Insulin‐like growth factor 1, insulin, and progesterone induce early and late increases in Xenopus oocyte sn‐1, 2‐diacylglycerol levels before meiotic cell division

Abstract

After a 3 to 6 hour incubation, addition of progesterone (the most effective), insulin-like growth factor 1 (IGF-1; the second most effective), or insulin induces meiotic cell division in Xenopus oocytes. Measurement of an endogenous activator of protein kinase C, sn-1,2-diacylglycerol (DAG), by an enzymatic method recording mass demonstrates that all three hormones alter DAG levels. Five seconds after addition, only progesterone transiently reduces DAG levels by about 25%. At 15 minutes after addition, all three hormones produce a peak of DAG (115% to 160% of control values), with the more effective hormones producing a larger increase in DAG. Insulin produces the smallest DAG increase, but the DAG release is longer lasting. Finally, all three hormones induce a second peak in DAG levels just before white spot appearance (at 0.85 GVBD50, where 1.0 GVBD50 is when 50% of the cells have divided). With these data and since an activator of protein kinase C, a phorbol ester, has been found to induce meiosis, the kinase may play a role in early proliferative events at the plasma membrane and in late events at the nucleus.

Xenopus Gq alpha subunit activates the phosphatidylinositol pathway in Xenopus oocytes but does not consistently induce oocyte maturation.

“…Similar results were obtained after injection of the mouse Gqa mRNA (see Fig. 4 [1][2][3][4][5][6][7] Tin was generated by stepping the membrane potential from -20 to -100 mV. All these data suggested strongly that the ability to generate Tin was from accumulation of newly synthesized xGqa.…”

“…In all cases the effect of progesterone was not potentiated, and the injected oocytes responded as the controls-that is, stage 4 …”

“…Immediately after exposure to progesterone the diacylglycerol (DAG) level in the oocyte falls "30%, and after 2 min it begins to rise, reaching control levels by 15 min and rising further until GVBD (3,4). A similar increase in DAG, but without the initial drop, has been reported (5), and a decrease in inositol 1,4,5-triphosphate (InsP3) immediately after progesterone exposure has also been reported (3).…”

sn-1,2-diacylglycerol and choline increase after fertilization in Xenopus laevis.

“…The mass of DAG was determined using a DAG kinase assay developed by Bell and associates (for a detailed procedure using Xenopus cells, see Stith et al, 1991). After fertilization, groups of 5-10 cells were homogenized in 1:2 chloroform:methanol and DAG was phosphorylated with the addition of [32PPATP (ICN, Costa Mesa, CA) and DAG kinase (Calbiochem, San Diego, CA or Lipidex, Westfield, NJ).…”

Requirement of protein kinase C pathway during progesterone‐induced oocyte maturation in amphibian,Rana dybowskii

“…Recently, Han and Lee (1995) have hypothesized that phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis as well as inositol 1,4,5-triphosphate [Ins (1,4,5)P 3 ]-induced Ca z+ release play a crucial role in regulating meiotic cell division in Xenopus oocytes. In contrast, other investigators have found that progesterone causes a marked decrease in DAG content within first 15 seconds and subsequent decrease in PKC activity in Xenopus oocytes, and these decrease in DAG and PKC activity may be necessary for the resumption of meiotic maturation (Smith, 1989;Varnold and Smith, 1990;Stith et al, 1991 …”