Arrest of postsynaptic maturation in Lama4^−/−;Lama5^M/M mice. (A) NMJs from Lama4^−/−;Lama5^M/M mice at P36 lack laminins α4 and α5 but retain laminin β2. (B) Most postsynaptic sites retained a simple plaque-like topology and remained only partially occupied by nerve terminals in Lama4^−/−;Lama5^M/M mice at P60. (C) NMJs from Lama4^−/−;Lama5^M/M mice at P36 retained acetylcholinesterase (AChE). Bars, 10 μm. (D and E) Quantification of topological maturation of AChR clusters (D) and completeness of innervation of AChR clusters (E) in control (open circles), Lama4^−/− (closed circles), and Lama4^−/−;Lama5^M/M mice (closed triangles). Counts are from two animals per age, >40 NMJs per animal.