . To be determined is whether genes specifying receptor proteins for metamorphic inducers share homology and whether metamorphic signals are transduced by the same intracellular pathways across invertebrate phyla. Metamorphic competence can be a developmentally unique condition where non‐growing, non‐feeding larvae are primed to metamorphose when signaled; a genetic explanation for competence merits intense exploration. The acquisition for marine invertebrate larvae of knowledge comparable to that for the genetic basis of timing of photic responses and pupal eclosion in Drosophila will provide material for exciting research in the years ahead. Many species (e.g. the polychaete Hydroides elegans) offer excellent models for laboratory genetic studies of invertebrate settlement and metamorphosis.

Studies in developmental cytomechanic.

One of the most promising trends in modern developmental and cell biology, recently defined as <<cyto>>, or <<morphomechanics>>, is directed towards revealing the role of mechanical stresses, chemomechanical transduction and active stress responses of cells antissues of developing embryos. We review here the results obtained in this field by our research group and compare them with those from other labs. Our studies relate to the buds of hydroid polypes and to amphibian embryos. We describe the space-temporal patterns of mechanical stresses in these species, analyze their morphogenetical role and the tissue responses to the experimental modulations of stress patterns. In hydroid polypes we explore also the molecular events involved in mechanochemical coupling. A model, linking the passive mechanical stresses with the active stress-responses of embryonic tissues is suggested. We consider these investigations as a first approach to a developing embryo as to an <<active solid body>>.

The importance of being random

The importance of being random

Pattern formation in dictyostelids

We make two main points about the present and the future of the study of pattern formation, which is perhaps the most interesting problem in modern developmental biology. One is that a complete understanding of a developing organism will require the integration of knowledge from a wide variety of disciplines. Our other main point is the importance of comparing organisms to find universal solutions. Here we compare two dictyostelids that have somewhat different development, to point a way toward understanding how fundamental mechanisms can vary to produce altered shapes.

Crossroads, milestones and landmarks in insect development and evolution: implications for systematics.

Our understanding of insect development and evolution has increased greatly due to recent advances in the comparative developmental approach. Modern developmental biology techniques such as in situ hybridization and molecular analysis of developmentally important genes and gene families have greatly facilitated these advances. The role of the comparative developmental approach in insect systematics is explored in this paper and we suggest two important applications of the approach to insect systematics--character dissection and morphological landmarking. Existing morphological characters can be dissected into their genetic and molecular components in some cases and this will lead to more and richer character information in systematic studies. Character landmarking will he essential to systematic studies for clarifying structures such as shapes or convergences, which are previously hard to analyze anatomical regions. Both approaches will aid greatly in expanding our understanding of homology in particular, and insect development in general.

Embryologie: Ein Lehrbuch auf allgemein biologischer Grundlage

Developmental Anatomy: A Textbook and Laboratory Manual of Embryology, by Leslie Brainerd Arey, ed 7; 695 pp, 638 illus, $10, Philadelphia: W. B. Saunders Co., 1965. This edition of Starck's Embryologie aims at incorporating new knowledge generated in the decade since its first publication. The book retains its primary emphasis on descriptive embryology, which is established within a framework of traditional comparative embryology, and related to data and concepts of modern developmental biology. The text presents the full range of vertebrate development, beginning with the germ cells and extending through the formation of special organs in animals ranging from Branchiostomes to the human. Consistently, each subject is discussed in thorough detail, with careful attention to the relevant phylogenetic relations and appropriate experimental data. The author's splendid grasp of the myriad facets of comparative embryology appears in the many admirable syntheses throughout the work. The book abounds in details, but without