In the tunicate Styela, immediately after fertilization, different colored cytoplasms become localized to specific parts of the embryo. Cells containing differently colored cytoplasm become determined to have a different fate. In particular, a yellow cytoplasm is segregated into a crescent just before the first cleavage. Cells that come to contain this cytoplasm become muscle. Keep [...]

Stem cells are undifferentiated cells able to take on various fates. They divide throughout the life of the organism, making more identical cells, providing precursor cells for a pathway of differentiation. Examples: blood-forming cells like erythroblasts; stem cells in gut; stem cells in nervous system; and spermatogonia. Induced pluripotent stem (iPS) cells are cells that [...]

Development The process by which a single cell (the zygote, a fertilized egg) cleaves and grows to a multicellular organism with: differentiated cells, tissues and organs; and an organized body plan. Development involves cell proliferation (growth) and progressive cell specification (differentiation). Embryogenesis Embryogenesis gives rise to the embryo by generating increasing complexity via differential gene [...]

Invertebrate Vertebrate Nematode Xenopus Drosophila Chicken Sea Urchin Zebrafish Mouse Different model organisms are used to study development, chosen for their: length of embryonic development: length of life cycle; size of organism; ease of lab growth; size of genome; number of chromosomes; and experimental techniques available for that organism. Embryos that develop internally are difficult [...]

The development of an entire organ can be triggered by a single regulatory protein. Regulatory proteins can be either activators or repressors of transcription. Controlling activity of regulatory proteins: protein synthesis; ligand binding; protein phosphorylation; addition of second subunit; unmasking. Regulatory genes are activated or inhibited by external signals (signal transduction). Synergy: the whole is [...]

In a morphogen gradient, different concentrations of a substance specify different cell fates. A morphogen can spread via: the extracellular matrix (ie, Dpp or BMP-4); vesicular transport; cytonemes (filopodia); or diffusion within a syncitial embryo (ie, bicoid or nanos). Drosophila In Drosophila the anterior and posterior systems establish morphogen gradients of bicoid and nanos protein [...]

An epithelium is an organized and polarized sheet of cells (the two sides are different). The apical surface of an epithelial sheet faces the so-called outside; the basal surface is bordered by an extracellular matrix called the basal lamina. Epithelial folding is microtubule-dependent. Epithelial cells are bound by tight junctions immediately beneath the apical surface. [...]

In homeotic transformation, a normal body part is replaced by a body part which is regularly found in other regions. Example Overview Antennapedia Antennapedia mutants of Drosophia have antennae replaced by legs. Ultrabithorax Ultrabithorax (Ubx) mutants of Drosophila have halteres (T3) replaced by wings (T2), imparting four total wings.

Many species have special factors which commit certain embryonic cells to the germline. Flies, nematode worm, frogs: germ cells inherit cytoplasmic determinants in the fertilized egg. Cytoplasmic determinants include RNA and protein. These factors, as well as evidence supporting their role, are described below. Granule Organism Overview Evidence P Granules Nematode P pranules, aka germ [...]

σ Factor Synonym Overview σ 32 RpoH Heat Shock σ Factor. σ E RpoE Extracytoplasmic σ factor. σ 54 RpoN Nitrogen responsive σ factor. σ S RpoS Stationary phase σ factor. The σ factor is a prokaryotic initiation factor that binds RNAP and promotes attachment to DNA promoter sites in response to significant environmental changes. [...]