FGF2 and cyst: Neither control nor experimental mammary epithelia, including both Spry2Δ/Δ and Spry2-GOF epithelia, invaded toward beads pre-soaked in bovine serum albumin (BSA) (Fig. 5G–J) or beads soaked in FGF2, which stimulate cyst formation (not shown), during the 72-hour time course.