Transcriptional regulation of Rab32/38, a specific marker of pigment cell formation in Ciona robusta

Serotonin Receptors and Their Involvement in Melanization of Sensory Cells in Ciona intestinalis

Serotonin (5-hydroxytryptamine (5-HT)) is a biogenic monoamine with pleiotropic functions. It exerts its roles by binding to specific 5-HT receptors (5HTRs) classified into different families and subtypes. Homologs of 5HTRs are widely present in invertebrates, but their expression and pharmacological characterization have been scarcely investigated. In particular, 5-HT has been localized in many tunicate species but only a few studies have investigated its physiological functions. Tunicates, including ascidians, are the sister group of vertebrates, and data about the role of 5-HTRs in these organisms are thus important for understanding 5-HT evolution among animals. In the present study, we identified and described 5HTRs in the ascidian Ciona intestinalis. During development, they showed broad expression patterns that appeared consistent with those reported in other species. Then, we investigated 5-HT roles in ascidian embryogenesis exposing C. intestinalis embryos to WAY-100635, an antagonist of the 5HT1A receptor, and explored the affected pathways in neural development and melanogenesis. Our results contribute to unraveling the multifaceted functions of 5-HT, revealing its involvement in sensory cell differentiation in ascidians.

Comparative transcriptome and miRNA analysis of skin pigmentation during embryonic development of Chinese soft-shelled turtle (Pelodiscus sinensis)

BACKGROUND

Aquatic animals show diverse body coloration, and the formation of animal body colour is a complicated process. Increasing evidence has shown that microRNAs (miRNAs) play important regulatory roles in many life processes. The role of miRNAs in pigmentation has been investigated in some species. However, the regulatory patterns of miRNAs in reptile pigmentation remain to be elucidated. In this study, we performed an integrated analysis of miRNA and mRNA expression profiles to explore corresponding regulatory patterns in embryonic body colour formation in the soft-shelled turtle Pelodiscus sinensis.

RESULTS

We identified 8 866 novel genes and 9 061 mature miRNAs in the skin of Chinese soft-shelled turtles in three embryonic stages (initial period: IP, middle period: MP, final period: FP). A total of 16 563 target genes of the miRNAs were identified. Furthermore, we identified 2 867, 1 840 and 4 290 different expression genes (DEGs) and 227, 158 and 678 different expression miRNAs (DEMs) in IP vs. MP, MP vs. FP, and IP vs. FP, respectively. Among which 72 genes and 25 miRNAs may be related to turtle pigmentation in embryonic development. Further analysis of the novel miRNA families revealed that some novel miRNAs related to pigmentation belong to the miR-7386, miR-138, miR-19 and miR-129 families. Novel_miR_2622 and novel_miR_2173 belong to the miR-19 family and target Kit and Gpnmb, respectively. The quantification of novel_miR_2622 and Kit revealed negative regulation, indicating that novel_miR_2622 may participate in embryonic pigmentation in P. sinensis by negatively regulating the expression of Kit.

CONCLUSIONS

miRNA act as master regulators of biological processes by controlling the expression of mRNAs. Considering their importance, the identified miRNAs and their target genes in Chinese soft-shelled turtle might be useful for investigating the molecular processes involved in pigmentation. All the results of this study may aid in the improvement of P. sinensis breeding traits for aquaculture.

The Combination of Niacinamide, Vitamin C, and PDRN Mitigates Melanogenesis by Modulating Nicotinamide Nucleotide Transhydrogenase

Nicotinamide nucleotide transhydrogenase (NNT) is involved in decreasing melanogenesis through tyrosinase degradation induced by cellular redox changes. Nicotinamide is a component of coenzymes, such as NAD+, NADH, NADP+, and NADPH, and its levels are modulated by NNT. Vitamin C and polydeoxyribonucleotide (PDRN) are also known to decrease skin pigmentation. We evaluated whether a mixture of nicotinamide, vitamin C, and PDRN (NVP-mix) decreased melanogenesis by modulating mitochondrial oxidative stress and NNT expression in UV-B-irradiated animals and in an in vitro model of melanocytes treated with conditioned media (CM) from UV-B-irradiated keratinocytes. The expression of NNT, GSH/GSSG, and NADPH/NADP+ in UV-B-irradiated animal skin was significantly decreased by UV-B radiation but increased by NVP-mix treatment. The expression of NNT, GSH/GSSG, and NADPH/NADP+ ratios decreased in melanocytes after CM treatment, although they increased after NVP-mix administration. In NNT-silenced melanocytes, the GSH/GSSG and NADPH/NADP+ ratios were further decreased by CM compared with normal melanocytes. NVP-mix decreased melanogenesis signals, such as MC1R, MITF, TYRP1, and TYRP2, and decreased melanosome transfer-related signals, such as RAB32 and RAB27A, in UV-B-irradiated animal skin. NVP-mix also decreased MC1R, MITF, TYRP1, TYRP2, RAB32, and RAB27A in melanocytes treated with CM from UV-irradiated keratinocytes. The expression of MC1R and MITF in melanocytes after CM treatment was unchanged by NNT silencing. However, the expression of TYRP1, TYRP2, RAB32, and RAB27A increased in NNT-silenced melanocytes after CM treatment. NVP-mix also decreased tyrosinase activity and melanin content in UV-B-irradiated animal skin and CM-treated melanocytes. In conclusion, NVP-mix decreased mitochondrial oxidative stress by increasing NNT expression and decreased melanogenesis by decreasing MC1R/MITF, tyrosinase, TYRP1, and TYRP2.

