William W. Ballard

Bio: William W. Ballard is an academic researcher from Dartmouth College. The author has contributed to research in topics: Hypoblast & Endoderm. The author has an hindex of 18, co-authored 21 publications receiving 10692 citations. Previous affiliations of William W. Ballard include University of Paris.

Stages of embryonic development of the zebrafish.

Abstract: We describe a series of stages for development of the embryo of the zebrafish, Danio (Brachydanio) rerio. We define seven broad periods of embryogenesis--the zygote, cleavage, blastula, gastrula, segmentation, pharyngula, and hatching periods. These divisions highlight the changing spectrum of major developmental processes that occur during the first 3 days after fertilization, and we review some of what is known about morphogenesis and other significant events that occur during each of the periods. Stages subdivide the periods. Stages are named, not numbered as in most other series, providing for flexibility and continued evolution of the staging series as we learn more about development in this species. The stages, and their names, are based on morphological features, generally readily identified by examination of the live embryo with the dissecting stereomicroscope. The descriptions also fully utilize the optical transparancy of the live embryo, which provides for visibility of even very deep structures when the embryo is examined with the compound microscope and Nomarski interference contrast illumination. Photomicrographs and composite camera lucida line drawings characterize the stages pictorially. Other figures chart the development of distinctive characters used as staging aid signposts.

A series of normal stages for development of Scyliorhinus canicula, the lesser spotted dogfish (Chondrichthyes: Scyliorhinidae)

Abstract: By observing numerous living eggs from the lesser spotted dogfish Scyliorhinus canicula (L.) caught near Roscoff (France) and reared at recorded temperatures as they developed from first cleavage to hatching, the first reasonably complete developmental table was worked out for this classical material in vertebrate embryology. The successive stages, described and numbered from 1 to 34, correct and replace the incomplete stages A–Q proposed by Balfour (J.Anat. Physiol., 10:555–576,1876) and other even less complete series later published, and is unique in the inclusion of a timetable at 16°C. The stages can be identified, usually through the cleared eggshell wall, with naked eye or low magnification. This table of normal stages of Scyliorhinus can be adapted with slight modification to other chondrichthyan fishes. © 1993 Wiley-Liss, Inc.

Normal embryonic stages for salmonid fishes, based on Salmo gairdneri Richardson and Salvelinus fontinalis (Mitchill)

Abstract: As a byproduct of a re-examination of teleost morphogenetic movements, 23 stages in the normal development of salmonid fishes are presented, from fertilization to and beyond hatching, together with rates of their appearance at several constant temperatures. To aid in planning experiments, the period before closure of the germ ring is divided into 13 stages, with detailed discussion of internal structures and movements as well as external features, especially during gastrulation. The literature of salmonid development suggests that the stages are closely applicable to the embryos of any genera of Suborder Salmonoidei. except as to the rates of their appearance. Illustrations are designed for ready identification of stages. Tofacilitate their correlation with the older morphological literature, the principal events of organogenesis in the ectodermal, mesodermal, and endodermal categories are listed according to the stages at which they occur, as determined by dissections and serial sections.

Morphogenetic Movements and Fate Maps of Vertebrates

Abstract: SYNOPSIS. Fate maps are totally lacking for hagfishes, rays, holocephals, dipnoi, holostei and mammals, and for all except two of the thirty or so orders of the huge teleost assemblage. Important errors have been found in earlier studies of the movements by closer control of marking techniques, but there are still major elements in the literature that remain unconfirmed. Recent studies on Salmo, Xenopus and chick suggest that a wider sampling of major vertebrate groups will uncover more unsuspected variations in this phase of embryology. Experimental results on the chondrostean sturgeon Acipenser are here compared and contrasted with those on Salmo and Xenopus . Though chondrostei and teleosts had a relatively recent common ancestry, the morphogenetic movements and fate map of Acipenser give no hint as to how the uniquely teleostean behavior could have arisen. Instead the experiments have shown in new elaborate detail how close the early development of Acipenser is to that of modern amphibia, closer to Xenopus than to Rana , closer to anura than to urodeles. The search for unity in the field of comparative morphogenetic movements is plagued by lack of breadth in the sample of vertebrates hitherto studied but also by a vocabulary too much loaded with ancient homological thinking. It is pointed out that when a group of movements, all called invagination—or all called epiboly, is studied closely it can be discovered that they may be doing quite different things, controlled by different environmental factors. General theory of this part of embryology requires the bringing together of the knowledge of cellular movements from in vitro and non-embryonic systems with the knowledge of the full variety of normal patterns of morphogenetic movements in the vertebrates. Before this can be accomplished, we will need a precise knowledge of what the cells are actually doing in all the sectors of these patterned movements, and in all the major patterns that the phylum has produced.

