Developmental Biology

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Developmental biology

A large field of investigation that includes the study of all changes associated with an organism as it progresses through the life cycle. The life cycles of all multicellular organisms exhibit many similarities. That is, as an organism progresses from one generation to the next there is a series of common processes: for example, gametogenesis, fertilization, embryogenesis, cell differentiation, tissue differentiation, organogenesis, maturation, growth, reproduction, senescence, and death.

Analysis of all of the events associated with an organism as it progresses through its life cycle employs a multiplicity of approaches. Tremendous strides have been made in describing at the molecular level the developmental process of cell differentiation. However, the molecular control mechanisms which regulate cell differentiation are not known. Tissue and organ differentiation, as well as morphogenesis, are processes which have been described in detail for many situations, but little is known about the physical and chemical nature of the mechanisms involved. A complete understanding of the development of an organism will require an appreciation and comprehension of the changes which occur at all levels of organization as an organism traverses its life cycle.

The major unifying theme in biology is evolution. Not only has evolution led to the wide variety of organisms now present on Earth, but also evolution has modified the initial processes and patterns of development to the diversity of types currently encountered. This evolution of developmental parameters in multicellular organisms began as single-celled organisms became multicellular. The development of a multicellular organism entails a host of problems not faced by a single-celled organism. For example, cells in one part of the aggregate must coordinate their activities with cells in other parts, nutrients and oxygen must be provided to all cells, and water balance must be maintained.

Developmental biologists have focused on two central areas: the processes and associated mechanisms by which cells become different, that is, cell differentiation; and the processes and associated mechanisms by which patterns are created, that is, morphogenesis.

Current theories state that cells become different by expressing different genes. Thus, a liver cell is different from a muscle cell, not because it contains different genes or genetic information, but because it expresses different sets of genes. This explanation of cell differences is based upon the results of three types of experimental analysis. (1) Some plant cells are totipotent; that is, for tobacco, carrot, and a few other plant species, it has been demonstrated that a single cell (not a gamete) can divide and undergo morphogenesis to form a fertile plant. (2) Nuclei from some differentiated animal cells are totipotent. That is, a nucleus from a differentiated cell can be injected into a mature egg which has had its nucleus removed or destroyed, and the injected nucleus can direct normal development of the organism. (3) The sequences of nucleotides in the DNA of all cells in an organism appear to be the same; that is, DNA-DNA hybridization of DNA from different cell types indicates that the different cell types do not have unique DNA base sequences. Since these results indicate that all cells contain the complete genome for an organism, different cell types appear to arise as a result of the expression of unique sets of genes in each cell type. See Cell differentiation, Developmental genetics, Gene action, Somatic cell genetics

Initially the cells of a developing embryo are not restricted in their developmental potential or fate, but as embryogenesis proceeds, a cell's developmental potential becomes restricted or fixed. Restriction of developmental fate is called determination. Two mechanisms have been identified that bring about determination. The first involves the presence of unique factors, called cytoplasmic determinants, which are products of the maternal genome and are located in specific areas of some animal eggs. The cells which come to contain these determinants differentiate along specific pathways. The second mechanism is induction, a process by which two tissues interact so that one or both differentiate along specific pathways. A classic example of induction is the action of mesoderm on the overlaying ectoderm in the frog embryo at the time of gastrulation. The mesoderm acts on the ectoderm, causing it to form the neural plate. Only ectoderm of a certain developmental age is capable of responding to the mesoderm, and this ectoderm is said to be competent. See Embryonic induction

Developmental biologists have gained substantial insights into the molecular bases for determination in model organisms such as Drosophila. At least three sets of cytoplasmic determinants (maternal gene products) are present in the fly egg: determinants for germ-cell formation, determinants controlling dorsal-ventral polarity, and determinants for the anterior-posterior polarity. Some of these determinants are messenger ribonucleic acids (mRNAs) coding for proteins which are transcriptional regulators (that is, proteins that regulate gene activity).

