Drosophila embryogenesis, the process by which Drosophila embryos form, is a favorite model system for genetics and developmental biology. The study of its embryogenesis unlocked the century-long puzzle of how development was controlled, creating the field of evolutionary developmental biology. The small size, short generation time, and large brood size make it ideal for genetic studies. Transparent embryos facilitate developmental studies. Drosophila melanogaster was introduced into the field of genetic experiments by Thomas Hunt Morgan in 1909.
The Wnt signaling pathways are a group of signal transduction pathways which begin with proteins that pass signals into a cell through cell surface receptors. The name Wnt is a portmanteau created from the names Wingless and Int-1. Wnt signaling pathways use either nearby cell-cell communication (paracrine) or same-cell communication (autocrine). They are highly evolutionarily conserved in animals, which means they are similar across animal species from fruit flies to humans.
Chondrocytes are the only cells found in healthy cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans. Although the word chondroblast is commonly used to describe an immature chondrocyte, the term is imprecise, since the progenitor of chondrocytes can differentiate into various cell types, including osteoblasts.
A morphogen is a substance whose non-uniform distribution governs the pattern of tissue development in the process of morphogenesis or pattern formation, one of the core processes of developmental biology, establishing positions of the various specialized cell types within a tissue. More specifically, a morphogen is a signaling molecule that acts directly on cells to produce specific cellular responses depending on its local concentration.
Compartments can be simply defined as separate, different, adjacent cell populations, which upon juxtaposition, create a lineage boundary. This boundary prevents cell movement from cells from different lineages across this barrier, restricting them to their compartment. Subdivisions are established by morphogen gradients and maintained by local cell-cell interactions, providing functional units with domains of different regulatory genes, which give rise to distinct fates. Compartment boundaries are found across species. In the hindbrain of vertebrate embryos, rhobomeres are compartments of common lineage outlined by expression of Hox genes. In invertebrates, the wing imaginal disc of Drosophila provides an excellent model for the study of compartments. Although other tissues, such as the abdomen, and even other imaginal discs are compartmentalized, much of our understanding of key concepts and molecular mechanisms involved in compartment boundaries has been derived from experimentation in the wing disc of the fruit fly.
The Hedgehog signaling pathway is a signaling pathway that transmits information to embryonic cells required for proper cell differentiation. Different parts of the embryo have different concentrations of hedgehog signaling proteins. The pathway also has roles in the adult. Diseases associated with the malfunction of this pathway include cancer.
Ultrabithorax (Ubx) is a homeobox gene found in insects, and is used in the regulation of patterning in morphogenesis. There are many possible products of this gene, which function as transcription factors. Ubx is used in the specification of serially homologous structures, and is used at many levels of developmental hierarchies. In Drosophila melanogaster it is expressed in the third thoracic (T3) and first abdominal (A1) segments and represses wing formation. The Ubx gene regulates the decisions regarding the number of wings and legs the adult flies will have. The developmental role of the Ubx gene is determined by the splicing of its product, which takes place after translation of the gene. The specific splice factors of a particular cell allow the specific regulation of the developmental fate of that cell, by making different splice variants of transcription factors. In D. melanogaster, at least six different isoforms of Ubx exist.
Mothers against decapentaplegic homolog 1 also known as SMAD family member 1 or SMAD1 is a protein that in humans is encoded by the SMAD1 gene.
SMAD4, also called SMAD family member 4, Mothers against decapentaplegic homolog 4, or DPC4 is a highly conserved protein present in all metazoans. It belongs to the SMAD family of transcription factor proteins, which act as mediators of TGF-β signal transduction. The TGFβ family of cytokines regulates critical processes during the lifecycle of metazoans, with important roles during embryo development, tissue homeostasis, regeneration, and immune regulation.
Decapentaplegic (Dpp) is a key morphogen involved in the development of the fruit fly Drosophila melanogaster and is the first validated secreted morphogen. It is known to be necessary for the correct patterning and development of the early Drosophila embryo and the fifteen imaginal discs, which are tissues that will become limbs and other organs and structures in the adult fly. It has also been suggested that Dpp plays a role in regulating the growth and size of tissues. Flies with mutations in decapentaplegic fail to form these structures correctly, hence the name. Dpp is the Drosophila homolog of the vertebrate bone morphogenetic proteins (BMPs), which are members of the TGF-β superfamily, a class of proteins that are often associated with their own specific signaling pathway. Studies of Dpp in Drosophila have led to greater understanding of the function and importance of their homologs in vertebrates like humans.
Frizzled is a family of atypical G protein-coupled receptors that serve as receptors in the Wnt signaling pathway and other signaling pathways. When activated, Frizzled leads to activation of Dishevelled in the cytosol.
