Determination of cellular identity is crucial in a variety of developmental frameworks.
Fate specification typically involves an initial identity/pathway choice, which can be either
deterministic or stochastic. Once selected this identity is reinforced and remembered
using mechanisms that are often distinct from those deployed in the initial choice. Lastly,
the chosen pathway must be faithfully executed so that cells differentiate appropriately.
Over the years, we’ve investigated the process of cell fate specification in several
distinct developmental contexts using the genetically tractable fruit fly, Drosophila
melanogaster as our model system. Depending on the developmental pathway and the
“step” in the specification process (e.g., pathway maintenance) the precise molecular
mechanisms needed for proper specification can be at many different levels (cell-cell
signaling, transcription, splicing, chromosome structure). In the first part of this proposal
we examine the specification of primordial germ cells (PGCs) in the early embryo. In
mammals PGC specification depends upon inductive BMP and Wnt signals. In contrast,
in multicellular animals other than mammals, PGC specification has long been thought to
be a cell-autonomous process that depends upon maternally deposited factors.
However, we have recently discovered that BMP signals from somatic cells play an
important role in PGC specification in the fly. This discovery suggests that the process of
PGC specification across the animal kingdom may be much more similar than previously
believed. Our proposed experiments are directed towards understanding the functional
coordination between the cell autonomous factors and the BMP pathway during
acquisition and maintenance of PGC identity. The second part of the proposal is focused
on chromosome architectural elements (boundary elements, Polycomb Response
Elements and Chromatin Entry Sites). The proposed experiments will examine how
these elements function to determine the topological organization of eukaryotic
chromosomes. We will also explore how the activities of these elements impact pathway
initiation, memory and execution in several distinct developmental pathways.