Lyngekok7694

Given the distinctive nature of peptide morphogens and small RNAs, how might mechanisms underlying the function of traditionally morphogens be adapted to create morphogen-like behavior using small RNAs? In this review, we highlight the contributions of mobile small RNAs to pattern formation in plants and summarize recent studies that have advanced our understanding regarding the formation, stability, and interpretation of small RNA gradients. © 2020 Elsevier Inc. All rights reserved.The root meristem-one of the plant's centers of continuous growth-is a conveyer belt in which cells of different identities are pushed through gradients along the root's longitudinal axis. An auxin gradient has long been implicated in controlling the progression of cell states in the root meristem. Recent work has shown that a PLETHORA (PLT) protein transcription factor gradient, which is under a delayed auxin response, has a dose-dependent effect on the differentiation state of cells. The direct effect of auxin concentration on differential transcriptional outputs remains unclear. Genomic and other analyses of regulatory sequences show that auxin responses are likely controlled by combinatorial inputs from transcription factors outside the core auxin signaling pathway. The passage through the meristem exposes cells to varying positional signals that could help them interpret auxin inputs independent of gradient effects. One open question is whether cells process information from the changes in the gradient over time as they move through the auxin gradient. © 2020 Elsevier Inc. All rights reserved.Gastrulation is the process whereby cells exit pluripotency and concomitantly acquire and pattern distinct cell fates. This is driven by the convergence of WNT, BMP, Nodal and FGF signals, which are tightly spatially and temporally controlled, resulting in regional and stage-specific signaling environments. The combination, level and duration of signals that a cell is exposed to, according its position within the embryo and the developmental time window, dictates the fate it will adopt. The key pathways driving gastrulation exhibit complex interactions, which are difficult to disentangle in vivo due to the complexity of manipulating multiple signals in parallel with high spatiotemporal resolution. Thus, our current understanding of the signaling dynamics regulating gastrulation is limited. In vitro stem cell models have been established, which undergo organized cellular differentiation and patterning. These provide amenable, simplified, deconstructed and scalable models of gastrulation. While the foundation of our understanding of gastrulation stems from experiments in embryos, in vitro systems are now beginning to reveal the intricate details of signaling regulation. Here we discuss the current state of knowledge of the role, regulation and dynamic interaction of signaling pathways that drive mouse gastrulation. © 2020 Elsevier Inc. All rights reserved.Embryogenesis is coordinated by signaling pathways that pattern the developing organism. Many aspects of this process are not fully understood, including how signaling molecules spread through embryonic tissues, how signaling amplitude and dynamics are decoded, and how multiple signaling pathways cooperate to pattern the body plan. Optogenetic approaches can be used to address these questions by providing precise experimental control over a variety of biological processes. Here, we review how these strategies have provided new insights into developmental signaling and discuss how they could contribute to future investigations. © 2020 Elsevier Inc. All rights reserved.One of the most powerful ideas in developmental biology has been that of the morphogen gradient. SC144 in vivo In the classical view, a signaling molecule is produced at a local source from where it diffuses, resulting in graded levels across the tissue. This gradient provides positional information, with thresholds in the level of the morphogen determining the position of different cell fates. While experimental studies have uncovered numerous potential morphogens in biological systems, it is becoming increasingly apparent that one important feature, not captured in the simple model, is the role of time in both the formation and interpretation of morphogen gradients. We will focus on two members of the transforming growth factor-β family that are known to play a vital role as morphogens in early vertebrate development the Nodals and the bone morphogenetic proteins (BMPs). Primarily drawing on the early zebrafish embryo, we will show how recent studies have demonstrated the importance of feedback and other interactions that evolve through time, in shaping morphogen gradients. We will further show how rather than simply reading out levels of a morphogen, the duration of ligand exposure can be a crucial determinant of how cells interpret morphogens, in particular through the unfolding of downstream transcriptional events and in their interactions with other pathways. © 2020 Elsevier Inc. All rights reserved.In bilaterally-symmetric animals (Bilateria), condensation of neurons and ganglia into a centralized nervous system (CNS) constitutes a salient feature. In most, if not all, Bilateria another prominent aspect is that the anterior regions of the CNS are typically larger than the posterior ones. Detailed studies in Drosophila melanogaster (Drosophila) have revealed that anterior expansion in this species stems from three major developmental features the generation of more progenitors anteriorly, an extended phase of proliferation of anterior progenitors, and more proliferative daughter cells in anterior regions. These brain-specific features combine to generate a larger average lineage size and higher cell numbers in the brain, when compared to more posterior regions. Genetic studies reveal that these anterior-posterior (A-P) differences are controlled by the modulation of temporal programs, common to all progenitors, as well as by Hox homeotic genes, expressed in the nerve cord, and brain-specific factors. All of these regulatory features are gated by the action of the PRC2 epigenetic complex. Studies in mammals indicate that most, if not all of these anterior expansion principles and the underlying genetic programs are evolutionarily conserved. These findings further lend support for the recently proposed idea that the brain and nerve cord may have originated from different parts of the nervous system present in the Bilaterian ancestor. This brain-nerve cord "fusion" concept may help explain a number of the well-known fundamental differences in the biology of the brain, when compared to the nerve cord. © 2020 Elsevier Inc. All rights reserved.