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Deterioration of the Gαo vomeronasal pathway in sexually dimorphic mammals.

Suárez R, Fernández-Aburto P, Manger PR, Mpodozis J - PLoS ONE (2011)

Bottom Line: We noted that the species that lost the Gαo pathway belong to Laurasiatheria and Primates lineages, both clades with ubiquitous sexual dimorphisms across species.We found that both species show uniform expression of Gαi2-protein throughout AOB glomeruli, while Gαo expression is restricted to main olfactory glomeruli only.Our results suggest that the degeneration of the Gαo-expressing vomeronasal pathway has occurred independently at least four times in Eutheria, possibly related to the emergence of sexual dimorphisms and the ability of detecting the gender of conspecifics at distance.

View Article: PubMed Central - PubMed

Affiliation: Laboratorio de Neurobiología y Biología del Conocer, Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile. rsuarezsaa@gmail.com

ABSTRACT
In mammals, social and sexual behaviours are largely mediated by the vomeronasal system (VNS). The accessory olfactory bulb (AOB) is the first synaptic locus of the VNS and ranges from very large in Caviomorph rodents, small in carnivores and ungulates, to its complete absence in apes, elephants, most bats and aquatic species. Two pathways have been described in the VNS of mammals. In mice, vomeronasal neurons expressing Gαi2 protein project to the rostral portion of the AOB and respond mostly to small volatile molecules, whereas neurons expressing Gαo project to the caudal AOB and respond mostly to large non-volatile molecules. However, the Gαo-expressing pathway is absent in several species (horses, dogs, musk shrews, goats and marmosets) but no hypotheses have been proposed to date to explain the loss of that pathway. We noted that the species that lost the Gαo pathway belong to Laurasiatheria and Primates lineages, both clades with ubiquitous sexual dimorphisms across species. To assess whether similar events of Gαo pathway loss could have occurred convergently in dimorphic species we studied G-protein expression in the AOB of two species that independently evolved sexually dimorphic traits: the California ground squirrel Spermophilus beecheyi (Rodentia; Sciurognathi) and the cape hyrax Procavia capensis (Afrotheria; Hyracoidea). We found that both species show uniform expression of Gαi2-protein throughout AOB glomeruli, while Gαo expression is restricted to main olfactory glomeruli only. Our results suggest that the degeneration of the Gαo-expressing vomeronasal pathway has occurred independently at least four times in Eutheria, possibly related to the emergence of sexual dimorphisms and the ability of detecting the gender of conspecifics at distance.

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Patterns of Gαi2 and Gαo expression in the accessory olfactory bulb (AOB) of the ground squirrel Spermophilus beecheyi.Sagittal sections through the olfactory bulb reveal that the AOB is located dorsocaudal to the main olfactory bulb (MOB) and expresses Gαi2 throughout its rostrocaudal extent (A, B), at the vomeronasal nerve layer (VN) and glomerular layer (Gl) but not in glomeruli of the MOB (C). Gαo expression is restricted to MOB glomeruli (D, F) and deep layers of the AOB, including some expression at the Gl, but not at the VN, layers (E). Panels G, H, and I correspond to cresyl violet stained sections, where cell layering and relative sizes of AOB and MOB can be appreciated. EP, external plexiform layer; Gr, granule cell layer; LOT, lateral olfactory tract; M/T, mitral/tufted cell layer. Dorsal is to the top and anterior is to the right. Scale bar: 500 µm in A, D and G; 200 µm in B, C, E, F, H and I.
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pone-0026436-g002: Patterns of Gαi2 and Gαo expression in the accessory olfactory bulb (AOB) of the ground squirrel Spermophilus beecheyi.Sagittal sections through the olfactory bulb reveal that the AOB is located dorsocaudal to the main olfactory bulb (MOB) and expresses Gαi2 throughout its rostrocaudal extent (A, B), at the vomeronasal nerve layer (VN) and glomerular layer (Gl) but not in glomeruli of the MOB (C). Gαo expression is restricted to MOB glomeruli (D, F) and deep layers of the AOB, including some expression at the Gl, but not at the VN, layers (E). Panels G, H, and I correspond to cresyl violet stained sections, where cell layering and relative sizes of AOB and MOB can be appreciated. EP, external plexiform layer; Gr, granule cell layer; LOT, lateral olfactory tract; M/T, mitral/tufted cell layer. Dorsal is to the top and anterior is to the right. Scale bar: 500 µm in A, D and G; 200 µm in B, C, E, F, H and I.

Mentions: The AOB of S. beecheyi is located at the dorsocaudal extent of the main olfactory bulb (MOB). It is very small in relation to the MOB, specially when compared with Caviomorph (South American) rodents [2], [3] (Figure 2A, 2D and 2G).


