During Drosophila embryogenesis, an extra-embryonic tissue, known as the amnioserosa (AS), is required for the morphogenetic processes of germ band retraction (GBR) and dorsal closure (DC). Being extra-embryonic, the AS is not part of the embryo proper but is eliminated via programmed cell death (PCD) in the late stages of embryogenesis. Programmed elimination of the AS during normal development can be prevented by directly inhibiting apoptosis, either through the deletion of the pro-apoptotic genes hid, grim and reaper, or through the expression of the pan-caspase inhibitor P-35. PCD in the AS can also be prevented by indirect inhibition of apoptosis via inactivation of autophagy, either through activation of the InR/PI3K pathway, or through activation of the Ras signalling pathway. The timing of AS elimination is critical to development as mutants associated with premature AS loss fail in GBR. To better characterize this premature AS death, a detailed phenotypic analysis of the AS behaviour in the GBR mutant hindsight (hnt) was performed. Direct inactivation of apoptosis failed to rescue the GBR defects in hnt mutant, though the premature AS death was completely rescued. Inactivation of autophagy, however, rescued AS cell behaviour and contacts during GBR, with partial rescue of the GBR defects in the hnt mutant. The nature of premature AS loss is characterized as a possible model for anoikis, a form of cell death that is triggered through reduced cell-cell or cell- matrix contact.

During Drosophila embryogenesis, an extra-embryonic tissue, known as the amnioserosa (AS), is required for the morphogenetic processes of germ band retraction (GBR) and dorsal closure (DC). Being extra-embryonic, the AS is not part of the embryo proper but is eliminated via programmed cell death (PCD) in the late stages of embryogenesis. Programmed elimination of the AS during normal development can be prevented by directly inhibiting apoptosis, either through the deletion of the pro-apoptotic genes hid, grim and reaper, or through the expression of the pan-caspase inhibitor P-35. PCD in the AS can also be prevented by indirect inhibition of apoptosis via inactivation of autophagy, either through activation of the InR/PI3K pathway, or through activation of the Ras signalling pathway. The timing of AS elimination is critical to development as mutants associated with premature AS loss fail in GBR. To better characterize this premature AS death, a detailed phenotypic analysis of the AS behaviour in the GBR mutant hindsight (hnt) was performed. Direct inactivation of apoptosis failed to rescue the GBR defects in hnt mutant, though the premature AS death was completely rescued. Inactivation of autophagy, however, rescued AS cell behaviour and contacts during GBR, with partial rescue of the GBR defects in the hnt mutant. The nature of premature AS loss is characterized as a possible model for anoikis, a form of cell death that is triggered through reduced cell-cell or cell- matrix contact.

Partially-observable Markov decision processes (POMDPs) are especially good at modeling real-world problems because they allow for sensor and effector uncertainty. Unfortunately, such uncertainty makes solving a POMDP computationally challenging. Traditional approaches, which are based on value iteration, can be slow because they find optimal actions for every possible situation. With the help of the Fast Forward (FF) planner, FF- Replan and FF-Hindsight have shown success in quickly solving fully-observable Markov decision processes (MDPs) by solving classical planning translations of the problem. This thesis extends the concept of problem determination to POMDPs by sampling action observations (similar to how FF-Replan samples action outcomes) and guiding the construction of policy trajectories with a conformant (as opposed to classical) planning heuristic. The resultant planner is called POND-Hindsight.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 59-63).

Thesis (M.A.)--University of Toronto, 2005. / Includes bibliographical references (leaves 43-45).

No description available.

Hindsight (HNT) is a zinc finger transcription factor that is required for morphogenesis of the Drosophila embryo, having roles in germ band retraction (GBR) as well as dorsal closure (DC). HNT expression is also found in sensory organ precursors (SOP) of the developing pupal peripheral nervous system, and muscle progenitor cells, but the role of HNT in neurogenesis and myogenesis during embryogenesis has not been investigated in any depth. Microarray analysis of embryos over-expressing HNT during GBR and DC identified 1290 genes with significant changes in expression. This data set included many potential HNT targets, including genes associated with myogensis, and a disruption of muscle development was observed in embryos over-expressing HNT. It is possible that HNT may function to repress muscle identity genes in muscle founder cells. In addition, HNT over expressing embryos were found to resemble the neurogenic class of mutants. Among the potential target genes, D-Pax2 (shaven, sparkling, CG11049) expression, which is known to be expressed in the developing peripheral nervous system, was confirmed to be up-regulated following HNT over-expression. Interestingly, D-Pax2 and HNT expression were found to co-localize at the onset of their expression at stages 10-12 in embryos, but were not co-localized in later stages of embryogenesis. The up-regulation of D-Pax2 by HNT over-expression was further characterized and was found to be associated with strong ectopic HNT expression. The relevance of HNT to the regulation of D-Pax2 during normal development remains to be determined, but it is possible that endogenous expression of HNT is involved in D-Pax2 repression.

