Introduction to developmental biology

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"Views of a Fetus in the Womb", Leonardo da Vinci, ca. 1510-1512. Fetal development is a major subject of developmental biology

Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis," which is the process that gives rise to tissues, organs and anatomy. Embryology is a subfield, the study of organisms between the one-cell stage (generally, the zygote) and the end of the embryonic stage, which is not necessarily the beginning of free living. Embryology was originally a more descriptive science until the 20th century. Embryology and developmental biology today deal with the various steps necessary for the correct and complete formation of the body of a living organism.

The related field of evolutionary developmental biology was formed largely in the 1990s and is a synthesis of findings from molecular developmental biology and evolutionary biology which considers the diversity of organismal form in an evolutionary context.

The findings of developmental biology can help to understand developmental malfunctions such as chromosomal aberrations, for example, Down syndrome. An understanding of the specialization of cells during embryogenesis may yield information on how to specialize stem cells to specific tissues and organs, which could lead to the specific cloning of organs for medical purposes. Another biologically important process that occurs during development is apoptosis - programmed cell death or "suicide". For this reason, many developmental models are used to elucidate the physiology and molecular basis of this cellular process. Similarily, a deeper understanding of developmental biology can foster greater progress in the treatment of congenital disorders and diseases, e.g. studying human sex determination can lead to treatment for disorders such as congenital adrenal hyperplasia.

Stages of Development

Stages of Development in Developmental Biology

Early Embryonic Development
Fertilization - Egg activation - Clevage - Gastrulation - Regional specification
Late Embryonic Development
Endoderm	Neurulation - Neural crest - Eye development - Cutaneous structure development
Mesoderm	Heart development
Other	Limb development - Germ line development - Programmed cell death - Stem cells
Post Embryonic Development
Metamorphosis - Regeneration - Aging

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Molecular mechanisms of development

During the second half of the 20th century the types of molecules involved in embryonic development were identified. Transcription factors are the key regulators of which genes are expressed in cells. Transcriptional control in the various differentiated cell types allows each type of cell (epithelial, muscle, neuron, etc) to express different amounts of the possible proteins. The transcription factors are regulated by signal transduction pathways that relay signals from outside of cells to the cell nucleus. Signal transduction pathways often involve receptors, receptor ligands and enzymes such as protein kinases. One key class of genes that are differentially regulated by transcription factors in different cell types are genes for cell adhesion proteins. Cell adhesion proteins are among the key regulators of morphogenesis. Functions of these various proteins in development are often elucidated experimentally using gene knockdown techniques in embryos.

Concepts in developmental biology

allantois, amnion, blastocyst, blastomere, blastula, blastulation, chorion, chrysalis, cleavage, embryo, embryogenesis, embryogeny, embryology, extra-embryonic membrane, fetus, gastrula, gastrulation, germ layer, germ plasm, germination, induction, juvenile, larva, maternal effect, metamorphosis, genome, morphogenesis, morula, neoteny, neural development, nymph, ontogeny, oosperm, ovism, paedogenesis, pangenesis, phylogeny, primordium, pupa, rudiment, seed, self-organization, teratology, zygote

Developmental model organisms

Often used model organisms in developmental biology include the following:

• Chordates
  • Lancelet Branchiostoma lanceolatum
  • Zebrafish Danio rerio
  • Medakafish Oryzias latipes
  • Fugu Takifugu rubripes
  • Frogs Xenopus laevis
  • Chicken Gallus gallus
  • Mouse Mus musculus (Mammalian embryogenesis)
• Invertebrates
  • Sea urchin
  • Round worm Caenorhabditis elegans
  • Fruit fly Drosophila melanogaster (Drosophila embryogenesis)
• Plants (Plant embryogenesis)
  • Arabidopsis thaliana
  • Maize
  • Snapdragon

Developmental systems biology

Computer simulation of multicellular development is a research methodology to understand the function of the very complex processes involved in the development of organisms. This includes simulation of cell signaling, multicell interactions and regulatory genomic networks in development of multicellular structures and processes (see Biological Physics of the Developing Embryo). Minimal genomes for minimal multicellular organisms may pave the way to understand such complex processes in vivo.

See also

• altricial and precocial
• auxology
• embryogenesis
• Important publications in developmental biology
• morphogenesis

Sources

• Developmental Biology by Scott Gilbert (online textbook)
• Virtual Library - Developmental Biology
• Latest Developmental Biology News
• Max Planck Institute for Developmental Biology