A full lifespan model of vertebrate lens growth

The mathematical determinants of vertebrate organ growth have yet to be elucidated fully. Here, we utilized empirical measurements and a dynamic branching process-based model to examine the growth of a simple organ system, the mouse lens, from E14.5 until the end of life. Our stochastic model used difference equations to model immigration and emigration between zones of the lens epithelium and included some deterministic elements, such as cellular footprint area. We found that the epithelial cell cycle was shortened significantly in the embryo, facilitating the rapid growth that marks early lens development. As development progressed, epithelial cell division becomes non-uniform and four zones, each with a characteristic proliferation rate, could be discerned. Adjustment of two model parameters, proliferation rate and rate of change in cellular footprint area, was sufficient to specify all growth trajectories. Modelling suggested that the direction of cellular migration across zonal boundaries was sensitive to footprint area, a phenomenon that may isolate specific cell populations. Model runs consisted of more than 1000 iterations, in each of which the stochastic behaviour of thousands of cells was followed. Nevertheless, sequential runs were almost superimposable. This remarkable degree of precision was attributed, in part, to the presence of non-mitotic flanking regions, which constituted a path by which epithelial cells could escape the growth process. Spatial modelling suggested that clonal clusters of about 50 cells are produced during migration and that transit times lengthen significantly at later stages, findings with implications for the formation of certain types of cataract

Proteomic analysis of the bovine and human ciliary zonule

PURPOSE: The zonule of Zinn (ciliary zonule) is a system of fibers that centers the crystalline lens on the optical axis of the eye. Mutations in zonule components underlie syndromic conditions associated with a broad range of ocular pathologies, including microspherophakia and ectopia lentis. Here, we used HPLC–mass spectrometry to determine the molecular composition of the zonule. METHODS: Tryptic digests of human and bovine zonular samples were analyzed by HPLC–mass spectrometry. The distribution of selected components was confirmed by immunofluorescence confocal microscopy. In bovine samples, the composition of the equatorial zonule was compared to that of the hyaloid zonule and vitreous humor. RESULTS: The 52 proteins common to the zonules of both species accounted for >95% of the zonular protein. Glycoproteins constituted the main structural components, with two proteins, FBN1 and LTBP2, constituting 70%–80% of the protein. Other abundant components were MFAP2, EMILIN-1, and ADAMTSL-6. Lysyl oxidase-like 1, a crosslinking enzyme implicated in collagen and elastin biogenesis, was detected at significant levels. The equatorial and hyaloid zonular samples were compositionally similar to each other, although the hyaloid sample was relatively enriched in the proteoglycan opticin and the fibrillar collagens COL2A1, COL11A1, COL5A2, and COL5A3. CONCLUSIONS: The zonular proteome was surprisingly complex. In addition to structural components, it contained signaling proteins, protease inhibitors, and crosslinking enzymes. The equatorial and hyaloid zonules were similar in composition, but the latter may form part of a composite structure, the hyaloid membrane, that stabilizes the vitreous face

A method for determining cell number in the undisturbed epithelium of the mouse lens

The anterior face of the mouse lens is covered by a layer of epithelial cells. The epithelial cells serve a barrier function at the lens surface and as a progenitor population from which lens fiber cells, the predominant cell type of the lens, are derived. Decreased epithelial cell density is commonly observed during aging and cataract formation in humans and animal models and may contribute directly to tissue opacification. However, the loss of cells from the epithelium is often not easy to quantify, in part because the cells are arrayed across a near-spherical surface and, as a consequence, are difficult to image and count. Here, we describe a technique for determining epithelial cell number in the undisturbed lens of the mouse, a popular cataract model. The method utilizes orthographic projections of confocal images collected from the anterior and equatorial regions of the lens. The overlapping projections are brought into register using the unique distribution of proliferating cells as fiduciary points. Cell counts are performed using a computer-assisted method. This approach offers several advantages over flat-mount methods employed previously

Somatic variants in the human lens epithelium: A preliminary assessment

PURPOSE: We hypothesize that somatic mutations accumulate in cells of the human lens and may contribute to the development of cortical or posterior sub-capsular cataracts. Here, we used a Next-generation sequencing (NGS) strategy to screen for low-allelic frequency variants in DNA extracted from human lens epithelial samples. METHODS: Next-Generation sequencing of 151 cancer-related genes (WUCaMP2 panel) was performed on DNA extracted from post-mortem or surgical specimens obtained from 24 individuals. Usually, pairwise comparisons were made between two or more ocular samples from the same individual, allowing putative somatic variants detected in lens samples to be differentiated from germline variants. RESULTS: Use of a targeted hybridization approach enabled high sequence coverage (>1000-fold) of the WUCaMP2 genes. In addition to high-frequency variants (corresponding to homozygous or heterozygous SNPs and Indels), somatic variants with allelic frequencies of 1-4% were detected in the lens epithelial samples. The presence of one such variant, a T > C point substitution at position 32907082 in BRCA2, was verified subsequently using droplet digital PCR. CONCLUSIONS: Low-allelic fraction variants are present in the human lens epithelium, at frequencies consistent with the presence of millimeter-sized clones

Conceptualising the geographic world: the dimensions of negotiation in crowdsourced cartography

In crowdsourced cartographic projects, mappers coordinate their efforts through online tools to produce digital geospatial artefacts, such as maps and gazetteers, which were once the exclusive territory of professional surveyors and cartographers. In order to produce meaningful and coherent data, contributors need to negotiate a shared conceptualisation that defines the domain concepts, such as road, building, train station, forest, and lake, enabling the communi- cation of geographic knowledge. Considering the OpenStreetMap Wiki website as a case study, this article investigates the nature of this negotiation, driven by a small group of mappers in a context of high contribution inequality. De- spite the apparent consensus on the conceptualisation, the negotiation keeps unfolding in a tension between alternative representations, which are often in- commensurable, i.e., hard to integrate and reconcile. In this study, we identify six complementary dimensions of incommensurability that recur in the nego- tiation: (i) ontology, (ii) cartography, (iii) culture and language, (iv) lexical definitions, (v) granularity, and (vi) semantic overload and duplication

Endogenous bioelectric currents promote differentiation of the mammalian lens

Acknowledgements We are grateful to Kevin S. Mackenzie in our imaging core facility. This work was supported by the University of Aberdeen (at which the majority of the experimental work was conducted). The work was supported by Action Medical Research (GN2299) and Fight for Sight (RG13315-10).Peer reviewedPublisher PD