Linker cell death regulation in C. elegans - Our long-term goal is to understand the molecular basis of a novel morphologically-conserved non-apoptotic
developmental cell-death program we uncovered, and to determine its roles in mammalian development and
disease. Programmed cell death is a major cell fate. Apoptosis, an extensively studied cell death process,
requires caspase proteases and is accompanied by chromatin compaction and cytoplasmic shrinkage.
Surprisingly, mice lacking apoptotic effectors survive to adulthood. These observations suggest that non-
apoptotic cell death may play key roles in animal development. Although genes promoting necrotic cell death
have been described, these are not required for development. Thus, whether alternative developmental cell
death pathways exist, and if so, what molecular mechanisms govern their execution, is a major outstanding
question. Our studies of the C. elegans linker cell provide direct evidence that caspase-independent non-
apoptotic cell death pathways operate during animal development. Linker cell death occurs in the absence of
C. elegans caspases, and other apoptosis genes are also not required, nor are genes implicated in autophagy
or necrosis. The morphology of a dying linker cell is characterized by lack of chromatin condensation, a
crenellated nucleus, and swelling of cytoplasmic organelles. Remarkably, cell death with similar features (linker
cell-type death, LCD) also occurs in vertebrates, and is characteristic of neuronal degeneration in
polyglutamine diseases. We recently described a pathway governing C. elegans LCD. This is the first such
framework for a non-apoptotic developmental cell-death program. LCD is controlled by Wnt signals that
function in parallel with a developmental-timing and a MAPKK pathway to control non-canonical activity of
HSF-1, a conserved heat-shock transcription factor. let-70/Ube2D2, encoding a conserved E2 ubiquitin-
conjugating enzyme, is a key target of HSF-1. The E3 components CUL-3/cullin, RBX-1, BTBD-2, and EBAX-1
function with LET-70/UBE2D2 for LCD. Our recent evidence suggests that histone methylation may be a target
of this pathway, likely resulting in genome-wide chromatin opening, allowing nuclease access and DNA
degradation. LCD pathway components promote vertebrate cell-degenerative processes. pqn-41, a glutamine-
rich protein, is reminiscent of polyQ proteins causing neurodegeneration. and tir-1/Sarm and BTBD-2 promote
distal axon degeneration following axotomy, supporting conserved cell dismantling roles. We recently showed
that treatment of mammalian cells with the kinase inhibitor staurosporin (STS) causes LCD like death. Here we
will build on these studies to uncover LCD pathway targets, and study relevance to mammals. We will: (1)
Investigate the role of SAMS-4, a BTBD-2 target, and NUC-1, a DNaseII enzyme, in LCD, and test an
hypothesized pathway for these in chromatin modification and DNA degradation. (2) Identify EBAX-1 target
genes and assess roles in LCD control. (3) Characterize STS-induced death in mammalian cells, define
conservation with C. elegans LCD, and identify relevant genes.
