2 research outputs found
Functional Dicer Is Necessary for Appropriate Specification of Radial Glia during Early Development of Mouse Telencephalon
Early telencephalic development involves transformation of neuroepithelial stem cells into radial glia, which are themselves neuronal progenitors, around the time when the tissue begins to generate postmitotic neurons. To achieve this transformation, radial precursors express a specific combination of proteins. We investigate the hypothesis that micro RNAs regulate the ability of the early telencephalic progenitors to establish radial glia. We ablate functional Dicer, which is required for the generation of mature micro RNAs, by conditionally mutating the Dicer1 gene in the early embryonic telencephalon and analyse the molecular specification of radial glia as well as their progeny, namely postmitotic neurons and basal progenitors. Conditional mutation of Dicer1 from the telencephalon at around embryonic day 8 does not prevent morphological development of radial glia, but their expression of Nestin, Sox9, and ErbB2 is abnormally low. The population of basal progenitors, which are generated by the radial glia, is disorganised and expanded in Dicer1-/- dorsal telencephalon. While the proportion of cells expressing markers of postmitotic neurons is unchanged, their laminar organisation in the telencephalic wall is disrupted suggesting a defect in radial glial guided migration. We found that the laminar disruption could not be accounted for by a reduction of the population of Cajal Retzius neurons. Together, our data suggest novel roles for micro RNAs during early development of progenitor cells in the embryonic telencephalon
Role of monoamines in the development and regeneration of the zebrafish spinal cord
The hallmark of an adult mammalian central nervous system is the inability to regenerate
after an injury. Zebrafish, on the other hand, have an astounding regenerative capacity. After
a spinal cord lesion, zebrafish can re-establish the damaged neuronal network and regain
their swimming ability within weeks. This is partly due to the presence of the ependymal
radial glia (ERGs), which line the wall of the central canal and act as the stem/progenitor
cells of the spinal cord. Under homeostatic conditions the ERGs are largely quiescent,
however, the lesion triggers them to proliferate and replace cells that have been lost due to
the damage. Previous studies have shown that the regeneration of the motor neurons is
affected by the signalling pathways similar to those governing the first development of these
cells during embryogenesis, such as Sonic hedgehog, Notch and dopamine signalling.
Serotonin (5-HT), similar to dopamine, is a monoaminergic neurotransmitter with a wide
range of physiological and behavioural functions. It has also been shown to play a role
during development of the nervous system. In this doctoral thesis I address the hypothesis
that 5-HT has a positive effect on the development and adult regeneration of motor neurons.
In addition, I expand on the previously discovered augmenting effect of dopamine on motor
neuron development, by analysing the downstream pathways of its action.
I show that during the development, incubating embryos in 5-HT increases the proliferation
of the motor neuron progenitor (pMN) cells, which leads to augmented motor neuron
production. RT-PCR on FAC sorted pMN cells highlights a number of serotonergic
receptors that might be responsible for this effect. Although the downstream pathways are
still unknown, 5-HT appears not to act on the sonic hedgehog canonical pathway, as shown
by the unchanged expression of the hedgehog effector gene, patched2 after 5-HT treatment. I
show that 5-HT does not affect the generation of vsx1+ or pax2a+ interneurons, suggesting
that it has a predominant effect on motor neuron production.
In the intact spinal cord of an adult zebrafish, the pMN-like ERGs express serotonergic
receptors, indicating they are responsive to 5-HT stimulation. After a lesion, 5-HT
administration enhances the proliferation of the pMN-like ERGs caudal to the lesion site
resulting in an increase in the number of newborn motor neurons. Rostral to the lesion site,
administration of exogenous 5-HT does not have an effect on the ERG proliferation, possibly
due to the fact that the endogenous source of 5-HT, in the form of the descending axons, is
still present and might already elicit a maximal response of the progenitor cells. 5-HT does
not have an effect on the proliferation of the progenitor cells dorsal or ventral to the pMNlike
domain, nor does it affect the regeneration of the serotonergic interneurons. These
results suggest that 5-HT from the brain preferentially contributes to the regeneration of the
motor neurons.
Dopamine is another monoamine shown to enhance motor neuron production during the
development and regeneration. To investigate the downstream pathways of dopamine
signalling on motor neuron production during embryogenesis, RNA-sequencing was
performed on FAC sorted pMN cells after a treatment with a dopamine agonist, pergolide.
The results yielded 14 differentially expressed genes (FDR<0.05) with diverse functions in
the cell, indicating that dopamine might act on multiple targets to promote motor neuron
production.
Taken together, these results demonstrate the positive effect of monoaminergic stimulation
on motor neuron development and regeneration. They provide an insight into the pathways
that govern the proliferation of stem/progenitor cells in the embryonic and adult spinal cord,
which might contribute to the research working on enhancing adult neurogenesis in
mammals