Biology subjects

Ramos, A. P.

Publications and source records attributed to Ramos, A. P..

5 recordsLinked to original sources

bioRxiv2025

The Optic cup is actively shape programmed by independently patterned apical forces

During morphogenesis, initially flat tissues often must transition into complex 3D shapes, reminiscent of shape-programmable systems in physics and engineering. One key question in developmental biology and physics alike is therefore how distinct mechanical inputs interact to produce the correct shape. To investigate this, we here study the onset of optic cup invagination during vertebrate eye development, combining 3D shape analysis, perturbation experiments, and physical modelling inspired by shape-programmable materials. We find that basal invagination is initiated at the apical surfaces through active, patterned cell behaviours. These behaviours generate in-plane strain patterns reshaping the apical surface and thereby bending the tissue basally. Surprisingly, this means that basal shape initiation is driven by apical dynamics. While retinal pigmented epithelium and neuroepithelium exhibit distinct shape transitions, these are temporally coordinated to jointly shape the optic cup. These findings highlight that 3D shape can emerge from local apical activity of two coordinated patterns.

developmental biology↗

bioRxiv2024

Nuclear deformability facilitates apical nuclear migration in the developing zebrafish retina

Nuclear positioning is an important aspect of cell and developmental biology. One example is the apical positioning of nuclei in retinal and other neuroepithelia. Here, apical nuclear migration is crucial for correct tissue formation. Cytoskeletal mechanisms that drive nuclei to the apical side have been explored. Yet, whether also nuclear properties influence apical nuclear migration remained comparatively less understood. Lamin A/C expression levels have been shown to be directly related to nuclear deformability. Further, it was shown that many nuclei in early development, including neuroepithelial nuclei, express only low levels of Lamin A/C. Thus, we asked whether increased expression of Lamin A in the densely packed zebrafish retinal neuroepithelium affects nuclear migration phenomena. We find that overexpressing Lamin A in retinal nuclei of single cells or in the whole tissue increased nuclear stiffness and consequently impaired apical positioning. Interestingly, also nuclei of control cells embedded in a Lamin A overexpressing environment displayed impaired apical nuclear migration. When Lamin A is overexpressed at the tissue level this further leads to a delay in mitotic entry. Thus, nuclear material properties, within cells but also in the surrounding environment, can influence nuclear and cell behavior in densely packed neuroepithelia. Overall, this work quantitatively shows a relevance of low Lamin A/C levels in early neuroepithelial development. These findings are most likely also applicable for other developing tissues which feature nuclear and cell motion through crowded environments.

developmental biology↗

bioRxiv2023

Unravelling the relationship between isolated bone matrix vesicles and forming mineral at the nanometer scale

Matrix vesicles (MVs) are involved in the initial deposition of hydroxyapatite (HAp) during bone mineralization, but their mechanism of action is not yet fully understood. In vitro studies propose two pathways by which MVs can trigger HAp precipitation: the first is mediated by their enhanced phosphatase activity, and the second suggested to depend on structural components present in MVs to mediate nucleation directly from soluble ions without the requirement of phosphatase activity. However, the relevance of these two pathways for bone mineralization and the relationship between MVs and forming mineral in such in vitro experiments remains unclear. Here, we used near-native cryoTEM nanoscale imaging in combination with bulk characterizations to disentangle the content and action of MVs during in vitro mineralization. We show that MVs isolation by conventional ultracentrifugation results in heterogeneous dispersions containing non-vesicular particles, including collagens and proteoglycans, in addition to bilayered vesicles. The separation of phosphatase-enriched MVs from non-vesicular particles and comparative mineralization experiments demonstrated that the ability of MVs to induce fast mineralization, independently of phosphatase activity, depends on the presence of non-vesicular particles. Therefore, we conclude that the primary pathway by which MVs trigger mineralization is through the action of their resident phosphatase enzymes, with the direct mineral nucleation to be a secondary event consequential of their membrane components. Lastly, we observed mineral formation restricted to the extravesicular space or in close proximity to the membrane interface, suggesting that the relationship between MVs and forming mineral is more intricate than previously understood.

biophysics↗

bioRxiv2022

Matrix topology guides collective cell migration in vivo

Diverse modes of cell migration shape organisms in health and disease and much research has focused on the role of intracellular and extracellular components in different cell migration phenomena. What is less explored, however, is how the arrangement of the underlying extracellular matrix that many cells move upon in vivo influences migration. Combining novel transgenic lines and image analysis pipelines, reveals that during zebrafish optic cup formation cells use cryptopodia-like protrusions to migrate collectively and actively over a topologically changing matrix. These changing topologies correspond to different cell-matrix interactions. Interference with matrix topology results in loss of cryptopodia and inefficient migration. Thus, matrix topology influences the efficiency of directed collective cell migration during eye morphogenesis, a concept likely conserved in other developmental and disease contexts. One-Sentence SummaryDynamic cell-matrix interactions, crucial for successful collective rim cell migration, rely on extracellular matrix topologies during optic cup development in vivo.

developmental biology↗

bioRxiv2019

The visual system of the genetically tractable crustacean Parhyale hawaiensis: diversification of eyes and visual circuits associated with low-resolution vision

BackgroundArthropod eyes have diversified during evolution to serve multiple needs, such as finding mates, hunting prey, and navigating in complex surroundings under varying light conditions. This diversity is reflected in the optical apparatus, photoreceptors and neural circuits that underpin vision. While this diversity has been extensively documented, our ability to genetically manipulate the visual system to investigate its function is largely limited to a single species, the fruitfly Drosophila melanogaster. Here, we describe the visual system of Parhyale hawaiensis, an amphipod crustacean for which we have established tailored genetic tools. ResultsAdult Parhyale have apposition-type compound eyes made up of [~]50 ommatidia. Each ommatidium contains four photoreceptor cells with large rhabdomeres (R1-4), expected to be sensitive to the polarisation of light, and one photoreceptor cell with a smaller rhabdomere (R5). The two types of photoreceptors express different opsins, belonging to families with distinct wavelength sensitivities. Using the cis.-regulatory regions of opsin genes, we established transgenic reporters expressed in each photoreceptor cell type. Based on these reporters, we show that R1-4 and R5 photoreceptors extend axons to the first optic lobe neuropil, revealing striking differences compared with the photoreceptor projections found in related crustaceans and insects. Investigating visual function, we show that Parhyale has a positive phototactic response and is capable of adapting its eyes to different levels of light intensity. ConclusionsWe propose that the visual system of Parhyale serves low-resolution visual tasks, such as orientation and navigation, based on broad gradients of light intensity and polarisation. Optic lobe structure and photoreceptor projections point to significant divergence from the conserved visual circuits found in other malacostracan crustaceans and insects, which could be associated with a shift to low-resolution vision. Our study provides the foundation for research in the visual system of this genetically tractable species.

zoology↗