Figure 13. Proprioceptive feedback and mouse genetics.

A) Selective removal of muscle spindles in Egr3-KO mice occurs through loss of neurotrophin 3 (NT3) expression in the muscle spindles resulting in their degeneration postnatally. B) Proprioceptive afferent neurons are selectively removed by making them selectively express the highly toxic DTA using the calcium binding protein Parvalbumin (Pv) and the transcription factor Isl2, both genes collectively expressed in proprioceptive afferents only. C) Alternatively, proprioceptive afferent neurons can be made susceptible to the diphtheria toxin (DTX) by making them express the gene that encodes the diphtheria toxin receptor (DTR), normally not expressed in mice. In these mice, systemic injection of DTX results in acute removal of the proprioceptors. D) The gene that encodes the DTR in a cre-dependent manner can be postnatally delivered via adeno associated virus (AAV) injections into selected muscles. Later, as in C, proprioceptive afferents only from the AAV injected muscles can be destroyed by systemic injection of DTX.