The tardigrade cuticle

Abstract

Tardigrades (phylum Tardigrada) are aquatic microecdysozoans that have adapted to survive extreme conditions through the formation of cysts or ametabolic tuns. Their body is covered by a cuticle that plays an important role in their life cycle, including their response and adaptation to environmental challenges. Cuticular characteristics are a critical component of tardigrade taxonomy. Therefore, research has often been focused on the relationship between cuticular morphology and ultrastructure and the evolutionary and phylogenetic positioning of the phylum and individual species herein. However, a deeper insight into the ultrastructural characteristics and chemical composition of the tardigrade cuticle is needed. This knowledge is important not only for a better understanding of tardigrade physiology and ecology but also for the development of efficient microinjection and/or electroporation techniques that would allow for genetic manipulation, opening new avenues in tardigrade research. Here, we review data on cuticle ultrastructure and chemical composition. Further, we discuss how the cuticle is affected during moulting, encystment, cyclomorphosis, and anhydrobiosis. Our work indicates that more systematic studies on the molecular composition of the tardigrade cuticle and on the process of its formation are needed to improve our understanding of its properties and functions.

Diversity in Expression Biases of Lineage-Specific Genes During Development and Anhydrobiosis Among Tardigrade Species

“…Chitin involved in tardigrade cuticle formation, remodeling and the molting cycle. 40 Interestingly, genes associated with chitin-binding functions were also enriched among tardigrade-specific gene (TSG) expansions, as defined as genes with more paralogs than the combined number of orthologs in all 3 non-tardigrade outgroup species. The expansion of gene families coding for proteins with chitin binding properties in tardigrades might have evolved to help regulate physiological responses to environmental stresses.…”

External and internal microbiomes of Antarctic nematodes are distinct, but more similar to each other than the surrounding environment

“…As the two nematodes are comprised of similar cuticle physical structure, there may be other host-specific interactions occurring. As part of the secretory and excretory system, pores exist in the cuticle of nematodes (Bird and Bird, 1991 ) and tardigrades ( Schill, 2018 ; Czerneková and Vinopal, 2021 ) that produce secretions and other organic molecules. The functions of these compounds are mostly unknown, but in nematodes, these secretions produce a surface coat (i.e., glycocalyx) that is involved in protection against fungal pathogens ( Blaxter et al, 1992 ).…”

“…Nematodes also actively disseminate bacteria through the soil matrix, but it is unclear if this spread occurs through defecation or from shedding of bacteria attached to the cuticle ( Anderson et al, 2003 ). In comparison, tardigrades have 8 legs, each terminating in four to six claws, providing even more surficial space for microbes ( Schill 2018 ; Czerneková and Vinopal 2021 ). Through scanning electron microscopy (SEM) and FISH, bacteria have been observed on the cuticle of nematodes and tardigrades ( Bellec et al, 2018 ; Guidetti et al, 2019 ), but it is unclear if this represents a cohesive and functioning community or random microorganisms.…”

Storage cell proliferation during somatic growth establishes that tardigrades are not eutelic organisms

“…This clade is characterized by the presence of an exoskeleton or a cuticle, which acts as a protection for their bodies (1). Tardigrades’ cuticle plays pivotal roles in their life cycle, enabling them to respond and adapt to diverse environmental challenges (2). Like other ecdysozoans, tardigrades must undergo a process called ecdysis ( i.e., molting), which involves producing a new cuticle and shedding the old one (known as exuvium), in order to grow in size (1, 2).…”