Morphogenesis involves the production of form and structure by integrating the differentiation of many different cells and cell types into specific spatial patterns. This higher level of organization has been difficult to investigate in terms of establishing mechanisms. The processes of determination, competence, and induction are involved. One of the greatest challenges faced by developmental biologists is to bridge the gap between genes and patterns. It is clear that patterns are a result of gene activity, but the relationship between genes and patterns in most organisms is not well understood. See Animal morphogenesis, Plant morphogenesis

Developmental Biology


ontogeny, a branch of biology that studies in detail the processes and motive forces of individual or ontogenetic development of the organism. Developmental biology is the successor of such earlier branches of research in ontogeny as developmental mechanics (or experimental embryology) and developmental dynamics, which were distinguished by their narrower approach to the subject and by their isolation from other biological disciplines. As an independent field of research, developmental biology originated in the middle of the 20th century at the junction of biochemistry, cytology, genetics, embryology, and experimental morphology. One of the conditions and important prerequisites for the synthesis of these previously isolated branches of general biology in the field of individual development was the appearance and development of molecular biology. Developmental biology engages in comprehensive study at all levels of organization (molecular, cellular, tissue, and organismic) of such aspects of development as biosynthesis; cellular, embryonic, and tissue differentiation; organogenesis and growth; manifestation of genetic information in the course of ontogeny; regulatory mechanisms of development; and regeneration. Developmental biology is becoming increasingly popular both in the USSR and abroad, where many scientific research institutes are working in the field and journals and monographs are published. In the USSR, the center of research is the Institute of Developmental Biology of the USSR Academy of Sciences, and the main publication is the journal Ontogenez (Ontogeny; since 1970).


References in periodicals archive ?
Delving into the earliest embryonic events may give researchers new insights into infertility and human development, says Janet Rossant, a developmental biologist at the Hospital for Sick Children and the University of Toronto.
In close collaboration with the developmental biologist Prof.
Shapiro is a pioneering developmental biologist whose work on the single-celled Caulobactor bacterium illuminated the mechanisms that control the differentiation of cells in all living things, from the simplest organisms to the most complex.
The developmental biologist gives an intricate lecture about how people emerge from a single cell into a multi-trillion-celled organism known as the human body on December 28, which sounds fascinating stuff.
Even before a child eats their first mouthful of food, they are learning about flavour through the amniotic fluid in the womb, and later through their mother's milk," the paper quoted Julie Mennella, a developmental biologist at the Monell Chemical Senses Centre in Philadelphia as saying.
Uchida, a biomathematician and developmental biologist associated with the department of cardiac development and remodeling at the Max Planck Institute for Heart and Lung Research, Germany, outlines an approach to the analysis of evolutionarily-conserved, heart-enriched genes with unknown functions and the steps of the procedure, from screening to validation.
The doctors had to take out all of the extra tendons and bones, and basically cut out a whole wedge of his hand," says Henk Roelink, a developmental biologist at the University of California, Berkeley.
Lead investigator James Wells, PhD, a developmental biologist at Cincinnati Children's Hospital Medical Center in Ohio, observed that scientists can use the new protocol to investigate the molecular basis of human intestinal development and disease, design drugs that get absorbed better and grow tissue for transplantation therapies.
The flatfish eyes and skeletal structure underwent small, incremental changes, says Alex Schreiber, a developmental biologist who studies flatfish at St.
In 1979, Jesuit theologian Richard McCormick and frog developmental biologist Clifford Grobstein introduced the "scientific" myth that the product of fertilization, for up to fourteen days after fertilization, was not an embryo because it was not, as yet, the source of one individual; i.
Until now, experiments with frogs have shown us how vertebrates develop from an egg to an organism," said Richard Harland, a developmental biologist at the University of California, Berkeley, and an early advocate of the project.
Dr Nigel Brown, a developmental biologist at St George's Hospital, London, said: "I will never be happy about Thalidomide.

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