Oocyte-specific protein tyrosine kinase that phosphorylates and inhibits CDK1 and acts as a key regulator of meiosis during both prophase I and metaphase II. Required to maintain meiotic arrest in oocytes during the germinal vesicle (GV) stage, a long period of quiescence at dictyate prophase I, by phosphorylating CDK1 at 'Tyr-15', leading to inhibit CDK1 activity and prevent meiotic reentry. Also required for metaphase II exit during egg activation by phosphorylating CDK1 at 'Tyr-15', to ensure exit from meiosis in oocytes and promote pronuclear formation. ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Localizes mainly in the nucleus. Exported from the nucleus to the cytoplasm before germinal vesicle breakdown (GVBD), allowing meiosis resumption. Ovary-specific. Detected only in the oocytes at all developmental stages of the follicle including primary, secondary, preantral, and antral follicles with an increase in signal during development. Readily detectable at the mature oocyte, but disappears at 2.5 dpc. Detected in germinal vesicle (GV) and metaphase II-stage oocyte (at protein level). Phosphorylated by PKA at Ser-15 in vitro, leading to activate kinase activity. Phosphorylation at Ser-15 by CaMK2, leading to increase its activity and promote metaphase II exit during egg activation. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. WEE1 subfamily.