功能分析線蟲php-3在細胞屍體吞噬過程的角色

Abstract

在多細胞生物的發育過程中，部分細胞會進行計劃性細胞死亡，這些凋亡的細胞必須被迅速地辨識及吞噬分解，以免引起發炎和自體免疫反應。在線蟲，已發現數個基因與吞噬作用有關，它們分成兩條功能部分重疊的路徑：ced-1，ced-6，ced-7和dyn-1路徑以及ced-2，ced-5，ced-12路徑，ced-10的功能則位在這兩條路徑的下游。吞噬作用起始於吞噬細胞上的受器，辨認死細胞表面上的“eat me”signal。在細胞凋亡的過程中，原本只會出現在細胞膜內層的phosphatidylserine (PS)，會翻轉到細胞膜外層，作為一個“eat me”signal，被phosphatidylserine receptor (PSR) 辨識。在線蟲，psr-1 已被證實參與在ced-2，ced-5，ced-12這條路徑 (Wang et al., 2003)。在本篇研究，我們發現PHP-3這個posterial Hox 轉錄因子，其與PSR-1的intracellular區域和extracellular區域都會形成interaction。將php-3基因knockout和knockdown都會影響胚胎發育期間死細胞屍體的數目。php-3突變株的細胞屍體持續時間也有增長的現象。php-3和psr-1的雙重突變分析顯示這兩個基因可能位在同一條功能路徑。由php-3和ced-1，ced-2，ced-5，ced-6，ced-7，ced-10，和ced-12雙重突變分析的結果顯示：php-3突變會降低ced-1，ced-2和ced-7突變株的細胞屍體數目，對於ced-5，ced-6，ced-10和ced-12突變株則無影響，所以php-3 可能與ced-1，ced-2，和ced-7有拮抗效應。

Programmed cell death (PCD) plays an important role in the development of multicellular organisms. After cells undergo PCD, the cell corpses are recognized and engulfed by engulfing cells. In C. elegans, there are two partially redundant pathways for engulfment: ced-1/ced-6/ced-7/dyn-1, and ced-2/ced-5/ced-12. These two pathways converge at ced-10. During apotosis, phosphatidylserine (PS), which is normally restricted to the inner leaflet of the plasma membrane, is exposed on the surface of apoptotic cells and act as an “eat me” signal to trigger phagocytosis. In C. elegans, the phosphatidylserine receptor PSR-1 binds cells with exposed PS and acts upstream in the ced-2/ced-5/ced-12 pathway (Wang et al., 2003). In this study, we found that PHP-3, a posterior Hox protein, can interacts with both intracellular and extracellular region of PSR-1. Like psr-1 embryos, php-3 mutants have more corpse number and longer cell-corpse-duration time than wild type. Genetic analysis of psr-1; php-3 double mutants suggest that psr-1 and php-3 likely act in the same pathway during programmed cell death. Double mutant analysis with previously identified engulfment genes showed that the php-3 mutation reduced the persistent corpse number of ced-1, ced-2 and ced-7 mutants, but not ced-5, ced-6, ced-10 and ced-12 mutants, suggesting that php-3 may have antagonistic effect with ced-1, ced-2 and ced-7.