FIG 5.

RTK/MAPK signaling circuitry. The receptor tyrosine kinase (RTK)/mitogen-activated protein kinase (MAPK) signaling pathway is represented as a circuit diagram, whereby RTKs are represented as parallel arranged power sources (green batteries) that transmit signal (e.g., electricity) downstream through functionally redundant paralogs, represented as parallel switches. (A) The loss of one paralog (single switch) still permits downstream signaling (MAPK signaling is represented as a lamp). (B) SHOC2 functions as a critical point of passage for RTK signal transduction to the MAPK pathway due to a lack of functionally redundant paralogs. The loss of SHOC2 alone is sufficient to abrogate the activation of the MAPK pathway.