Fig 2: Diminished chromogranin A (ChrgA) levels in ß-neurexins- (ß-Nrxns-) deficient hippocampal neurons. (A) Primary hippocampal neurons from floxed ß-Nrxn knock-in (ß-KI) mice were transduced with lentivirus expressing inactive Cre recombinase (Cremut) and immunostained at DIV18 with anti-ChrgA (A1) and anti-neurofilament H (NFH, A2). Merged image (A3) shows the presence of the dense-core vesicle (DCV) marker ChrgA in axons. Scale bar: 3 µm. (B,C) Cultured neurons as in panel (A) but colabeled for ChrgA (B1,C1) and the dendritic marker MAP2 (B2,C2). Successful transduction of neurons with lentivirus is demonstrated by nuclear expression of inactive Cremut or active Cre recombinase (Cre) fused to GFP (B3,C3). Merged images (B4,C4) show the exclusion of ChrgA (arrows) from MAP-positive dendrites (arrowheads) independent of the presence of ß-Nrxn. Scale bars: 20 µm. (D) Representative images of ChrgA-positive axons of Cremut control (D1) and Cre transduced conditional knockout (cKO) (D2) neurons from experiments as in panel (A) that were used for measurements of fluorescence intensity (yellow boxes). Note that the fluorescence intensity appears to be overall reduced in ß-Nrxn-deficient axons with no change in the labeling pattern and without apparent ectopic accumulation. Scale bar: 4 µm. (E) Histogram comparing the ChrgA fluorescence intensity over axons from Cremut control (black bars) and ß-Nrxn-deficient Cre neurons (red bars) as shown in panel (D). Intensities (AU = arbitrary units) were normalized to control values. Data are shown as mean ± SEM, measurements are based on n = 15 axonal regions from the three independent cultures per genotype; significance difference indicated as **p < 0.01, two-tailed unpaired t-test.