Are FoxP2, Otx1 and FoxO3 candidates for deep homology in weakly electric fish?
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1
University of Ottawa, Cellular and Molecular Medecine, Canada
During embryological development the teleost telencephalon undergoes eversion while tetrapod telencephalon goes through evagination. This difference in development has caused major problems to establish any homology between teleost and tetrapod telencephalon.
We recently determined the extrinsic and intrinsic neuronal connections of weakly electric fish (Apteronotus leptorhynchus) telencephalon. In particular, we observed that the dorsocentral division of the pallium (DC) contains glutamatergic spiny neurons that receive inputs from the dorsolateral (DL) pallium (homologous to the tetrapod hippocampus) and project to midbrain sensory nuclei (optic tectum, torus semicircularis) involved in visual and electrosensory signal processing.
This pattern of connectivity is similar to that of the spiny glutamatergic pyramidal cells within the deep neocortical layers (V/VI). We wondered if there was a deep homology between teleost DC neurons and tetrapod neocortical neurons. To test that hypothesis, we investigated some molecular markers from deep neocortical layers (FoxP2 and Otx1) and hippocampus (FoxO3).
First, we have cloned the apteronotid homologs of FoxP2, Otx1 and FoxO3. There was, in the case of all three genes, good similarity between the apteronotid and human amino acid sequences: FoxP2 – 78%, Otx1 – 54%, FoxO3 – 71%. The functional domains of these genes were conserved to a far greater extent – on average: FoxP2 – 89%, Otx1 – 76%, FoxO3 – 82%. This led us to hypothesize that the cellular functions of these genes may also be conserved.
We then used in situ hybridization to examine the distribution of the mRNA transcripts of these genes in the apteronotid telencephalon. We found that AptFoxP2 and AptOtx1 transcripts were expressed predominantly in DC, with only a few weakly labeled neurons in DL. In contrast, we found that most neurons in DL strongly expressed AptFoxO3 mRNA, while there was only weak expression in a small number of cells within DC.
Together with our previous hodological and anatomical data, these data suggest a deep homology exists between teleost DC and tetrapod neocortical deep layers. Furthermore, in accordance with previous studies in other teleosts, our data suggest that there is also a direct homology between teleost DL and mammal hippocampus.
Keywords:
Apteronotus leptorhynchus,
Deep homology,
dorsal telencephalon,
pallium,
FOXO3,
FoxP2,
Hippocampus,
Neocortex,
Otx1
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Evolution
Citation:
Harvey-Girard
E,
Giassi
A and
Maler
L
(2012). Are FoxP2, Otx1 and FoxO3 candidates for deep homology in weakly electric fish?.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00089
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Received:
18 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Erik Harvey-Girard, University of Ottawa, Cellular and Molecular Medecine, Ottawa, Ontario, K1H 8M5, Canada, erikhg@uottawa.ca