A new fate map for Salmo gairdneri

Abstract: Chalk granules implanted among the cells of the stage 7 blasto-disc are carried along with the cells to final location in the differentiating tissues and organs. The results, more often than not, are inconsistent with predictions suggested by an earlier fate map for Salmo (Pasteels, (36). Granules vertically thrust into a given spot on the blastodisc are usually carried to various levels of the trunk and to a variety of organs, presumably because cells at different depths of one spot and at different distances from the center are moving at different rates. Data from hundreds of such implants are assembled into charts showing the areas from which cells are drawn, to contribute to formation of the endoderm, notochord, five separate zones of the central nervous system, the head mesoderm, anterior and posterior trunk somites, tail somites, lateral plate, and heart. Using evidence of the overlapping and intergradation of these areas, as well as evidence from vital dyes when allowed to penetrate to various depths of the pregastrular blastodisc, a three-dimensional fate map is synthesized for Salmo gairdneri, which is very different from the earlier map, but consistent with the previously reported patterns of morphogenetic movements in this species (Ballard, (73b). In contrast with the gastrulation of amphibia and birds, Salmo germ layers arise without any invagination, and there is at no time an anterior mesoderm-free area. Previous efforts to generalize upon vertebrate gastrulation and its evolution within the phylum seem to have been premature.

Stages of embryonic development of the zebrafish.

Abstract: We describe a series of stages for development of the embryo of the zebrafish, Danio (Brachydanio) rerio. We define seven broad periods of embryogenesis--the zygote, cleavage, blastula, gastrula, segmentation, pharyngula, and hatching periods. These divisions highlight the changing spectrum of major developmental processes that occur during the first 3 days after fertilization, and we review some of what is known about morphogenesis and other significant events that occur during each of the periods. Stages subdivide the periods. Stages are named, not numbered as in most other series, providing for flexibility and continued evolution of the staging series as we learn more about development in this species. The stages, and their names, are based on morphological features, generally readily identified by examination of the live embryo with the dissecting stereomicroscope. The descriptions also fully utilize the optical transparancy of the live embryo, which provides for visibility of even very deep structures when the embryo is examined with the compound microscope and Nomarski interference contrast illumination. Photomicrographs and composite camera lucida line drawings characterize the stages pictorially. Other figures chart the development of distinctive characters used as staging aid signposts.

Spatial reconstruction of single-cell gene expression data

Abstract: Spatial localization is a key determinant of cellular fate and behavior, but methods for spatially resolved, transcriptome-wide gene expression profiling across complex tissues are lacking. RNA staining methods assay only a small number of transcripts, whereas single-cell RNA-seq, which measures global gene expression, separates cells from their native spatial context. Here we present Seurat, a computational strategy to infer cellular localization by integrating single-cell RNA-seq data with in situ RNA patterns. We applied Seurat to spatially map 851 single cells from dissociated zebrafish (Danio rerio) embryos and generated a transcriptome-wide map of spatial patterning. We confirmed Seurat's accuracy using several experimental approaches, then used the strategy to identify a set of archetypal expression patterns and spatial markers. Seurat correctly localizes rare subpopulations, accurately mapping both spatially restricted and scattered groups. Seurat will be applicable to mapping cellular localization within complex patterned tissues in diverse systems.

The Tol2kit: a multisite gateway-based construction kit for Tol2 transposon transgenesis constructs.

Abstract: Transgenesis is an important tool for assessing gene function. In zebrafish, transgenesis has suffered from three problems: the labor of building complex expression constructs using conventional subcloning; low transgenesis efficiency, leading to mosaicism in transient transgenics and infrequent germline incorporation; and difficulty in identifying germline integrations unless using a fluorescent marker transgene. The Tol2kit system uses site-specific recombination-based cloning (multisite Gateway technology) to allow quick, modular assembly of [promoter]-[coding sequence]-[3' tag] constructs in a Tol2 transposon backbone. It includes a destination vector with a cmlc2:EGFP (enhanced green fluorescent protein) transgenesis marker and a variety of widely useful entry clones, including hsp70 and beta-actin promoters; cytoplasmic, nuclear, and membrane-localized fluorescent proteins; and internal ribosome entry sequence-driven EGFP cassettes for bicistronic expression. The Tol2kit greatly facilitates zebrafish transgenesis, simplifies the sharing of clones, and enables large-scale projects testing the functions of libraries of regulatory or coding sequences.

The identification of genes with unique and essential functions in the development of the zebrafish, Danio rerio

Abstract: In a large-scale screen, we isolated mutants displaying a specific visible phenotype in embryos or early larvae of the zebrafish, Danio rerio. Males were mutagenized with ethylnitrosourea (ENU) and F2 families of single pair matings between sibling F1 fish, heterozygous for a mutagenized genome, were raised. Egg lays were obtained from several crosses between F2 siblings, resulting in scoring of 3857 mutagenized genomes. F3 progeny were scored at the second, third and sixth day of development, using a stereomicroscope. In a subsequent screen, fixed embryos were analyzed for correct retinotectal projection. A total of 4264 mutants were identified. Two thirds of the mutants displaying rather general abnormalities were eventually discarded. We kept and characterized 1163 mutants. In complementation crosses performed between mutants with similar phenotypes, 894 mutants have been assigned to 372 genes. The average allele frequency is 2.4. We identified genes involved in early development, notochord, brain, spinal cord, somites, muscles, heart, circulation, blood, skin, fin, eye, otic vesicle, jaw and branchial arches, pigment pattern, pigment formation, gut, liver, motility and touch response. Our collection contains alleles of almost all previously described zebrafish mutants. From the allele frequencies and other considerations we estimate that the 372 genes defined by the mutants probably represent more than half of all genes that could have been discovered using the criteria of our screen. Here we give an overview of the spectrum of mutant phenotypes obtained, and discuss the limits and the potentials of a genetic saturation screen in the zebrafish.