August Rauber (1841-1917): from the primitive streak to Cellularmechanik. (57/116)

In the early 19th century Karl Ernst von Baer initiated a new research program searching for the mechanisms by which an egg transforms itself into an embryo. August Rauber (1841-1917) took up this challenge. He considered the phylogenetic principle as the right tool to explain the similitude of embryogenetic processes. In extending Baer's approach, he combined comparative embryology and histology in his studies of avian and mammalian embryos. His earlier work demonstrated that the two-layered chick embryo is a modified gastrula and not a "disc" as Wilhelm His had claimed. From the 1880s onwards, he concentrated on the issue of how the development of germ layers is related to tissue differentiation. To address this, he studied the blastopore, epiblast, primitive streak, teratology and the relative importance of nucleus and cytoplasm in heredity. This paper reconstructs some of Rauber's work and concludes that his observations and reflections constituted a new approach combining embryology and histology with "phylogenetic" reasoning.  (+info)

Evolutionary embryology resurrected in Japan with a new molecular basis: Nori Satoh and the history of ascidian studies originating in Kyoto during the 20th century. (58/116)

This article briefly summarizes the scientific contributions of Nori Satoh, the winner of the 2005 edition of the Kowalevsky Medal, to Developmental Biology and especially to Evo-Devo with his 30 years of research on tunicates - a primitive chordate species. His research began with his pure developmental interest in the clock mechanism of cell differentiation and later expanded into various aspects of evolutionary and developmental phenomena. He is not only known as a founder of molecular biology-based tunicate studies, but also for his world-wide service to education and his prestigious publications in international scientific journals.  (+info)

Interobserver agreement and intraobserver reproducibility of embryo quality assessments. (59/116)

BACKGROUND: The objective of this investigation was to determine the inter- and intraobserver agreement when assessing embryo quality. METHODS: This investigation included 4002 cleaved embryos from 7535 oocytes retrieved in 688 patients undergoing IVF cycles in a multicentre trial. Embryos were evaluated locally at the inverted microscope at 28, 44 and 68 h (+/-1 h) post-insemination. Digital images of the embryos were assessed centrally by three blinded embryologists. To assess reproducibility, 215 randomly selected cleaved embryos from 33 patients were re-evaluated by the three central embryologists. RESULTS: The interobserver agreement among the central embryologists (using the same method of evaluation; 2D images) was good for classification of top-quality embryos (kappa 0.71-0.73), excellent for classification of normally developed embryos (kappa 0.83-0.86) and good-excellent for classification of transferable embryos (kappa 0.78-0.82). The interobserver agreement between local and consolidated central assessment (different methods of evaluation, inverted microscopy versus 2D images) was good for all three embryo classifications (kappa 0.64-0.79). The intraobserver reproducibility for all three overall embryo classifications was excellent for the consolidated central assessment (kappa 0.80-0.91). CONCLUSION: Embryo quality can be determined with a good degree of interobserver agreement independently of the method of evaluation. Embryologists classify embryos with excellent intraobserver reproducibility.  (+info)

An epigenetic state associated with areas of gene duplication. (60/116)

Asynchronous DNA replication is an epigenetically determined feature found in all cases of monoallelic expression, including genomic imprinting, X-inactivation, and random monoallelic expression of autosomal genes such as immunoglobulins and olfactory receptor genes. Most genes of the latter class were identified in experiments focused on genes functioning in the chemosensory and immune systems. We performed an unbiased survey of asynchronous replication in the mouse genome, excluding known asynchronously replicated genes. Fully 10% (eight of 80) of the genes tested exhibited asynchronous replication. A common feature of the newly identified asynchronously replicated areas is their proximity to areas of tandem gene duplication. Testing of other clustered areas supported the idea that such regions are enriched with asynchronously replicated genes.  (+info)

Ernest Everett Just (1883-1941)--an early ecological developmental biologist. (61/116)

