Growth factors classes

Cytokine receptors are a group of structurally related receptors, which couple to the JAK-STAT pathway. Cytokine receptors function as homodimers or heterooligomers. They are divided into two main subclasses, class I, which contains receptors for a variety of hematopoietic growth factors and interleukins and class II, which contains receptors for interferons and interleukins 10, 20/24 and 22. 

Immunoglobulins A, E, G, M IgG I Immunc obulin G class 1 IgGa, Immunoglobulin G class 2a IGF-I Insulin-like growth factor Ig-SF Immunoglobulin supergene family... 

CLASSES OF GROWTH FACTORS ACTING IN THE NERVOUS SYSTEM 473... 

The neurotrophins interact with two distinct cell surface receptor species [5,6,9] (Fig. 27-2). The neurotrophins bind to the Trk family of receptors, which serve as the principal signal transducer for this class of growth factors. The Trk receptors comprise a small, highly related family of molecules that possess an extracellular ligand binding domain that selectively interacts with the individual neurotrophin species. Trk A specifically binds NGF, TrkB interacts with BDNF and NT4/5, and TrkC preferentially binds NT3. Importantly, the Trk receptors have an intracellular tyrosine kinase domain that is activated upon neurotrophin binding. The kinase domains of the Trk family members are highly conserved and the Trks differ mainly in the structure of their extracellular domains. Trk receptor expression is limited to neurons and the... 

Motor neurons provide a compelling example of how a single class of neurons can be supported by an extraordinarily wide range of factors. More than 15 growth factors have been shown in vitro or in vivo to sustain these cells. Some of these are derived from the muscle target, while others are elaborated by ensheathing Schwann cells and by cells resident within the spinal cord. It is likely that motor neurons rely upon multiple factors for their survival and different subpopulations of motor neurons may exhibit unique combinations of trophic factor dependence [4]. 

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