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We compared expression of the paralogous LIM-homeodomain
genes Lhx1 and Lhx5 in the developing rostral
forebrain of mouse and chicken. Both genes are
expressed in similar patterns in the septum, preoptic
region, and related areas of the basal telencephalon,
including the medial septum/diagonal band nuclei and
the medial extended amygdala. In the septum, the
expression of Lhx5 and Lhx1 appears to be specifically
related to the pallial septum and its derivatives in
mouse and chicken, and may produce the glutamatergic
neurons observed in the diagonal band/medial septum
nuclei. The preoptic area expresses both Lhx1 and
Lhx5 in mouse and chicken, and appears to produce caminobutyric
acid (GABA)ergic, glutamatergic, and cholinergic
cells for the preoptic region and basal telencephalon.
In addition, in mouse and chicken Lhx5 is
expressed in two extratelencephalic domains that
appear to contribute Lhx5-expressing cells to the basal
telencephalon, including the supraoptoparaventricular
hypothalamic domain and the eminentia thalami. In
contrast, there are striking differences in the pallial
expression of Lhx1 and Lhx5 between mouse and
chicken. Both genes are expressed in Cajal-Retzius
cells, and Lhx5 is also present in most pallial sources
of Cajal-Retzius cells (including the cortical hem and
retrobulbar area) and in the olfactory bulbs in the
mouse. In contrast, putative Cajal-Retzius cells, the retrobulbar
area, and the olfactory bulb of chicken do not
express the paralog genes cLhx1/cLhx5. Moreover, the
cortical hem—although it expresses cLhx5—is very tiny
in chicken. We discuss the consequences of these differences
in Lhx1/Lhx5 expression between mouse and
chicken for pallial/cortical evolution.
Grant sponsor: the Spanish Ministry of Education and Science and the Spanish Federation for Rare Diseases (DGICYT-FEDER); Grant numbers: BFU2006-14804-C02-02/BFI and BFU2009-07212/BFI (to L.M.); Grant sponsor: ANR-Neuro (to S.R.); Grant sponsor: the Spanish Ministry of Education and Science (predoctoral fellowship to A.A). |
