1,721,438 research outputs found
The time of timing: how Polycomb proteins regulate neurogenesis
No full textThe study of mammalian corticogenesis has revealed a critical role for Polycomb group (PcG) factors in timing the execution of developmental choices. Meanwhile, the study of post-translational modifications of PcG factors marks a symmetrical point, namely that the activity of PcG proteins is itself timed in a manner that links progression through the cell cycle to targeting of downstream genes. Finally, in a third symmetrical twist, the studies that dissect the timing of neural fate by Polycomb are also uncovering the importance of timing in the experimental mutation, since ablation of the same PcG member at different developmental stages yields dramatically different results. Here, I weave together these three lines of evidence and develop a unifying model that clarifies the dynamics of Polycomb function in neural development and defines the salient challenges ahead
The identity of living beings, epigenetics, and the modesty of philosophy
No full textTwo problems related to the biological identity of living beings are faced: the who-problem (which are the biological properties making that living being unique and different from the others?); the persistence-problem (what does it take for a living being to persist from a time to another?). They are discussed inside a molecular biology framework, which shows how epigenetics can be a good ground to provide plausible answers. That is, we propose an empirical solution to the who-problem and to the persistence-problem on the basis of the new perspectives opened by a molecular understanding of epigenetic processes. In particular, concerning the former, we argue that any living being is the result of the epigenetic processes that have regulated the expression of its genome; concerning the latter, we defend the idea that the criterion for the persistence of its identity is to be indicated in the continuity of those epigenetic processes. We also counteract possible objections, in particular (1) whether our approach has something to say at a metaphysical level; (2) how it could account for the passage from the two phenotypes of the parental gametes to the single phenotype of the zygote; (3) how it could account for the identity of derivatives of one living being that continue to live disjoined from that original living being; (4) how it could account for higher mental functions
Gene : an entity in search of concepts?
No full textIn this paper, we address both ontological and epistemological problems related to the concept of ‘gene’. Interrupted genes, alternative splicing, overlapping genes, nested genes, genome-wide transcription and regulatory RNAs, regulatory sequences, somatic recombination in immunoglobulin genes and other molecular evidences represent a serious challenge to the classic way of framing the question ‘what is a gene?’.
In the first part of the paper, after showing that the Dna polymer is an entity without bona fide boundaries, we outline ways to extract gene functionalities from it by taking into account the most recent insights of molecular biology. In particular, we argue that a gene is not merely a continuous Dna sequence, but it is an entity identifiable as a functional part of Dna which enters in a polypeptide/functional Rna/nucleus organization coding process. Thus, a gene needs not be an isolated segment of Dna, but it can be productively understood as the sum of non spatially contiguous Dna sequences, since, even if it is scattered, it still constitutes a functional unit. Moreover, a single segment of Dna can be involved in many different polypeptide/functional Rna/nucleus organization coding processes and can thus be a functional component of different genes. Conversely, distinct gene functionalities can be attributed, partially or totally, to the same Dna fragment.
On the basis of this foundational analysis, we then develop an epistemological critique to expand the current popular distinction drawn by Lenny Moss (2003) between Gene-P (preformistic gene) and Gene-D (developmental gene). We argue that some uses of the concept of ‘gene’ in experimental molecular biomedicine and evolutionary biology make Moss’ distinction not exhaustive, for example in the case of so-called “reporter” genes (i.e. luciferase gene) or genes predicted by many evolutionary models (i.e. Fisher’s sex ratio) that do not align neatly along the Gene-P/Gene-D dichotomy
Gypsum-anhydrite transformations in Messinian evaporites of central Tuscany (Italy)
No full textThe Messinian succession of Tuscany (central Italy) contains three evaporitic units. Among the several exposed evaporitic lithofacies, only selenitic gypsum precipitated directly from evaporating brines. All the other facies, nodular microcrystalline gypsum, gypsarenites and gypsum laminites, despite their macroscopic differences, display the same petrographic textures, indicating that they are the product of dehydration of gypsum to give anhydrite which has been successively rehydrated to secondary gypsum. These secondary facies show an entire array of textures ranging from cloudy ameboid (xenotopic) with anhydrite relies, to idiotopic without anhydrite relies, that are here interpreted as a sequence of progressive stages of rehydration. The presence of completely hydrated petrofacies at the core of nodules which display a less hydrated rim suggests that these rocks have undergone at least two cycles of a dehydration-rehydration process. This interpretation is supported by the presence of satin spar veins that are replaced by microcrystalline gypsum. Satin spar itself is considered to be a by-product of anhydrite hydration. The first dehydration-rehydration event affected the entire gypsum deposit, producing a completely hydrated (idiotopic) facies together with satin spar veins; the second affected only veins, fractures and the rims of nodules, turning the first generation of satin spar and idiotopic gypsum into cloudy ameboid gypsum, Sedimentary structures typical of sabkha environments indicate for the youngest formation that the first dehydration and rehydration process occurred syndepositionally. The preservation of primary gypsum facies only at sites with condensed sections, indicate for the oldest two formations that the first dehydration event occurred upon burial, This event has been estimated to have occurred in the earliest Pliocene. After the Early Pliocene, dehydration was favored even at shallow depths, due to an increased heat flow related with the emplacement of local crustal magmatic bodies. Rehydration possibly occurred when these formations were uplifted and exposed to ground and/or meteoric water, The Volterra Basin has undergone alternating subsidence and uplift events, that can account for two dehydration-rehydration processes at least, also driven by alternating circulation, in the tectonic fractures, of fresh and salty water, the latter derived from dissolution of Messinian halite. (C) 2000 Elsevier Science B.V. All rights reserved
Consuming genomes : scientific and social innovation in direct-to-consumer genetic testing
No full textSince 2006 companies in the US have started to offer direct-to-consumer (DTC) genetic testing for a variety of diseases and traits. Recently, the activities of 23andMe and Navigenics, the two leading providers of DTC genetic services, have come under the scrutiny of various regulators and institutions, including the Food and Drug Administration (FDA) and the House Committee on Energy and Commerce and, in 2008, the California and New York Departments of Health. In this work we first situate this DTC innovation within the historical trajectory of gene testing as it developed in the context of clinical medicine around the three key criteria of analytic validity, clinical validity, and clinical utility. We then analyze the recent encounters between DTC providers and regulators to identify the key scientific and discursive resources that are being employed to position this innovation with respect to analytic validity, clinical validity, and clinical utility. Our empirical analysis of a rich set of primary sources (including websites, policy documents, and interviews) shows that the emergence of DTC gene testing is a conspicuous instance of co-production: a new kind of genetic knowledge and a new kind of biological citizenship is being articulated around the figure of the genetic consumer
- …
