Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth The term cell growth is used in the contexts of cell development and cell division When used in the context of cell division, it refers to growth of cell populations, where one cell (the "mother cell") grows and divides to produce two "daughter cells", differentiation In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a single zygote to a complex system of tissues and cell types. Differentiation is a common and "morphogenesis Morphogenesis , is the biological process that causes an organism to develop its shape. It is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation. The process controls the organized spatial distribution of cells during the embryonic development of an organism. Morphogenetic", which is the process that gives rise to tissues Tissue is a cellular organizational level intermediate between cells and a complete organism. Hence, a tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues, organs In biology and anatomy, an organ is a collection of tissues joined in structural unit to serve a common function and anatomy Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy (zootomy) and plant anatomy (phytotomy). In some of its facets anatomy is closely related to embryology, comparative anatomy and comparative embryology, through common roots in.

Contents 1 Related fields of study 2 Perspectives 3 Developmental model organisms 4 Studied phenomena 4.1 Cell differentiation 4.2 Embryonal development 4.3 Growth 4.4 Metamorphosis 4.5 Regeneration 5 Developmental systems biology 6 See also 7 References 8 External links

Related fields of study

Embryology Embryology is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage. After cleavage, the dividing cells, or morula, becomes a hollow ball, or blastula, which develops a hole or pore at one end is a subfield, the study of organisms between the one-cell stage (generally, the zygote A zygote , or zygocyte, is the initial cell formed when a new organism is produced by means of sexual reproduction. A zygote is synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development. Zygotes are usually produced by a fertilization event between two haploid cells — an ovum from a female and) and the end of the embryonic stage. 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 With regard to living things, a body is the physical body of an individual. "Body" often is used in connection with appearance, health issues and death. The study of the workings of the body is physiology of a living organism.

The related field of evolutionary developmental biology Evolutionary developmental biology is a field of biology that compares the developmental processes of different animals and plants in an attempt to determine the ancestral relationship between organisms and how developmental processes evolved. It addresses the origin and evolution of embryonic development; how modifications of development and was formed largely in the 1990s and is a synthesis of findings from molecular developmental biology and evolutionary biology Evolutionary biology is a sub-field of biology concerned with the origin of species from a common descent and descent of species, as well as their change, multiplication and diversity over time. Someone who studies evolutionary biology is known as an evolutionary biologist. To philosopher Kim Sterelny, "the development of evolutionary biology which considers the diversity of organismal form in an evolutionary context.

Perspectives

The development of a new life is a spectacular process and represents a masterpiece of temporal and spatial control of gene expression. Developmental genetics studies the effect that genes have in a phenotype A phenotype is any observable characteristic or trait of an organism: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior . Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and the interactions between the two, given normal or abnormal epigenetic In biology, and specifically genetics, epigenetics is the study of inherited changes in phenotype or gene expression caused by mechanisms other than changes in the underlying DNA sequence, hence the name epi- (Greek: επί- over, above) -genetics. These changes may remain through cell divisions for the remainder of the cell's life and may also parameters. The findings of developmental biology can help to understand developmental abnormalities such as chromosomal aberrations A chromosome anomaly, abnormality or aberration reflects an atypical number of chromosomes or a structural abnormality in one or more chromosomes. A karyotype refers to a full set of chromosomes from an individual which can be compared to a "normal" karyotype for the species via genetic testing. A chromosome anomaly may be detected or that cause Down syndrome Down syndrome, or Down's syndrome , trisomy 21, or trisomy G, is a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British physician who described the syndrome in 1866. The disorder was identified as a chromosome 21 trisomy by Jérôme Lejeune in 1959. The condition. An understanding of the specialization of cells The cell is the functional basic unit of life. It was discovered by Robert Hooke and is the functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Some organisms, such as most bacteria, are unicellular . Other organisms, such as humans, during embryogenesis Embryogenesis is the process by which the embryo is formed and develops, until it develops into a fetus. It starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote. The zygote undergoes rapid mitotic divisions with no significant growth (a process known as cleavage) and cellular differentiation, leading has provided information on how stem cells Stem cells are cells found in all multi cellular organisms. They are characterized by the ability to renew themselves through mitotic cell division and differentiate into a diverse range of specialized cell types. Research in the stem cell field grew out of findings by Canadian scientists Ernest A. McCulloch and James E. Till in the 1960s. The two specialize into specific tissues and organs. This information has led, for example, to the cloning Cloning in biology is the process of similar producing populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments , cells (cell cloning), or organisms. The term also refers to the of specific organs for medical purposes.^[1][2] Another biologically important process that occurs during development is apoptosis Apoptosis is the process of programmed cell death (PCD) that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes include blebbing, loss of cell membrane asymmetry and attachment, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA—programmed cell death or "suicide." Many developmental models are used to elucidate the physiology Physiology is the science of the functioning of living systems. It is a subcategory of biology. In physiology, the scientific method is applied to determine how organisms, organ systems, organs, cells and biomolecules carry out the chemical or physical function that they have in a living system. The word physiology is from Ancient Greek: φύσις and molecular basis of this cellular process. Similarly, a deeper understanding of developmental biology can foster greater progress in the treatment of congenital Congenital disorder or anomaly involves defects in or damage to a developing fetus. It may be the result of genetic abnormalities, the intrauterine environment, errors of morphogenesis, infection, or a chromosomal abnormality. The outcome of the disorder will further depend on complex interactions between the pre-natal deficit and the post-natal disorders and diseases, e.g. studying human sex determination can lead to treatment for disorders such as congenital adrenal hyperplasia Congenital adrenal hyperplasia refers to any of several autosomal recessive diseases resulting from mutations of genes for enzymes mediating the biochemical steps of production of cortisol from cholesterol by the adrenal glands (steroidogenesis).

