Biology subjects

Saxena, N.

Publications and source records attributed to Saxena, N..

3 recordsLinked to original sources

bioRxiv2018

Fate Before Function: Specification of the Hair Follicle Niche Occurs Prior to its Formation and Is Progenitor Dependent

Cell fate transitions are essential for specialization of stem cells and their niches, but the precise timing and sequence of molecular events during embryonic development are largely unknown. Here, we show that dermal condensates (DC), signaling niches for epithelial progenitors in hair placodes, are specified before niche formation and function. With 3D/4D microscopy we identify unclustered DC precursors. With population-based and single-cell transcriptomics we define a molecular time-lapse of dynamic niche signatures and the developmental trajectory as the DC lineage emerges from fibroblasts. Co-expression of downregulated fibroblast and upregulated DC genes in niche precursors reveals a transitory molecular state following a proliferation shutdown. Waves of transcription factor and signaling molecule expression then consolidate DC niche formation. Finally, ablation of epidermal Wnt signaling and placode-derived FGF20 demonstrates their requirement for DC-precursor specification. These findings uncover a progenitor-dependent niche precursor fate and the transitory molecular events controlling niche formation and function.\n\nGraphical Abstract\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC=\"FIGDIR/small/414839_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (78K):\norg.highwire.dtl.DTLVardef@13fa73aorg.highwire.dtl.DTLVardef@1fbd280org.highwire.dtl.DTLVardef@1b8f66borg.highwire.dtl.DTLVardef@3a1ef9_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LIPrecursors of the hair follicle niche are specified before niche cluster formation\nC_LIO_LIBulk/single cell RNA-seq defines early niche fate at molecular transitional state\nC_LIO_LISuccessive waves of transcription factor/signaling genes mark niche fate acquisition\nC_LIO_LINiche fate acquisition is not \"pre-programmed\" and requires FGF20 from progenitors\nC_LI

developmental biology↗

bioRxiv2018

Gene Correction for SCID-X1 in Long-Term Hematopoietic Stem Cells

Gene correction in human long-term hematopoietic stem cells (LT-HSCs) could be an effective therapy for monogenic diseases of the blood and immune system. High frequencies of reproducible targeted integration of a wild-type cDNA into the endogenous start codon of a gene in LT-HSCs could provide a robust genome editing approach to cure genetic diseases in which patients have different mutations throughout the gene. We describe a clinically relevant method for correcting X-linked severe combined immunodeficiency (SCID-X1). By using a highly specific and active CRISPR/Cas9-AAV6 based strategy and selection-free approach, we achieve up to 20% genome integration frequencies in LT-HSCs of a full-length IL2RG cDNA at the endogenous start site as demonstrated by serial transplantation and analysis of genome edited human cells eight months following initial transplantation. In addition to high frequencies of functional gene correction in LT-HSCs we observed no evidence of abnormal hematopoiesis following transplantation, a functional measure of the lack of genotoxicity. Deep analysis of potential off-target activity detected two sites with low frequency (<0.3%) of off-target mutations. The level of off-target mutations was reduced to below the limit of detection using a high fidelity Cas9. Moreover, karyotype evaluation identified no genomic instability events. We achieved high levels of genome targeting frequencies (median 45%) in CD34+ HSPCs from six SCID-X1 patients and demonstrate rescue of lymphopoietic defect of patient derived cells both in vitro and in vivo. In sum, our study provides specificity, toxicity and efficacy data supportive of clinical development of genome editing to treat SCID-Xl.

bioengineering↗

bioRxiv2017

Odor source localization in complex visual environments by fruit flies

Flying insects routinely forage in complex and cluttered sensory environments. Their search for a food or a pheromone source typically begins with a whiff of odor, which triggers a flight response, eventually bringing the insect in the vicinity of the odor source. The precise localization of an odor source, however, requires the use of both visual and olfactory modalities, aided by air currents that trap odor molecules into turbulent plumes, which the insects track. Here, we investigated odor tracking behavior in fruit flies (Drosophila melanogaster) presented with low- or high-contrast visual landmarks, which were either paired with or separate from an attractive odor cue. These experiments were conducted either in a gentle air stream which generated odor plumes, or in still air in which odor dissipates uniformly in all directions. The trajectories of the flies revealed several novel features of their odor-tracking behavior in addition to those that have been previously documented (e.g. cast- and-surge maneuvers). First, in both moving and still air, odor-seeking flies rely on the co-occurrence of visual landmarks with olfactory cues to guide them to putative odorant objects in the decisive phase before landing. Second, flies abruptly decelerate when they encounter an odor plume, and thereafter steer towards nearby visual objects that had no inherent salience in the absence of odor. This indicates that the interception of an attractive odor increases their salience to nearby high-contrast visual landmarks. Third, flies adopt distinct odor tracking strategies during flight in moving vs. still air. Whereas they weave in and out of plumes towards an odor source when airflow is present, their approach is more gradual and incremental in still air. Both strategies are robust and flexible, and can ensure that the flies reliably find the odor source under diverse visual and airflow environments. Our experiments also indicate the possibility of an olfactory \" working memory\" that enables flies to continue their search even when the olfactory feedback is reduced or absent. Together, these results provide insights into how flies determine the precise location of an odor source.

animal behavior and cognition↗