Orai1 internalization and STIM1 clustering inhibition modulate SOCE inactivation during meiosis

Store-operated Ca2+ entry (SOCE) is a ubiquitous Ca2+ influx pathway activated in response to depletion of intracellular Ca2+ stores. SOCE is a primary modulator of intracellular Ca2+ dynamics, which specify cellular responses. Interestingly, SOCE inactivates during M phase but the mechanisms involved remain unclear. SOCE is mediated by clustering of the ER Ca2+ sensor STIM1 in response to Ca2+ store depletion, leading to gating of the plasma membrane SOCE channel Orai1. Here we show that SOCE inactivation in meiosis is the result of internalization of Orai1 into an intracellular vesicular compartment and to the inability of STIM1 to cluster in response to store depletion. At rest, Orai1 continuously recycles between the cell membrane and an endosomal compartment. We further show that STIM1-STIM1 interactions are inhibited during meiosis, which appears to mediate the inability of STIM1 to form puncta following store depletion. In contrast, STIM1-Orai1 interactions remain functional during meiosis. Combined, the removal of Orai1 from the cell membrane and STIM1 clustering inhibition effectively uncouple store depletion from SOCE activation in meiosis. Although STIM1 is phosphorylated during meiosis, phosphomimetic and alanine substitution mutations do not modulate STIM1 clustering, arguing that phosphorylation does not mediate STIM1 clustering inhibition during meiosis.