Table 1.

Quantification of agrin-induced clustering of CD4-subunit loops and β loop fragments

CD4-chimera	No. of experiments	No. of myotubes counted	% myotubes with clusters
CD4	5	80	1
CD4−
α loop	5	88	0
β loop	6	94	73
γ loop	3	57	0
δ loop	5	63	3
ε loop	5	75	0
β333–406	6	117	74
β407–469	5	84	2
β333–406/ε	6	111	77
β370–406	3	60	45
β loop Y390F	6	100	1
β333–406 Y390F	3	57	2
β333–406/ε Y390F	3	53	0
β370–406 Y390F	3	60	3
CD4ct−
β382–401	3	60	88
β382–401 Y390F	3	60	15
β385–396	3	60	5
δ385–404	3	60	22

CD4-chimera-positive myotubes were identified in random fields and scored for the presence or absence of CD4 clusters that colocalized with AChR clusters. Agrin induced robust clustering of CD4-β loop chimeras encompassing amino acids 382–401, with 45–88% of the expressing myotubes having clusters. Mutation of Y390 abolished clustering of these constructs, and all other CD4-loops showed background or weak colocalization with AChR clusters.