Abstract
In order to understand the mechanism of the endocannabinoid (eCB) signal, which has so far been shown to work in oocyte genesis and maturation, it is critical to clarify detailed localization of the eCB synthesizing enzyme molecules as well as receptors for eCBs in oocytes in the ovary in situ. For this purpose, diacylglycerol lipase (DGL) α and β are involved in the synthesis of an eCB 2-arachidonoylglycerol (2-AG). DGLα/β and the cannabinoid receptor 1 (CB1) for 2-AG were shown to be localized to the primary oocytes of postnatal mice using immuno-light and electron microscopy. It was found that two types of localization existed: first, immunoreactivities for DGLα and β were weakly detected throughout the ooplasm in light microscopy for which the intracellular membranes of vesicles forming tiny scattered aggregates were responsible. Secondly, DGLβ-immunoreactivity was distinctly confined to the nuage of Balbiani bodies and small nuage-derivative structures; both amorphous materials and membranes of vesicles were responsible for their localization. On the other hand, the weak immunoreactivity for CB1 was localized in a pattern similar to the first one for DGLs, but not found in a pattern for the Balbiani nuage. Two routes of functional exertion of 2-AG synthesized by DGLs were suggested from the two types of localization: one was that the eCB synthesized at all the sites of DGLs is released from the oocytes and exerts paracrine or autocrine effects on adjacent intra-ovarian cells as well as the oocytes themselves. The other was that the eCB synthesized within the nuage was involved in the modulation of the posttranscriptional processing of oocytes. Owing to the failure in the detection of CB1 in the Balbiani nuage, however, the validity of the latter possibility remains to be elucidated.