Effects of magnesium deprivation on development and biomineralization in the sea urchin Arbacia lixula

ABSTRACT

Echinoderms have an extensive endoskeleton composed of magnesian calcite and occluded matrix proteins. As biomineralization in sea urchin larvae is sensitive to the Magnesium:Calcium ratio of seawater, we investigated the effects of magnesium deprivation on development and skeletogenesis in the sea urchin Arbacia lixula. We focused on the localization of the skeletogenic cells (primary mesenchyme cells) and the spatial expression of associated genes. Embryos reared in Mg-free seawater exhibited developmental delay from 6-h post-fertilization and at 24 h embryos showed complete lack of biomineral formation. Larvae (48–72 h) exhibited severe skeleton malformations. Fluorescent labelling revealed that the primary mesenchyme cells and the developing skeleton of treated embryos were in an abnormal ectopic location. Expression of the skeleton matrix protein gene (msp130) in the primary mesenchyme cells as seen using in situ hybridization was normal at 24 h. At 48 h this gene was down-regulated in control larvae, but not in treated larvae. Development of the pigment cells, immune cells that, like the skeleton, are mesodermal derivatives, was also impaired. Our results highlight the essential role of Mg in skeleton formation in sea urchin embryos with an indication that this element is also generally important for the development of mesoderm.

Abbreviations: hpf: hours post fertilization; PMCs: primary mesenchyme cells; ACC: amorphous calcium carbonate; MgFSW: magnesium-free seawater; FSW: filtered seawater

Impact statement

• Echinoderms have an extensive endoskeleton composed of magnesian calcite

• We investigated the effects of magnesium deprivation on development and skeletogenesis in the sea urchin Arbacia lixula

• Magnesium deprivation caused developmental delay and skeleton malformations

• Primary mesenchyme cells of treated embryos were in an abnormal ectopic location

• The spatial and temporal expression profile of the skeleton matrix protein gene (msp130) was found to be different from controls

Our results highlight the essential role of Mg across developmental processes in sea urchin embryos.

KEYWORDS:

• Skeletogenesis
• echinopluteus
• magnesium calcite
• primary mesenchyme cells
• pigment cells

Ethical approval

All applicable international, national, and institutional guidelines for the care and use of animals were followed.

Acknowledgements

This work is dedicated to the memory of Valeria Matranga, our great colleague and scientist. We thank Dr Thierry Lepage (Institute of Biology Valrose University of Nice Sophia Antipolis and CNRS, Nice, France) and Dr. Caterina Costa (IBIM-CNR) for kindly providing the probe for msp130 and Mr Mauro Biondo for his technical assistance and help in the maintenance of sea urchins in aquaria. This study was supported by the BIOMINTEC Project to V.M. (European Commission, grant number PITN-GA-2008-215,507) and by a PhD Grant to C.M. from Dept. STEBICEF, University of Palermo (grant number D50002D15 + 1001).

Author contributions

Conceived and designed the experiments: CM, VM, MCR. Performed the experiments and the statistical analysis: CM. Analysed the data: CM, RC, VM, MB. Wrote the paper: CM, MB.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Università degli Studi di Palermo [PhD Grant D50002D15 + 1001]; FP7 People: Marie-Curie Actions [PITN-GA-2008-215507].