Trafficking of bdelloid rotifer late embryogenesis abundant proteins.

The bdelloid rotifer Adineta ricciae is an asexual microinvertebrate that can survive desiccation by entering an ametabolic state known as anhydrobiosis. Two late embryogenesis abundant (LEA) proteins, ArLEA1A and ArLEA1B, have been hypothesized to contribute to desiccation tolerance in these organisms, since in vitro assays suggest that ArLEA1A and ArLEA1B stabilize desiccation-sensitive proteins and membranes, respectively. To examine their functions in vivo, it is important to analyse the cellular distribution of the bdelloid LEA proteins. Bioinformatics predicted their translocation into the endoplasmic reticulum (ER) via an N-terminal ER translocation signal and persistence in the same compartment via a variant C-terminal retention signal sequence ATEL. We assessed the localization of LEA proteins in bdelloids and in a mammalian cell model. The function of the N-terminal sequence of ArLEA1A and ArLEA1B in mediating ER translocation was verified, but our data showed that, unlike classical ER-retention signals, ATEL allows progression from the ER to the Golgi and limited secretion of the proteins into the extracellular medium. These results suggest that the N-terminal ER translocation signal and C-terminal ATEL sequence act together to regulate the distribution of rotifer LEA proteins within intracellular vesicular compartments, as well as the extracellular space. We speculate that this mechanism allows a small number of LEA proteins to offer protection to a large number of desiccation-sensitive molecules and structures both inside and outside cells in the bdelloid rotifer.