Frederike Alwes

Development from zygote to hatchling occurs through a complex and coordinated series of mitotic divisions, or cleavages. Cleavage patterns and the associated cell movements during early arthropod embryonic development have been relatively overlooked in favour of the study of later developmental stages (such as segmentation, neurogenesis, organogenesis etc). However, past and present literature shows that many arthropods, particularly crustaceans, display a stereotyped pattern of early cleavage. This makes their embryonic development an interesting topic of study in furthering our understanding of the evolution of arthropod development.

Using a combination of classical and computer-based tools, we are detailing the early stages of the amphipod Parhyale hawaiensis development up to germ band formation.  This work will contribute to a greater understanding of embryonic cellular movements in the amphipod, and provide the basis for research into the molecular genetic mechanism(s) orchestrating these movements.

Franz Kainz (lab alumnus)

Although the insect body plan is well conserved, the developmental mechanisms of body patterning are surprisingly varied. The fruit fly Drosophila melanogaster has long served as a model organism illustrating how a fertilized egg generates a structured segmented body. A cascade of transcription factors defines the body into smaller and smaller units in this species, specifying all segments essentially simultaneously.

However, less evolutionarily derived insects develop their posterior segments during a later secondary growth phase in a sequential fashion, similar to non-insect arthropods and to vertebrates. This mode of segmentation (called short-germ segmentation) is poorly understood, although most genes of the Drosophila network are conserved in all insects despite the different modes of embryogenesis.

We would like to understand differences in the underlying genetic mechanisms that result in the differences in body patterning between different insects.  As a case study, we are looking at how repeated body units are formed in the field cricket Gryllus bimaculatus. This is one of the few hemimetabolous insects, where RNA interference has been shown to work efficiently, allowing us to carry out functional genetic analysis in an insect branching basal in the phylogenetic tree.  We work on different cell-signalling pathways to understand which pathway might be crucial for cellular communication during this patterning process.

Frederike Alwes

An important evolutionary novelty in the evolution of the multicellular animals was the emergence of three distinct tissue layers (the germ layers: ectoderm, mesoderm, and endoderm) and a dedicated germ line.  We still have little understanding of how early embryonic events changed over evolutionary time to give rise to these tissue types.  Since a close relationship between crustaceans and hexapods is now generally accepted, choosing crustacean species for study allows us to take advantage of the wealth of molecular developmental data available for the model insect species Drosophila melanogaster, as a basis for direct comparison.

There are many examples of stereotyped cell division patterns in crustaceans, but exactly how these early cleavage patterns lead to the establishment of the three germ layers and the germ line is not yet well understood.  In the amphipod Parhyale hawaiensis, cell fate restriction to a single germ layer is connected to a cytoplasmatic germ line determinant, whose existence has been demonstrated experimentally in the case of the germline, but not of the mesoderm.  In contrast, mesoderm founder cell lineage has been well described in several other decapod crustaceans, but the origins of the germ line are less clear.

We are studying the relationship between mesoderm differentiation and germ line differentiation.  This addresses the question of whether and how these two different fates can be distinguished in the cell lineage.  This project will provide the basis for subsequent studies on how germ layer formation is regulated on a molecular level and on the role of cell-cell interactions on germ layer specification.