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molecularly well characterized (for review, see
Dusart & Flamant, 2012
).
Neurogenesis in the cerebellum extends over a protracted period of time
between embryonic day 10.5 and postnatal day 15 in mice. The post-
embryonic period is particularly important as there is a maturation event that
is especially spectacular for the Purkinje neurons. Indeed, the development
of mouse Purkinje cells occurs largely during the first three postnatal
weeks of life, during which Purkinje cells undergo a two-phase remodeling
process of their dendrites and establish synaptic connections (
Sotelo &
Dusart, 2009
). This also coincides with granule cell proliferation, maturation
of GABAergic interneuron precursors in neighboring cerebellar layers, as
well as with the terminal differentiation of oligodendrocytes. This postnatal
maturation program is clearly driven by THs (
Dusart & Flamant, 2012
). In
rodents, T3 deficiency results in a number of histological alterations visible
in cerebellum. Purkinje cell alignment is affected, their dendritic arbo-
risations are drastically reduced, and they have fewer synapses (
Fauquier
et al., 2011
). This cellular phenotype can be rescued only if the TH level
is restored at an early stage. Oligodendrocyte proliferation arrest that oc-
curred during their postnatal differentiation process is controlled in a cell au-
tonomous fashion (
Picou, Fauquier, Chatonnet, & Flamant, 2012
). Recent
data have suggested that Purkinje neurons have a central role in the coordi-
nation of cellular interactions that are instrumental for this maturation pro-
cess and that THmay play an important role in setting the timing of Purkinje
cell differentiation (
Fauquier et al., 2011; Picou et al., 2012
). However, the
maturation event is controlled by TH, the precise cellular target(s) of the
hormone, the role played by TR
(that are both expressed in cer-
ebellum), and the target genes controlled by the receptors are far from fully
understood. Nevertheless, it is clear from the situation in mice that TH plays
a critical role in nervous system maturation in mice.
a
and TR
b
5.3. What about other mammals?
The question is whether these data largely derived from mouse models, and
to a lesser extent human cases, can be generalized to other mammalian spe-
cies. Again, it is important to mention that the data available on other species
are rare, and having a general view is still impossible. However, some iso-
lated observations are revealing.
Returning to the guinea pig model, it has been shown that the only dif-
ference between weaning stage and adult intestine is the neuron density that is
lower in weaning intestine which suggests that, except for a subpopulation of