Stem-cell niche refers to a microenvironment, within the specific anatomic location where stem cells are found, which interacts with stem cells to regulate cell fate. The word 'niche' can be in reference to the in vivo or in vitro stem-cell microenvironment. During embryonic development, various niche factors act on embryonic stem cells to alter gene expression, and induce their proliferation or differentiation for the development of the fetus. Within the human body, stem-cell niches maintain adult stem cells in a quiescent state, but after tissue injury, the surrounding micro-environment actively signals to stem cells to promote either self-renewal or differentiation to form new tissues. Several factors are important to regulate stem-cell characteristics within the niche: cell–cell interactions between stem cells, as well as interactions between stem cells and neighbouring differentiated cells, interactions between stem cells and adhesion molecules, extracellular matrix components, the oxygen tension, growth factors, cytokines, and the physicochemical nature of the environment including the pH, ionic strength and metabolites, like ATP, are also important. The stem cells and niche may induce each other during development and reciprocally signal to maintain each other during adulthood.
Medea is a gene from the fruit fly Drosophila melanogaster that was one of the first two Smad genes discovered. For both genes, the maternal effect lethality was the basis for selection of their names. Medea was named for the mythological Greek Medea, who killed her progeny fathered by Jason.
Glypicans constitute one of the two major families of heparan sulfate proteoglycans, with the other major family being syndecans. Six glypicans have been identified in mammals, and are referred to as GPC1 through GPC6. In Drosophila two glypicans have been identified, and these are referred to as dally and dally-like. One glypican has been identified in C. elegans. Glypicans seem to play a vital role in developmental morphogenesis, and have been suggested as regulators for the Wnt and Hedgehog cell signaling pathways. They have additionally been suggested as regulators for fibroblast growth factor and bone morphogenic protein signaling.
The French flag model is a conceptual definition of a morphogen, described by Lewis Wolpert in the 1960s. A morphogen is defined as a signaling molecule that acts directly on cells to produce specific cellular responses dependent on morphogen concentration. During early development, morphogen gradients generate different cell types in distinct spatial order. French flag patterning is often found in combination with others: vertebrate limb development is one of the many phenotypes exhibiting French flag patterning overlapped with a complementary pattern.
Cytonemes are thin, cellular projections that are specialized for exchange of signaling proteins between cells. Cytonemes emanate from cells that make signaling proteins, extending directly to cells that receive signaling proteins. Cytonemes also extend directly from cells that receive signaling proteins to cells that make them.
A segmentation gene is a generic term for a gene whose function is to specify tissue pattern in each repeated unit of a segmented organism. Animals are constructed of segments; however, Drosophila segments also contain subdivided compartments. There are five gene classes which each contribute to the segmentation and development of the embryonic drosophila. These five gene classes include the coordinate gene, gap gene, pair-rule gene, segment polarity gene, and homeotic gene. In embryonic drosophila, the pair-rule gene defines odd-skipped and even-skipped genes as parasegments, showing 7 stripes in the embryo. In the next gene class, segment polarity gene, individual segments each have their own anterior and posterior pole, resulting in 14 segments. In the fruit fly Drosophila melanogaster, segment polarity genes help to define the anterior and posterior polarities within each embryonic parasegment by regulating the transmission of signals via the Wnt signaling pathway and Hedgehog signaling pathway. Segment polarity genes are expressed in the embryo following expression of the gap genes and pair-rule genes. The most commonly cited examples of these genes are engrailed and gooseberry in Drosophila melanogaster. The segment polarity is the last step in embryonic development and a repeated pattern where each half of each segment is deleted and a mirror-image is duplicated and reversed to replace that half segment; thus, forming a pattern element.
Naked cuticle (Nkd) is a conserved family of intracellular proteins encoded in most animal genomes. The original mutants were discovered by 1995 Nobel laureates Christiane Nüsslein-Volhard and Eric F. Wieschaus and colleagues in their genetic screens for pattern-formation mutants in the fruit fly Drosophila melanogaster. The Nkd gene family was first cloned in the laboratory of Matthew P. Scott. Like many cleverly named fly mutants, the name "naked cuticle" derives from the fact that mutants lack most of the hair-like protrusions from their ventral cuticle and thus appear "naked".
Barry James Thompson is an Australian and British developmental biologist and cancer biologist. He is a professor of the John Curtin School of Medical Research at the Australian National University in Canberra. Thompson is known for identifying genes, proteins and mechanisms involved in epithelial polarity, morphogenesis and cell signaling via the Wnt and Hippo signaling pathways, which have key roles in human cancer.
Gary Struhl is an American research scientist whose primary areas of research are developmental biology and genetics and genomics. He works as a professor at Columbia University Medical Center, teaching neuroscience within the Department of Genetics and Development.
