In:
eLife, eLife Sciences Publications, Ltd, Vol. 7 ( 2018-05-01)
Abstract:
Many marine organisms such as mussels, sea urchins or corals, have skeletons and shells, which – due to their beautiful colors and shapes – are often desirable collector pieces. These structures are made from calcium and carbonate ions that react to form calcium carbonate crystals in a process known as biomineralization. In sea urchin larvae, for example, the skeleton is built by so-called primary mesenchyme cells, which work similar to the bone forming cells in mammals. These mesenchyme cells use calcium from the sea water, which travels to the site where the shell starts to form. About half of the carbonate comes from carbon dioxide that the animals make as they breathe, but it is not known how the other half gets to the site of biomineralization. Producing a skeleton generates acid, and marine animals need to be able to regulate their pH levels, as too acidic environments can dissolve the calcium carbonate and threatening to destroy the developing shell. How cells accumulate enough carbonate to make their shells, and how they cope with acidity is still poorly understood. Here, Hu et al. address this problem by studying purple sea urchin larvae, revealing that they use ion transporters to gather bicarbonate from seawater. These structures are part of a group of bicarbonate transporters known as the ‘SLC4 transporter family’, which sit across the membrane of the mesenchyme cells and move the bicarbonate ions along. As the sea urchin larvae develop, the levels of the transporter protein start to rise in mesenchyme cells, peaking around the time they are producing the skeleton. Stopping the production of the transporter hindered the larvae from building normal skeletons and also made their cells more acidic. It turns out that bicarbonate is more than a skeleton ingredient – it also helps to buffer the acid made in the process. Bicarbonate ions can combine with acidic molecules to form water and carbon dioxide. Bicarbonate pumped in from the sea neutralises the acidic molecules made during calcium carbonate formation, which helps to stabilize pH levels. When the acidity of the water was experimentally increased, it prompted the sea urchins to produce more of the SLC4 transporters, revealing that they may have another role to play. Their acid-neutralizing capability helped the animals to cope with changes in their environment. Taking on more bicarbonate could therefore help to compensate for rising acidity, allowing skeleton production to carry on as normal. This last finding is important in the context of ocean acidification. As the amount of carbon dioxide in the atmosphere increases, more of the gas dissolves in the sea. The chemical reactions that follow make the water more acidic and decreases the pH levels of the sea. Understanding how animals make their skeletons and shells, and manage acid, could reveal how they will cope as the environment changes in the future.
Type of Medium:
Online Resource
ISSN:
2050-084X
DOI:
10.7554/eLife.36600.001
DOI:
10.7554/eLife.36600.002
DOI:
10.7554/eLife.36600.003
DOI:
10.7554/eLife.36600.004
DOI:
10.7554/eLife.36600.005
DOI:
10.7554/eLife.36600.006
DOI:
10.7554/eLife.36600.007
DOI:
10.7554/eLife.36600.008
DOI:
10.7554/eLife.36600.009
DOI:
10.7554/eLife.36600.010
DOI:
10.7554/eLife.36600.011
DOI:
10.7554/eLife.36600.012
DOI:
10.7554/eLife.36600.013
DOI:
10.7554/eLife.36600.014
DOI:
10.7554/eLife.36600.015
DOI:
10.7554/eLife.36600.016
DOI:
10.7554/eLife.36600.018
DOI:
10.7554/eLife.36600.019
Language:
English
Publisher:
eLife Sciences Publications, Ltd
Publication Date:
2018
detail.hit.zdb_id:
2687154-3
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