分子與遺傳分析線蟲的ced-12 基因在細胞死亡過程中的功能

Abstract

計劃性細胞死亡在生物體是重要的發育過程和生理現象。而計劃性細胞死亡過程中迅速吞噬死細胞屍體的現象具有避免引起免疫反應的重要功能，但吞噬過程的作用機制尚未十分明瞭。在線蟲（Caenorhabditis elegans) ，已知有六個吞噬基因作用在吞噬死細胞屍體的過程，由遺傳分析，可將這六個吞噬基因分為兩群：ced-2 、 ced - 5 和 ced - 10 一群，及ced - 1 、ced - 6 和ced - 7 一群，研究指出若ced - 2 、ced -5和 ced - 10 這一群的基因發生突變，除了會有吞噬功能的缺失外，還會使線蟲的生殖器官頂端的兩個細胞 DTCs 產生移走方向錯誤的情形。 我們發現了一個新基因ced -12，作用在線蟲細胞死亡路徑上，負責吞噬細胞死亡產生的死細胞屍體。 ced-12 突變株有過多的死細胞屍體未被吞噬，另一方面， ced -12 突變株的生殖器官頂端的兩個細胞 DTCs 也會產生移走方向錯誤的情形。我們進行 ced -12基因的 cloning 。進一步由遺傳分析，我們發現 ced -12基因作用在吞噬細胞，而且 ced - 12可能作用在 ced -10的上游，參與在 ced - 2 、 ced -5 和 ced - 10吞噬死細胞屍體的路徑上。因此推測 ced -12基因在吞噬細胞中負責延伸細胞表面以吞噬死細胞屍體。已知 CED-2 蛋白和人類 CrkII類似， CED-5蛋白和人類DOCK180 類似， CED-10 蛋白和人類 GTPase Rac類似。因此我們推測可能的模式是CED-2 / CrkII、CED-5 / DOCK180 和 CED-12 一起作用以活化 CED-10/Rac 的 GTPase 的訊息傳遞路徑。

The rapid engulfment (phagocytosis) of cells undergoing programmed cell death (apoptosis) is a fundamental biological process that is not well understood. In C. elegans, six genes known to control cell corpse removal have been identified and grouped into two classes, ced-2, ced-5, and ced-l0, and ced-1, ced-6 and ced-7, on the basis of their genetic interactions. More recently, of a defect in the migrations of the two gonadal distal tip cells (DTCs) in mutants of the ced-2 ced-5 and ced-10 class but not the other. Here we report the cloning of and functional characterization of ced-12, a new gene required for the engulfment of apoptotic cells and DTC migration in the nematode C. elegans. We found that ced-12 encodes a novel protein. Ectopic expression study suggests that ced-12 acts within engulfing cells during cell-corpse engulfment. We also show that ced-12 may function upstream of ced-10 in a genetic pathway controlling cell corpse engulfment. Together with the published results that ced-2, ced-5, and ced-l0 encode proteins similar to human CrkII, human DOCK 180, and human GTPase Rac, respectivityly. We propose that CED-2/CrkII, CED-5/DOCK 180, and CED- 12 function to activate CED- 10/Rae in a GTPase signaling pathway that controls the polarized extension of cell surfaces.