University of Macau / Institute of Chinese Medical Sciences

University of Macau / Institute of Chinese Medical Sciences

Growing tissues are communities of cells that cooperate to form a robust, functional organ. Cooperative behavior is enforced by cell competition, wherein comparisons of fitness lead to selective elimination of cells sensed as relatively less healthy. Elimination of these ‘loser’ cells from Drosophila wing imaginal discs results in cell death induced by deployment of a genetic module consisting of the secreted Toll ligand Spätzle (Spz), several Toll related receptors, and NFkB factors. How signaling by this module is activated and restricted only to competing cells is unknown. Here, we investigate the signaling role of Spz in Myc-induced cell competition. We demonstrate that elimination of wild-type loser cells requires local synthesis and activation of Spz in the wing disc. We identify Spätzle Processing Enzyme (SPE) and Modular Serine Protease (modSP) as upstream mediators of Spz-mediated loser cell elimination, and show that an increase in SPE in ‘winner’ cells is required for Spz to kill loser cells. Finally, we show that Spz requires both Toll and Toll-8 to induce apoptosis of wing disc cells. Our results indicate that during cell competition, Spz-mediated signaling is strictly confined to the imaginal disc, allowing errors in tissue fitness to be corrected without compromising organismal physiology.

Not available / text

Much effort has been spent over the last decade in producing so called "Machine Vision" systems for use in robotics, automated inspection, assembly and numerous other fields. Because of the large amount of data involved in an image (typically ¼ MByte) and the complexity of many algorithms used, the processing times required have been far in excess of real time on a VAX-class serial processor. We review a number of image understanding algorithms that compute a globally defined "state", and show that they may be computed using simple local operations that are suited to parallel implementation. In recent years, many massively parallel machines have been designed to apply local operations rapidly across an image. We review several vision machines. We develop an algebraic analysis of the performance of a vision machine and show that, contrary to the commonly-held belief, the time taken to relay images between serial streams can exceed by far the time spent processing. We proceed to investigate the roles that a variety of pipelining techniques might play. We then present three pipelined designs for vision, one of which has been built. This is a parallel pipelined bit slice convolution processor, capable of operating at video rates. This design is examined in detail, and its performance analysed in relation to the theoretical framework of the preceeding chapters. The construction and debugging of the device, which is now operational in its hardware is detailed.

published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Physiology / Master / Master of Philosophy

The goal of my doctoral work is to understand how proteins involved in vesicle trafficking contribute to proper animal development. To understand aspects of this process, I studied how two vesicle trafficking proteins, Liquid facets(Lqf)/epsin1 and D-Epsin-Related, affect Drosophila eye development. I determined that Lqf, an endocytosis protein, together with Fat facets (Faf), a deubiquitinating enzyme, regulate the Notch and Delta signaling in the developing Drosophila eye. Notch signaling pathway is used in most developmental processes and is dependent on its ligand Delta. Faf deubiquitinates Lqf in the signaling cells, thereby increasing Lqf protein levels and also levels of Delta endocytosis. This event is necessary for Notch activation in neighboring cells. Lqf probably works in concert with the E3 ubiquitin ligase Neuralized (Neur), which ubiquitinates Delta. These conclusions are consistent with a relatively new model describing an obligate role for endocytosis in the signaling cells to effect activation in neighboring cells. To understand how Lqf functions mechanistically in this process, I performed a structure/function analysis of the Lqf protein. Lqf proteins with strategic deletions of certain functional domains were tested for their ability to function in vivo. The major result of these experiments is that the N-terminal ENTH domain of Lqf and a protein without the ENTH domain each retain significant activity. This suggests that Lqf has two functions: the ENTH domain function and the ENTH-less function. These data are in contrast with the most popular model suggesting that ENTH-less epsins are non-functional proteins. I present possible models for how ENTH-less epsins may retain function. The final part of my thesis focuses on D-Epsin-Related (D-Epsin-R) protein. I showed that D-Epsin-R is a Golgi protein, like its homologs. Surprisingly, D-Epsin-R ENTH domain is not required for function because an ENTH-less D-Epsin-R can substitute for endogenous D-Epsin-R. Also, D-Epsin-R has essential and probably specific developmental roles in the eye as D-Epsin-R mutants exhibit impaired cell growth. This work suggests that epsins are specific components of certain developmental pathways. / text

An experiment was conducted in Phoenix in 1986 to determine effects of water and N deficits on ABA and IAA concentrations in young bolls and their abscission zones in relation to boll retention, and to determine the effects of N on growth of fruiting branches through the season. Water deficit decreased boll retention, decreased the concentration of free IAA in bolls and their abscission zones, and increased ABA in bolls and abscission zones. But, the concentration of ester IAA increased with water deficit (in contrast to free IAA). Because ester IAA resists degradation during stress, it may facilitate recovery when stress is relieved and some of it is converted to free IAA. N-deficiency symptoms were mild and did not appear early in the season. N had no effect on the ABA and IAA contents of bolls and their abscission zones, and had only a small effect on growth of fruiting branches. The N test is to be repeated in 1987 when N deficiency should be more severe.

No description available.