A SLC4 family bicarbonate transporter is critical for intracellular pH regulation and biomineralization in sea urchin embryos

Abstract

Efficient pH regulation is a fundamental requisite of all calcifying systems in animals and plants but with the underlying pH regulatory mechanisms remaining largely unknown. Using the sea urchin larva, this work identified the SLC4 HCO₃^- transporter family member <i>SpSlc4a10</i> to be critically involved in the formation of an elaborate calcitic endoskeleton. <i>SpSlc4a10</i> is specifically expressed by calcifying primary mesenchyme cells with peak expression during de novo formation of the skeleton. Knock-down of <i>SpSlc4a10</i> led to pH regulatory defects accompanied by decreased calcification rates and skeleton deformations. Reductions in seawater pH, resembling ocean acidification scenarios, led to an increase in <i>SpSlc4a10</i> expression suggesting a compensatory mechanism in place to maintain calcification rates. We propose a first pH regulatory and HCO₃^- concentrating mechanism that is fundamentally linked to the biological precipitation of CaCO₃. This knowledge will help understanding biomineralization strategies in animals and their interaction with a changing environment.