Neurotrophins (NTF) are a family of secreted nerve growth factors with affinity for tyrosine kinase (Ntrk) and p75 receptors. To fully understand the variety of developmental roles played by NTFs, it is critical to know when and where genes encoding individual ligands and receptors are transcribed. Identification of ntf and ntrk transcripts in zebrafish development remains to be fully characterized for further uncovering the potential function(s) of the NTF signal transduction pathway. Here, we conducted a systematic analysis of the expression profiles of four ntf and five ntrk genes during zebrafish development using whole-mount in situ hybridization. Our study unveils new expression domains in the developing embryo, confirms those previously known, and shows that ntf and ntrk genes have different degrees of cell- and tissue-type specificity. The unique and overlapping expression patterns here depicted indicate the coordination of the redundant and divergent functions of NTFs and represent valuable tools for deciphering the molecular pathways involved in the specification and function of embryonic cell types.

The paired-type homeodomain transcription factor Uncx is involved in multiple processes of embryogenesis in vertebrates. Reasoning that zebrafish genes uncx4.1 and uncx are orthologs of mouse Uncx , we studied their genomic environment and developmental expression. Evolutionary analyses indicate the zebrafish uncx genes as being paralogs deriving from teleost-specific whole-genome duplication. Whole-mount in situ mRNA hybridization of uncx transcripts in zebrafish embryos reveals novel expression domains, confirms those previously known, and suggests sub-functionalization of paralogs. Using genetic mutants and pharmacological inhibitors, we investigate the role of signaling pathways on the expression of zebrafish uncx genes in developing somites. In identifying putative functional role(s) of zebrafish uncx genes, we hypothesized that they encode transcription factors that coordinate growth and innervation of somitic muscles.

The intra-tissue level of thyroid hormones (THs) regulates organ functions. Environmental factors can impair it by damaging the thyroid gland and/or the peripheral TH metabolism. We investigated the effects of embryonic and/or long-life exposure to low-dose pesticides, ethylenethiourea (ETU), chlorpyrifos (CPF) and their mixture, on the intra-tissue T4/T3 metabolism/signalling in zebrafish at different life stages. Hypothyroidism was evidenced in exposed larvae that showed reduced number of follicle and induced tshb mRNAs. Despite that, we evidenced the increase of free T4 (fT4) and free T3 (fT3) levels/signalling that was confirmed by the transcriptional regulation of TH metabolic enzymes (deiodinases) and T3-regulated mRNAs (cpt1, igfbp1a). The second-generation larvae showed effects on thyroid and TH signalling even when not directly exposed, suggesting a role of the parental exposure. In adult zebrafish we found a sex-dependent damage of hepatic T3 level/signalling associated to liver steatosis, more pronounced in female, with a sex-dependent alteration of transcripts codifying the key enzymes involved in “de novo lipogenesis” and of β- oxidation. We found an impaired activation of liver T3 and PPARα/Foxo3a pathways whose deregulation was already involved in mammalian liver steatosis. The data underscore the intra-tissue imbalance of T3 level as a target of thyroid endocrine disruptors (THDC) and suggest that the effects of slight modification of T3 signalling might be amplified by its direct regulation or crosstalk with PPAR/Foxo3a pathways. Because T3 levels define the hypothyroid/hyperthyroid status of each organ, our findings might explain the pleiotropic and site-dependent effects of pesticides.

BackgroundThe concerted activity of Meis and Hoxa11 transcription factors is essential for the subdivision of tetrapod limbs into proximo-distal (PD) domains; however, little is know about the evolution of this patterning mechanism. Here, we aim to study the expression of meis and hoxa11 orthologues in the median and paired rayed fins of zebrafish and in the lobed fins of the Australian lungfish.ResultsFirst, a late phase of expression of meis1.1 and hoxa11b in zebrafish dorsal and anal fins relates with segmentation of endochondral elements in proximal and distal radials. Second, our zebrafish in situ hybridization results reveal spatial and temporal changes between pectoral and pelvic fins. Third, in situ analysis of meis1, meis3 and hoxa11 genes in Neoceratodus pectoral fins identifies decoupled domains of expression along the PD axis.ConclusionsOur data raise the possibility that the origin of stylopod and zeugopod lies much deeper in gnathostome evolution and that variation in meis and hoxa11 expression has played a substantial role in the transformation of appendage anatomy. Moreover, these observations provide evidence that the Meis/Hoxa11 profile considered a hallmark of stylopod/zeugopod patterning is present in Neoceratodus.Electronic supplementary materialThe online version of this article (10.1186/s13227-018-0099-9) contains supplementary material, which is available to authorized users.

Thyroid hormones (THs) regulate many biological processes in vertebrates, including reproduction. Testicular somatic and germ cells are equipped with the arrays of enzymes (deiodinases), transporters, and receptors necessary to locally maintain the optimal level of THs and their signalling, needed for their functions and spermatogenesis. Pesticides, as chlorpyrifos (CPF) and ethylene thiourea (ETU), impair the function of thyroid and testis, affecting male fertility. However, their ability to disarrange testicular T3 (t-T3) metabolism and signalling is poorly considered. Here, a multi-species analysis involving zebrafish and mouse suggests the damage of t-T3 metabolism and signalling as a mechanism of gonadic toxicity of low-doses CPF and ETU. Indeed, the developmental exposure to both compounds reduces Dio2 transcript in both models, as well as in ex-vivo cultures of murine seminiferous tubules, and it is linked to alteration of steroidogenesis and germ cell differentiation. A major impact on spermatogonia was confirmed molecularly by the expression of their markers and morphologically evidenced in zebrafish. The results reveal that in the adopted models, exposure to both pesticides alters the t-T3 metabolism and signalling, affecting the reproductive capability. Our data, together with previous reports suggest zebrafish as an evaluable model in assessing the action of compounds impairing locally T3 signalling.