2009. Columbia University. PhD.
Although all insects are composed of identical fundamental units (head, abdomen and thorax), the way in which these units arise are rooted in distinct embryologies. Specifically, mechanisms of segmentation have divided insects into a number of different classes termed short, intermediate and long germ. Long germ insects form all segments, more or less, simultaneously in a syncytial blastoderm while short germ insects form anterior segments in this way, but add posterior segments subsequently and sequentially in a cellularized posterior growth zone. Intermediate insects lie somewhere between short and long. The convergent evolution of long germ embryogenesis has provided us with the opportunity to characterize both ancestral and derived components of this process through comparative studies using the extensively described Drosophila and the parasitoid wasp, Nasonia vitripennis, which lies much more basal in the phylogenetic lineage.
I am currently focusing on gap genes in an effort to uncover and understand how novel factors are contributing to segment formation and identity in Nasonia as compared with Drosophila and how these gap genes interact with other segmentation factors known to be instructing early stages of embryogenesis. We currently have expression data suggesting slight, yet likely important spatial variation in gap gene expression in these two species (Figure). This knowledge will help plot a map of the fundamental process of long germ embryogenesis and the kind of general alterations that had to occur in order for it to derive from the ancestral short form. With continued efforts, we hope to learn about conservation among the gene network conferring segment identity at the earliest stages of development, how differential regulation of these factors results in the same basic outcome (head, thorax and abdomen) and the selective pressures on different genomes that could drive them, separately, to the same general conclusion.
Spatial expression pattern of maternal and gap genes in Drosophila and Nasonia
The exclusive expression of specific rhodopsins in the photoreceptors of the Drosophila ommatidia is crucial for correct discrimination and processing of visual cues. The inner photoreceptors (R7 and R8) are divided into two subtypes (pale (p) and yellow (y)), which are stochastically distributed across the compound eye and required for color vision. I’m trying to characterize the subtype-specific signaling mechanisms initiating in pR7 (Rh3) or yR7 (Rh4) that are required to specify pR8 (Rh5) or yR8 (Rh6) respectively. Dpp signaling, initiated in R7, appears to act through the Activin receptor, Baboon (in R8) in a non-canonical pathway to establish R8 fate, likely by interacting with the bi-stable warts/melted loop. To identify other members of the pathway, we are conducting an RNAi-based screen of over 3,000 membrane-associated and signaling molecules looking at subtype expression of p and y R7 and R8.
NIH Post-Doctoral Fellowship