描繪在計畫性細胞死亡和尾部型態中有缺陷線蟲突變株的特性

Abstract

Apoptosis is an evolutionarily conserved program of developmental cell death. During the development of the Caenorhabditis elegans hermaphrodite, 131 of the 1030 somatic cells acquire cell death fate and finally undergo apoptosis. The process of programmed cell death can be divided into four distinct steps: decision, execution, engulfment and degradation. The essential four players of the execution step consist of egl-1(BH3-only), ced-9(BCL-2), ced-4(APAF-1) and ced-3(Caspases). It has been shown that transcriptional activation of egl-1 occurs in some destined cell to die. EGL-1 promotes cell death by antagonizing the cell-death inhibitory function of CED-9, thereby allowing pro-apoptotic CED-4 interacts with CED-3 caspase, which in turn results in destruction of the cell. However, how the expression level of egl-1 is regulated and the identities of CED-3 substrates are largely unknown. Previous studies showed that the double mutations of grp-1(The C. elegans ortholog of the cytohesin family of ARF GEFs functions in signaling cells to control asymmetric neuroblast divisions) and pro-apoptotic genes but not single mutations result in abnormal tail morphology. Therefore, we undertook a genetic enhancer screen for novel pro-apoptotic genes in the grp-1 background. Here we report the characterization of two mutants, tp189 and tp71 isolated from the screen. Single nucleotide polymorphism (SNP) mapping was used to position tp189 to the right arm of linkage group IV. We then used deficiency mapping to map tp189 to a 0.5c.m. interval containing approximately 200 genes on 50 fosmids. Finally, we rescued the abnormal tail-defect of tp189 with fosmid WRM064aB04 containing 13 candidate genes including pme-3. tp189 fails to complement a pme-3 allele, suggesting that tp189 may have a mutation in the pme-3 gene. We also used the SNP method to define the other mutation tp71 between pkP2150 and CE2-244 on LG II. However, the tp71 tail-defect phenotype is independent of grp-1. We conclude that tp71 probably functions in hermaphrodite tail tip morphogenesis. In addition to the forward genetic approach, we simultaneously utilized a reverse genetic approach to identify a kinase gene kin-2 that may act together with src kinase, csk-1 to regulate programmed cell death. Our data shown that kin-2, a regulatory subunit of a cAMP-dependent protein kinase may have pro-apoptotic function.