Structural and functional analysis of the human cone-rod homeobox transcription factor.

The cone-rod homeobox (CRX) protein is a critical K50 homeodomain transcription factor responsible for the differentiation and maintenance of photoreceptor neurons in the vertebrate retina. Mutant alleles in the human gene encoding CRX result in a variety of distinct blinding retinopathies, including retinitis pigmentosa, cone-rod dystrophy, and Leber congenital amaurosis. Despite the success of using in vitro biochemistry, animal models, and genomics approaches to study this clinically relevant transcription factor over the past 25 years since its initial characterization, there are no high-resolution structures in the published literature for the CRX protein. In this study, we use bioinformatic approaches and small-angle X-ray scattering (SAXS) structural analysis to further understand the biochemical complexity of the human CRX homeodomain (CRX-HD). We find that the CRX-HD is a compact, globular monomer in solution that can specifically bind functional cis-regulatory elements encoded upstream of retina-specific genes. This study presents the first structural analysis of CRX, paving the way for a new approach to studying the biochemistry of this protein and its disease-causing mutant protein variants.

Transcriptome dataset of Caenorhabditis elegans responses to varied microbial pathogens.

Transcriptome analysis through next-generation sequencing (NGS) is an invaluable tool for investigating changes in gene expression across diverse organisms. The nematode Caenorhabditis elegans (C. elegans) serves as an excellent model organism for dissecting host responses to bacterial infections. Here, our dataset obtained from bulk RNA-sequencing (RNA-seq) can be used to provide in-depth characterization of the mRNA transcriptome profiles of wild-type N2 animals and null mutants of the cytoskeletal regulatory gene unc-53/Nav2 following exposure to distinct bacterial environments: their natural laboratory food source, Escherichia coli OP50, the human and nematode pathogen Pseudomonas aeruginosa PA14, and the emerging pathogen Elizabethkingia anophelis Ag1. As proof of the dataset quality, downstream differential gene expression analysis reveals significant shifts in gene expression patterns within N2 and unc-53 mutants under varying bacterial conditions that will be useful for our companion studies investigating these pathways. These data provide an effective methodological framework for future investigators to investigate the interplay between cytoskeletal proteins and the innate immune response. The raw FASTQ files generated from our transcriptome experiment is deposited in the publicly available NCBI Sequence Read Archive (SRA) under the BioProject accession number PRJNA1010192, for further exploration and validation by the C. elegans research community.

Transcriptome dataset of light-dependent expression in the early onset retinal degeneration model, Mcoln1-/- mouse.

Retinal degenerative diseases (RDDs) are a diverse group of retinal disorders that cause visual impairment. While RDD prevalence is high, little is known about the molecular mechanisms underlying the pathogenesis within many of these disorders. Here we use transcriptome analysis to elucidate the molecular mechanisms that drive early onset photoreceptor neuron function loss in the mouse model of the RDD Mucolipidosis type IV (MLIV). MLIV is a lysosomal storage disorder resulting from loss of function mutations in the MCOLN1 gene. MCOLN1 encodes a lysosomal cation channel, the transient receptor potential channel mucolipin 1 (Trpml1). To identify changes in gene expression during onset in MLIV we used a genetic mouse model (Mcoln1-/-) which recapitulates clinical attributes of the human disease. We conducted transcriptome analysis in 6-week old control and Mcoln1-/- mice under normal 12:12 light cycle as well as low and high light stress conditions. These data will be valuable to the vision research community for identifying differentially expressed in early onset MLIV potentially leading to new insights into the pathophysiology of this RDD. Raw FASTQ files and processed counts files for the RNA-seq libraries are deposited in the NCBI Sequence Read Archive (SRA) and have been assigned BioProject accession PRJNA1002601 [1].

Bulk RNA sequencing analysis of developing human induced pluripotent cell-derived retinal organoids.

Retinogenesis involves the transformation of the anterior developing brain into organized retinal lamellae coordinated by intricate gene signalling networks. This complex process has been investigated in several model organisms such as birds, fish, mammals and amphibians, yet many facets of retinal development are different in humans and remain unexplored. In this regard, human pluripotent stem cell (hPSC)-derived 3D retinal organoids and Next Generation Sequencing (NGS) have emerged as key technologies that have facilitated the discovery of previously unknown details about cell fate specification and gene regulation in the retina. Here we utilized hPSCs integrated with fluorescent reporter genes (SIX6-p2A-eGFP/CRX-p2A-h2b-mRuby3) to generate retinal organoids and carry out bulk RNA sequencing of samples encompassing the majority of retinogenesis (D0-D280). This data set will serve as a valuable reference for the vision research community to characterize differentially expressed genes in the developing human eye.

The Functional Biogeography of eDNA Metacommunities in the Post-Fire Landscape of the Angeles National Forest.

