A vesicular Na+/Ca2+ exchanger in coral calcifying cells

Abstract

The calcium carbonate skeletons of corals provide the underlying structure of coral reefs; however, the cellular mechanisms responsible for coral calcification remain poorly understood. In osteoblasts from vertebrate animals, a Na+/Ca2+ exchanger (NCX) present in the plasma membrane transports Ca2+ to the site of bone formation. The aims of this study were to establish whether NCX exists in corals and its localization within coral cells, which are essential first steps to investigate its potential involvement in calcification. Data mining identified genes encoding for NCX proteins in multiple coral species, a subset of which were more closely related to NCXs from vertebrates (NCXA). We cloned NCXA from Acropora yongei (AyNCXA), which, unexpectedly, contained a peptide signal that targets proteins to vesicles from the secretory pathway. AyNCXA subcellular localization was confirmed by heterologous expression of fluorescently tagged AyNCXA protein in sea urchin embryos, which localized together with known markers of intracellular vesicles. Finally, immunolabeling of coral tissues with specific antibodies revealed AyNCXA was present throughout coral tissue. AyNCXA was especially abundant in calcifying cells, where it exhibited a subcellular localization pattern consistent with intracellular vesicles. Altogether, our results demonstrate AyNCXA is present in vesicles in coral calcifying cells, where potential functions include intracellular Ca2+ homeostasis and Ca2+ transport to the growing skeleton as part of an intracellular calcification mechanism.

Dilution of Seawater Affects the Ca2 + Transport in the Outer Mantle Epithelium of Crassostrea gigas

“…In this study, we show that the NCX is expressed in the mantle tissue of C. gigas and could thus potentially participate in the Ca 2+ transporting mechanisms necessary for shell calcification. NCX, together with PMCA are proposed to participate in calcification in larval M. edulis (Ramesh et al, 2019) and coral Acropora yongei (Barron et al, 2018).…”

Mineral formation in the primary polyps of pocilloporoid corals

“…Currently, there is growing evidence supporting the biological controlled process [e.i., 8, 9–12], and the ongoing question is focusing on how the animal concentrates and transports the ions from the seawater to the site of calcification. Is it by the transcellular pathways through the cells, with calcium channels [12, 13], PMCA (P-type calcium ATPase) [14] or vesicles [10, 15]? Or by the paracellular pathways between the cells [16], or possibly it is a combination of the two [9].…”

Modes of Calcium Regulation in Ischemic Neuron

“…In contrast, after milder episodes of cerebral ischemia, which normally results in neuronal recovery of delayed neuronal death, the NCX operates in calcium exit mode in an attempt to restore calcium homeostasis. At this point, proteolytic inactivation of NCX3 has been elaborated which occur following cerebral ischemia, rendering the channel inactive and resulting in reduced calcium efflux, contributing to calcium dysregulation and cell death [28].…”