Genes encoding putative bicarbonate transporters as a missing molecular link between molt and mineralization in crustaceans

Abstract

During their life, crustaceans undergo several molts, which if theoretically compared to the human body would be equivalent to replacing all bones at a single event. Such a dramatic repetitive event is coupled to unique molecular mechanisms of mineralization so far mostly unknown. Unlike human bone mineralized with calcium phosphate, the crustacean exoskeleton is mineralized mainly by calcium carbonate. Crustacean growth thus necessitates well-timed mobilization of bicarbonate to specific extracellular sites of biomineralization at distinct molt cycle stages. Here, by looking at the crayfish Cherax quadricarinatus at different molting stages, we suggest that the mechanisms of bicarbonate ion transport for mineralization in crustaceans involve the SLC4 family of transporters and that these proteins play a key role in the tight coupling between molt cycle events and mineral deposition. This discovery of putative bicarbonate transporters in a pancrustacean with functional genomic evidence from genes encoding the SLC4 family—mostly known for their role in pH control—is discussed in the context of the evolution of calcium carbonate biomineralization.

How Does Carbon Dioxide–Induced Acidification Affect Postecdysial Exoskeletal Mineralization in the Blue Crab (Callinectes sapidus)?

“…Calhoun & Zou (2016) proposed the existence of hypothetical bicarbonate transporters in both apical and basolateral membranes of epidermal cells in their mineralization model that explains the formation of carbonate salts in the hardening exoskeleton. Abehsera et al (2021) recently reported genes encoding putative bicarbonate transporters in the epidermis of the crayfish, Cherax quadricarinatus , with CqSLC4A1 presumably located in the apical membrane and CqSLC4A7 putatively residing in the basolateral membrane. Whether increased postecdysial mineralization in the exoskeleton following CO 2 treatment occurs concurrently with an elevated bicarbonate influx urgently needs to be investigated.…”

Molecular Identification of Anion Exchange Protein 3 in Pacific White Shrimp (Litopenaeus vannamei): mRNA Profiles for Tissues, Ontogeny, Molting, and Ovarian Development and Its Potential Role in Stress-Induced Gill Damage

“…In crustaceans, molting is a process for shedding the old exoskeleton that limits the growth of organisms ( Gao et al, 2015 ; Luo et al, 2015 ). The shrimp body may mineralized during the inter-molt stages ( Abehsera et al, 2021 ). After every ecdysis, the shrimp has shed the old shell and the new exoskeleton is still soft and flexible, and it needs to expand the new exoskeleton to make room for the growth of new tissues by absorbing water ( Chang, 1995 ).…”

The moulting arthropod: a complete genetic toolkit review

“…Ecdysis initiates the release of calcium biphosphate from gastroliths (Abehsera et al, 2018a). In the freshwater C. quadricarinatus, transportation of calcium salts to and from the gastrolith depends on two bicarbonate transporters from the SLC4 family distributed in the cuticular epithelium and in the gastrolith discs with different activation times (Abehsera et al, 2021). In this crayfish and in the prawn Penaeus japonicus, the deposition of calcium salts within the cuticle is probably mediated through CPs with chitin-binding and calcium-binding abilities such as the calcification-associated proteins (Ikeya et al, 2001;Roer et al, 2015).…”