Mitochondria and calcium signaling in embryonic development.

Calcium (Ca2+) is a simple but critical signal for controlling various cellular processes and is especially important in fertilization and embryonic development. The dynamic change of cellular Ca2+ concentration and homeostasis are tightly regulated. Cellular Ca2+ increases by way of Ca2+ influx from extracellular medium and Ca2+ release from cellular stores of the endoplasmic reticulum (ER) and sarcoplasmic reticulum (SR). The elevated Ca2+ is subsequently sequestered by expelling it out of the cell or by pumping back to the ER/SR. Mitochondria function as a power house for energy production via oxidative phosphorylation in most eukaryotes. In addition to this well-known function, mitochondria are also recognized to regulate Ca2+ homeostasis through different mechanisms. Although critical roles of Ca2+ signaling in fertilization and embryonic development are known, the involvement of mitochondria in these processes are not fully understood. This review is focused on the role of mitochondrial respiratory chain complex I in the regulation of Ca2+ signaling pathway and gene expression in embryonic development, especially on the new findings in the cardiac development of Xenopus embryos. The data demonstrate that mitochondria modulate Ca2+ signaling and the Ca2+-dependent NFAT pathway and its target gene which are essential for embryonic heart development.