Developmental model organisms

Gene expression pattern determined by histochemical GUS assays in Physcomitrella patens Physcomitrella patens is a moss used as a model organism for studies on plant evolution, development and physiology. The Polycomb gene FIE is expressed (blue) in unfertilised egg cells of the moss Physcomitrella patens (right) and expression ceases after fertilisation in the developing diploid sporophyte (left). In situ GUS staining of two female sex organs (archegonia) of a transgenic plant expressing a translational fusion of FIE-uidA under control of the native FIE promoter^[3]

Often used model organisms A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. In particular, model organisms are widely used to explore potential causes and treatments for human disease in developmental biology include the following:

• Vertebrates
  • Zebrafish Danio rerio The zebrafish, Danio rerio, is a tropical freshwater fish belonging to the minnow family . It is a popular aquarium fish, frequently sold under the trade name zebra danio, and is an important vertebrate model organism in scientific research^[4]
  • Medakafish Oryzias latipes
  • Fugu (pufferfish Tetraodontidae is a family of primarily marine and estuarine fish of the Tetraodontiformes order. The family includes many familiar species which are variously called pufferfish, balloonfish, blowfish, bubblefish, globefish, swellfish, toadfish, toadies, honey toads, and sea squab. They are morphologically similar to the closely related) Takifugu rubripes
  • Frog Xenopus laevis The African clawed frog is a species of South African aquatic frog of the genus Xenopus. (The word Xenopus means "Strange Foot" and laevis means "Smooth".) It can grow up to a length of 5 in (12 cm) with a flattened head and body, but no external ear or tongue. Its name is derived from the three short claws on each of its hind, Xenopus tropicalis^[5]
  • Chicken Gallus gallus The Red Junglefowl is a tropical member of the Pheasant family, and is often believed to be a direct ancestor of the domestic chicken. While the domestic chicken was previously believed to be a descendant of the Red Junglefowl, recent research done by Eriksson et al. suggests possible hybridisation with the Grey Junglefowl. It was first raised in
  • Mouse Mus musculus The house mouse is a small rodent, a mouse, one of the most numerous species of the genus Mus (Mammalian embryogenesis Mammalian embryogenesis is the process of cell division and cellular differentiation during early prenatal development which leads to the development of a mammalian embryo)^[6]