Brain Sensory Organs of the Ascidian Ciona robusta: Structure, Function and Developmental Mechanisms

During evolution, new characters are designed by modifying pre-existing structures already present in ancient organisms. In this perspective, the Central Nervous System (CNS) of ascidian larva offers a good opportunity to analyze a complex phenomenon with a simplified approach. As sister group of vertebrates, ascidian tadpole larva exhibits a dorsal CNS, made up of only about 330 cells distributed into the anterior sensory brain vesicle (BV), connected to the motor ganglion (MG) and a caudal nerve cord (CNC) in the tail. Low number of cells does not mean, however, low complexity. The larval brain contains 177 neurons, for which a documented synaptic connectome is now available, and two pigmented organs, the otolith and the ocellus, controlling larval swimming behavior. The otolith is involved in gravity perception and the ocellus in light perception. Here, we specifically review the studies focused on the development of the building blocks of ascidians pigmented sensory organs, namely pigment cells and photoreceptor cells. We focus on what it is known, up to now, on the molecular bases of specification and differentiation of both lineages, on the function of these organs after larval hatching during pre-settlement period, and on the most cutting-edge technologies, like single cell RNAseq and genome editing CRISPR/CAS9, that, adapted and applied to Ciona embryos, are increasingly enhancing the tractability of Ciona for developmental studies, including pigmented organs formation.

Immune properties of invertebrate phenoloxidases

Melanin production from different types of phenoloxidases (POs) confers immunity from a variety of pathogens ranging from viruses and microorganisms to parasites. The arthropod proPO expresses a variety of activities including cytokine, opsonin and microbiocidal activities independent of and even without melanin production. Proteolytic processing of proPO and its activating enzyme gives rise to several peptide fragments with a variety of separate activities in a process reminiscent of vertebrate complement system activation although proPO bears no sequence similarity to vertebrate complement factors. Pathogens influence proPO activation and thereby what types of immune effects that will be produced. An increasing number of specialised pathogens - from parasites to viruses - have been identified who can synthesise compounds specifically aimed at the proPO-system. In invertebrates outside the arthropods phylogenetically unrelated POs are participating in melanization reactions obviously aimed at intruders and/or aberrant tissues.

The Cis-Regulatory Code for Kelch-like 21/30 Specific Expression in Ciona robusta Sensory Organs

The tunicate Ciona robusta is an emerging model system to study the evolution of the nervous system. Due to their small embryos and compact genomes, tunicates, like Ciona robusta, have great potential to comprehend genetic circuitry underlying cell specific gene repertoire, among different neuronal cells. Their simple larvae possess a sensory vesicle comprising two pigmented sensory organs, the ocellus and the otolith. We focused here on Klhl21/30, a gene belonging to Kelch family, that, in Ciona robusta, starts to be expressed in pigmented cell precursors, becoming specifically maintained in the otolith precursor during embryogenesis. Evolutionary analyses demonstrated the conservation of Klhl21/30 in all the chordates. Cis-regulatory analyses and CRISPR/Cas9 mutagenesis of potential upstream factors, revealed that Klhl21/30 expression is controlled by the combined action of three transcription factors, Mitf, Dmrt, and Msx, which are downstream of FGF signaling. The central role of Mitf is consistent with its function as a fundamental regulator of vertebrate pigment cell development. Moreover, our results unraveled a new function for Dmrt and Msx as transcriptional co-activators in the context of the Ciona otolith.

Hox-dependent coordination of mouse cardiac progenitor cell patterning and differentiation

Perturbation of addition of second heart field (SHF) cardiac progenitor cells to the poles of the heart tube results in congenital heart defects (CHD). The transcriptional programs and upstream regulatory events operating in different subpopulations of the SHF remain unclear. Here, we profile the transcriptome and chromatin accessibility of anterior and posterior SHF sub-populations at genome-wide levels and demonstrate that Hoxb1 negatively regulates differentiation in the posterior SHF. Spatial mis-expression of Hoxb1 in the anterior SHF results in hypoplastic right ventricle. Activation of Hoxb1 in embryonic stem cells arrests cardiac differentiation, whereas Hoxb1-deficient mouse embryos display premature cardiac differentiation. Moreover, ectopic differentiation in the posterior SHF of embryos lacking both Hoxb1 and its paralog Hoxa1 results in atrioventricular septal defects. Our results show that Hoxb1 plays a key role in patterning cardiac progenitor cells that contribute to both cardiac poles and provide new insights into the pathogenesis of CHD.