Congress Abstracts - Society for Developmental Biology

Program/Abstract # 92
The C. elegans RB protein LIN-35 induces germ cell apoptosis under starvation
Rosa Navarro, Laura Láscarez-Lagunas, Carlos Silva-García, Tzventanka Dinkova (UNAM,
Mexico)
In Caenorhabditis elegans, physiological germ cell apoptosis eliminates more than half of the germ cells in the hermaphrodite gonad
to support gamete quality and germline homeostasis by a still unidentified mechanism. External factors that act through different
pathways can also affect germ cell apoptosis. The BH3-only protein EGL-1 induces germ cell apoptosis when animals are exposed to
pathogens or agents that cause DNA damage. DNA damage-induced germ cell apoptosis also requires the nematode p53 homolog
CEP-1. Previously, we found that environmental conditions such as heat shock, oxidative and osmotic stress induce germ cell
apoptosis through an EGL-1 and CEP-1 independent mechanism that requires the MAPK pathway. However, we observed that
starvation increases germ cell apoptosis by an unknown pathway. Using polysomal gradients to compare mRNA translation levels
from well-fed to 6h starved adult hermaphrodites; we found that general mRNAs translation is inhibited under these conditions.
Among the translational arrested mRNAs is ced-9, which encodes for the anti-apoptotic Bcl2 homolog in C. elegans. However, the
mRNA of lin-35, the C. elegans RB homolog, avoids this general translational arrest condition and its protein accumulates
considerably. It has been previously shown than LIN-35 represses ced-9 transcription under normal conditions to partially induce
physiological germ cell apoptosis. We observed that under starvation ced-9 expression decreases dramatically in a LIN-35 manner.
We proposed a model where under starvation germ cell apoptosis is triggered due to higher LIN-35 accumulation and a reduction of
ced-9 transcription and translation levels.
Program/Abstract # 93
Caspase-8 regulates hematopoiesis at two distinct stages during embryonic development
Christopher P. Dillon (St. Jude Children’s Res Hosp, USA); Andrew Overst (Seattle, USA); Ricardo Weinlich, Laura Janke, Douglas
Green (St. Jude Children’s Res Hosp, USA)
Caspase-8, the initiator caspase of the death receptor pathway of apoptosis, is essential for embryonic development. Caspase-8
knockout animals die at E10.5 due to a failure of yolk sac vascularization. Ablation of RIPK3, a kinase that promotes necrosis, a form
of programmed cell death, rescues caspase-8-deficient mice, suggesting a dynamic interplay between these two death pathways during
development. While the tissues affected and the signals that lead to death in the Casp8-/- embryos are still poorly characterized, the
specific ablation of casp8 in endothelial or hematopoietic tissues provides evidence that Casp8 may play a key role in the development
of the hematopoietic system. To investigate whether TNF triggered the embryonic death of Casp8-/- deficient animals at E10.5, we
crossed these mice onto a Tnfr1-/- background. Intriguingly, Casp8-/-Tnfr1-/- mice had normal yolk sac development and progressed
appropriately until ~E15.5 before the embryos died. Histological examination of the embryos suggested that this later embryonic
lethality might be the result of liver defects. As the fetal liver is an important site of hematopoiesis, we sought to test the
hematopoietic potential of cells from these embryos. Casp8-/-Tnfr1-/- fetal livers failed to reconstitute the immune system of lethally
irradiated recipients. Together, these results demonstrate two essential windows during development where caspase-8 regulates
hematopoiesis. These observations further suggest that caspase-8 mediated cell death likely regulates ongoing perinatal hematopoiesis
and additional investigation could provide important insights for enhancing immune response against pathogens.
Program/Abstract # 94
Characterization of Integrins function in specific cells for cell-corpses engulfment in Caenorhabditis elegans
Tsung-Yuan Hsu, Hsiao-Han Hsieh (National Taiwan U, Taiwan)
Clearance of apoptotic cells by engulfment plays an important role in the homeostasis and development of multicellular organisms.
Despite the fact that the recognition of apoptotic cells by engulfment receptors is critical in inducing the engulfment process, the
molecular mechanisms are still poorly understood. Here, we characterize a novel cell corpse engulfment pathway mediated by the
integrin α subunits INA-1 and PAT-2 in Caenorhabditis elegans and show that they specifically function in hypodermal and musclemediated
engulfment during embryogenesis. Inactivation of ina-1or pat-2 resulted in a defect in apoptotic cell internalization. We first
identified that the extracellular region of INA-1 and PAT-2 recognize and then binding to the surface of apoptotic cells in vivo, and the
intracellular region mediate specific signaling for engulfment. We identify essential roles of the integrin α subunit INA-1 acts
upstream and directly interaction of SRC-1, non-receptor tyrosine kinase, and CED-2 (CrkII) to transmit engulfment signaling which
through the conserved signaling molecules CED-5 (DOCK180)/CED-12 (ELMO)/CED-10 (RAC) respectively, preferentially act in
epithelial cells to mediate cell corpse removal during mid-embryogenesis. Moreover, in contrast to INA-1, small GTPase CDC-42 and
its activator UIG-1, a guanine-nucleotide exchange factor, in PAT-2–mediated cell corpse removal. The PAT-2 and CDC-42 both
function in muscle cells for apoptotic cell removal and are co-localized in growing muscle pseudopods around apoptotic cells. Our
results demonstrated that PAT-2 functions through UIG-1 for CDC-42 activation, which in turn leads to cytoskeletal rearrangement
and apoptotic cell internalization by muscle cells. Take together, basis of our results demonstrated that provided the non-canonical
regulatory through alpha subunite, but not beta subunite for cell-corpse engulfment. Furthermore, different engulfing cells utilize
distinct repertoires of receptors for engulfment at the whole organism level.
Program/Abstract # 95
Morphogenetic apoptosis/compensatory proliferation at the borders of DPP expression in the genital disc of Drosophila
27