Deterioration of the Gαo vomeronasal pathway in sexually dimorphic mammals.

Suárez R, Fernández-Aburto P, Manger PR, Mpodozis J - PLoS ONE (2011)

Patterns of Gαi2 and Gαo expression in the accessory olfactory bulb (AOB) of the ground squirrel Spermophilus beecheyi.Sagittal sections through the olfactory bulb reveal that the AOB is located dorsocaudal to the main olfactory bulb (MOB) and expresses Gαi2 throughout its rostrocaudal extent (A, B), at the vomeronasal nerve layer (VN) and glomerular layer (Gl) but not in glomeruli of the MOB (C). Gαo expression is restricted to MOB glomeruli (D, F) and deep layers of the AOB, including some expression at the Gl, but not at the VN, layers (E). Panels G, H, and I correspond to cresyl violet stained sections, where cell layering and relative sizes of AOB and MOB can be appreciated. EP, external plexiform layer; Gr, granule cell layer; LOT, lateral olfactory tract; M/T, mitral/tufted cell layer. Dorsal is to the top and anterior is to the right. Scale bar: 500 µm in A, D and G; 200 µm in B, C, E, F, H and I.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3198400&req=5

pone-0026436-g002: Patterns of Gαi2 and Gαo expression in the accessory olfactory bulb (AOB) of the ground squirrel Spermophilus beecheyi.Sagittal sections through the olfactory bulb reveal that the AOB is located dorsocaudal to the main olfactory bulb (MOB) and expresses Gαi2 throughout its rostrocaudal extent (A, B), at the vomeronasal nerve layer (VN) and glomerular layer (Gl) but not in glomeruli of the MOB (C). Gαo expression is restricted to MOB glomeruli (D, F) and deep layers of the AOB, including some expression at the Gl, but not at the VN, layers (E). Panels G, H, and I correspond to cresyl violet stained sections, where cell layering and relative sizes of AOB and MOB can be appreciated. EP, external plexiform layer; Gr, granule cell layer; LOT, lateral olfactory tract; M/T, mitral/tufted cell layer. Dorsal is to the top and anterior is to the right. Scale bar: 500 µm in A, D and G; 200 µm in B, C, E, F, H and I.
Mentions: The AOB of S. beecheyi is located at the dorsocaudal extent of the main olfactory bulb (MOB). It is very small in relation to the MOB, specially when compared with Caviomorph (South American) rodents [2], [3] (Figure 2A, 2D and 2G).

Bottom Line: We noted that the species that lost the Gαo pathway belong to Laurasiatheria and Primates lineages, both clades with ubiquitous sexual dimorphisms across species.We found that both species show uniform expression of Gαi2-protein throughout AOB glomeruli, while Gαo expression is restricted to main olfactory glomeruli only.Our results suggest that the degeneration of the Gαo-expressing vomeronasal pathway has occurred independently at least four times in Eutheria, possibly related to the emergence of sexual dimorphisms and the ability of detecting the gender of conspecifics at distance.

View Article: PubMed Central - PubMed

Affiliation: Laboratorio de Neurobiología y Biología del Conocer, Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile. rsuarezsaa@gmail.com

ABSTRACT
In mammals, social and sexual behaviours are largely mediated by the vomeronasal system (VNS). The accessory olfactory bulb (AOB) is the first synaptic locus of the VNS and ranges from very large in Caviomorph rodents, small in carnivores and ungulates, to its complete absence in apes, elephants, most bats and aquatic species. Two pathways have been described in the VNS of mammals. In mice, vomeronasal neurons expressing Gαi2 protein project to the rostral portion of the AOB and respond mostly to small volatile molecules, whereas neurons expressing Gαo project to the caudal AOB and respond mostly to large non-volatile molecules. However, the Gαo-expressing pathway is absent in several species (horses, dogs, musk shrews, goats and marmosets) but no hypotheses have been proposed to date to explain the loss of that pathway. We noted that the species that lost the Gαo pathway belong to Laurasiatheria and Primates lineages, both clades with ubiquitous sexual dimorphisms across species. To assess whether similar events of Gαo pathway loss could have occurred convergently in dimorphic species we studied G-protein expression in the AOB of two species that independently evolved sexually dimorphic traits: the California ground squirrel Spermophilus beecheyi (Rodentia; Sciurognathi) and the cape hyrax Procavia capensis (Afrotheria; Hyracoidea). We found that both species show uniform expression of Gαi2-protein throughout AOB glomeruli, while Gαo expression is restricted to main olfactory glomeruli only. Our results suggest that the degeneration of the Gαo-expressing vomeronasal pathway has occurred independently at least four times in Eutheria, possibly related to the emergence of sexual dimorphisms and the ability of detecting the gender of conspecifics at distance.

Show MeSH
Related in: MedlinePlus