Analyzing the function of BLMP-1 in tail-spike cell death in C. elegans
Date Issued
2014
Date
2014
Author(s)
Lin, Huang-Chin
Abstract
Programmed cell death (PCD) plays an important role in animal development. In Caenorhabditis elegans, transcriptional up-regulation of egl-1/BH-3-only gene promotes most somatic cell deaths. The increased level of EGL-1 induces the release of the proapoptotic CED-4(Apaf-1) from the CED-4-CED-9 complex and hence activating the downstream CED-3 caspase. However, some cell deaths, such as tail-spike cell death, use alternative mechanisms to switch on the core PCD pathway, because egl-1 is not absolutely required for these deaths. Two tail-spike cells are generated in the tail region before the bean stage. They fuse to become a binuclear cell at the comma stage. The binuclear cell differentiates and extends a long, thin, microtubule-based spike to help tail elongation during later embryogenesis. The binuclear cell undergoes apoptosis at about the 3.2-fold to 3.6-fold stage, when tail morphogenesis is complete. The temporal regulation of tail-spike cell death is poorly understood. We found that blmp-1, which encodes a zinc finger transcriptional repressor, is required for the death of some embryonic cells, including that of tail-spike cell. Using the blmp-1 transcriptional GFP reporter in the ced-3(n717) mutant, the expression of blmp-1 was detected in the tail-spike cell from 3-fold to late embryogenesis stage. This result suggests that blmp-1 is transcriptional up-regulated prior to tail-spike cell death. We next examined the relationship of blmp-1 with the key PCD genes ced-3, ced-4 and ced-9. First, over-expression of ced-3 specifically in the tail-spike cell rescues the PCD defect in the blmp-1(s71) mutant, suggesting that blmp-1 acts upstream of, or in parallel to, ced-3 to promote tail-spike cell death. Intriguingly, over-expression of high dosage of the ced-4 full-length cDNA results in abnormal tail-spike cell survival in the wild type. Further experiment is maded to unravel this unexpected result. Second, loss of ced-9 partially suppresses the tail-spike cell death phenotype of the blmp-1(s71) mutant, suggesting that blmp-1 acts upstream of, or in parallel to ced-9. Dr. Shai Shaham lab found that dre-1, which encodes an F-box protein of an SCF (Skp1-Cullin-F-box protein) E3 ubiquitin ligase mediating protein degradation, promotes tail-spike cell death. Using transgenic approaches, we observed the expression of dre-1 disappeared suddenly in tail-spike cell at the 3-fold stage, but it reappeared at about the 3.2-fold to 3.6-fold stage, suggesting that dre-1 expression is also critical for timely tail-spike cell death. Interestingly, over-expression of blmp-1 can rescue the tail-spike cell death defect in the dre-1(RNAi) mutant, indicating blmp-1 may act downstream of, or in parallel to dre-1. Therefore, we have characterized the temporal expression pattern of blmp-1 and dre-1,and positioned blmp-1 genetically to core PCD genes ced-3 and ced-9.
Subjects
細胞凋亡
尾突細胞
blmp-1
細胞凋亡核心路徑
dre-1
Type
thesis
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