Abstract:
The mammalian eminentia thalami (EmT) (or
thalamic eminence) is an embryonic forebrain structure of
unknown function. Here, we examined the molecular and
cellular properties of the mouse EmT. We first studied
mRNA expression of signalling molecules and found that
the EmT is a structure, rich in expression of secreted factors,
with Wnts being the most abundantly detected. We
then examined whether EmT tissue could induce cell fate
changes when grafted ectopically. For this, we transplanted
EmT tissue from a tau-GFP mouse to the ventral telencephalon
of a wild type host, a telencephalic region where
Wnt signalling is not normally active but which we showed
in culture experiments is competent to respond to Wnts.
We observed that the EmT was able to induce in adjacent
ventral telencephalic cells ectopic expression of Lef1, a
transcriptional activator and a target gene of the Wnt/bcatenin
pathway. These Lef1-positive;GFP-negative cells
expressed the telencephalic marker Foxg1 but not Ascl1,
which is normally expressed by ventral telencephalic cells.
These results suggest that the EmT has the capacity to
activate Wnt/b-catenin signalling in the ventral telencephalon
and to suppress ventral telencephalic gene expression. Altogether, our data support a role of the EmT
as a signalling centre in the developing mouse forebrain.
