University of Cologne > Biology Department > Dev. Biol. Institute > Panfilio Lab >

Research Group Members Publications Lab News Teaching

Extraembryonic research

Morphogenesis ~ Molecular regulation ~ Macroevolution ~ Genomics

Extraembryonic development (EED) is an essential and unique, but little-studied, aspect of insect development. Our main aim is to understand how the extraembryonic tissue achieves the correct three-dimensional form and topography in relation to the embryo proper, and how this is coordinated over time as a succession of rearrangements occur. By taking a comparative approach across species, we are examining the degree to which these morphogenetic events have been conserved, or not, during insect evolution.

We are investigating EED via developmental genetic, evolutionary, and bioinformatic approaches. To do so even more effectively, we are also developing new resources to further our work. Below is an overview of some of the projects we are currently working on.

Morphogenetic and molecular analyses of candidate EE genes

In the insects, the extraembryonic tissue within the egg has evolved into the two distinct epithelial membranes known as serosa and amnion. Playing distinct roles, the two membranes first develop to fully enclose and protect the embryo, and later actively withdraw so as to leave the embryo free to complete development. Extraembryonic development (EED) was well-known and examined during the time of classical, comparative embryological studies of the 1880's to 1970s. However, we know remarkably little about the morphogenetic details or molecular underpinnings of EED, as the modern era's model system, the fruit fly Drosophila, has a secondarily reduced EED program. For comparative study, we focus on two insects that represent the two main modes of EED, the milkweed bug Oncopeltus fasciatus and the red flour beetle Tribolium castaneum. Both species are considered "emerging" model systems, which are amenable to experimental techniques such as RNA interference (RNAi).

For the handful of genes that we know to be involved in EED, we are analyzing their function(s) in detail in both species. On the one hand, we are learning more about the diverse and ancestral roles of these genes and their regulatory networks. At the same time, we are using RNAi for these genes as a reverse genetics tool for functionally dissecting the components of the serosa's and amnion's developmental programs. Our phenotypic analyses make use of diverse microscopy techniques for visualizing gene expression, tissue structure, and time-lapse live imaging of morphogenesis.

RNAi screen for new EE genes

By taking a candidate gene approach, we are already investigating a number of genes that are proving to be important regulators of EED. However, as the model system fruit fly Drosophila melanogaster has a very reduced form of EED, a fly-centric list of candidates clearly only scratches the surface. To identify new genes that are essential for EED, we are participating in a large, unbiased RNAi screen in Tribolium, an initiative known as iBeetle. The several labs in Germany that are involved in this research unit are screening for a wide array of phenotypes, including those that could suggest a gene's involvement in EED. As an associated lab, we are performing rescreening validation of potential genes of interest as well as more in-depth, live imaging analyses of interesting phenotypes. The ongoing screen has already surveyed nearly half of the genome, turning up dozens of potential EE genes that could not have been identified by other means.

Tool development for visualization and misexpression studies

We are working on establishing tissue specific and developmental-stage specific tools for visualization and misexpression in the amnion and the serosa. A number of recent technical advances in the Tribolium community provide a strong foundation for this purpose, including established transgenesis for fluorescent live imaging [1], for GAL4-UAS controlled expression [2], and for heat-shock mediated expression [3]. Furthermore, a large-scale transposon insertion screen [4; GEKU database] generated a number of enhancer trap lines. We are presently working with selected enhancer trap lines and using these as a starting point for creating new tools for targeted EED research.

Genome sequencing in Oncopeltus fasciatus and comparative genomics

We are also furthering the resources available for our other study species, Oncopeltus. In collaboration, we recently sequenced a maternal and embryonic transcriptome that has already aided hugely in orthologous gene discovery [1]. Now, we are in the process of sequencing the entire genome, to provide a more comprehensive resource that includes non-coding sequence data. This is part of a larger initiative to sequence many insect and arthropod genomes under the umbrella of the i5k initiative. The Oncopeltus genome is being sequenced as part of a pilot project under the auspices of Baylor College of Medicine's Human Genome Sequencing Center. Oncopeltus was selected for sequencing in the pilot as a result of a white paper that we co-authored with several other hemipteran evo-devo researchers. Excitingly, the i5K pilot and other concurrent initiatives will soon provide a wealth of genomic data for comparative studies at multiple scales of phylogenetic resolution, particularly within the Hemiptera. Toward this end, we provided the Oncopeltus source material from our lab culture and are one of two co-contacts for this species. At the time of writing, most of the libraries are now sequenced, and we will be busy with the post-sequencing informatics for assembly and annotation from Summer of 2013. All colleagues interested in participating in this project are encouraged to get in touch and to peruse our community page.

Page last updated 23 Jun. 2013, K. Panfilio