Wildfires have continued to increase in frequency and severity in Southern California due in part to climate change. To gain a further understanding of microbial soil communities' response to fire and functions that may enhance post-wildfire resilience, soil fungal and bacterial microbiomes were studied from different wildfire areas in the Gold Creek Preserve within the Angeles National Forest using 16S, FITS, 18S, 12S, PITS, and COI amplicon sequencing. Sequencing datasets from December 2020 and June 2021 samplings were analyzed using QIIME2, ranacapa, stats, vcd, EZBioCloud, and mixomics. Significant differences were found among bacterial and fungal taxa associated with different fire areas in the Gold Creek Preserve. There was evidence of seasonal shifts in the alpha diversity of the bacterial communities. In the sparse partial least squares analysis, there were strong associations (r > 0.8) between longitude, elevation, and a defined cluster of Amplicon Sequence Variants (ASVs). The Chi-square test revealed differences in fungi−bacteria (F:B) proportions between different trails (p = 2 × 10−16). sPLS results focused on a cluster of Green Trail samples with high elevation and longitude. Analysis revealed the cluster included the post-fire pioneer fungi Pyronema and Tremella. Chlorellales algae and possibly pathogenic Fusarium sequences were elevated. Bacterivorous Corallococcus, which secretes antimicrobials, and bacterivorous flagellate Spumella were associated with the cluster. There was functional redundancy in clusters that were differently composed but shared similar ecological functions. These results implied a set of traits for post-fire resiliency. These included photo-autotrophy, mineralization of pyrolyzed organic matter and aromatic/oily compounds, potential pathogenicity and parasitism, antimicrobials, and N-metabolism.

Chromatin Accessibility and Transcriptional Differences in Human Stem Cell-Derived Early-Stage Retinal Organoids.

Retinogenesis involves the specification of retinal cell types during early vertebrate development. While model organisms have been critical for determining the role of dynamic chromatin and cell-type specific transcriptional networks during this process, an enhanced understanding of the developing human retina has been more elusive due to the requirement for human fetal tissue. Pluripotent stem cell (PSC) derived retinal organoids offer an experimentally accessible solution for investigating the developing human retina. To investigate cellular and molecular changes in developing early retinal organoids, we developed SIX6-GFP and VSX2-tdTomato (or VSX2-h2b-mRuby3) dual fluorescent reporters. When differentiated as 3D organoids these expressed GFP at day 15 and tdTomato (or mRuby3) at day 25, respectively. This enabled us to explore transcriptional and chromatin related changes using RNA-seq and ATAC-seq from pluripotency through early retina specification. Pathway analysis of developing organoids revealed a stepwise loss of pluripotency, while optic vesicle and retina pathways became progressively more prevalent. Correlating gene transcription with chromatin accessibility in early eye field development showed that retinal cells underwent a clear change in chromatin landscape, as well as gene expression profiles. While each dataset alone provided valuable information, considering both in parallel provided an informative glimpse into the molecular nature eye development.

Temporal and Isoform-Specific Expression of CTBP2 Is Evolutionarily Conserved Between the Developing Chick and Human Retina.

Complex transcriptional gene regulation allows for multifaceted isoform production during retinogenesis, and novel isoforms transcribed from a single locus can have unlimited potential to code for diverse proteins with different functions. In this study, we explored the CTBP2/RIBEYE gene locus and its unique repertoire of transcripts that are conserved among vertebrates. We studied the transcriptional coregulator (CTBP2) and ribbon synapse-specific structural protein (RIBEYE) in the chicken retina by performing comprehensive histochemical and sequencing analyses to pinpoint cell and developmental stage-specific expression of CTBP2/RIBEYE in the developing chicken retina. We demonstrated that CTBP2 is widely expressed in retinal progenitors beginning in early retinogenesis but becomes limited to GABAergic amacrine cells in the mature retina. Inversely, RIBEYE is initially epigenetically silenced in progenitors and later expressed in photoreceptor and bipolar cells where they localize to ribbon synapses. Finally, we compared CTBP2/RIBEYE regulation in the developing human retina using a pluripotent stem cell derived retinal organoid culture system. These analyses demonstrate that similar regulation of the CTBP2/RIBEYE locus during chick and human retinal development is regulated by different members of the K50 homeodomain transcription factor family.

RNA sequencing analysis of the human retina and associated ocular tissues.

The retina is a stratified layer of sensory neurons lining the posterior portion of the eye. In humans, fine detail and color vision are enabled by the macula, a central region of the retina dense in cone photoreceptors (PRs). Achromatic low light and peripheral vision are facilitated by rod PRs found with increasing density outside the macula in the peripheral retina. The outer retina is nourished by choroidal blood flow regulated by a single layer of intervening retinal pigment epithelial (RPE) cells. Existing human retinal transcriptome projects have been critical for studying aspects of retinal development and disease however, there are currently no publicly available data sets accurately describing the aging human central retina, peripheral retina, and supporting RPE/choroid. Here we used Illumina RNA sequencing (RNA-seq) analysis to characterize the mRNA transcriptome of rod and cone PR-enriched human retina as well as supporting macular RPE/choroid tissue. These data will be valuable to the vision research community for characterizing global changes in gene expression in clinically relevant ocular tissues.