Strain- and lineage-specific regulation of lipid droplet metabolism in the mouse blastocyst†.

Lipid droplets (LDs) are multifunctional organelles that serve as reservoirs of fatty acids, and act as substrates for β-oxidation and ATP synthesis during mammalian preimplantation development. However, the genetic and lineage-specific regulation of their biogenesis and utilization remains poorly understood. Here, we report a mouse model of embryonic LD deficiency, the BTBR T+  Itpr3tf/J inbred strain, characterized by the absence of oocyte-inherited LD clusters in zygotes and a rapid depletion of de novo generated LDs at the morula-to-blastocyst transition stage, as compared to C57BL/6J controls. Lineage-resolved analyses revealed a selective depletion of large LDs in the trophectoderm while lipids were consistently accumulated in the inner cell mass, indicating lineage-specific lipid utilization. Pharmacological inhibition of autophagy or cytoplasmic lipase activity caused LD accumulation and developmental arrest specifically in BTBR, indicating an essential dependence on lipid mobilization. Modulation of mitochondrial fatty acid β-oxidation by etomoxir inhibition and L-carnitine stimulation shifted lipid droplet enlargement and allocation between lineages in a strain-specific manner, and altered epiblast cell numbers, linking lipid catabolism to lineage fitness. These findings identify a genetically encoded, lineage-specific LD program linking lipid mobilization to blastocyst morphogenesis, embryonic survival, and lineage homeostasis.