mer-1基因在C. elegans細胞吞噬訊息傳遞路徑上的功能分析

Abstract

計畫性細胞死亡在多細胞生物體的發育過程中扮演著重要角色，它負責調控細胞數目的恒定性以及避免因細胞死亡所引發的發炎反應。如果計畫性細胞死亡的機制出現缺陷將有可能引發自體免疫疾病。在計畫性細胞死亡的末期，死細胞的屍體必須由吞噬細胞清除乾淨，目前已知在線蟲裡有兩條具有相同功能的細胞吞噬路徑。一者為經由ced-2, ced-5,以及ced-12這條路徑；另一為經由ced-1, ced-6以及ced-7這路徑來達成細胞吞噬的目的。而在ced-2這條路徑裡，接受來自死亡細胞訊息的受器尚未完全找出。之前以RNAi的方式對線蟲進行一連串細胞吞噬缺陷突變株的screen，找出了一個tyrosine kinase： MER-1。在這篇報告中，我們試著釐清這個屬於tyro3 RTK家族成員的蛋白質MER-1在細胞吞噬路徑中所扮演的角色。由mer-1 在線蟲中胚胎進行RNA干擾的數據來看，胚胎的細胞屍體數目在2-fold時期前相較於野生種有顯著增加的趨勢，顯示出mer-1能影響細胞吞噬路徑的正常作用。而經由mer-1和ced-1, 6, 7, 2, 5, 10和12的雙重突變株cell corpse assay的結果來看，mer-1應是屬於ced-2, 5 和12的這條訊息傳遞路徑。MER-1具有一tyorsine kinase domain， 而根據kinase assay的結果證明， MER-1的tyrosine kinase domain在活體外確實具有酵素活性。

Programmed cell death (PCD) plays an important role in the developmental process of multicellular organisms. After cells undergo PCD, cell corpses are recognized and phagocytosed by engulfing cells. There are two redundant genetic pathways for cell corpse engulfment in C. elegans. One is through ced-2, ced-5, and ced-12 pathway, and the other is ced-1, ced-6 and ced-7. In the former pathway, an engulfing cell receives the “eat-me” signal from apoptotic cells through phosphatidylserine receptor-1(PSR-1). In previous RNAi based screen for receptor tyrosine kinase that functions in cell corpse engulfment, mer-1 was identified. In this report showed that mer-1 RNAi increased cell corpses number in C. elegans’ embryo, especially at the 2-fold stage. This result indicates mer-1 may function in cell corpse engulfment pathway. Double mutant cell corpse analysis showed that mer-1 acts with ced-2, ced-5, ced-10 and ced-12 to control cell corpse engulfment. MER-1 has a potential tyrosine kinase domain. On the basis of kinase assay, MER-1 has autophosphorylation activity in vitro.