Cellular mechanisms of carbon concentration and pH regulation in the calcifying cells of the sea urchin (Strongylocentrotus purpuratus) larva

• Main Author: Matt, Ann-Sophie
• Other Authors: Hu, Marian Yong-An, Roeder, Thomas
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Christian-Albrechts-Universität zu Kiel 2024
• Subjects: thesis; ddc:590; biomineralziation; intracellular pH; ocean acidification; metabolic CO2; proton channel; sea urchin larva; carbonic anhydrase; aquaglyceroporin; skeletogenesis; Ocean acidification
• Online Access: https://nbn-resolving.org/urn:nbn:de:gbv:8:3-2024-00865-9; https://macau.uni-kiel.de/receive/macau_mods_00005162; https://macau.uni-kiel.de/servlets/MCRFileNodeServlet/macau_derivate_00006509/Dissertation_Ann-SophieMatt_2024.pdf

Biomineralization is an ancient evolutionary process that enables various organisms to harden their tissues for protection and support. In marine ecosystems, many species produce calcium carbonate (CaCO3) minerals, like calcite and aragonite, for their skeletons and shells. This calcification process involves acquiring calcium ions and dissolved inorganic carbon (DIC), and regulating pH to facilitate CaCO3 formation. While researchers have long been interested in calcification, the cellular mechanisms remain poorly understood, especially given the current challenges of climate change and ocean acidification (OA), which threaten these processes. This study focuses on the cellular carbon concentration mechanism (CCM) in calcifying primary mesenchyme cells (PMCs) of sea urchin larvae. Using molecular techniques, it identifies two key carbonic anhydrases (CAs)—cytosolic (iCA) and extracellular membrane-bound (eCA)—in PMCs, which show dynamic expression during re-mineralization. Experiments reveal that eCA, specifically Cara7, plays a crucial role in the CCM by facilitating the extracellular hydration of CO2 and HCO3- uptake, crucial for maintaining pH balance during calcification. Additionally, the study discovers a proton channel, Otop2l, also expressed in PMCs, that exports H+, which accrue during the calcification process and regulates intracellular pH in a way that is sensitive to oceanic pH conditions. This proton channel could be vulnerable to OA, potentially making calcification more energy-intensive under such conditions. Furthermore, the study identifies the aquaglyceroporin spAQP9, acting as a dual H2O and CO2 channel in PMCs, crucial for skeletogenesis.