• Invertebrates
  • Lancelet The lancelets , or known as amphioxus are the modern representatives of the subphylum Cephalochordata, usually said to be the sister group of the craniates. They are usually found buried in sand in shallow parts of temperate or tropical seas. In Asia, they are harvested commercially as food for humans and domesticated animals. They are an Branchiostoma lanceolatum
  • Ascidian Ciona intestinalis Ciona intestinalis or vase tunicate is a Urochordata whose genome has been sequenced. It has become, over the past decade, a major experimental model for developmental biologists. It is widely distributed in North European waters, but has also spread to other parts of the world as an invasive species
  • Sea urchin Strongylocentrotus purpuratus
  • Roundworm Caenorhabditis elegans Caenorhabditis elegans is a free-living, transparent nematode (roundworm), about 1 mm in length, which lives in temperate soil environments. Research into the molecular and developmental biology of C. elegans was begun in 1974 by Sydney Brenner and it has since been used extensively as a model organism
  • Fruit fly Drosophila melanogaster (Drosophila embryogenesis)

• Plants (Plant embryogenesis Plant embryogenesis is the process that produces a plant embryo from a fertilised ovule by asymmetric cell division and the differentiation of undifferentiated cells into tissues and organs. It occurs during seed development, when the single-celled zygote undergoes a programmed pattern of cell division resulting in a mature embryo. A similar)
  • Physcomitrella patens Physcomitrella patens is a moss used as a model organism for studies on plant evolution, development and physiology ^[7]
  • Arabidopsis thaliana Arabidopsis thaliana , is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, Arabidopsis is popular as a model organism in plant biology and genetics. Its genome is one of the smallest plant genomes and was the first plant genome to be sequenced. Arabidopsis is a popular
  • Maize Maize is a grass domesticated by indigenous peoples in Mesoamerica in prehistoric times. The Aztecs and Mayans cultivated it in numerous varieties throughout central and southern Mexico, to cook or grind in a process called nixtamalization. Later the crop spread through much of the Americas. Between 1250 A.D. and 1700 A.D. nearly the whole
  • Snapdragon Antirrhinum majus Antirrhinum majus is a species of plants belonging to the genus Antirrhinum. It is native to the Mediterranean region, from Morocco and Portugal north to southern France, and east to Turkey and Syria. The common name "snapdragon", originates from the flowers reaction to having their throats squeezed, which causes the "mouth" of

• Other
  • Slime mold Dictyostelium discoideum

Studied phenomena

Cell differentiation

Differentiation In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a single zygote to a complex system of tissues and cell types. Differentiation is a common is the formation of cell types A cell type is a distinct morphological or functional form of cell. When a cell switches state from one cell type to another, it undergoes cellular differentiation. A complete list of distinct cell types in the adult human body may include about 210 distinct types.[citation needed], from what is originally one cell – the zygote A zygote , or zygocyte, is the initial cell formed when a new organism is produced by means of sexual reproduction. A zygote is synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development. Zygotes are usually produced by a fertilization event between two haploid cells — an ovum from a female and or spore In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoans. A chief difference between spores and seeds as dispersal units is that spores have very little stored. The formation of cell types like nerve cells A neuron (pronounced /ˈnjʊərɒn/ NOOR-on, also known as a neurone or nerve cell) is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core occurs with a number of intermediary, less differentiated cell types. A cell stays a certain cell type by maintaining a particular pattern of gene expression Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as rRNA genes or tRNA genes, the product is a functional RNA. The process of gene expression is used by all known life - eukaryotes , prokaryotes (bacteria.^[8] This depends on regulatory genes, e.g. for transcription factors In the field of molecular biology, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the transfer (or transcription) of genetic information from DNA to mRNA. Transcription factors perform this function alone or with other proteins in a complex, by promoting (as an activator), or blocking (as a repressor) and signaling proteins. These can take part in self-perpetuating circuits in the gene regulatory network A gene regulatory network or genetic regulatory network is a collection of DNA segments in a cell which interact with each other (indirectly through their RNA and protein expression products) and with other substances in the cell, thereby governing the rates at which genes in the network are transcribed into mRNA. In general, each mRNA molecule, circuits that can involve several cells that communicate Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. The ability of cells to perceive and correctly respond to their microenvironment is the basis of development, tissue repair, and immunity as well as normal tissue homeostasis. Errors in cellular information processing with each other.^[9] External signals can alter gene expression by activating a receptor In biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or the cytoplasm of a cell, to which one or more specific kinds of signaling molecules may attach. A molecule which binds to a receptor is called a ligand, and may be a peptide (short protein) or other small molecule, such as a neurotransmitter, a hormone, a, which triggers a signaling cascade that affects transcription factors. For example, the withdrawal of growth factors from myoblasts A myoblast is a type of embryonic progenitor cell that gives rise to myocytes causes them to stop dividing and instead differentiate into muscle cells.^[10]

Embryonal development

The initial stages of human embryogenesis.