The Drosophila hindsight (hnt) gene encodes a C2H2-type zinc-finger (ZNF) protein crucial for epithelial morphogenesis. The human HNT homologue, RREB1, functions as a transcriptional modulator and regulates several tumor suppressor genes. HNT’s functional motifs, target genes and its regulatory abilities have not been elucidated. Here I showed that the C-terminal region of HNT containing the last five of 14 ZNFs (ZNF 10-14) binds in vitro to DNA-elements similar to those identified for RREB-1. I then mapped HNT’s endogenous binding sites on polytene chromosomes and focus on two, at 4C and 60C, which are associated with the hnt and nervy (nvy) loci, respectively. Sequence analysis of the bound fragments shows conservation of motifs similar to those bound by HNT in vitro. Data from both hnt loss- and gain-of-function experiments show that HNT attenuates the transcription of the hnt and nvy genes in several tissues and developmental stages. I show that the identified HNT C-terminal DNA binding domain ZNF 10-14 is not required for these regulatory functions. I further delineate the minimal functional motifs of HNT in transcriptional regulation and show that its ninth ZNF in isolation has a repressive activity and is sufficient to confer many regulatory functions of HNT. On the other hand, mutation of ZNF 9 in the context of the full-length protein indicates that it is not necessary for HNT functions. Interestingly, ZNF 9 has been lost from HNT vertebrate homologues. I propose two redundant mechanisms of transcriptional regulation by HNT: one is mediated by the potential protein-interaction abilities of ZNF 9; another is through cooperation of other ZNF motifs of HNT; the DNA binding abilities conferred by the C-terminal five fingers may be essential for the latter mechanism.

The Drosophila hindsight (hnt) gene encodes a C2H2-type zinc-finger (ZNF) protein crucial for epithelial morphogenesis. The human HNT homologue, RREB1, functions as a transcriptional modulator and regulates several tumor suppressor genes. HNT’s functional motifs, target genes and its regulatory abilities have not been elucidated. Here I showed that the C-terminal region of HNT containing the last five of 14 ZNFs (ZNF 10-14) binds in vitro to DNA-elements similar to those identified for RREB-1. I then mapped HNT’s endogenous binding sites on polytene chromosomes and focus on two, at 4C and 60C, which are associated with the hnt and nervy (nvy) loci, respectively. Sequence analysis of the bound fragments shows conservation of motifs similar to those bound by HNT in vitro. Data from both hnt loss- and gain-of-function experiments show that HNT attenuates the transcription of the hnt and nvy genes in several tissues and developmental stages. I show that the identified HNT C-terminal DNA binding domain ZNF 10-14 is not required for these regulatory functions. I further delineate the minimal functional motifs of HNT in transcriptional regulation and show that its ninth ZNF in isolation has a repressive activity and is sufficient to confer many regulatory functions of HNT. On the other hand, mutation of ZNF 9 in the context of the full-length protein indicates that it is not necessary for HNT functions. Interestingly, ZNF 9 has been lost from HNT vertebrate homologues. I propose two redundant mechanisms of transcriptional regulation by HNT: one is mediated by the potential protein-interaction abilities of ZNF 9; another is through cooperation of other ZNF motifs of HNT; the DNA binding abilities conferred by the C-terminal five fingers may be essential for the latter mechanism.

Hindsight (HNT) is a zinc finger transcription factor that is required for morphogenesis of the Drosophila embryo, having roles in germ band retraction (GBR) as well as dorsal closure (DC). HNT expression is also found in sensory organ precursors (SOP) of the developing pupal peripheral nervous system, and muscle progenitor cells, but the role of HNT in neurogenesis and myogenesis during embryogenesis has not been investigated in any depth. Microarray analysis of embryos over-expressing HNT during GBR and DC identified 1290 genes with significant changes in expression. This data set included many potential HNT targets, including genes associated with myogensis, and a disruption of muscle development was observed in embryos over-expressing HNT. It is possible that HNT may function to repress muscle identity genes in muscle founder cells. In addition, HNT over expressing embryos were found to resemble the neurogenic class of mutants. Among the potential target genes, D-Pax2 (shaven, sparkling, CG11049) expression, which is known to be expressed in the developing peripheral nervous system, was confirmed to be up-regulated following HNT over-expression. Interestingly, D-Pax2 and HNT expression were found to co-localize at the onset of their expression at stages 10-12 in embryos, but were not co-localized in later stages of embryogenesis. The up-regulation of D-Pax2 by HNT over-expression was further characterized and was found to be associated with strong ectopic HNT expression. The relevance of HNT to the regulation of D-Pax2 during normal development remains to be determined, but it is possible that endogenous expression of HNT is involved in D-Pax2 repression.