Formation Of Neuronal Cells Research Articles

Exposure of Zebrafish Embryos to Urea Affects NOS1 Gene Expression in Neuronal Cells

Nitrogen-based fertilizers represent the most common fertilization tools, particularly used in crop food agriculture, despite the low cost-efficiency and the high negative environmental impact. At present, there is still inadequate information available about the effects of urea on human health; nevertheless, previous studies in animals observed that high urea concentration exposure can damage different tissues, including the brain. In several vertebrates, a crucial factor involved in neuronal cell formation is represented by the gas molecule, nitric oxide (NO), derived from the conversion of arginine to citrulline through the enzymatic activity of nitric oxide synthases (NOS). In zebrafish, three different isoforms of the NOS gene are known: nos1, nos2a, and nos2b. In the present study we show that nos1 represents the unique isoform with a stable high expression in the brain and spinal cord during all the embryonic stages of zebrafish development. Then, by using a specific transgenic zebrafish line, Tg(HuC:GFP), to mark neuronal cells, we observed nos1 to be specifically expressed in neurons. Interestingly, we observed that urea exposure at sub-lethal doses affected cell proliferation and the number of nos1-expressing cells, inducing apoptosis. Consistently, brain NO levels were observed to be reduced in urea-treated animals compared to untreated ones. This finding represents the first evidence that urea exposure affects the expression of a key gene involved in neuronal cell formation during embryonic development.

Breaking dogma for future therapy using stem cell - Where we have reached?

Breaking dogma for future therapy using stem cell - Where we have reached?

Sox2 Induces Neuronal Formation in the Developing Mammalian Cochlea

In the cochlea, spiral ganglion neurons play a critical role in hearing as they form the relay between mechanosensory hair cells in the inner ear and cochlear nuclei in the brainstem. The proneural basic helix-loop-helix transcription factors Neurogenin1 (Neurog1) and NeuroD1 have been shown to be essential for the development of otocyst-derived inner ear sensory neurons. Here, we show neural competence of nonsensory epithelial cells in the cochlea, as ectopic expression of either Neurog1 or NeuroD1 results in the formation of neuronal cells. Since the high-mobility-group type transcription factor Sox2, which is also known to play a role in neurogenesis, is expressed in otocyst-derived neural precursor cells and later in the spiral ganglion neurons along with Neurog1 and NeuroD1, we used both gain- and loss-of-function experiments to examine the role of Sox2 in spiral ganglion neuron formation. We demonstrate that overexpression of Sox2 results in the production of neurons, suggesting that Sox2 is sufficient for the induction of neuronal fate in nonsensory epithelial cells. Furthermore, spiral ganglion neurons are absent in cochleae from Sox2(Lcc/Lcc) mice, indicating that Sox2 is also required for neuronal formation in the cochlea. Our results indicate that Sox2, along with Neurog1 and NeuroD1, are sufficient to induce a neuronal fate in nonsensory regions of the cochlea. Finally, we demonstrate that nonsensory cells within the cochlea retain neural competence through at least the early postnatal period.

NSCL-1 and NSCL-2 synergistically determine the fate of GnRH-1 neurons and control necdin gene expression.

To study the role of the bHLH genes NSCL-1 and NSCL-2 in the development of GnRH-1 neurons, we have generated compound mutant mice. Mutant animals die at birth and show a virtually complete absence of GnRH-1 neurons in the posterior parts of the brain at E18.5 and an aberrant morphology of the remaining GnRH-1 neurons in the anterior parts of the brain indicating that NSCL-1 and NSCL-2 might concomitantly control differentiation/migration of GnRH-1 neurons in a cell autonomous manner. To gain further insights into this process, we screened for NSCL target genes using DNA array hybridization and detected necdin, which is deleted in the human Prader-Willi syndrome phenotypically resembling the NSCL-2 mutation. Using chromatin immunoprecipitation and site-directed mutagenesis of the necdin promoter, we demonstrate that NSCLs together with additional cofactors directly control transcription of the necdin gene. NSCL-dependent control of necdin expression might be instrumental for proper neuronal cell differentiation and enable GnRH-1 neurons to migrate.

Differential Induction of HNF-3 Transcription Factors during Neuronal Differentiation

We have investigated the regulation of transcription factors HNF-3α and HNF-3β during the retinoic acid-mediated differentiation of mouse P19 cells. Retinoic acid treatment converts P19 stem cells into neurons and astrocytes and we have clearly shown that gene expression of both HNF-3α and HNF-3β is activated during this process. HNF-3α transcription was detected 2 h after addition of retinoic acid and took place in the absence ofde novoprotein synthesis. This suggests that HNF-3α is a primary target for retinoic acid action. HNF-3α induction displays a biphasic profile and HNF-3α mRNA reaches maximal levels at 2 and 6 days postdifferentiation. Additional experiments strongly suggest that the second peak is due to HNF-3α induction in postmitotic neurons. P19 stem cells, on the other hand, do not contain any detectable HNF-3α mRNA. According to our studies, the retinoic acid-mediated induction of HNF-3α occurs at the level of transcriptional initiation and is conferred by distal promoter sequences. In comparison to HNF-3α, HNF-3β induction is a subsequent event and detectable levels of HNF-3β mRNA materialize approximately 1 day after addition of retinoic acid to P19 stem cells. Time course studies firmly demonstrate that HNF-3β mRNA peaks at about 2 days postdifferentiation and then declines to virtually unreadable levels. This temporal pattern is consistent with HNF-3β being a secondary target for retinoic acid. In analogy to HNF-3α, HNF-3β activation also takes place at the level of transcriptional initiation. Recent studies implicate HNF-3α and HNF-3β in early mammalian neurogenesis. The detection of HNF-3α/β activation during P19 cell differentiation provides us with a convenient cell culture system to elucidate the induction mechanism and the precise role of both transcriptional regulators in the formation of neuronal cells.