LET-2 is the more abundant type IV collagen α-chain. (A) Boxplots display the mRuby2 abundance represented by the log₂ protein intensity (a.u.) determined using LC-MS/MS. The samples displayed are the larval matrix fractions of Strain 1 (EMB-9::mRuby2 [C]; LET-2::mNG [C]) and Strain 2 (EMB-9-mNG [C]; LET-2::mRuby2 [C]). The log₂ fold change from the comparison between strains is listed above the graph. mRuby2 (LET-2) was ∼2 times more abundant in Strain 2 than mRuby2 (EMB-9) in Strain 1 (n = 5 samples for each strain, P < 0.0001, unpaired two-tailed Student’s t test). (B) Schematic demonstrates trimerization of C. elegans EMB-9 and LET-2 α-chains in the ER prior to secretion into the BM. (C) Schematic showing possible types of collagen IV trimers and the LET-2/EMB-9 ratios expected for each timer type. Mass spectrometry on whole animals suggests a preference for the LLE trimer type but does not rule out different trimers being made and localized to the BM.