Carnevali O, Cionna C, Tosti L, Lubzens E, Maradonna F
Dipartimento di Scienze del Mare, Università Politecnica delle Marche, Via Brecce Bianche 60131, Ancona, Italy.
Gen Comp Endocrinol. 2006 May 1;146(3):195-203. doi: 10.1016/j.ygcen.2005.12.007. Epub 2006 Jan 23.
Several complex processes are involved in the production of viable eggs. The aim of this review is to provide an overview on the role played by lysosomal enzymes, especially cathepsins B, D, and L, during ovarian follicle growth and maturation. Specific attention is focused on the relationship between the second proteolytic cleavage of yolk proteins (YP) and the resumption of the meiosis during germinal vesicle break down (GVBD). Maturation represents the final stage of oocytes development prior to ovulation. Oocytes in this phase appear translucent. In many teleosts GVBD is accompanied by water uptake and among marine teleosts with pelagic eggs, most of the final volume is reached by this process. The last phase of maturation in benthonic eggs also occurs concomitant to a second proteolytic cleavage and is related with a slight hydration process. In vitro maturation by 17alpha,20beta-dihydroxy-4-pregnen-3one in class III Danio rerio oocytes, induced 80% of GVBD. The maturation of these oocytes is known to be associated with proteolysis of their major yolk components. In the present study, we show that inhibition of specific enzymes (cathepsins) involved in the second YP processing, did not affect the occurrence of GVBD as the oocytes become translucent and display a slight increase in size. More specifically, in vitro incubation of the maturing oocytes with a cathepsin B inhibitor suppressed both cathepsin B and L activities and the proteolysis of YP. On the contrary, the addition of cathepsin L inhibitor, only affected cathepsin L activity, indicating that cathepsin B is probably involved in Cathepsin L activation, and this enzyme is probably responsible for the second YP processing. These results, together with previous studies, indicate that the GVBD process is independent of the occurrence of the second proteolytic process. It supports the hypothesis that the maturation process is under K+ ion flux control, while yolk proteolysis is related to the temporal and specific activation of cathepsins by acidification of yolk spheres.
产生有活力的卵子涉及几个复杂的过程。本综述的目的是概述溶酶体酶，特别是组织蛋白酶B、D和L在卵泡生长和成熟过程中所起的作用。特别关注卵黄蛋白（YP）的第二次蛋白水解切割与生发泡破裂（GVBD）期间减数分裂恢复之间的关系。成熟是排卵前卵母细胞发育的最后阶段。此阶段的卵母细胞呈半透明状。在许多硬骨鱼中，GVBD伴随着水分吸收，在产浮性卵的海洋硬骨鱼中，大部分最终体积是通过这个过程达到的。底栖卵成熟的最后阶段也伴随着第二次蛋白水解切割，并且与轻微的水合过程有关。在III类斑马鱼卵母细胞中，17α,20β - 二羟基 - 4 - 孕烯 - 3 - 酮诱导的体外成熟导致80%的GVBD。已知这些卵母细胞的成熟与它们主要卵黄成分的蛋白水解有关。在本研究中，我们表明，抑制参与第二次YP加工的特定酶（组织蛋白酶），并不影响GVBD的发生，因为卵母细胞变得半透明且大小略有增加。更具体地说，用组织蛋白酶B抑制剂体外孵育成熟的卵母细胞，可抑制组织蛋白酶B和L的活性以及YP的蛋白水解。相反，添加组织蛋白酶L抑制剂仅影响组织蛋白酶L的活性，表明组织蛋白酶B可能参与组织蛋白酶L的激活，并且这种酶可能负责第二次YP加工。这些结果与先前的研究一起表明，GVBD过程独立于第二次蛋白水解过程的发生。它支持这样一种假设，即成熟过程受K + 离子通量控制，而卵黄蛋白水解与卵黄球酸化导致组织蛋白酶的时间性和特异性激活有关。
