Juniorprofessor Dr. Steffen Lemke
Lemke S, Antonopoulos DA, Meyer F, Domanus MH, Schmidt-Ott U. (2011). BMP signaling components in embryonic transcriptomes of the hover fly Episyrphus balteatus (Syrphidae). BMC Genomics.12:278.
BACKGROUND: In animals, signaling of Bone Morphogenetic Proteins (BMPs) is essential for dorsoventral (DV) patterning of the embryo, but how BMP signaling evolved with changes in embryonic DV differentiation is largely unclear. Based on the extensive knowledge of BMP signaling in Drosophila melanogaster, the morphological diversity of extraembryonic tissues in different fly species provides a comparative system to address this question. The closest relatives of D. melanogaster with clearly distinct DV differentiation are hover flies (Diptera: Syrphidae). The syrphid Episyrphus balteatus is a commercial bio-agent against aphids and has been established as a model organism for developmental studies and chemical ecology. The dorsal blastoderm of E. balteatus gives rise to two extraembryonic tissues (serosa and amnion), whereas in D. melanogaster, the dorsal blastoderm differentiates into a single extraembryonic epithelium (amnioserosa). Recent studies indicate that several BMP signaling components of D. melanogaster, including the BMP ligand Screw (Scw) and other extracellular regulators, evolved in the dipteran lineage through gene duplication and functional divergence. These findings raise the question of whether the complement of BMP signaling components changed with the origin of the amnioserosa. RESULTS: To search for BMP signaling components in E. balteatus, we generated and analyzed transcriptomes of freshly laid eggs (0-30 minutes) and late blastoderm to early germband extension stages (3-6 hours) using Roche/454 sequencing. We identified putative E. balteatus orthologues of 43% of all annotated D. melanogaster genes, including the genes of all BMP ligands and other BMP signaling components. CONCLUSION: The diversification of several BMP signaling components in the dipteran linage of D. melanogaster preceded the origin of the amnioserosa.[Transcriptome sequence data from this study have been deposited at the NCBI Sequence Read Archive (SRP005289); individually assembled sequences have been deposited at GenBank (JN006969-JN006986).].
Rafiqi AM, Lemke S, Schmidt-Ott U. (2011). Megaselia abdita: cuticle preparation from injected embryos. Cold Spring Harb Protoc.2011(4):pdb.prot5603.
PMID: 21460052 [PubMed - indexed for MEDLINE]
Rafiqi AM, Lemke S, Schmidt-Ott U. (2011). Megaselia abdita: fixing and devitellinizing embryos. Cold Spring Harb Protoc.2011(4):pdb.prot5602.
PMID: 21460051 [PubMed - indexed for MEDLINE]
Rafiqi AM, Lemke S, Schmidt-Ott U. (2011). Megaselia abdita: preparing embryos for injection. Cold Spring Harb Protoc.2011(4):pdb.prot5601.
PMID: 21460050 [PubMed - indexed for MEDLINE]
Rafiqi AM, Lemke S, Schmidt-Ott U. (2011). Megaselia abdita: culturing and egg collection. Cold Spring Harb Protoc.2011(4):pdb.prot5600.
PMID: 21460049 [PubMed - indexed for MEDLINE]
Rafiqi AM, Lemke S, Schmidt-Ott U. (2011). The scuttle fly Megaselia abdita (Phoridae): a link between Drosophila and Mosquito development. Cold Spring Harb Protoc.2011(4):pdb.emo143.
PMID: 21460041 [PubMed - indexed for MEDLINE]
Lemke S, Busch SE, Antonopoulos DA, Meyer F, Domanus MH, Schmidt-Ott U. (2010). Maternal activation of gap genes in the hover fly Episyrphus. Development.137(10):1709-19.
Rafiqi AM, Lemke S, Schmidt-Ott U. (2010). Postgastrular zen expression is required to develop distinct amniotic and serosal epithelia in the scuttle fly Megaselia. Dev Biol.341(1):282-90.
The amnioserosa is an extraembryonic epithelium that evolved in higher cyclorrhaphan flies from distinct serosal and amniotic epithelia. The underlying genetic mechanism of this evolutionary transition is unknown. Amnioserosa development of Drosophila correlates with novel expression characteristics of the homeobox gene zerknüllt (zen), including a broad zen expression domain in the syncytial blastoderm and the complete absence of postgastrular zen expression. Here we examine the functional significance of these features by altering the activity profile of zen in Megaselia (a lower cyclorrhaphan fly with distinct serosal and amniotic epithelia) and Drosophila, and by examining in Megaselia the function of u-shaped group (ush-group) genes, which in Drosophila maintain the amnioserosa after gastrulation when zen is no longer expressed. In Megaselia, loss of postgastrular zen expression abrogates serosa development but allows amnion development. Ectopic expression of zen in early Megaselia embryos allows serosa formation but perturbs amnion development. Megaselia homologues of u-shaped group genes are not essential for serosa formation but mediate germband retraction and dorsal closure. Finally, ectopic postgastrular zen expression in Drosophila causes an enlargement of amnioserosa cells and interferes with the morphogenetic functions of the amnioserosa. Our results suggest that the origin of the amnioserosa involved the loss of postgastrular zen expression from extraembryonic tissue, that the early broad expression domain of Drosophila zen evolved afterwards, and that the ush-group genes ancestrally played a role in morphogenetic functions of the amnion.
