AbstractsBiology & Animal Science

Super-resolution fluorescence microscopy performed via 3D structured illumination microscopy (3D-SIM) features an 8-fold volumetric resolution improvement over conventional microscopy and is well established on flat, adherent cells. However, blastomeres in mammalian embryos are non-adherent, round and large. Scanning whole mount mammalian embryos with 3D-SIM is prone to failure due to non-adherent embryos moving during scanning and a large distance to the cover glass. The biggest challenge and achievement of this doctorate thesis was the development of a novel method to perform 3D-SIM on mammalian embryos (“3D structured illumination microscopy of mammalian embryos and spermatozoa” published in BMC Developmental Biology). The development and fine-tuning of this method took over two years due to the time-intense generation of embryos and the subsequent two day long embryo staining, embedding and scanning with steps that required novel techniques such as micromanipulation which was not associated with sample preparation prior to this protocol. Problem identification was time-intensive since each of the numerous steps necessary could negatively affect the image quality. This method was fine-tuned during three studies. The first study “Reprogramming of fibroblast nuclei in cloned bovine embryos involves major structural remodeling with both striking similarities and differences to nuclear phenotypes of in vitro fertilized embryos” (published in Nucleus) investigates the profound changes of nuclear architecture during cattle preimplantation development of embryos generated by somatic cell nuclear transfer (SCNT) and in vitro fertilization (IVF). Fibroblast nuclei in embryos generated by SCNT go through similar changes in nuclear architecture as embryos generated by IVF. In both embryo types the occurrence of a large, chromatin-free lacuna in the center of nuclei around major embryonic genome activation (EGA) was noted. Similarly, the chromosome territory-interchromatin compartment (CT-IC) model applied to both types of embryos, featuring a lacuna or not, with an enrichment of RNA polymerase II and H3K4me3, a histone modification for transcriptionally competent chromatin, in less concentrated chromatin and an enrichment of H3K9me3, a transcriptionally restrictive histone modification, in more concentrated chromatin. However, large, highly concentrated H3K4me3 and H3K9me3 clusters were noted in both embryo types at chromatin concentrations that did not fit to the model. The chromatin-free lacunas were highly enriched in newly synthesized mRNA. The second study “Remodeling of the Nuclear Envelope and Lamina during Bovine Preimplantation Development and Its Functional Implications” (published in PLOS ONE) presents the changes of the nuclear envelope and lamina during bovine preimplantation development. Before major EGA, chromatin-free areas of the nuclear periphery were also free of nuclear pore complexes (NPCs), whereas after major EGA, the entire nuclear periphery was equipped with at least a fine layer of chromatin and… Advisors/Committee Members: Cremer, Thomas (advisor).