Embryogenesis is the step in the life cycle after fertilisation – the development of the embryo, starting from the zygote (fertilised egg). Organisms can differ drastically in the how embryo develops, especially when they belong to different phyla. For example, embryonal development in placental mammals starts with cleavage of the zygote into eight uncommited cells, which then form a ball (morula). The outer cells become the trophectoderm or trophoblast, which will form in combination with maternal uterine endometrial tissue the placenta, needed for fetal nurturing via maternal blood, while inner cells become the inner cell mass that will form all fetal organs (the bridge between these two parts eventually forms the umbilical cord). In contrast, the fruit fly zygote first forms a sausage-shaped syncytium, which is still one cell but with many cell nuclei.^[11]

Patterning is important for determining which cells develop into which organs. This is mediated by signaling between adjacent cells by proteins on their surfaces, and by gradients of signaling secreted molecules.^[12] An example is retinoic acid, which forms a gradient in the head to tail direction in animals. Retinoic acid enters cells and activates Hox genes in a concentration-dependent manner – Hox genes differ in how much retinoic acid they require for activation and will thus show differential rostral expression boundaries, in a colinear fashion with their genomic order. As Hox genes code for transcription factors, this causes different activated combinations of both Hox and other genes in discrete anteroposterior transverse segments of the neural tube (neuromeres) and related patterns in surrounding tissues, such as branchial arches, lateral mesoderm, neural crest, skin and endoderm, in the head to tail direction.^[13] This is important for e.g. the segmentation of the spine in vertebrates.^[12]

Embryonal development does not always proceed correctly, and errors can result in birth defects or miscarriage. Often the reason is genetic (mutation or chromosome abnormality), but there can be environmental influence (like teratogens) or stochastic events.^[14][15] Abnormal development caused by mutation is also of evolutionary interest as it provides a mechanism for changes in body plan (see evolutionary developmental biology).^[16]

Growth

Growth is the enlargement of a tissue or organism. Growth continues after the embryonal stage, and occurs through cell proliferation, enlargement of cells or accumulation of extracellular material. In plants, growth results in an adult organism that is strikingly different from the embryo. The proliferating cells tend to be distinct from differentiated cells (see stem cell and progenitor cell). In some tissues proliferating cells are restricted to specialised areas, such as the growth plates of bones.^[17] But some stem cells migrate to where they are needed, such as mesenchymal stem cells which can migrate from the bone marrow to form e.g. muscle, bone or adipose tissue.^[18] The size of an organ frequently determines its growth, as in the case of the liver which grows back to its previous size if a part is removed. Growth factors, such as fibroblast growth factors in the animal embryo and growth hormone in juvenile mammals, also control the extent of growth.^[17]

Metamorphosis

Most animals have a larval stage, with a body plan different from that of the adult organism. The larva abrubtly develops into an adult in a process called metamorphosis. For example, caterpillars (butterfly larvae) are specialized for feeding whereas adult butterflies (imagos) are specialised for flight and reproduction. When the caterpillar has grown enough, it turns into an immobile pupa. Here, the imago develops from imaginal discs found inside the larva.^[19]

Regeneration

Regeneration is the reactivation of development so that a missing body part grows back. This phenomenon has been studied particularly in salamanders, where the adults can reconstruct a whole limb after it has been amputated.^[20] Researchers hope to one day be able to induce regeneration in humans (see regenerative medicine).^[21] There is little spontaneous regeneration in adult humans, although the liver is a notable exception. Like for salamanders, the regeneration of the liver involves dedifferentiation of some cells to a more embryonal state.^[20]

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 French flag model or Biological Physics of the Developing Embryo for literature). Minimal genomes for minimal multicellular organisms may pave the way to understand such complex processes in vivo.

