Jasmin Balmer

Postembryonic development of transit amplifying neuroblast lineages in the Drosophila brain.

BackgroundSpecific dorsomedial (DM) neuroblast lineages of the Drosophila brain amplify their proliferation through generation of transit amplifying intermediate progenitor cells. Together, these DM neuroblast lineages comprise over 5,000 adult-specific neural cells and thus represent a substantial part of the brain. However, no information is currently available about the structure or function of any of the neural cells in these DM lineages. In this report we use MARCM-based clonal analysis together with immunocytochemical labeling techniques to investigate the type and fate of neural cells generated in the DM lineages.ResultsGenetic cell lineage-tracing and immunocytochemical marker analysis reveal that DM neuroblasts are multipotent progenitors that produce a set of postembryonic brain glia as well as a large number of adult-specific protocerebral neurons. During larval development the adult-specific neurons of each DM lineage form several spatially separated axonal fascicles, some of which project along larval brain commissural structures that are primordia of midline neuropile. By taking advantage of a specific Gal4 reporter line, the DM-derived neuronal cells can be identified and followed into early pupal stages. During pupal development the neurons of the DM lineages arborize in many parts of the brain and contribute to neuropile substructures of the developing central complex, such as the fan-shaped body, noduli and protocerebral bridge.ConclusionsOur findings provide cellular and molecular evidence for the fact that DM neuroblasts are multipotent progenitors; thus, they represent the first identified progenitor cells in the fly brain that have neuroglioblast functions during postembryonic development. Moreover, our results demonstrate that the adult-specific neurons of the DM lineages arborize widely in the brain and also make a major contribution to the developing central complex. These findings suggest that the amplification of proliferation that characterizes DM lineages may be an important requirement for generating the large number of neurons required in highly complex neuropile structures such as the central complex in the Drosophila brain.

Transplanted photoreceptor precursors transfer proteins to host photoreceptors by a mechanism of cytoplasmic fusion.

Photoreceptor transplantation is a potential future treatment for blindness caused by retinal degeneration. Photoreceptor transplantation restores visual responses in end-stage retinal degeneration, but has also been assessed in non-degenerate retinas. In the latter scenario, subretinal transplantation places donor cells beneath an intact host outer nuclear layer (ONL) containing host photoreceptors. Here we show that host cells are labelled with the donor marker through cytoplasmic transfer—94±4.1% of apparently well-integrated donor cells containing both donor and host markers. We detect the occurrence of Cre-Lox recombination between donor and host photoreceptors, and we confirm the findings through FISH analysis of X and Y chromosomes in sex-discordant transplants. We do not find evidence of nuclear fusion of donor and host cells. The artefactual appearance of integrated donor cells in host retinas following transplantation is most commonly due to material transfer from donor cells. Understanding this novel mechanism may provide alternate therapeutic strategies at earlier stages of retinal degeneration.

Visual acuity and contrast sensitivity of adult zebrafish

BackgroundThe aim of this study was to evaluate the visual acuity of adult zebrafish by assessing the optokinetic reflex. Using a modified commercially available optomotor device (OptoMotry®), virtual three-dimensional gratings of variable spatial frequency or contrast were presented to adult zebrafish. In a first experiment, visual acuity was evaluated by changing the spatial frequency at different angular velocities. Thereafter, contrast sensitivity was evaluated by changing the contrast level at different spatial frequencies.ResultsAt the different tested angular velocities (10, 15, 20, 25, and 30 d/s) and a contrast of 100%, visual acuity values ranged from 0.56 to 0.58 c/d. Contrast sensitivity measured at different spatial frequencies (0.011, 0.025, 0.5, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.55 c/d) with an angular velocity of 10 d/s and 25 d/s revealed an inverted U-shaped contrast sensitivity curve. The highest mean contrast sensitivity (±SD) values of 20.49 ± 4.13 and 25.24 ± 8.89 were found for a spatial frequency of 0.05 c/d (angular velocity 10 d/s) and 0.1 c/d (angular velocity 25 d/s), respectively.ConclusionsVisual acuity and contrast sensitivity measurements in adult zebrafish with the OptoMotry® device are feasible and reveal a remarkably higher VA compared to larval zebrafish and mice.

