title: Calcium signaling in mouse oocyte maturation: the roles of STIM1, ORAI1 and SOCE.
abstract: Calcium handling is critical for the oocyte function, since the first steps of fertilization are dependent on the appropriate Ca(2+) mobilization to originate transient spikes of the cytosolic Ca(2+) concentration. It is well known that the Ca(2+) influx from the extracellular milieu is required to maintain this signaling in mammalian oocytes. However, the regulation of the Ca(2+) channels involved in this process is still unknown in oocytes. STIM1, a key regulator of store-operated Ca(2+) entry (SOCE), relocates in the mouse oocyte shortly after sperm stimulation, suggesting that SOCE is involved in the maintenance of cytosolic Ca(2+)-spiking in the fertilized oocyte. Here, we show that there is an up-regulation of the expression of STIM1 at the germinal vesicle breakdown stage, and this expression remains steady during following maturation stages. We found that oocytes express ORAI1, a store-operated Ca(2+) channel, and that ORAI1 expression level was stable during oocyte maturation. Immature oocytes showed no Ca(2+) entry and no increase in STIM1-ORAI1 colocalization in response to the store depletion induced by thapsigargin. On the contrary, in mature oocytes, STIM1-ORAI1 colocalization is enhanced 3-fold by depletion of Ca(2+) stores, enabling the activation of store-operated calcium channels and therefore Ca(2+) entry. Finally, the correlation between SOCE activation during the maturation of oocytes and STIM1-ORAI1 colocalization strongly suggests that ORAI1 is involved in the Ca(2+) entry pathway in the mature oocyte. SOCE up-regulation in the final stage of maturation is further evidence of a major role for SOCE in fully mature oocytes, and therefore in Ca(2+) signaling at fertilization.
authors: Department of Cell Biology,  College of Life Sciences, University of Extremadura, Badajoz 06006,  Spain.
authors: Carolina
authors: C
authors: Gómez-Fernández
authors: Aida M
authors: AM
authors: López-Guerrero
authors: Eulalia
authors: E
authors: Pozo-Guisado
authors: Ignacio S
authors: IS
authors: Álvarez
authors: Francisco Javier
authors: FJ
authors: Martín-Romero
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D020013:Calcium Signaling; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D006824:Hybridization, Genetic; D008540:Meiosis / Q000502:physiology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D000071740:ORAI1 Protein; D009865:Oocytes / Q000254:growth & development* / Q000378:metabolism; D000071737:Stromal Interaction Molecule 1
chemical_list: D015220:Calcium Channels; D008562:Membrane Glycoproteins; D000071740:ORAI1 Protein; C520430:Orai1 protein, mouse; C100757:Stim1 protein, mouse; D000071737:Stromal Interaction Molecule 1