Effects of seawater acidification on cell cycle control mechanisms in Strongylocentrotus purpuratus embryos.

Sean P Place,Bryan W Smith,Howard Browman

doi:10.1371/journal.pone.0034068

Abstract

Previous studies have shown fertilization and development of marine species can be significantly inhibited when the pH of sea water is artificially lowered. Little mechanistic understanding of these effects exists to date, but previous work has linked developmental inhibition to reduced cleavage rates in embryos. To explore this further, we tested whether common cell cycle checkpoints were involved using three cellular biomarkers of cell cycle progression: (1) the onset of DNA synthesis, (2) production of a mitotic regulator, cyclin B, and (3) formation of the mitotic spindle. We grew embryos of the purple sea urchin, Strongylocentrotus purpuratus, in seawater artifically buffered to a pH of ∼7.0, 7.5, and 8.0 by CO2 infusion. Our results suggest the reduced rates of mitotic cleavage are likely unrelated to common cell cycle checkpoints. We found no significant differences in the three biomarkers assessed between pH treatments, indicating the embryos progress through the G1/S, G2/M and metaphase/anaphase transitions at relatively similar rates. These data suggest low pH environments may not impact developmental programs directly, but may act through secondary mechanisms such as cellular energetics.

Highlights

Artificial changes in intracellular and extracellular pH have long been known to impact sea urchin sperm motility, embryogenesis, and developmental patterns [1,2]
Sea urchin development under low pH environments To verify similar reductions in the rate or number of cleavage events in S. purpuratus embryos reared in low pH seawater are observed in our system, we tracked the synchronous development of sea urchin embryos for 140 min post fertilization and determined the number of embryos that had successfully completed the first mitotic division at 10 min intervals
For embryos cultured at a pH of 8.0 and 7.5, the percentage of cells that had completed the first division by 120 min was 82.03961.613 and 78.7761.002 respectively, while embryos cultured in seawater held at a pH of 7.0 showed a significant decrease, with only 70.63461.36% completing the first division by 120 min

Summary

Introduction

Artificial changes in intracellular and extracellular pH have long been known to impact sea urchin sperm motility, embryogenesis, and developmental patterns [1,2]. A growing body of literature has highlighted the significant impacts anthropogenically driven decreases in sea surface pH can have on marine life, and in particular, marine calcifiers [3,4]. Recent studies performed at the level of the gene transcript in sea urchin larvae are beginning to shed light on the molecular underpinnings of the biological response to low pH environments. These studies highlight a general decrease in a broad range of biological processes for developing larvae suggesting the mechanism may be related to regulation of gene expression [8,9,10,11]. To gain insight into some of the earliest cellular pathways impacted during development in a high CO2 world, we can look to early developmental studies for formulation of plausible hypothesis

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Conclusion