Ultrastructural diversity of mitochondrial morphology and its remodeling by PCAF inhibition in porcine blastocysts

Background: Mitochondrial morphological homeostasis is essential for energy production and developmental competence in preimplantation embryos.While epigenetic modifications, particularly histone acetylation, are primarily recognized as regulators of gene transcription, accumulating evidence suggests that acetylation-dependent signaling also governs mitochondrial biogenesis and quality control.However, how PCAF-mediated acetyltransferase activity specifically modulates mitochondrial morphology during early embryonic development remains unknown.Methods: Porcine parthenogenetic embryos were cultured for seven days in PZM-5 medium.Garcinol (5 μM) was applied from the 4-cell stage to inhibit PCAF activity, and mitochondrial ultrastructure was assessed by transmission electron microscopy using a Bio-HVEM system.Results: Ultrastructural analysis of porcine blastocysts revealed morphologically diverse mitochondrial populations, encompassing spherical, hooded, cap-shaped, ringshaped, horseshoe-shaped, elongated, and shell-like configurations.Mitochondrial fusion predominantly occurred in a side-to-side orientation, with tip-to-tip and side-totip contacts observed less frequently, and these combinatorial fusion states collectively contributed to the morphological heterogeneity of the organelle pool.PCAF inhibition disrupted this dynamic equilibrium, inducing aberrant fusion events and the formation of hyperfused clusters containing three or more organelles.Concurrently, mitochondriaderived vesicles, mitochondrial multivesicular body-like structures, and mitophagyassociated autophagy were increased throughout the cytoplasm, reflecting quality-control responses to mitochondrial damage.Conclusions: Collectively, these findings highlight that PCAF-mediated acetyltransferase activity is required for mitochondrial morphostasis, and that its suppression disrupts the fission-fusion balance while activating compensatory quality control responses.These results provide new insight into how epigenetic acetylation signaling is functionally coupled to mitochondrial structural integrity during early embryonic development.