Abstract 2330 Dynamic localization of the endoplasmic reticulum during conjugation in Tetrahymena thermophila

Cell-cell fusion is pivotal in various biological processes such as tissue development, fertilization, and homeostasis. In the ciliate, Tetrahymena thermophila, cell-cell fusion, known as conjugation, is crucial for nuclear exchange during sexual reproduction. Previous work has shown that lipid composition the conjugation junction between the membrane of mating cells, shifts from curvature resisting lipids to curvature accommodating lipids, yet the mechanism for this shift remains unclear. We proposed that lipid exchange proteins, which transfer lipids between adjacent membranes, might facilitate this shift. Our earlier studies employing serial-section transmission electron microscopy and three-dimensional (3D) electron tomography, suggested a possible interaction between a membrane continuous with the nuclear envelope and plasma membrane at the conjugation junction. We hypothesized that this membrane was likely the endoplasmic reticulum (ER) but did not confirm this. In the current study we wanted to determine if the endoplasmic reticulum indeed contacts the conjugation junction. To achieve this, we observed the ER during conjugation using two ER probes: reticulon-GFP and GFP-KDEL. Our findings demonstrate that both markers prominently label the clear periphery and extend into the cytoplasm, making contact with the plasma membrane at the conjugation junction. Additionally, we observed that the staining diminishes in nuclei destined for degradation. This study advances our understanding of the role of the ER in cell-cell fusion. The current work was supported by the John Hauck Foundation, the Student-Faculty Collaborative Research Fund, and the Rollins College Office of the Dean