We are interested in a series of inter-related genetic,
developmental, evolutionary, cell biology questions.

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Genomic Imprinting

In genomic imprinting a fully functional gene is marked so that it becomes inactivated when it is transmitted by one, but not, the other parent. This inactivation can be reset, by an unknown process, each generation by passage through the germline. Genomic imprinting is involved in many human diseases and is probably crucial in the evolution of sexual reproduction. But despite its medical and theoretical importance, virtually nothing is known about the mechanism that results in this form of epigenetic gene silencing.

My interest in gene regulation and gene silencing led me to the study of an imprinted gene in Drosophila. We are using this gene, which affects the easily assessed phenotype of eye colour, as an assay system for the imprinting process. We have shown that genomic imprinting is a result of at least two separate processes; establishment of the imprint and the maintenance of that decision (Lloyd 2000). The maintenance event relies on highly conserved chromatin proteins (Joanis and Lloyd 2002) but little is known about the mechanism which establishes and resets the initial imprint. We are using a whole genome scanning technique to dissect the genetic regulation of the establishment of the imprint (W. MacDonald - Ph.D. student, J.A. Tynan and S. Jesweit - honours students), and the evolutionary forces which might have given rise to this unique form of epigenetic gene regulation (A. Haigh - Ph.D. student, L. McEachern - Ph.D. student, N. Gorguy - M.Sc. student).

Cloning

In 1997 the first mammal, Dolly the sheep was cloned and during the past few years the cloning of other mammals has moved from a novelty in developmental biology to an industry driven by powerful economic and social forces. Regardless of the underlying ethical, religious and legal considerations, it is clear that the technology to clone mammals, including humans, has been developed and is and will continue to be used. One of the major problems arising from such cloning work is the very high rate of abnormal embryos and fetuses which result. These abnormalities include severe defects in organ formation, generally resulting in spontaneous abortion, to more subtle but potentially as devastating metabolic defects such as obesity, premature aging, endocrine malfunction and neurological dysfunction including mental retardation. It is generally assumed that many of these abnormalities, arise from misregulation of genes which fail to be correctly silenced following their abrupt re-activation upon the transfer of the somatic nucleus to the egg nucleus - the first step in cloning. While such epigenetic gene silencing occurs in all animals and is essential for normal development, the molecular events which result in gene silencing are best understood in Drosophila. We have successfully produced cloned Drosophila (Haigh, MacDonald and Lloyd, submitted, Nature Genetics, March 2004) and are currently using the cornucopia of developmental mutants available in Drosophila to investigate the genetic factors responsible for the development of defective clones.

A Drosophila Model for Hermansky-Pudlak Syndrome
and Other Vesicle Transport Defects.

Initially a side project, the analysis of the cell biology of the imprinting marker gene garnet, has proven interesting in its own right. Correct intracellular localization of a newly synthesized protein is essential for cell, and hence, organismal viability. This requires a complex protein trafficking system which relies heavily on directed budding and fusion of intracellular transport vesicles. Defects in this system have dire consequences for the cell and the organism, including Hermansky-Pudlak Syndrome. As is true of many rare genetic diseases, too few people are affected to justify research into curative therapies, a fact which offers little comfort to the families of affected children. Our understanding of this, and related, syndromes has recently been aided by the finding of animal model systems. The garnet mutation in Drosophila is homologous to the Hermansky-Pudlak Syndrome defect. By cloning and sequencing this gene, I discovered that the Drosophila garnet gene encodes the a subunit of the adaptin complex which directs vesicles budding from the Golgi body to lysosomes. The finding of this homology means that we can use the power of Drosophila genetics to understand the regulation of this vesicle transport system and its roles in the various cell types of the body. We have generated transgenic fly strains and are in a position to make "humanized" versions of these flies (transgenic flies for the human homologues of these genes) which could be used for further research and the testing of potentially therapeutic pharmacological products. The role of AP-3 in neurons is particularly interesting. We have been examining the role of this gene in transporting serotonin pumps to synaptic vesicles in neurons. Defects in this process result in hypersexual behavior, a situation which is pharmacologically mirrored in humans given inappropriate does of serotonin re-uptake inhibitors.