Thompson Group - Chromatin and Gene Expression
A major challenge in developmental molecular biology is to understand how alterations in chromatin structure regulate changes in gene expression which determine different cell fates.
Nuclei in oikoplastic
epithelium of O. dioica.
I have been working in this area on the role of chromatin structure in the activation of the zygotic genome and the regulation of very early gene expression in preimplantation mouse embryos up to the blastocyst stage. Direct molecular analysis of changes in chromatin structure on the regulatory elements of developmentally expressed genes in the mouse, and in other common model organisms in developmental biology, is rendered difficult by both the complexity of the genomes and the need to isolate small subpopulations of cells from the overall embryo.
The appendicularia, an important class of metazoans near the transition from invertebrates to vertebrates, represent a new biological model with significant advantages in overcoming the problems described above. Despite the evolutionary complexity of the animal, its genome size is estimated to be only 3 to 4 times the size of the yeast genome.
An interesting feature of the animal is that it lives inside a house which it secretes from a terminally differentiated and highly specialized oikplastic epithelium. In the species we will be studying, this house is completely resynthesized every 3 to 4 hours, demonstrating a considerable capacity for high rates of protein synthesis. The house contains a complex set of inlet and feeding filters which allow the appendicularians to graze on a wide range of both decaying and living organic particles. There are at least 70 species world wide found over a depth range from the surface to greater than 2000 m. With their high filtering rates, capacity for rapid production blooms (up to 10-fold increase in biomass within 24 hours), and importance as a food source for marine fish populations, the appendicularia occupy a place of fundamental importance in marine ecosystems.
Cloned cDNA with expression
pattern restricted to
giant cells of the Fol anlage.
The research effort in our group is concentrated on how different regions of the oikoplastic epithelium become differentiated and organized to synthesize the proteins that make up the house which the animal lives in and the specialized filters that it uses to feed. We have shown that the epithelium is formed through fine regulation of endocycle lengths in different cellular fields. Both timing of DNA replication and ploidy level are bilaterally symmetric and patterns are controlled at the level of individual identifiable cells. We have isolated 8 families of genes expressed from distinct subregions of the epithelium and are currently analysing how changes in chromatin structure and nuclear localisation may be implicated in regulating the differential expression of these genes both during development of the oikoplastic epithelium and after its terminal differentiation. We are also developing transgenic and gene knockdown technologies to fully exploit the potential of this highly fecund chordate that remains transparent throughout its entire rapid life cycle (4-5 days).
