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Fig. 4. Deficiency of {alpha}1(IV)/{alpha}2(IV) collagen is not compensated by the increased expression of other collagen IV chains. (A) Relative mRNA levels of collagen IV isoforms ({alpha}3-{alpha}6), laminin {alpha}1 chain (Ln-{alpha}1) and nidogen-1 (Nd-1) were determined by quantitative RT-PCR in RNA isolated from individual wild-type (white bars) and {alpha}1(IV)/{alpha}2(IV)-deficient embryos (black bars) from E9.5 and E10.5 littermates. The {alpha}3(IV), {alpha}4(IV) and {alpha}6(IV) mRNAs are not detectable or are present at only very low levels in any genotype. In mutant embryos no compensatory upregulation of {alpha}5(IV), laminin {alpha}1 chain and nidogen-1 is observed. Relative mRNA levels are expressed as a percentage of GAPDH expression. (B) No deposition of {alpha}5(IV) protein is observed by immunofluorescence in the Reichert's membrane of normal (+/+) or mutant embryos (–/–) at E10.5. A faint intracellular staining in trophoblast cells indicates the expression of low levels of non-secreted {alpha}5(IV) protein. Antibodies detecting laminins containing the {alpha}1, ß1 or {gamma}1 chains and {alpha}2(IV) collagen were used as positive controls. Scale bar: 10 µm.