Characteristics of rod regeneration in a novel zebrafish retinal degeneration model using N-methyl-N-nitrosourea (MNU)

Primary loss of photoreceptors caused by diseases such as retinitis pigmentosa is one of the main causes of blindness worldwide. To study such diseases, rodent models of N-methyl-N-nitrosourea (MNU)-induced retinal degeneration are widely used. As zebrafish (Danio rerio) are a popular model system for visual research that offers persistent retinal neurogenesis throughout the lifetime and retinal regeneration after severe damage, we have established a novel MNU-induced model in this species. Histology with staining for apoptosis (TUNEL), proliferation (PCNA), activated Müller glial cells (GFAP), rods (rhodopsin) and cones (zpr-1) were performed. A characteristic sequence of retinal changes was found. First, apoptosis of rod photoreceptors occurred 3 days after MNU treatment and resulted in a loss of rod cells. Consequently, proliferation started in the inner nuclear layer (INL) with a maximum at day 8, whereas in the outer nuclear layer (ONL) a maximum was observed at day 15. The proliferation in the ONL persisted to the end of the follow-up (3 months), interestingly, without ongoing rod cell death. We demonstrate that rod degeneration is a sufficient trigger for the induction of Müller glial cell activation, even if only a minimal number of rod cells undergo cell death. In conclusion, the use of MNU is a simple and feasible model for rod photoreceptor degeneration in the zebrafish that offers new insights into rod regeneration.

Retinal Cell Death Caused by Sodium Iodate Involves Multiple Caspase-Dependent and Caspase-Independent Cell-Death Pathways.

Herein, we have investigated retinal cell-death pathways in response to the retina toxin sodium iodate (NaIO3) both in vivo and in vitro. C57/BL6 mice were treated with a single intravenous injection of NaIO3 (35 mg/kg). Morphological changes in the retina post NaIO3 injection in comparison to untreated controls were assessed using electron microscopy. Cell death was determined by TdT-mediated dUTP-biotin nick end labeling (TUNEL) staining. The activation of caspases and calpain was measured using immunohistochemistry. Additionally, cytotoxicity and apoptosis in retinal pigment epithelial (RPE) cells, primary retinal cells, and the cone photoreceptor (PRC) cell line 661W were assessed in vitro after NaIO3 treatment using the ApoToxGlo™ assay. The 7-AAD/Annexin-V staining was performed and necrostatin (Nec-1) was administered to the NaIO3-treated cells to confirm the results. In vivo, degenerating RPE cells displayed a rounded shape and retracted microvilli, whereas PRCs featured apoptotic nuclei. Caspase and calpain activity was significantly upregulated in retinal sections and protein samples from NaIO3-treated animals. In vitro, NaIO3 induced necrosis in RPE cells and apoptosis in PRCs. Furthermore, Nec-1 significantly decreased NaIO3-induced RPE cell death, but had no rescue effect on treated PRCs. In summary, several different cell-death pathways are activated in retinal cells as a result of NaIO3.

