THG signal changes in a stage and region specific manner. (A - F) Optical sections. (A' - E' and F'') Opacity rendered 3D views. (F') Extended focus maximum intensity projection. (A - C) Up to the morula stage, THG signal is predominantly from LD which are uniformly distributed throughout the embryo and polar body (arrowheads in A and B). Nucleoli also generate faint THG signal (arrows in A and B). (D) In blastocysts, LD are fewer in number and present in both the ICM (arrow) and TE. Plasma membrane starts to generate more distinct THG signal, visible more clearly in the volume rendering in D'. (E) In the implantation stage embryo, LD are mostly localised to the mural TE (green arrowheads). Plasma membrane is faintly visible and the primitive endoderm (magenta arrow) can be discerned from the epiblast (magenta arrowhead). The blastocoel cavity is marked by an asterisk in (D) and (E). (F) At post-implantation stages, LD are more abundant in the ectoplacental cone (arrowhead in F') and in the distal regions of the egg cylinder (vertical line in F'). Plasma membrane signal becomes more distinct, but is not uniform throughout the embryo, being strongest in the basolateral aspect of the VE (arrows). Nuclei are also now visible, but only in the ExE (arrowhead in F). (G) LD size distribution at different embryonic stages. The distribution shifts towards larger LD as the embryo develops. The inset shows mean LD number at the different stages (n = 4 for all stages except for the 2 cell stage where n = 3). Scale bar in (A) represents 20 μm for (A and C), 30 μm for (B), 32.6 μm for (D), 27.6 μm for (E) and 113.5 μm for (F).