High-resolution episcopic microscopy: a rapid technique for high detailed 3D analysis of gene activity in the context of tissue architecture and morphology.

We describe a new methodology for rapid 2D and 3D computer analysis and visualisation of gene expression and gene product pattern in the context of anatomy and tissue architecture. It is based on episcopic imaging of embryos and tissue samples, as they are physically sectioned, thereby producing inherently aligned digital image series and volume data sets, which immediately permit the generation of 3D computer representations. The technique uses resin as embedding medium, eosin for unspecific tissue staining, and colour reactions (beta-galactosidase/Xgal or BCIP/NBT) for specific labelling of gene activity and mRNA pattern. We tested the potential of the method for producing high-resolution volume data sets of adult human and porcine tissue samples and of specifically and unspecifically stained mouse, chick, quail, frog, and zebrafish embryos. The quality of the episcopic images resembles the quality of digital images of true histological sections with respect to resolution and contrast. Specifically labelled structures can be extracted using simple thresholding algorithms. Thus, the method is capable of quickly and precisely detecting molecular signals simultaneously with anatomical details and tissue architecture. It has no tissue restrictions and can be applied for analysis of human tissue samples as well as for analysis of all developmental stages of embryos of a wide variety of biomedically relevant species.