Permount sp15 500

Animals were perfused with 4% PFA in PBS. The brains were isolated and post-fixed overnight. The brains were then cryo-protected in 30% sucrose in PBS and serially cross-sectioned into 40-μm sections using Cryostat (Leica). The brain sections were dipped in a Nissl stain solution, 1% w/v Cresyl Violet (C5042, Sigma-Aldrich, Missouri, United states) and 1% v/v glacial acetic acid at 50 °C for 5 to 10 min. After a wash with distilled water, the tissues were differentiated in ethyl alcohol for 10 to 20 min. The dehydrated tissues were cleared in xylene and mounted with Permount (SP15-500, Thermo Fisher Scientific, Massachusetts, United States). The images of the sections were taken using a slide-scanner (Axio scan Z1, Zeiss).
See the Supplementary Information for details on the generation of the polyclonal anti-FAM19A1 antibody, western blot analysis, reverse transcription PCR^{61 (link)}, in situ hybridization, body weight measurement, whole-brain size measurement, cerebral cortex analysis with unbiased stereology⁶² , cortical thickness measurement^{62 ,63 (link)} and neuronal and glial cell density analysis^{62 ,63 (link)}.

Tissue samples were fixed in 10% formalin and embedded in paraffin, and the sections were deparaffinized with xylene and rehydrated in a graded series of ethanol. The slides were then stained with hematoxylin and washed with water. After counterstaining with eosin, the slides were dehydrated in alcohol and cleared in xylene.
For IHC, pancreatic FFPE sections were immunostained with antibodies to cytokeratin 19 (CK19, 1:100), pSmad2 (1:100), anti-Muc5Ac (1:100), Sox9 (1:100), insulin (1:100), CD31 (1:100), or JunB (1:100). The slides were then washed, incubated with the appropriate secondary antibody conjugated with peroxidase, and revealed by DAB using standard techniques.
For both pancreas histology and IHC, the slides were mounted using Permount (SP15-500; Thermo Fisher Scientific), viewed on a bright-field microscope (Nikon Eclipse 80i), and the images were captured with Nis Elements BR 3.2 64 bit.