Nuevos mecanismos de regulación de la apoptosis en Drosophila melanogaster

Tesis doctoral inédita. Universidad Autónoma de Madrid, facultad de Ciencias, Departamento de Biología Molecular. Fecha de lectura: 11/02/201

The role of Dpp and Wg in compensatory proliferation and in the formation of hyperplastic overgrowths caused by apoptotic cells in the Drosophila wing disc

Non-lethal stress treatments (X-radiation or heat shock) administered to Drosophila imaginal discs induce massive apoptosis, which may eliminate more that 50% of the cells. Yet the discs are able to recover to form final structures of normal size and pattern. Thus, the surviving cells have to undergo additional proliferation to compensate for the cell loss. The finding that apoptotic cells ectopically express dpp and wg suggested that ectopic Dpp/Wg signalling might be responsible for compensatory proliferation. We have tested this hypothesis by analysing the response to irradiation-induced apoptosis of disc compartments that are mutant for dpp, for wg, or for both. We find that there is compensatory proliferation in these compartments, indicating that the ectopic Dpp/Wg signalling generated by apoptotic cells is not involved. However, we demonstrate that this ectopic Dpp/Wg signalling is responsible for the hyperplastic overgrowths that appear when apoptotic ('undead') cells are kept alive with the caspase inhibitor P35. We also show that the ectopic Dpp/Wg signalling and the overgrowths caused by undead cells are due to a non-apoptotic function of the JNK pathway. We propose that the compensatory growth is simply a homeostatic response of wing compartments, which resume growth after massive cellular loss until they reach the final correct size. The ectopic Dpp/Wg signalling associated with apoptosis is inconsequential in compartments with normal apoptotic cells, which die soon after the stress event. In compartments containing undead cells, the adventitious Dpp/Wg signalling results in hyperplastic overgrowths.Ministerio de Educación y Ciencia and by an Institutional Grant from the Fundación Ramón ArecesPeer Reviewe

A dp53/JNK-dependant feedback amplification loop is essential for the apoptotic response to stress in Drosophila

Programmed cell death (apoptosis) is a conserved process aimed to eliminate unwanted cells. The key molecules are a group of proteases called caspases that cleave vital proteins, which leads to the death of cells. In Drosophila, the apoptotic pathway is usually represented as a cascade of events in which an initial stimulus activates one or more of the proapoptotic genes (hid, rpr, grim), which in turn activate caspases. In stress-induced apoptosis, the dp53 (Drosophila p53) gene and the Jun N-terminal kinase (JNK) pathway function upstream in the activation of the proapoptotic genes. Here we demonstrate that dp53 and JNK also function downstream of proapoptotic genes and the initiator caspase Dronc (Drosophila NEDD2-like caspase) and that they establish a feedback loop that amplifies the initial apoptotic stimulus. This loop plays a critical role in the apoptotic response because in its absence there is a dramatic decrease in the amount of cell death after a pulse of the proapoptotic proteins Hid and Rpr. Thus, our results indicate that stress-induced apoptosis in Drosophila is dependant on an amplification loop mediated by dp53 and JNK. Furthermore, they also demonstrate a mechanism of mutual activation of proapoptotic genes. Cell Death and Differentiation (2012) 19, 451¿460; doi:10.1038/cdd.2011.113; published online 2 September 2011Ministerio de Ciencia e Innovación (Consolider CSD 20700008-B and BFU 2008 03196/BMC); Fundación Ramón Areces; FPU scholarship (AP2005-4875)Peer Reviewe