Protease cascades are essential for many biological events, including the LH-induced process of ovulation. ADAMTS1 (a disintegrin and metalloproteinase with thrombospondin-like repeats-1) is expressed and hormonally regulated in the ovary by LH and the progesterone receptor. To determine whether other family members might be expressed and regulated in the rodent ovary, those closely related to ADAMTS1 (ADAMTS4 and ADAMTS5) were analyzed in the mouse ovary by reverse transcription-polymerase chain reaction as well as by Western blot, immunohistochemical, and immunocytochemical analyses using highly specific antibodies. Prior to ovulation, ADAMTS4 and ADAMTS5 were coexpressed in granulosa cells of most follicles, whereas ADAMTS5 was also present in granulosa cells of atretic follicles. Following ovulation, ADAMTS1 and ADAMTS4 (but not ADAMTS5) were expressed in multiple cell types, including those within the highly vascular ovulation cone that marks the site of follicle rupture, endothelial cells of newly forming corpora lutea, and cumulus cells within the ovulated cumulus cell-oocyte complex (COC). Versican, a substrate for ADAMTS1 and ADAMTS4, colocalized with these proteases and hylauronan on the cumulus cell surface. To further characterize induction of these proteases and associated molecules, COCs and granulosa cells were isolated from preovulatory follicles and treated with FSH. In expanded COCs and differentiated granulosa cells, FSH induced expression of ADAMTS4 and versican message and protein, whereas increased levels of ADAMTS1 protein was observed in the media of granulosa cells where it was stabilized by heparin in this in vitro system. These studies provide the first evidence that ADAMTS1, ADAMTS4, and ADAMTS5 are expressed in spatiotemporal patterns that suggest distinct as well as some overlapping functions that relate to the broad expression pattern of versican in granulosa cells of small follicles, expanded COCs, and endothelial cells of the mouse ovary.