This study examines the retinal transdifferentiation (TD) of retinal pigmented epithelium (RPE) fragments dissected from Xenopus laevis larvae and implanted into the vitreous chamber of non-lentectomized host eyes. In these experimental conditions, most RPE implants transformed into polarized vesicles in which the side adjacent to the lens maintained the RPE phenotype, while the side adjacent to the host retina transformed into a laminar retina with the photoreceptor layer facing the cavity of the vesicle and with the ganglionar cell layer facing the host retina. The formation of a new retina with a laminar organization is the result of depigmentation, proliferation and differentiation of progenitor cells under the influence of inductive factors from the host retina. The phases of the TD process were followed using BrdU labelling as a marker of the proliferation phase and using a monoclonal antibody (mAbHP1) as a definitive indicator of retina formation. Pigmented RPE cells do not express Pax6. In the early phase of RPE to retinal TD, all depigmented and proliferating progenitor cells expressed Pax6. Changes in the Pax6 expression pattern became apparent in the early phase of differentiation, when Pax6 expression decreased in the presumptive outer nuclear layer (ONL) of the new-forming retina. Finally, during the late differentiation phase, the ONL, which contains photoreceptors, no longer expressed Pax6, Pax6 expression being confined to the ganglion cell layer and the inner nuclear layer. It is well known that larval and adult newts are able to regenerate the neural retina (NR) from the retinal pigmented epithelium (RPE) through a transdifferentiation (TD) process (Stone, '50; Hasegawa, '58; Reyer, '77; Stroeva and Mitashov, '83) and that the RPE of larval and adult frogs transdifferentiates into NR when implanted into the vitreous chamber of a host tadpole (Lopashov and Sologub, '72; Sologub, '77). The regeneration of NR via TD from RPE also occurs in the chick and rat embryos, but this capacity is restricted to early stages of ocular development prior to the irreversible commitment of the RPE to the pigmented cell fate (Park and Hollenberg, '89; Pittack et al., '91; Zhao et al., '95). Some recent studies have begun to investigate the molecular nature of factors involved in this TD process. The basic fibroblast growth factor (FGF2) has been demonstrated to be a potent factor capable of triggering the retinal TD of the embryonic chick RPE both in vivo and in vitro (Park and Hollenberg, '89; Pittack et al., '91; Araki et al., '98), as well as triggering the retinal TD of the embryonic rat RPE cultured in vitro (Zhao et al., '95). Sakaguchi et al. ('97) demonstrated that FGF2 also promoted retinal TD of larval Xenopus laevis RPE cultured in vitro, supporting the idea that retinal TD undergone by X. laevis RPE fragments implanted into the vitreous chamber of host tadpoles is the result of retinal-derived FGF2 accumulated into the vitreous chamber. However, the retina regeneration in newts is a u...
Abstract. Glacier detachments are a rare, but hazardous, phenomenon of glacier instability, whereof only a handful have been documented to date. Common to all known cases is that many million cubic meters of ice detached from the bed of relatively low-angle valley glaciers and turned into long-runout mass flows. Recently, two such detachments were observed in the Petra Pervogo range in Tajikistan. Using a variety of satellite imagery, including Landsat 1–8, Sentinel-2, ASTER, TanDEM-X, WorldView, and Keyhole, we characterized these events and identified in total 17 mass flows involving glacier ice (detachments, ice, and rock-ice avalanches; rock avalanches falling on glaciers) that clustered in four different catchments between 1973 and 2019. The runout distances range from 2 to 19 km, and the largest detached glacier volume was 8.8×106 m3. A total of 11 out of 13 detachments, ice, or rock-ice avalanches occurred between July and September in years with mean annual air temperatures above the trend of the past 46 years. The relatively large number of locally clustered events indicates that the Petra Pervogo range has particularly favorable conditions for glacier instabilities. The images and geology of the region suggest that easily erodible lithologies are widespread. These soft lithologies may be also one reason for the high density of surging glaciers in the Petra Pervogo range and the wider Pamir region. We conclude that high temperatures, combined with soft, fine-grained sediments, may increase the likelihood of mass wasting events and appear to be critical factors facilitating the detachment of entire valley glaciers, whereas such events appear to be relatively robust against earthquakes for our study area. The observed recurrence of mass wasting events make the Petra Pervogo range a potential candidate to witness glacier detachments by field studies.
This work proposes a novel approach for overcoming the current inconsistencies in ESG scores by using Machine Learning (ML) techniques to identify those indicators that better contribute to the construction of efficient portfolios. ML can achieve this result without needing a model-based methodology, typical of the modern portfolio theory approaches. The ESG indicators identified by our approach show a discriminatory power that also holds after accounting for the contribution of the style factors identified by the Fama-French five-factor model and the macroeconomic factors of the BIRR model. The novelty of the paper is threefold: a) the large array of ESG metrics analysed, b) the model-free methodology ensured by ML and c) the disentangling of the contribution of ESG-specific metrics to the portfolio performance from both the traditional style and macroeconomic factors. According to our results, more information content may be extracted from the available raw ESG data for portfolio construction purposes and half of the ESG indicators identified using our approach are environmental. Among the environmental indicators, some refer to companies' exposure and ability to manage climate change risk, namely the transition risk.
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