RESUMO
Vertebrate locomotor circuitry contains distinct classes of ventral spinal cord neurons which each have particular functional properties. While we know some of the genes expressed by each of these cell types, we do not yet know how several of these neurons are specified. Here, we investigate the functions of Tal1, Gata2a, and Gata3 transcription factors in the development of two of these populations of neurons with important roles in locomotor circuitry: V2b neurons and cerebrospinal fluid-contacting Kolmer-Agduhr (KA) neurons (also called CSF-cNs). Our data provide the first demonstration, in any vertebrate, that Tal1 and Gata3 are required for correct development of KA and V2b neurons, respectively. We also uncover differences in the genetic regulation of V2b cell development in zebrafish compared to mouse. In addition, we demonstrate that Sox1a and Sox1b are expressed by KA and V2b neurons in zebrafish, which differs from mouse, where Sox1 is expressed by V2c neurons. KA neurons can be divided into ventral KAâ³ neurons and more dorsal KA' neurons. Consistent with previous morpholino experiments, our mutant data suggest that Tal1 and Gata3 are required in KA' but not KAâ³ cells, whereas Gata2a is required in KAâ³ but not KA' cells, even though both of these cell types co-express all three of these transcription factors. In gata2a mutants, cells in the KAâ³ region of the spinal cord lose expression of most KAâ³ genes and there is an increase in the number of cells expressing V3 genes, suggesting that Gata2a is required to specify KAâ³ and repress V3 fates in cells that normally develop into KAâ³ neurons. On the other hand, our data suggest that Gata3 and Tal1 are both required for KA' neurons to differentiate from progenitor cells. In the KA' region of these mutants, cells no longer express KA' markers and there is an increase in the number of mitotically-active cells. Finally, our data demonstrate that all three of these transcription factors are required for later stages of V2b neuron differentiation and that Gata2a and Tal1 have different functions in V2b development in zebrafish than in mouse.
RESUMO
BACKGROUND: It has been shown that nanomaterials (NMs) are able to translocate to secondary tissues one of the important being the kidneys. Oxidative stress has been implicated as a possible mechanism for NM toxicity, hence effects on the human renal proximal tubule epithelial cells (HK-2) treated with a panel of engineered nanomaterials (NMs) consisting of two zinc oxide particles (ZnO - coated - NM 110 and uncoated - NM 111), two multi walled carbon nanotubes (MWCNT) (NM 400 and NM 402), one silver (NM 300) and five TiO2 NMs (NM 101, NRCWE 001, 002, 003 and 004) were evaluated. METHODS: In order to assess the toxicological impact of the engineered NMs on HK-2 cells - WST-1 cytotoxicity assay, FACSArray, HE oxidation and the comet assays were utilised. For statistical analysis, the experimental values were compared to their corresponding controls using an ANOVA with Tukey's multiple comparison. RESULTS: We found the two ZnO NMs (24 hr LC50 - 2.5 µg/cm2) and silver NM (24 hr LC50 - 10 µg/cm2) were highly cytotoxic to the cells. The LC50 was not attained in the presence of any of the other engineered nanomaterials (up to 80 µg/cm2). All nanomaterials significantly increased IL8 and IL6 production. Meanwhile no significant change in TNF-α or MCP-1 was detectable. The most notable increase in ROS was noted following treatment with the Ag and the two ZnO NMs. Finally, genotoxicity was measured at sub-lethal concentrations. We found a small but significant increase in DNA damage following exposure to seven of the ten NMs investigated (NM 111, NRCWE 001 and NRCWE 003 being the exception) with this increase being most visible following exposure to Ag and the positively charged TiO2. CONCLUSIONS: While the NMs could be categorised as low and highly cytotoxic, sub-lethal effects such as cytokine production and genotoxicity were observed with some of the low toxicity materials.