See also

• Altricial and Precocial
• Auxology
• Body plan
• Cell signaling
• Embryogenesis
• Embryology
• Evolutionary developmental biology
• Plant evolutionary developmental biology
• Fertilization
• Fish development
• Cell signaling networks
• Developmental noise
• Enhancer
• Enhanceosome
• Gene regulatory network
• promoter (biology)
• Signal transduction
• Transcription factor

References

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6. ^ Keller G (2005). "Embryonic stem cell differentiation: emergence of a new era in biology and medicine". Genes Dev. 19 (10): 1129–55. doi:10.1101/gad.1303605. PMID 15905405. http://genesdev.cshlp.org/content/19/10/1129.long.
7. ^ Mosquna, Katz, Decker, Rensing, Reski, Ohad (2009): Regulation of stem cell maintenance by the Polycomb protein FIE has been conserved during land plant evolution. Development 136, 2433-2444. doi:10.1242/10.1242/dev.035048
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External links

Wikibooks has more on the topic of Developmental biology

• Developmental Biology of Plants and Animals
• Developmental Biology - 8th Edition by Scott Gilbert (online textbook)

Major subfields of biology Anatomy · Astrobiology · Biochemistry · Biomechanics · Biophysics · Bioinformatics · Biostatistics · Botany · Cell biology · Chemical biology · Chronobiology · Conservation biology · Developmental biology · Ecology · Epidemiology · Evolutionary biology · Genetics · Genomics · Histology · Human biology · Immunology · Marine biology · Mathematical biology · Microbiology · Molecular biology · Mycology · Neuroscience · Nutrition · Origin of life · Paleontology · Parasitology · Pathology · Pharmacology · Physiology · Quantum biology · Systems biology · α-Taxonomy · Toxicology · Zoology

Developmental biology Embryology Embryogenesis (Human embryogenesis · Drosophila embryogenesis · Fish embryogenesis) · Polarity in embryogenesis Other Metamorphosis · Regeneration · Ageing · Model organisms · Compartment · Metamerism

Developmental biology > Human embryogenesis (development of embryo) and development of fetus First three weeks Week 1 Fertilization · Egg activation · Zygote · Cleavage · Morula · Blastula (Blastomere) · Blastocyst · Inner cell mass Week 2 (Bilaminar) Hypoblast · Epiblast Week 3 (Trilaminar) Germ layers Archenteron/Primitive streak (Primitive pit, Primitive knot/Blastopore, Primitive groove) · Gastrula/Gastrulation · Regional specification Ectoderm Surface ectoderm · Neuroectoderm · Somatopleure · Neurulation · Neural crest Endoderm Splanchnopleure Mesoderm Chorda- · Paraxial (Somite/Somitomere/Sclerotome/Myotome/Dermatome) · Intermediate · Lateral plate (Intraembryonic coelom, Splanchnopleure/Somatopleure) Extraembryonic/ uterus Trophoblast (Cytotrophoblast, Syncytiotrophoblast) Blastocoele · Yolk sack/exocoelomic cavity · Heuser's membrane · Extraembryonic coelom · Vitelline duct Umbilical cord (Umbilical artery, Umbilical vein, Wharton's jelly) · Allantois Placenta · Decidua (Decidual cells) · Chorionic villi/Intervillous space · Gestational sac (Amnion/Amniotic sac/Amniotic cavity, Chorion) Histogenesis Programmed cell death (Apoptosis) · Stem cells · Germ line development Organogenesis Limb development: Limb bud · Apical ectodermal ridge/AER other structures: Eye development · Cutaneous structure development · Heart development · Development of the urinary and reproductive organs (Some dates are approximate—see Carnegie stages and a timeline.) : OBS / //, , drug(/)

Human Development: Biological • Psychological Pre- and perinatal Biological Prenatal development Psychological Pre- and perinatal psychology Infancy Biological Infant Psychological Infant and child psychology Childhood Biological Child development · Child development stages · Toddler Psychological Infant and child psychology · Preadolescence Adolescence Biological Puberty Psychological Youth development · Adolescent psychology Young adulthood Psychological Young adult (psychology) Middle adulthood Biological Middle age Maturity Biological Ageing · Senescence Psychological Old age Legal and general definitions Minor (law) · Infancy · Child · Childhood · Adolescence · Age of majority · Adult Theorists and theories Bowlby—attachment · Brofenbrenner—ecological systems · Erikson—psychosocial dev. · Freud—psychosexual dev. · Kohlberg—moral dev. · Piaget—cognitive dev. · Vygotsky—cultural-historical psych.

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