Whole-mount in situ hybridization: Minimizing the folding problem of thin-sheet tissue-like crayfish haematopoietic tissue

Crayfish haematopoietic tissue (HPT) has a thin-sheet-like structure with a thickness of 100- 160 μm and a width of approximately 1-2 cm. This structure makes HPT extremely easy to fold after removal from the animal. Therefore, it is difficult to handle the tissue without folding when processing for sectioning and histological study. The degree of tissue folding reflects the size of the tissue sections obtained, how complicated it is to interpret the location of each tissue section, and the accuracy of the interpretation of the location of a specific transcript. To facilitate the interpretation of a specific transcript location in the HPT, we optimized a whole-mount in situ hybridization technique to minimize tissue folding. This optimized protocol effectively reduced the tissue folding. Therefore, the location of a specific transcript in the HPT was easily and accurately defined. This protocol will be useful for whole-mount staining of other tissues with similar structure.