Cathepsin D localization and processing in wild-type and homozygous Cb Cln3Δex7/8 cells a. Immunostaining of wild-type and homozygous CbCln3Δex7/8 precursor cells with anti-cathepsin D antibody, recognizing unprocessed and processed forms of cathepsin D protein is shown. CbCln3+/+ cells (left panel) exhibited a perinuclear and cytoplasmic punctate signal. Cathepsin D signal in homozygous CbCln3Δex7/8 cells (right panel) was more often perinuclear, with less cytoplasmic punctate signal, compared to wild-type CbCln3+/+ cells. 40 × magnification. b. α-Cathepsin D-probed immunoblots of total wild-type versus homozygous Cln3Δex7/8 knock-in tissue or CbCln3Δex7/8 cellular extracts are shown. The ~45 kDa cathepsin D band, representing precursor, was the predominant band in wild-type (wt) tissue and cellular extracts, with lower levels of mature enzyme (single chain, ~43 kDa, and heavy chain, ~31 kDa). Conversely, homozygous Cln3Δex7/8 and CbCln3Δex7/8 mutant (m) extracts exhibited reduced levels of precursor and heavy chain of the double-chain form of the enzyme, with elevated levels of single-chain mature enzyme.