Histological cut of a paraffin-embedded blastocyst: Optimized protocol for murine blastocysts

Abstract

Paraffin-embedded tissues have been used for research and therapeutic applications for decades, as they represent a valuable tool in histology and for molecular analysis, as well as being a way to preserve tissue samples for long periods at a low cost. For tissues such as the liver, lungs, kidney, heart or brain, there are many protocols available, already optimized. The purpose of this work is to optimize and simplify the protocols already available to take a single blastocyst from a mouse, fix it and embed it into a paraffin block without using gelatin, to then perform histological cuts using a microtome, with no need of sophisticated equipment or trained personnel. •The protocol presented here preserves well the morphology of the blastocyst.•Paraffin-embedded sections of the sample can be used for studies such as in situ hybridization, immunohistochemistry, enzyme histochemistry, DNA, RNA or protein extractions, analysis of biomarkers, characterization of surface markers of stem cells integrated into the embryo, to prepare histological material for educational purposes, etc.•Some of these studies could represent a valuable source of new information for the field of reproductive biology.

Keywords: Assisted reproduction; Blastocyst; Histology; Mice; Paraffin.

Graphical abstract

Fig. 1

Slide with a few drops of eosin, in which the blastocyst was stained for 15 s.

Fig. 2

Paraffin dispenser and embedding mold.

Fig. 3

Water bath set at 35 °C to stretch the paraffin sections.

Fig. 4

Histological cuts of various paraffin-embedded blastocysts. A. Histological cut of a blastocyst with the morphology of the trophoblast well preserved. B. Histological cut of a blastocyst in which part of the trophoblast was well preserved, but half of it appears folded. C, D. Histological cuts of a blastocyst in which the cells of the trophoblast cannot be properly visualized.

Fig. 5

Histological cuts of various paraffin-embedded blastocysts. A, B, D. Cells of part of the trophoblast of the blastocyst. C. Whole blastocyst folded onto itself. E. Histological cut of a blastocyst with the morphology of the trophoblast well preserved, but poorly stained, due to an insufficient time of staining. F. Disaggregation of cells of the blastocyst, probably caused by the microtome when the cut is performed.