Inhibitor of apoptosis proteins (IAPs) provide a critical barrier to inappropriate apoptotic cell death through direct binding and inhibition of caspases. We demonstrate that degradation of IAPs is an important mechanism for the initiation of apoptosis in vivo. Drosophila Morgue, a ubiquitin conjugase-related protein, promotes DIAP1 down-regulation in the developing retina to permit selective programmed cell death. Morgue complexes with DIAP1 in vitro and mediates DIAP1 degradation in a manner dependent on the Morgue UBC domain. Reaper (Rpr) and Grim, but not Hid, also promote the degradation of DIAP1 in vivo, suggesting that these proteins promote cell death through different mechanisms.

Selective cell death provides developing tissues with the means to precisely sculpt emerging structures. By imposing patterned cell death across a tissue, boundaries can be created and tightened. As such, programmed cell death is becoming recognized as a major mechanism for patterning of a variety of complex structures. Typically, cell types are initially organized into a fairly loose pattern; selective death then removes cells between pattern elements to create correct structures. In this review, we examine the role of selective cell death across the course of Drosophila development, including the tightening of embryonic segmental boundaries, head maturation, refining adult structures such as the eye and the wing, and the ability of cell death to correct for pattern defects introduced by gene mutation. We also review what is currently known of the relationship between signals at the cell surface that are responsible for tissue patterning and the basal cell death machinery, an issue that remains poorly understood.

The correct organization of cells within an epithelium is essential for proper tissue and organ morphogenesis. The role of Decapentaplegic/Bone morphogenetic protein (Dpp/BMP) signaling in cellular morphogenesis during epithelial development is poorly understood. In this paper, we used the developing Drosophila pupal retina -looking specifically at the reorganization of glial-like support cells that lie between the retinal ommatidia -to better understand the role of Dpp signaling during epithelial patterning. Our results indicate that Dpp pathway activity is tightly regulated across time in the pupal retina and that epithelial cells in this tissue require Dpp signaling to achieve their correct shape and position within the ommatidial hexagon. These results point to the Dpp pathway as a third component and functional link between two adhesion systems, Hibris-Roughest and DEcadherin. A balanced interplay between these three systems is essential for epithelial patterning during morphogenesis of the pupal retina. Importantly, we identify a similar functional connection between Dpp activity and DE-cadherin and Rho1 during cell fate determination in the wing, suggesting a broader link between Dpp function and junctional integrity during epithelial development.

The structure of nuclear chromatin may limit the accessibility of carcinogenic agents to DNA. In the case of oxidative DNA strand cleavage mediated by the physiologically relevant iron chelate, iron-ADP, histone-associated nucleosomal DNA is protected while internucleosomal DNA is susceptible to damage. We now find that the distribution of iron-ADP-generated 8-hydroxydeoxyguanosine, a potentially mutagenic oxidative base change, shows relative targeting to internucleosomal sites (3.5-fold increased oxidative modification of internucleosomal compared with nucleosomal DNA as the minimal degree of enrichment). In contrast, iron-EDTA, which generates hydroxyl radical in the 'fluid phase', does not target internucleosomal DNA. Thus, physiologic iron chelates may promote site-specific damage and thereby be relevant to mechanisms of iron-dependent oxidative mutagenesis and carcinogenesis.

The sensory organs of the Drosophila adult leg provide a simple model system with which to investigate patternforming mechanisms. In the leg, a group of small mechanosensory bristles is organized into a series of longitudinal rows, a pattern that depends on periodic expression of the hairy gene (h) and the proneural genes achaete (