Lemke S, Schmidt-Ott U. (2009). Evidence for a composite anterior determinant in the hover fly Episyrphus balteatus (Syrphidae), a cyclorrhaphan fly with an anterodorsal serosa anlage. Development.136(1):117-27.
Erratum in Development. 2009 Feb;136(3):507.
Lemke S, Stauber M, Shaw PJ, Rafiqi AM, Prell A, Schmidt-Ott U. (2008). Bicoid occurrence and Bicoid-dependent hunchback regulation in lower cyclorrhaphan flies. Evol Dev.10(4):413-20.
The homeobox gene bicoid functions as an anterior pattern organizer of the Drosophila embryo, but other than in higher flies (Cyclorrhapha), bicoid orthologues appear to be absent from insect genomes. In Drosophila, bicoid is expressed in an anterior-to-posterior protein gradient and regulates spatially restricted expression domains of segmentation genes in a concentration-dependent manner. hunchback, a direct transcriptional target of Bicoid, complements the "morphogen" activity of Bicoid. hunchback is activated by Bicoid throughout the anterior half of the blastoderm and a Bicoid-binding cis-regulatory element has been identified immediately upstream of the proximal hunchback promoter P2 of Drosophila and other higher Cyclorrhapha (Schizophora). bicoid and Bicoid-dependent hunchback regulation are thought to have originated during or before the radiation of extant Cyclorrhapha, although the precise occurrence of these traits in lower Cyclorrhapha remains unknown. Previously, we have described a bicoid orthologue in Megaselia, a species of the lower cyclorrhaphan family Phoridae. Here, we report the occurrence of bicoid in two additional lower cyclorrhaphan families, Lonchopteridae and Platypezidae. We show that Megaselia Bicoid is required for anterior expression of Megaselia hunchback, and binds upstream of its P2 promoter. Furthermore, we report the expression of lacZ reporter constructs under the control of hunchback regulatory sequences from a range of lower cyclorrhaphan and non-cyclorrhaphan flies in transgenic Drosophila embryos. Our results are consistent with a cyclorrhaphan origin of bicoid and suggest that a Bicoid-binding enhancer upstream of the hunchback P2 promoter evolved at the latest in the last common ancestor of Megaselia and Schizophora.
Stauber M, Lemke S, Schmidt-Ott U. (2008). Expression and regulation of caudal in the lower cyclorrhaphan fly Megaselia. Dev Genes Evol.218(2):81-7.
The homeobox gene caudal (cad) regulates posterior development in Drosophila. In early embryos, the cad protein (CAD) is expressed in a posterior-to-anterior concentration gradient, which contributes polarity to the developing embryo. The CAD gradient is complementary to and dependent on the anterior pattern organizer Bicoid (BCD), which represses the translation of ubiquitous maternal cad transcripts in the anterior embryo through a direct interaction with the cad 3' untranslated region (UTR). Here, we show that early embryos of the lower cyclorrhaphan fly Megaselia express the putative cad orthologue Mab-cad throughout the posterior three quarters of the blastoderm but lack maternal transcripts. In transgenic blastoderm embryos of Drosophila, Mab-cad cis-regulatory DNA drives the expression of a reporter gene in a similar pattern, while Mab-cad 3' UTR fails to mediate translational repression of a ubiquitously transcribed reporter. For another lower cyclorrhaphan fly (Lonchoptera) and two related outgroup taxa of Cyclorrhapha (Empis, Haematopota), we report maternal cad expression in ovarian follicles. Together, our results suggest that BCD is not required for the translational repression of Mab-cad, and that maternal cad expression was lost in the Megaselia lineage.
Rafiqi AM, Lemke S, Ferguson S, Stauber M, Schmidt-Ott U. (2008). Evolutionary origin of the amnioserosa in cyclorrhaphan flies correlates with spatial and temporal expression changes of zen. Proc Natl Acad Sci U S A.105(1):234-9.
Higher cyclorrhaphan flies including Drosophila develop a single extraembryonic epithelium (amnioserosa), which closes the germband dorsally. In most other insects two extraembryonic epithelia, serosa and amnion, line the inner eggshell and the ventral germband, respectively. How the two extraembryonic epithelia evolved into one is unclear. Recent studies have shown that, in the flour beetle Tribolium and in the milkweed bug Oncopeltus, the homeobox gene zerknüllt (zen) controls the fusion of the amnion with the serosa before dorsal closure. To understand the origin of the amnioserosa in evolution, we examined the expression and function of zen in the extraembryonic tissue of lower Cyclorrhapha. We show that Megaselia abdita (Phoridae) and Episyrphus balteatus (Syrphidae) develop a serosa and a dorsal amnion, suggesting that a dorsal amnion preceded the origin of the amnioserosa in evolution. Using Krüppel (Kr) and pannier (pnr) homologues of Megaselia as markers for serosal and amniotic tissue, respectively, we show that after zen RNAi all extraembryonic tissue becomes indistinguishable from amniotic cells, like in Tribolium but unlike in Drosophila, in which zen controls all aspects of extraembryonic development. Compared with Megaselia and Episyrphus, zen expression in Drosophila is extended to cells that form the amnion in lower Cyclorrhapha and is down-regulated at the developmental stage, when serosa cells in lower Cyclorrhapha begin to expand. These expression differences between species with distinct extraembryonic tissue organizations and the conserved requirement of zen for serosa development suggest that the origin of an amnioserosa-like epithelium was accompanied by expression changes of zen.