Differentiation is the process by which cells become ❌; it involves a sequence of molecular events that result in differential ❌, which, in turn, determines the ❌ that a cell will express.

Animal development involves a series of overlapping processes. ❌ divisions, which form the ❌, are followed by ❌, during which the three germ layers (ec❌, m❌ and en❌) are formed and
specification of the n❌ and the anterior–posterior axis take place. The neural tube forms during ❌, and body segmentation begins.
Finally ❌ and in some species, metamorphosis, occur.

❌ involves molecules that are evolutionarily conserved between animal species, and act in different places and at different times during ❌. These molecules include ❌, and a number of different secreted and cell surface ❌, their receptors and downstream intercellular signalling molecules. Differential exposure to signalling molecules results in ❌ of transcription factors, leading to ❌.

Differentiation is studied by cell a❌, cell t❌, transplantation, genetic analysis and cell culture techniques.

Similar mechanisms are involved in differentiation of different cells and tissues, of all animal species studied. These mechanisms include ❌, cell interactions, protein and mRNA ❌ and ❌ control.

Development of the cells of the nervous system involves a series of events, including neural ❌, ❌, patterning of the ❌, neuronal ❌, migration of ❌ and ❌.

In amphibians, neural induction involves inhibition of the action of BMP and Wnt proteins, by proteins that include ❌ and Frzb secreted by cells of the ❌.

Inhibition of ❌ in the presumptive ❌ cells results in ❌ of the transcription factor GATA-1 which drives ❌ differentiation, and activation of ❌, including neurogenin and NeuroD.

Increased expression of the cell surface signalling protein ❌ results in increased activation of its receptor, ❌, and also of ❌ in adjacent cells. This upregulation results in ❌ reciprocal signalling from the adjacent cell, which stimulates ❌ expression of neurogenin in the first cell, which in turn promotes expression of the transcription factor ❌, and subsequent ❌.

A dorso-ventral gradient in ❌ expression along the developing nervous system provides positional information, which results in the formation of different ❌ along the anterior–posterior axis of the brain and ❌.

Different types of ❌ are specified by expression of different ❌, induced by exposure to different levels of ❌, such as ❌ and BMPs.

❌ cells give rise to a variety of cell types, including ❌ and melanocytes. They arise from the neural tube, and undergo a transition from an ❌ to a mesenchymal state, which involves a change in expression of ❌ and other adhesion molecules. Neural crest cells ❌ though the developing embryo along routes that are determined by cell surface molecules, ephrins, and by components of the ❌.

The projections of growing axons are determined by ❌; both diffusible and ❌ signalling are involved. Proteins in the environment of the growing axon are detected by ❌ expressed on the ❌. Axons of ❌ neurons, which cross the developing spinal cord, are first attracted by ❌, and then their onwards trajectory is determined by ❌ signals from the proteins ❌ and semaphorin.

Differentiation occurs in some tissues throughout life. An example is that of ❌ epithelial cells, which form from a pool of ❌ in the intestinal ❌.

Adult ❌ exist in many ❌ tissues. Evidence suggests that their ❌ in vivo and in vitro may be broader than previously thought.

❌ stem cells are derived from the inner cell mass of mammalian ❌. They can be engineered in culture to produce specific cell types. They are ❌, and can differentiate into any kind of cell, unlike most ❌ stem cells which are only ❌, where they can differentiate into several different types of cell, but not all.

Some cells may be able to ❌, after injury in vivo , or as a result of manipulation in vitro. And then ❌ into another type of cell. An example is a newt regrowing a limb.

The ❌ of a nucleus from a fully or partially ❌ cell into an enucleated egg for the purpose of cloning requires ❌ of the genetic material. (And it usually doesn't work!)