Complete deletion of major class IA PI3K regulatory subunits causes greatly reduced expression of catalytic isoforms. (A) Immunoblot analysis of catalytic and regulatory isoform expression in purified T cells from r1f/r2n (Cre⁻) mice or r1ΔT/r2n (Cre⁺) mice. p55γ could only be detected in the Cre⁺ lysates using high-sensitivity enhanced chemiluminescence (ECL) reagents (Pierce SuperSignal Femto ECL kit). Data are representative of 4 sets of littermates. (B) Intracellular detection of p85α in T cells of Cre⁻ or Cre⁺ mice. Fluorescent staining was also observed in T cells from p85α-null (Pik3r1^tm1) mice²⁴  and is likely due to cross-reacting proteins, because this antibody detects one other strong band on immunoblots (data not shown). Data are representative of 4 sets of littermates.