Show Advanced Search


Containing Text
- - -
Filter by author or institution
Filter by publication date
October, 2006
Filter by journal section

Filter by science education

Embryonic Structures: The anatomical parts that make up an organism in the early stages of development.

Drosophila melanogaster Embryo and Larva Harvesting and Preparation

JoVE 5094

Drosophila melanogaster embryos and larvae are easy to manipulate and develop rapidly by mechanisms that are analogous to other organisms, including mammals. For these reasons, many researchers utilize fly embryos and larvae to answer questions in diverse fields ranging from behavioral to developmental biology. Prior to experimentation, however, the embryos and larvae must first be…

 Biology I

Zebrafish Breeding and Embryo Handling

JoVE 5150

Zebrafish (Danio rerio) are an important model organism that is particularly valuable for research in developmental biology. Zebrafish are extremely fertile and can produce hundreds of progeny per week, so it is relatively easy to collect a large number of embryos for high sample numbers. Furthermore, zebrafish undergo rapid development and embryos are transparent, allowing for easy…

 Biology II

Seed Structure and Early Development of the Sporophyte

JoVE 11109

Seed structures are composed of a protective seed coat surrounding a plant embryo, and a food store for the developing embryo. The embryo contains the precursor tissues for leaves, stem, and roots. The endosperm and cotyledons—seed leaves—act as the food reserves for the growing embryo.

The embryo contains a double set of chromosomes, one set from each parent. Fertilization of the haploid egg by the haploid sperm gives rise to the zygote, which develops into the embryo.  The endosperm is a feature common to most flowering plants, and it is created during the process of double fertilization. Here, two sperm enter into each ovule. One sperm fertilizes the egg; the other fertilizes the central cell, producing the endosperm. Conifers and other gymnosperms do not undergo double fertilization, and therefore do not have a true endosperm. Seed structure differs between monocots and dicots, two types of flowering plants. Monocots, such as corn, have a single large cotyledon called the scutellum, which directly connects to the embryo vascular tissues. The endosperm acts as the food reserve. During germination, the scutellum absorbs enzymatically-released food materials and transports them to the developing embryo. The monocot embryo is surrounded by two protective sheaths. The first, the coleoptile, covers the young shoot. The secon

 Core: Biology


JoVE 10912

During embryogenesis, cells become progressively committed to different fates through a two-step process: specification followed by determination. Specification is demonstrated by removing a segment of an early embryo, “neutrally” culturing the tissue in vitro—for example, in a petri dish with simple medium—and then observing the derivatives. If the cultured region gives rise to cell types that it would normally generate in the embryo, this means that it is specified. In contrast, determination occurs if a region of the embryo is removed and placed in a “non-neutral” environment—such as in a dish containing complex medium supplemented with a variety of proteins, or even a different area of the embryo itself—and it still generates the expected derivatives. Specification and determination are two sequential steps in the developmental pathway of a cell, which precede the final stage of differentiation, during which mature tissues with unique morphologies and functions are produced. To study specification, researchers must first understand the normal derivatives of different regions of an embryo. To accomplish this, fate maps are often used, which are generated by dyeing or labeling cells early in embryonic development, culturing whole embryos and monitoring where the marked cells end up. For example, such te

 Core: Biology

The Angiosperm Life Cycle

JoVE 11108

Plants have a life cycle split between two multicellular stages: a haploid stage—with cells containing one set of chromosomes—and a diploid stage—with cells containing two sets of chromosomes. The haploid stage is the gamete-producing gametophyte, and the diploid stage is the spore-producing sporophyte.

Today, most plants grow from seeds and produce flowers and fruit; such plants are called angiosperms. Angiosperms begin as seeds—structures consisting of a protective seed coat, a nutrient supply, and an embryo. The seed develops into a sporophyte—the familiar, flower-producing plant form. The reproductive life cycle of angiosperms begins with flowering. Stamens and carpels contain sporangia, structures with spore-producing cells called sporocytes. Sporophytes produce spores as either eggs or sperm, depending on their origin. For example, male spores—called microspores—are produced within anthers at the tips of stamens. A microspore develops into a pollen grain—the male gametophyte. A pollen grain contains a tube cell and a generative cell, which develops into sperm. A carpel consists of an ovary and its ovules. Female spores, called megaspores, are produced within ovules. A megaspore develops into an embryo sac—the female gametophyte—which contains the egg. Pollination allows

 Core: Biology


JoVE 10909

Gastrulation establishes the three primary tissues of an embryo: the ectoderm, mesoderm, and endoderm. This developmental process relies on a series of intricate cellular movements, which in humans transforms a flat, “bilaminar disc” composed of two cell sheets into a three-tiered structure. In the resulting embryo, the endoderm serves as the bottom layer, and stacked directly above it is the intermediate mesoderm, and then the uppermost ectoderm. Respectively, these tissue strata will form components of the gastrointestinal, musculoskeletal and nervous systems, among other derivatives. Depending on the species, gastrulation is achieved in different ways. For example, early mouse embryos are uniquely shaped and appear as “funnels” rather than flat discs. Gastrulation thus produces a conical embryo, arranged with an inner ectoderm layer, outer endoderm, and the mesoderm sandwiched in between (similar to the layers of a sundae cone). Due to this distinct morphological feature of mice, some researchers study other models, like rabbit or chicken—both of which develop as flat structures—to gain insights into human development. One of the main morphological features of avian and mammalian gastrulation is the primitive streak, a groove that appears down the vertical center of the embryo, and through which cells migrate t

 Core: Biology


JoVE 10910

Neurulation is the embryological process which forms the precursors of the central nervous system and occurs after gastrulation has established the three primary cell layers of the embryo: ectoderm, mesoderm, and endoderm. In humans, the majority of this system is formed via primary neurulation, in which the central portion of the ectoderm—originally appearing as a flat sheet of cells—folds upwards and inwards, sealing off to form a hollow neural tube. As development proceeds, the anterior portion of the neural tube will give rise to the brain, with the rest forming the spinal cord. The central portion of the ectoderm that bends to generate the neural tube is aptly called the neural ectoderm, while the areas that flank it—along the periphery of the embryo—are the surface ectoderm. However, at the junction of the neural and surface ectoderm lies another population of cells, called the neural crest. As the neural folds (the edges of the elevating neural tube) begin to appear, neural crest cells (NCCs) can be visualized in their tips through the expression of characteristic markers, like the Pax7 transcription factor. As development proceeds and the neural folds fuse, NCCs can be observed either in the top-most portion of the neural tube or migrating along this structure’s sides towards lower regions of the embryo. To migrate, N

 Core: Biology

Zebrafish Reproduction and Development

JoVE 5151

The zebrafish (Danio rerio) has become a popular model for studying genetics and developmental biology. The transparency of these animals at early developmental stages permits the direct visualization of tissue morphogenesis at the cellular level. Furthermore, zebrafish are amenable to genetic manipulation, allowing researchers to determine the effect of gene expression on the…

 Biology II

Chick ex ovo Culture

JoVE 5157

One strength of the chicken (Gallus gallus domesticus) as a model organism for developmental biology is that the embryo develops outside the female and is easily accessible for experimental manipulation. Many techniques allow scientists to examine chicken embryos inside the eggshell (in ovo), but embryonic access can be limited at later stages of development.…

 Biology II
More Results...