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Contrasting evolutionary dynamics of the developmental regulator PAX9, among bats, with evidence for a novel post-transcriptional regulatory mechanism.

Phillips CD, Butler B, Fondon JW, Mantilla-Meluk H, Baker RJ - PLoS ONE (2013)

Bottom Line: Morphological evolution can be the result of natural selection favoring modification of developmental signaling pathways.Although a connection between morphology and binding element frequency was not apparent, results indicate this regulation would vary among craniofacially divergent bat species, but be static among conserved species.The presence of Musashi-binding elements within PAX9 of all mammals examined, chicken, zebrafish, and the fly homolog of PAX9, indicates this regulatory mechanism is ancient, originating basal to much of the animal phylogeny.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Texas Tech University, Lubbock, Texas, United States of America. caleb.phillips@ttu.edu

ABSTRACT
Morphological evolution can be the result of natural selection favoring modification of developmental signaling pathways. However, little is known about the genetic basis of such phenotypic diversity. Understanding these mechanisms is difficult for numerous reasons, yet studies in model organisms often provide clues about the major developmental pathways involved. The paired-domain gene, PAX9, is known to be a key regulator of development, particularly of the face and teeth. In this study, using a comparative genetics approach, we investigate PAX9 molecular evolution among mammals, focusing on craniofacially diversified (Phyllostomidae) and conserved (Vespertilionidae) bat families, and extend our comparison to other orders of mammal. Open-reading frame analysis disclosed signatures of selection, in which a small percentage of residues vary, and lineages acquire different combinations of variation through recurrent substitution and lineage specific changes. A few instances of convergence for specific residues were observed between morphologically convergent bat lineages. Bioinformatic analysis for unknown PAX9 regulatory motifs indicated a novel post-transcriptional regulatory mechanism involving a Musashi protein. This regulation was assessed through fluorescent reporter assays and gene knockdowns. Results are compatible with the hypothesis that the number of Musashi binding-elements in PAX9 mRNA proportionally regulates protein translation rate. Although a connection between morphology and binding element frequency was not apparent, results indicate this regulation would vary among craniofacially divergent bat species, but be static among conserved species. Under this model, Musashi's regulatory control of alternative human PAX9 isoforms would also vary. The presence of Musashi-binding elements within PAX9 of all mammals examined, chicken, zebrafish, and the fly homolog of PAX9, indicates this regulatory mechanism is ancient, originating basal to much of the animal phylogeny.

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Cladogram reconstructed from [22], [28]–[29] for phyllostomid bats included in this study.Node values are estimated divergence times taken from [22], [28]–[29]. Each leaf of the cladogram includes genus, lateral image of skulls, and symbols of insect, blood, flower, or fruit to indicate dietary strategy of that genus.
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pone-0057649-g001: Cladogram reconstructed from [22], [28]–[29] for phyllostomid bats included in this study.Node values are estimated divergence times taken from [22], [28]–[29]. Each leaf of the cladogram includes genus, lateral image of skulls, and symbols of insect, blood, flower, or fruit to indicate dietary strategy of that genus.

Mentions: Highly variable intra-ordinal and intra-familial patterns of craniofacial and dental evolution are observed within the order Chiroptera. Currently, 19 families of bats are recognized [19]–[20]. Although the family Phyllostomidae is thought to be among the youngest families, this group displays the most craniofacial, dental, and dietary diversity [21]–[22]. It is hypothesized that the morphological variability observed within Phyllostomidae is the result of niche adaptation as multiple dietary strategies are represented in the family, including insectivory, frugivory, nectarivory, sanguivory, omnivory, and carnivory [21]–[22]. Comparison of lineages illustrates often dramatic craniofacial morphological differences (Figure 1) for structures in which Pax9 is expressed during development. For example, there is extensive variation in rostral length, cranial morphology, dental formula, tooth shape, as well as extreme variation in tongue length among nectarivorous lineages. By comparison, the family Vespertilionidae, which is perhaps only slightly older than the Phyllostomidae [19], is very speciose, mostly represented by insectivorous taxa, and all maintain similarly conserved craniofacial and dental morphologies. The difference in occurrence of morphological diversification observed across these families enabled the development of a case-control type experimental design to understand open-reading frame and regulatory sequence evolution of PAX9. We investigated evolutionary rate, substitution patterns, and convergence of PAX9 in phyllostomids, vespertilionids, and other mammalian orders to understand if patterns were compatible with the hypothesis that PAX9 open-reading frame evolution has contributed to morphological diversification. Through comparison of regulatory regions, we developed a hypothesis for a novel translational regulatory mechanism, for which we provided experimental validation, and discussed potential developmental and evolutionary ramifications.


