Universität zu Köln

Frey, Nadine (2017). Genomic approaches to dorsoventral patterning and functional studies of epithelial morphogenesis in the short-germ beetle Tribolium castaneum. PhD thesis, Universität zu Köln.

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Abstract

A crucial step in early embryonic development is the determination of different cell fates along the dorsoventral (DV) axis. These cell fates are defined by the spatially and temporally restricted expression of gene sets, controlled by complex gene regulatory networks (GRN). Here, we address the evolution of the DV-GRN within insects. In the highly derived group of the drosophilids, dorsoventral patterning is dominated by Toll-signaling, which directly controls BMP-signaling. Whereas the DV-GRN of Drosophila melanogaster is well understood, little is known about the GRN that acts during establishment of the DV axis in more basally branching insects like the red flour beetle Tribolium castaneum. This work aimed to identify new potential DV patterning genes in Tribolium. To achieve this goal, a comparative transcriptome analysis after knockdown of Toll signaling and BMP signaling components by RNAi was performed. I analyzed the expression patterns of selected subgroups of the 796 differentially expressed genes. Furthermore, functional studies for genes exhibiting typical dorsoventral expression patterns were performed. The results suggest that some of the conserved DV-GRN components (e.g. Tartan) have a stronger and earlier influence on DV patterning in Tribolium. In addition, the expression of Notch signaling components clearly differs from the expression pattern of their Drosophila homologs. But the most striking finding was the identification of Zfh-1, which is required for maintaining Tc-twist expression during germ band extension and is thus essential for mesoderm development in Tribolium. Besides the establishment of the body axis, morphogenetic movements of epithelial sheets significantly contribute to the development of complex embryonic structures. The Fog signaling pathway is one of the best studied processes in initiating early morphogenetic movements by cell shape changes. Modifications of the acto-myosin cytoskeleton by Fog signaling result in apical cell constrictions which enable bending of epithelial sheets. In Drosophila, loss of Fog signaling causes defects in mesoderm and posterior midgut internalization. So far, it was assumed that Fog signaling is exclusively involved in gastrulation in some highly derived flies. In the second part of this work the role of Fog signaling was analyzed in Tribolium, which possesses a more ancestral mode of embryogenesis. Interestingly, knockdown of important Fog signaling components in Tribolium cause similar defects in ventral furrow formation and internalization of the posterior endoderm. This indicates the conservation of Fog signaling in tissue internalization during gastrulation outside of higher dipterans. In addition, this work presents so far unknown functions of the Fog signaling pathway in formation of the posterior amniotic fold, positioning of the primordial germ cells and spreading of the serosa. Furthermore, the results suggest another conserved more general role of Fog in coordinating cell shape changes in the blastoderm.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Frey, Nadine nfrey1086@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-79594
Date:	2017
Language:	German
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Institut für Entwicklungsbiologie
Subjects:	Life sciences
Uncontrolled Keywords:	Keywords Language Tribolium castaneum, DV patterning, RNA-seq, differential transcriptome analysis, morphogenetic movements, morphogenesis, Fog signaling, apical constrictions,mesoderm internalization, primordial germ cells English
Date of oral exam:	19 December 2017
Referee:	Name Academic Title Roth, Siegfried Prof. Dr. Kroiher, Michael Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/7959