Ecological developmental biology (Eco-Devo) involves the study of development in its natural environmental context as opposed to the laboratory setting. Ernest E. Just was an early 20th century African-American embryologist who devoted his career to studying the early development of marine invertebrates in the United States and abroad. Through detailed study of the fertilization process, he came to see the cell cortex as playing a central role in development, inheritance, and evolution. This paper, after presenting some of Just's scientific and philosophical contributions, argues that Just was an Eco-Devo biologist. Three lines of evidence are given. First, Just believed that intimate knowledge of the natural history of the marine animal under study--hence, the natural setting in which fertilization occurs--was essential. Second, he stressed the importance of the egg's "normality"--how well its condition in the laboratory corresponds to the natural, fertilizable state. Finally, Just was an organicist, believing that organisms are holistic systems with emergent properties that arise from their organization and complexity. Although other scientists may stand out more clearly as founding architects of Eco-Devo, E. E. Just, with his unwavering insistence on the normality and holistic integrity of the egg cell, was one of its purest adherents.  (+info)

The diverse functions of microRNAs in animal development and disease. (62/116)

MicroRNAs (miRNAs) control gene expression by translational inhibition and destabilization of mRNAs. While hundreds of miRNAs have been found, only a few have been studied in detail. miRNAs have been implicated in tissue morphogenesis, cellular processes like apoptosis, and major signaling pathways. Emerging evidence suggests a direct link between miRNAs and disease, and miRNA expression signatures are associated with various types of cancer. In addition, the gain and loss of miRNA target sites appears to be causal to some genetic disorders. Here, we discuss the current literature on the role of miRNAs in animal development and disease.  (+info)

The Fugu tyrp1 promoter directs specific GFP expression in zebrafish: tools to study the RPE and the neural crest-derived melanophores. (63/116)

In vertebrates, pigment cells account for a small percentage of the total cell population and they intermingle with other cell types. This makes it difficult to isolate them for analyzes of their functions in the context of development. To alleviate such difficulty, we generated two stable transgenic zebrafish lines (pt101 and pt102) that express green fluorescent protein (GFP) in melanophores under the control of the 1 kb Fugu tyrp1 promoter. In pt101, GFP is expressed in both retinal pigment epithelium (RPE) cells and the neural crest-derived melanophores (NCDM), whereas in pt102, GFP is predominately expressed in the NCDM. Our results indicate that the Fugu tyrp1 promoter can direct transgene expression in a cell-type-specific manner in zebrafish. In addition, our findings provide evidence supporting differential regulations of melanin-synthesizing genes in RPE cells and the NCDM in zebrafish. Utilizing the varying GFP expression levels in these fish, we have isolated melanophores via flow cytometry and revealed the capability of sorting the NCDM from RPE cells as well. Thus, these transgenic lines are useful tools to study melanophores in zebrafish.  (+info)

A history of normal plates, tables and stages in vertebrate embryology. (64/116)

Developmental biology is today unimaginable without the normal stages that define standard divisions of development. This history of normal stages, and the related normal plates and normal tables, shows how these standards have shaped and been shaped by disciplinary change in vertebrate embryology. The article highlights the Normal Plates of the Development of the Vertebrates edited by the German anatomist Franz Keibel (16 volumes, 1897-1938). These were a major response to problems in the relations between ontogeny and phylogeny that amounted in practical terms to a crisis in staging embryos, not just between, but (for some) also within species. Keibel's design adapted a plate by Wilhelm His and tables by Albert Oppel in order to go beyond the already controversial comparative plates of the Darwinist propagandist Ernst Haeckel. The project responded to local pressures, including intense concern with individual variation, but recruited internationally and mapped an embryological empire. Though theoretically inconclusive, the plates became standard laboratory tools and forged a network within which the Institut International d'Embryologie (today the International Society of Developmental Biologists) was founded in 1911. After World War I, experimentalists, led by Ross Harrison and Viktor Hamburger, and human embryologists, especially George Streeter at the Carnegie Department of Embryology, transformed Keibel's complex, bulky tomes to suit their own contrasting demands. In developmental biology after World War II, normal stages-reduced to a few journal pages-helped domesticate model organisms. Staging systems had emerged from discussions that questioned the very possibility of assigning an embryo to a stage. The historical issues resonate today as developmental biologists work to improve and extend stage series, to make results from different laboratories easier to compare and to take individual variation into account.  (+info)