FIGURE 1. Generation of somatic variability in the immune and neural systems.

From the following article:

Generation of neuronal variability and complexity

Alysson R. Muotri & Fred H. Gage

Nature 441, 1087-1093(29 June 2006)



In the immune system, vast numbers of antibodies are generated by the V(D)J recombination system. In the nervous system, neuronal diversity is twice as high as the cellular diversity produced by the immune system. There is no single intrinsic mechanism that can explain such diversity, but rather a combination of several systems acting in different substrates (DNA, RNA or proteins) might be involved in neuronal differentiation. Finally, a dynamic diversity is generated by experience, correctly tuning neuronal wiring and generating diversity within subtypes of neuron. Contrary to the immune system, extrinsic factors can act directly on the intrinsic mechanisms of neuronal diversity and not only on selected cells. Moreover, intrinsic events that occur early during differentiation might only contribute to diversity in a more mature brain.