we next examined the effect of SP600125 on grafted embryonic DA neurons in vivo, in an animal model of PD. We unilaterally injected the neurotoxin 6-OHDA into the right SNpc of rats to produce a complete ablation of cell bodies as well as fibers and terminals innervating the striatum. Based on previous findings, 20 all animals showing greater than 5 rotations per minute were assumed to have lesions greater than 90% and were selected for transplantation. At 2 weeks post-lesioning, 400 000 VM cells were treated with vehicle or SP600125 and grafted into the striatum of lesioned rats. 20 Animals received daily infusions of vehicle or SP600125 (75 mM) via a cannula in the striatum for 4 days and were killed 7 days post-transplantation. Striatal examination revealed that 100% of the VM grafts survived in animals infused with either vehicle or SP600125. However, total counts of TH þ cells in the grafts of animals infused with SP600125 showed significantly more (231%) DA cells than in the grafts of animals infused with vehicle (mean7S.E.M, 1228573436 and 2840675506, respectively, Figures 1e(i) and (f)). Thus, treatment of cells with SP600125 upon transplantation into 6-OHDA lesioned brains results in a two-fold increase in the survival of grafted DA neurons within the host striatum. Moreover, we found that within 7 days, these cells had adopted a typical bipolar DA phenotype with extensive processes, verifying that the cells incorporated within the host and did not form tumors (Figure 1e(ii)). These results indicate that SP600125 selectively prevents cell death, and does not induce excessive proliferation in vivo. From a clinical viewpoint, our results imply that the amount of DA precursors needed for transplantation in PD could be at least halved by using the SP600125 compound. Taken together, our study indicates that inhibition of apoptotic JNK signaling may contribute to overcome one of the major limitations of current cell replacement strategies in the treatment of PD.Acknowledgements.

wingless (wg) and its vertebrate homologues, the Wnt genes, play critical roles in the generation of embryonic pattern. In the developing Drosophila epidermis, wg is expressed in a single row of cells in each segment, but it influences cell identities in all rows of epidermal cells in the 10- to 12-cell-wide segment. Wg signaling promotes specification of two distinct aspects of the wild-type intrasegmental pattern: the diversity of denticle types present in the anterior denticle belt and the smooth or naked cuticle constituting the posterior surface of the segment. We have manipulated the expression of wild-type and mutant wg transgenes to explore the mechanism by which a single secreted signaling molecule can promote these distinctly different cell fates. We present evidence consistent with the idea that naked cuticle cell fate is specified by a cellular pathway distinct from the denticle diversity-generating pathway. Since these pathways are differentially activated by mutant Wg ligands, we propose that at least two discrete classes of receptor for Wg may exist, each transducing a different cellular response. We also find that broad Wg protein distribution across many cell diameters is required for the generation of denticle diversity, suggesting that intercellular transport of the Wg protein is an essential feature of pattern formation within the epidermal epithelium. Finally, we demonstrate that an 85 amino acid region not conserved in vertebrate Wnts is dispensable for Wg function and we discuss structural features of the Wingless protein required for its distinct biological activities.

During development, global patterning events initiate signal transduction cascades which gradually establish an array of individual cell fates. Many of the genes which pattern Drosophila are expressed throughout development and specify diverse cell types by creating unique local environments which establish the expression of locally acting genes. This process is exemplified by the patterning of leg microchaete rows. hairy (h) is expressed in a spatially restricted manner in the leg imaginal disc and functions to position adult leg bristle rows by negatively regulating the proneural gene achaete, which specifies sensory cell fates. While much is known about the events that partition the leg imaginal disc and about sensory cell differentiation, the mechanisms that refine early patterning events to the level of individual cell fate specification are not well understood. We have investigated the regulation of h expression along the dorsal/ventral (D/V) axis of the leg adjacent to the anterior/posterior (A/P) compartment boundary and have found that it requires input from both D/V and A/P patterning mechanisms. Expression of the D/V axis h stripe (D/V-h) is controlled by dorsal- and ventral-specific enhancer elements which are targets of Decapentaplegic (Dpp) and Wingless (Wg) signaling, respectively, but which are also dependent on Hedgehog (Hh) signaling for activation. D/V-h expression is lost in smoothened mutant clones and is specifically activated by exogenously supplied Cubitus interruptus (Ci). D/V-h expression is also lost in clones deficient for Dpp and Wg signaling, but ectopic activation of D/V-h by Dpp and Wg is limited to the A/P compartment boundary where endogenous levels of full-length Ci are high. We propose that D/V-h expression is regulated in a non-linear pathway in which Ci plays a dual role. In addition to serving as an upstream activator of Dpp and Wg, Ci acts combinatorially with them to activate D/V-h expression.