Ultrastructural analysis of the dehydrated tardigrade Hypsibius exemplaris unveils an anhydrobiotic-specific architecture

Myriam Richaud (1) , Emilie Le Goff (2) , Chantal Cazevielle (3) , Fumihisa Ono (4) , Yoshihisa Mori (4) , Naurang L Saini (5) , Pierre Cuq (1) , Stephen Baghdiguian (2) , Nelly Godefroy (2) , Simon Galas (1)

1 IBMM - Institut des Biomolécules Max Mousseron [Pôle Chimie Balard]
2 UMR ISEM - Institut des Sciences de l'Evolution de Montpellier
3 INM - Institut des Neurosciences de Montpellier
4 Okayama University of Science
5 UNIROMA - Università degli Studi di Roma "La Sapienza" = Sapienza University [Rome]

Tardigrades can cope with adverse environmental conditions by turning into anhydrobiotes with a characteristic tun shape. Tun formation is an essential morphological adaptation for tardigrade entry into the anhydrobiotic state. The tun cell structure and ultrastructure have rarely been explored in tardigrades in general and never in Hypsibius exemplaris. We used transmission electron microscopy to compare cellular organization and ultrastructures between hydrated and anhydrobiotic H. exemplaris. Despite a globally similar cell organelle structure and a number of cells not significantly different between hydrated and desiccated tardigrades, reductions in the sizes of both cells and mitochondria were detected in dehydrated animals. Moreover, in anhydrobiotes, secretory active cells with a dense endoplasmic reticulum network were observed. Interestingly, these anhydrobiote-specific cells are in a close relationship with a specific extracellular structure surrounding each cell. It is possible that this rampart-like extracellular structure resulted from the accumulation of anhydrobiotic-specific material to protect the cells. Interestingly, after five hours of rehydration, the number of secretory cells decreased, and the specific extracellular structure began to disappear. Twenty-four hours after the beginning of rehydration, the cellular structure and ultrastructure were comparable to those observed in hydrated tardigrades.

Domaines: Zoologie des invertébrés; Organisation et fonctions cellulaires [q-bio.SC]

Myriam Richaud, Emilie Le Goff, Chantal Cazevielle, Fumihisa Ono, Yoshihisa Mori, et al.. Ultrastructural analysis of the dehydrated tardigrade Hypsibius exemplaris unveils an anhydrobiotic-specific architecture. Scientific Reports, 2020, 10 (1), pp.4324. ⟨10.1038/s41598-020-61165-1⟩. ⟨inserm-02509447⟩