Abstracts (first author)

Talk 

A tale of two ends: axis polarity in the scuttle fly Megaselia abdita

Author(s): Wotton KR, Jimenez Guri E, Jaeger J

Summary:

In dipterans (flies, midges and mosquitoes), segment determination occurs early in embryogenesis through a hierarchy of genes activated by maternal factors. These include the anterior determinant bicoid (bcd), found only in Cyclorrhapha or "higher" flies, and also caudal (cad), hunchback (hb), and nanos (nos). Loss of any one of these genes in Drosophila results in the loss of segments, and in some cases duplication of anterior or posterior structures at the opposite pole of the egg. However, in none of these cases is global polarity lost. In contrast, removal of both maternal bcd and hb results in symmetrical embryos (mirror-abdomen or bicaudal phenotypes) in which global anterior-posterior polarity is lost. Similar bicaudal phenotypes can be generated in two other fly species, the hover fly Episyrphus balteatus and the scuttle fly Megaselia abdita, by knocking down only maternal bcd. In Episyrphus, this has been explained by a lack of maternal hb. However, in Megaselia this factor is present so another explanation must be found. We have generated gene knock-downs for each of the maternal factors in Megaselia and analysed the resulting gene expression patterns. We identify loss of Kr activation by maternal hb as the likely cause of the loss of polarity. Furthermore, we identify differences in cad and gap gene expression that account for the more anterior plane of symmetry observed in Megaselia bicaudal phenotypes. These differences suggest that a number of regulatory changes in the gap gene network have occurred since the divergence of these dipteran lineages. We are testing these inferred changes by performing more knock-down experiments, combined with data-driven modeling of the gap gene system in this species. Finally, we revisit the question of Kr activation in Drosophila and suggest an evolutionary scenario for the development of anterior-posterior polarity in dipterans.



Abstracts (coauthor)

Comparative transcriptomics of early Dipteran development

Author(s): Jimenez-Guri, E, Huerta-Cepas J, Cozzuto L, Wotton KR, Roma G, Gabaldon T, Jaeger J

Summary:

We are carrying out a comparative analysis of transcriptomic sequence data in early embryos of three emerging experimental dipteran model systems. Clogmia albipunctata belongs to a lineage of flies believed to have diverged early in the evolution of the dipterans, while the lineage leading to Megaselia abdita branched intermediately, at the base of the cyclorraphans, and the lineage leading to Episyrphus balteatus diverged later in the cyclorraphans.

We have acquired and assembled transcriptomic sequences at early embryonic stages in Clogmia albipunctata and Megaselia abdita. We compare these sequences to those from Episyrphus balteatus as well as transcriptomic and genomic sequences from drosophilids and/or mosquitoes. These datasets form the basis of a new phylogenomic assessment of dipteran relationships. It places psychodid moth midges (such as Clogmia) as a sister group to the brachycerans, rather than within the culicomorph lineage, in contrast to another recent study (Wiegman et al., 2011). Furthermore, we have analysed patterns of gene duplication in our datasets. Finally, we have verified information present in our transcriptomes by manual curation, in situ hybridization, and verification of alternative splicing events among a subset of genes present in the data.

Contacts

Chairman: Octávio S. Paulo
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email: mail@eseb2013.com

Address

XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon
Portugal

Website

Computational Biology & Population Genomics Group 
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