Contrasting evolutionary dynamics of the developmental regulator PAX9, among bats, with evidence for a novel post-transcriptional regulatory mechanism.

Phillips CD, Butler B, Fondon JW, Mantilla-Meluk H, Baker RJ - PLoS ONE (2013)

Cladogram reconstructed from [22], [28]–[29] for phyllostomid bats included in this study.Node values are estimated divergence times taken from [22], [28]–[29]. Each leaf of the cladogram includes genus, lateral image of skulls, and symbols of insect, blood, flower, or fruit to indicate dietary strategy of that genus.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585407&req=5

pone-0057649-g001: Cladogram reconstructed from [22], [28]–[29] for phyllostomid bats included in this study.Node values are estimated divergence times taken from [22], [28]–[29]. Each leaf of the cladogram includes genus, lateral image of skulls, and symbols of insect, blood, flower, or fruit to indicate dietary strategy of that genus.
Mentions: Highly variable intra-ordinal and intra-familial patterns of craniofacial and dental evolution are observed within the order Chiroptera. Currently, 19 families of bats are recognized [19]–[20]. Although the family Phyllostomidae is thought to be among the youngest families, this group displays the most craniofacial, dental, and dietary diversity [21]–[22]. It is hypothesized that the morphological variability observed within Phyllostomidae is the result of niche adaptation as multiple dietary strategies are represented in the family, including insectivory, frugivory, nectarivory, sanguivory, omnivory, and carnivory [21]–[22]. Comparison of lineages illustrates often dramatic craniofacial morphological differences (Figure 1) for structures in which Pax9 is expressed during development. For example, there is extensive variation in rostral length, cranial morphology, dental formula, tooth shape, as well as extreme variation in tongue length among nectarivorous lineages. By comparison, the family Vespertilionidae, which is perhaps only slightly older than the Phyllostomidae [19], is very speciose, mostly represented by insectivorous taxa, and all maintain similarly conserved craniofacial and dental morphologies. The difference in occurrence of morphological diversification observed across these families enabled the development of a case-control type experimental design to understand open-reading frame and regulatory sequence evolution of PAX9. We investigated evolutionary rate, substitution patterns, and convergence of PAX9 in phyllostomids, vespertilionids, and other mammalian orders to understand if patterns were compatible with the hypothesis that PAX9 open-reading frame evolution has contributed to morphological diversification. Through comparison of regulatory regions, we developed a hypothesis for a novel translational regulatory mechanism, for which we provided experimental validation, and discussed potential developmental and evolutionary ramifications.

Bottom Line: Morphological evolution can be the result of natural selection favoring modification of developmental signaling pathways.Although a connection between morphology and binding element frequency was not apparent, results indicate this regulation would vary among craniofacially divergent bat species, but be static among conserved species.The presence of Musashi-binding elements within PAX9 of all mammals examined, chicken, zebrafish, and the fly homolog of PAX9, indicates this regulatory mechanism is ancient, originating basal to much of the animal phylogeny.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Texas Tech University, Lubbock, Texas, United States of America. caleb.phillips@ttu.edu

ABSTRACT
Morphological evolution can be the result of natural selection favoring modification of developmental signaling pathways. However, little is known about the genetic basis of such phenotypic diversity. Understanding these mechanisms is difficult for numerous reasons, yet studies in model organisms often provide clues about the major developmental pathways involved. The paired-domain gene, PAX9, is known to be a key regulator of development, particularly of the face and teeth. In this study, using a comparative genetics approach, we investigate PAX9 molecular evolution among mammals, focusing on craniofacially diversified (Phyllostomidae) and conserved (Vespertilionidae) bat families, and extend our comparison to other orders of mammal. Open-reading frame analysis disclosed signatures of selection, in which a small percentage of residues vary, and lineages acquire different combinations of variation through recurrent substitution and lineage specific changes. A few instances of convergence for specific residues were observed between morphologically convergent bat lineages. Bioinformatic analysis for unknown PAX9 regulatory motifs indicated a novel post-transcriptional regulatory mechanism involving a Musashi protein. This regulation was assessed through fluorescent reporter assays and gene knockdowns. Results are compatible with the hypothesis that the number of Musashi binding-elements in PAX9 mRNA proportionally regulates protein translation rate. Although a connection between morphology and binding element frequency was not apparent, results indicate this regulation would vary among craniofacially divergent bat species, but be static among conserved species. Under this model, Musashi's regulatory control of alternative human PAX9 isoforms would also vary. The presence of Musashi-binding elements within PAX9 of all mammals examined, chicken, zebrafish, and the fly homolog of PAX9, indicates this regulatory mechanism is ancient, originating basal to much of the animal phylogeny.

Show MeSH
Related in: MedlinePlus