# The Role of Membrane-Bound Extracellular Vesicles During Co-Stimulation and Conjugation in the Ciliate Tetrahymena thermophila

## TL;DR

This paper explores how membrane-bound vesicles in the ciliate Tetrahymena thermophila help facilitate mating during sexual reproduction.

## Contribution

The study identifies specific roles for extracellular vesicles in mating and conjugation in Tetrahymena thermophila.

## Key findings

- 100 nm ciliary extracellular micro-vesicles (cEMVs) promote mating between complementary mating types.
- Smaller 60 nm junction vesicles (jEMVs) appear during mating junction formation and may aid in junction remodeling.
- Endocytosis is necessary for cells to internalize signals and trigger conjugation.

## Abstract

During sexual reproduction, the freshwater ciliate Tetrahymena thermophila sheds membrane-bound vesicles into the extracellular environment (cEMVs: ciliary extracellular micro-vesicles). We provide evidence that 100 nm vesicles shed from the cilia of starved cells promote mating between cells of complementary mating types. A proteomic analysis revealed that these EMVs are decorated with mating-type proteins expressed from the MAT locus, proteins that define a cell’s sex (one of seven). Once the mating junction is established between cells, smaller 60 nm vesicles (junction vesicles) appear within the extracellular gap that separates mating partners. Junction vesicles (jEMVs) may play a role in remodeling the mating junction through which gametic pronuclei are exchanged. Evidence is presented demonstrating that cells must be able to internalize extracellular signals via some form of endocytosis in order to trigger conjugation. Finally, an evolutionarily conserved fusogen (Hap2) implicated in pore formation also appears necessary for jEMV processing. This system offers an excellent opportunity for studies on ectosome shedding, intercellular signaling and shed vesicle uptake by macro-pinocytosis, as they relate to sexual reproduction in the ciliate Tetrahymena thermophila.