Vera Lahl et al. (2001) International C. elegans Meeting "Variations in pattern formation and cell specification during nematode embryogenesis"

Magdalena Laugsch, Einhard Schierenberg, Vera Lahl

[International C. elegans Meeting, 2001]

We have found that the cephalobid nematode A. nanus expresses considerable differences in the pattern of cell specification and spatial arrangement of cells during early embryogenesis compared to C. elegans (Wiegner and Schierenberg, Dev. Biol.,1998, 1999). Based on these results we have begun to analyze other free-living and parasitic nematodes in this respect. Here we report our findings on representatives belonging to the same family as C. elegans (Rhabditidae). We find major differences in the duration of cell cycles, early zygotic transcription, cellular pattern formation and cell-cell interactions required for proper fate assignment. In contrast, species with only distant relationship to C. elegans may nevertheless show more similarities in this respect. This indicates that variations cannot be explained by phylogenetic position alone. We suggest that the observed differences reflect alternative developmental strategies going along with the occupation of different ecological niches.

Einhard Schierenberg et al. (2002) European Worm Meeting "Phylogeny and ontogeny of free-living and parasitic nematodes"

Vera Lahl, Magdalena Laugsch, Einhard Schierenberg, Thomas Goedde

[European Worm Meeting, 2002]

Phylogenetic relationships between nematodes have always been discussed controversially. In recent years analysis of molecular data, particularly sequence data from genes coding for ribosomal RNA, have challenged some of the traditional taxonomic proposals based on morphological criteria. As a third means to identify characters of potential phylogenetic value, we are studying developmental processes during early embryogenesis. The study of free-living and parasitic represenatives of diverse taxa revealed differences in the establishement of axial polarity, separation of soma and germline, assignment of cell fates and the pattern of gastrulation. Some of the existing differences can be readily identified by comparative, light microscopical analysis while others require experimental interference. Our results support the notion that the classical separation into Secernentia and Adenophorea is artificial, and that at least three supertaxa should be defined. In some cases we identified major differences between species considered to be rather closely related, questioning their present position in the phylogenetic tree. To assess the phylogenetic value of specific developmental characters, cases are of particular interest where conclusions conflict with those from other approaches.

Vera Lahl et al. (2001) International C. elegans Meeting "Early embryogenesis differs even in close relatives of C. elegans"

Vera Lahl, Marzena Kutzowitz, Christian Halama, Stefan Ingensand, Einhard Schierenberg, Magdalena Laugsch

[International C. elegans Meeting, 2001]

We have started to study close and more distant relatives of C. elegans for their pattern of embryogenesis. While many differ only marginally from C. elegans, others show considerable differences. These include the sequence of divisions, variations in the spatial arrangement of blastomeres, presence or absence of polarity reversal in the germline, requirement of early zygotic transcription for cleavage, mode of cell specification, gastrulation, and temperature tolerance. Variations in many but not all variations can be understood as different aspects of heterochrony. We find that,depending on the parameter considered, species closer related to C. elegans may nevertheless express stronger differences than species phylogenetically more distant. This suggests that environmental factors influence the pattern of early development.