RAC1 and cyst: However, epidermal growth factor receptor (EGFR) pathway signaling activities in CySCs of the belKD testes were indistinguishable from those in the control testes, as revealed by the intensity of signals of the phosphorylated form of MAP kinase ERK, pERK, and of small GTPase Rac1, despite the fact that disruption of the EGFR pathway has been shown to exhibit a testis phenotype [60,61,62] similar to belKD in cyst cells.