What Can Pharmacological Models of Retinal Degeneration Tell Us

Animal models with pharmacologically induced retinal degeneration including sodium iodate (NaIO3) and N-methyl-N-nitrosourea (MNU) have been extensively used in ophthalmic research to investigate retinal degeneration. NaIO3 induces degeneration of the retinal pigment epithelium (RPE) followed by photoreceptor (PRC) cell death, mimicking features of age-related macular degeneration. In contrast, MNU leads to rapid destruction of the PRCs only, enabling the use of the MNU model to investigate degeneration induced in retinitis pigmentosa. It has been shown that multiple cell death pathways are involved in the cell-specific effects of the toxins. Necrosis has been identified as the cause of the NaIO3-induced RPE loss. PRC degeneration in the described models is mainly induced by programmed cell death, indicated by the upregulation of conventional apoptosis initiator and effector caspases. However, recent research points to the additional involvement of caspase-independent processes as endoplasmic reticulum stress and calpain activation. Since there is still a substantial amount of contradictory hypotheses concerning triggers of cell death, the use of pharmacological models is controversial. Thereby, the advantages of such models like the application reaching across species and strains as well as modulation of onset and severity of damage are not exploited to a full extent. Thus, the present review aims to give more insight into the involved cell death pathways and discusses recent findings in the most widely used retinal degeneration models. It might facilitate further studies aiming to develop putative therapeutic approaches for retinal degenerative diseases including combinatory treatment with cell death inhibitors and cell transplantation therapy.

Structural characterization of four different naturally occurring porcine collagen membranes suitable for medical applications

Collagen is the main structural element of connective tissues, and its favorable properties make it an ideal biomaterial for regenerative medicine. In dental medicine, collagen barrier membranes fabricated from naturally occurring tissues are used for guided bone regeneration. Since the morphological characteristics of collagen membranes play a crucial role in their mechanical properties and affect the cellular behavior at the defect site, in-depth knowledge of the structure is key. As a base for the development of novel collagen membranes, an extensive morphological analysis of four porcine membranes, including centrum tendineum, pericardium, plica venae cavae and small intestinal submucosa, was performed. Native membranes were analyzed in terms of their thickness. Second harmonic generation and two-photon excitation microscopy of the native membranes showed the 3D architecture of the collagen and elastic fibers, as well as a volumetric index of these two membrane components. The surface morphology, fiber arrangement, collagen fibril diameter and D-periodicity of decellularized membranes were investigated by scanning electron microscopy. All the membrane types showed significant differences in thickness. In general, undulating collagen fibers were arranged in stacked layers, which were parallel to the membrane surface. Multiphoton microscopy revealed a conspicuous superficial elastic fiber network, while the elastin content in deeper layers varied. The elastin/collagen volumetric index was very similar in the investigated membranes and indicated that the collagen content was clearly higher than the elastin content. The surface of both the pericardium and plica venae cavae and the cranial surface of the centrum tendineum revealed a smooth, tightly arranged and crumpled morphology. On the caudal face of the centrum tendineum, a compact collagen arrangement was interrupted by clusters of circular discontinuities. In contrast, both surfaces of the small intestinal submucosa were fibrous, fuzzy and irregular. All the membranes consisted of largely uniform fibrils displaying the characteristic D-banding. This study reveals similarities and relevant differences among the investigated porcine membranes, suggesting that each membrane represents a unique biomaterial suitable for specific applications.

The Rho regulator Myosin IXb enables nonlymphoid tissue seeding of protective CD8 T cells.

T cells are actively scanning pMHC-presenting cells in lymphoid organs and nonlymphoid tissues (NLTs) with divergent topologies and confinement. How the T cell actomyosin cytoskeleton facilitates this task in distinct environments is incompletely understood. Here, we show that lack of Myosin IXb (Myo9b), a negative regulator of the small GTPase Rho, led to increased Rho-GTP levels and cell surface stiffness in primary T cells. Nonetheless, intravital imaging revealed robust motility of Myo9b−/− CD8+ T cells in lymphoid tissue and similar expansion and differentiation during immune responses. In contrast, accumulation of Myo9b−/− CD8+ T cells in NLTs was strongly impaired. Specifically, Myo9b was required for T cell crossing of basement membranes, such as those which are present between dermis and epidermis. As consequence, Myo9b−/− CD8+ T cells showed impaired control of skin infections. In sum, we show that Myo9b is critical for the CD8+ T cell adaptation from lymphoid to NLT surveillance and the establishment of protective tissue–resident T cell populations.