Acute cell volume regulation by Janus kinase 2-mediated sodium/hydrogen exchange activation develops at the late one-cell stage in mouse preimplantation embryos.

Early preimplantation embryos are extremely sensitive to dysregulation of cell volume, which can lead to developmental arrest. It was previously shown that mouse embryos at the two-cell stage respond to a cell volume decrease by quickly activating Na+/H+ exchange via a signaling mechanism that involves the tyrosine kinase Janus kinase 2 (JAK2). However, it was not known whether this mechanism is active at the one-cell stage, when embryos are most sensitive to perturbed cell volume. Na+/H+ exchanger activity elicited by an induced cell volume decrease was significantly lower at the mid one-cell stage than at the late one-cell stage or during the two-cell stage. This activity could be completely blocked by the broad specificity tyrosine kinase inhibitor genistein at either stage, but only at the two-cell stage was there a substantial component of activity that was sensitive to low concentrations of the JAK2-selective inhibitors TG101348 or ruxolitinib. Western blots to detect active JAK2 phosphorylated on tyrosine Y1007/8 revealed that JAK2 became substantially phosphorylated in response to a cell volume decrease at the mid two-cell, but not mid one-cell stage. Such cell volume decrease-induced JAK2 phosphorylation appeared by the late one-cell stage. At least in part this appears to be due to an increase in total JAK2 protein at the late one-cell stage. Furthermore, TG101348 impaired maintenance of cell volume at the two-cell, but not mid one-cell, stages. Thus, cell volume homeostasis requiring Na+/H+ exchange signaled by JAK2 first becomes prominent during mouse embryonic development at the late one-cell stage.