Biomedical subjects

Urs Schmidt-Ott

Publications and source records attributed to Urs Schmidt-Ott.

5 recordsLinked to original sources

PubMed2025

Breaking anterior-posterior symmetry in the moth fly Clogmia albipunctata.

Establishing the anterior-posterior (AP) body axis is a fundamental process during embryogenesis, and the fruit fly, Drosophila melanogaster, provides one of the best-known case studies. But for unknown reasons, different species of flies (Diptera) establish the AP axis through unrelated, structurally distinct anterior determinants (ADs). The AD of Drosophila, Bicoid (Bcd), initiates symmetry-breaking during nuclear cleavage cycles (NCs) when ubiquitous pioneer factors, such as Zelda (Zld), drive zygotic genome activation (ZGA) at the level chromatin accessibility by nucleosome depletion. While Bcd engages in a concentration-dependent competition with nucleosomes at the loci of a small set of transcription factor (TF) genes that are expressed in the anterior embryo, it remains unknown whether unrelated ADs of other fly species function in the same way and target homologous genes. We have examined the symmetry-breaking mechanism of a moth fly, Clogmia albipunctata, in which a maternally expressed transcript isoform of the pair-rule segmentation gene odd-paired serves as AD. We provide a de novo assembly and annotation of the Clogmia genome and describe how Clogmia's orthologs of zelda (Cal-zld) and odd-paired (Cal-opa) affect chromatin accessibility and gene expression. Our results suggest direct roles of Cal-zld in opening and closing chromatin during nuclear cleavage cycles (NCs) and show that during the early phase of ZGA maternal Cal-opa activity promotes chromatin accessibility and anterior expression at Clogmia's homeobrain and sloppy-paired loci. These genes are not known as key targets of Bcd but may serve a more widely conserved role in the initiation of anterior pattern formation given their early anterior expression and function in head development in insects. We conclude that the ADs of Drosophila and Clogmia differ in their target genes but share the mechanism of concentration-dependent nucleosome depletion.

Journal Article↗

PubMed2005

Insect serosa: a head line in comparative developmental genetics.

A recent study reveals specific functions of Hox3/zerknüllt (zen) in the extraembryonic and embryonic primordia of the red flour beetle, Tribolium castaneum. The results shed light on the functional evolution of bicoid, a zen paralogue of higher flies, which determines anterior body parts.

Animals↗

PubMed2004

Differential cytoplasmic mRNA localisation adjusts pair-rule transcription factor activity to cytoarchitecture in dipteran evolution.

Establishment of segmental pattern in the Drosophila syncytial blastoderm embryo depends on pair-rule transcriptional regulators. mRNA transcripts of pair-rule genes localise to the apical cytoplasm of the blastoderm via a selective dynein-based transport system and signals within their 3'-untranslated regions. However, the functional and evolutionary significance of this process remains unknown. We have analysed subcellular localisation of mRNAs from multiple dipteran species both in situ and by injection into Drosophila embryos. We find that although localisation of wingless transcripts is conserved in Diptera, localisation of even-skipped and hairy pair-rule transcripts is evolutionarily labile and correlates with taxon-specific changes in positioning of nuclei. We show in Drosophila that localised pair-rule transcripts target their proteins in close proximity to the nuclei and increase the reliability of the segmentation process by augmenting gene activity. Our data suggest that mRNA localisation signals in pair-rule transcripts affect nuclear protein uptake and thereby adjust gene activity to a variety of dipteran blastoderm cytoarchitectures.

3' Untranslated Regions↗

PubMed2004

Evo-devo aspects of classical and molecular data in a historical perspective.

We discuss the interplay between evolution and development as reflected in data and concepts since about 1800. Darwin and his "continental apostle" Haeckel put the striking similarity between early vertebrate embryos in an evolutionary context. Haeckel's partly illicit generalizations discredited evolutionary thinking among early experimental embryologists who moreover noted riddles incompatible with contemporary concepts of homology and evolution. Relevant solutions were suggested by the more recent concept of ontogenetic networks that embody complex regulatory properties and genes with partly overlapping functions. Molecular data on development increasingly reveal evolutionary opportunism, for instance when a widespread signaling chain involved in primitive immune defense was apparently recruited later on for dorso-ventral axis determination in some evolutionarily advanced insect groups. Recently, Rickettsia-related bacteria colonizing many arthropod species were found to "manipulate" the first steps of host development to the advantage of their own propagation, but by ways that could also promote host speciation. Molecular genetics can now document evolutionary steps in ontogenetic networks. In the fruit fly for instance, the novel bicoid gene has superseded a crucial patterning function within a pre-existing network--a case of "molecular caenogenesis." The expression patterns of conserved genes that antagonistically determine dorso-ventral polarity support a literal revolution envisioned almost 200 years ago. This is the dorso-ventral inversion of the body plan in some metazoans--ascribed then to the Articulata, now to the Chordata. The final section posits that the opportunistic character of evolutionary innovations is detrimental to parsimony in development.

Animals↗

PubMed2002

A single Hox3 gene with composite bicoid and zerknullt expression characteristics in non-Cyclorrhaphan flies.

The members of the evolutionarily conserved Hox-gene complex, termed Hox genes, are required for specifying segmental identity during embryogenesis in various animal phyla. The Hox3 genes of winged insects have lost this ancestral function and are required for the development of extraembryonic epithelia, which do not contribute to any larval structure. Higher flies (Cyclorrhapha) such as Drosophila melanogaster contain Hox3 genes of two types, the zerknüllt type and the bicoid type. The zerknüllt gene is expressed zygotically on the dorsal side of the embryo and is required for establishing extraembryonic tissue. Its sister gene bicoid is expressed maternally and the transcripts are localized at the anterior pole of the mature egg. BICOID protein, which emerges from this localized source during early development, is required for embryonic patterning. All known direct bicoid homologues are confined to Cyclorrhaphan flies. Here, we describe Hox3 genes of the non-Cyclorrhaphan flies Empis livida (Empididae), Haematopota pluvialis (Tabanidae), and Clogmia albipunctata (Psychodidae). The gene sequences are more similar to zerknüllt homologues than to bicoid homologues, but they share expression characteristics of both genes. We propose that an ancestral Hox3 gene had been duplicated in the stem lineage of Cyclorrhaphan flies. During evolution, one of the gene copies lost maternal expression and evolved as zerknüllt, whereas the second copy lost zygotic expression and evolved as bicoid. Our finding correlates well with a partial reduction of zerknüllt-dependent extraembryonic tissue during Dipteran evolution.

Amino Acid Sequence↗