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Correlation between Hox code and vertebral morphology in archosaurs.

Böhmer C, Rauhut OW, Wörheide G - Proc. Biol. Sci. (2015)

Bottom Line: By using geometric morphometrics, we demonstrate a correlation between vertebral Hox code and quantifiable vertebral morphology in modern archosaurs, in which the boundaries between morphological subgroups of vertebrae can be linked to anterior Hox gene expression boundaries.Our findings reveal homologous units of cervical vertebrae in modern archosaurs, each with their specific Hox gene pattern, enabling us to trace these homologies in the extinct sauropodomorph dinosaurs, a group with highly variable vertebral counts.Based on the quantifiable vertebral morphology, this allows us to infer the underlying genetic mechanisms in vertebral evolution in fossils, which represents not only an important case study, but will lead to a better understanding of the origin of morphological disparity in recent archosaur vertebral columns.

View Article: PubMed Central - PubMed

Affiliation: Department für Geo- und Umweltwissenschaften und GeoBio-Center, Ludwig-Maximilians-Universität München, Richard-Wagner-Strasse 10, München 80333, Deutschland SNSB - Bayerische Staatssammlung für Paläontologie und Geologie, Richard-Wagner-Strasse 10, München 80333, Deutschland boehmer@vertevo.de.

ABSTRACT
The relationship between developmental genes and phenotypic variation is of central interest in evolutionary biology. An excellent example is the role of Hox genes in the anteroposterior regionalization of the vertebral column in vertebrates. Archosaurs (crocodiles, dinosaurs including birds) are highly variable both in vertebral morphology and number. Nevertheless, functionally equivalent Hox genes are active in the axial skeleton during embryonic development, indicating that the morphological variation across taxa is likely owing to modifications in the pattern of Hox gene expression. By using geometric morphometrics, we demonstrate a correlation between vertebral Hox code and quantifiable vertebral morphology in modern archosaurs, in which the boundaries between morphological subgroups of vertebrae can be linked to anterior Hox gene expression boundaries. Our findings reveal homologous units of cervical vertebrae in modern archosaurs, each with their specific Hox gene pattern, enabling us to trace these homologies in the extinct sauropodomorph dinosaurs, a group with highly variable vertebral counts. Based on the quantifiable vertebral morphology, this allows us to infer the underlying genetic mechanisms in vertebral evolution in fossils, which represents not only an important case study, but will lead to a better understanding of the origin of morphological disparity in recent archosaur vertebral columns.

No MeSH data available.


WISH results. Hox gene expression in the somites (so) of Nile crocodile embryos (ED 10–14). Arrowheads indicate the anterior and posterior expression boundary. (a) HoxB-4 has an anterior limit at C3 (so 7/8) and extends to C6 (so 10/11). (b) HoxD-4 expression starts at C3 (so 7/8) and fades out posteriorly at D1 (so 14/15). (c) HoxA-4 is expressed from C5 (so 9/10) to D3 (so 16/17). (d) HoxC-4 has an anterior boundary at C5 (so 9/10) and extends to C9 (so 13/14). (e) HoxC-5 expression starts at C8 (so 12/13) and fades out posteriorly at D1 (so 14/15). (f) HoxA-5 is expressed from C9 (so 13/14) to D4 (so 17/18).
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RSPB20150077F2: WISH results. Hox gene expression in the somites (so) of Nile crocodile embryos (ED 10–14). Arrowheads indicate the anterior and posterior expression boundary. (a) HoxB-4 has an anterior limit at C3 (so 7/8) and extends to C6 (so 10/11). (b) HoxD-4 expression starts at C3 (so 7/8) and fades out posteriorly at D1 (so 14/15). (c) HoxA-4 is expressed from C5 (so 9/10) to D3 (so 16/17). (d) HoxC-4 has an anterior boundary at C5 (so 9/10) and extends to C9 (so 13/14). (e) HoxC-5 expression starts at C8 (so 12/13) and fades out posteriorly at D1 (so 14/15). (f) HoxA-5 is expressed from C9 (so 13/14) to D4 (so 17/18).

Mentions: The gene expression analysis (figure 2) showed that C. niloticus expresses the same Hox genes (HoxA-4, B-4, C-4, D-4 as well as A-5, C-5) found in the neck of other tetrapods [22,23,29–32,50,51]. In crocodiles, which generally have nine cervicals, the anterior expression limit of HoxA-4 and C-4 is at the fifth cervical vertebra (C5), extending to the thoracic region (figure 2c,d). The expression of HoxB-4 and D-4 begins at the third cervical vertebra (figure 2a,b). HoxB-4 is only active until C6, whereas HoxD-4 is expressed to the end of the neck. Whereas the expression of HoxB-5 already starts at C2 [23], the anterior expression boundary of HoxA-5 is at the last cervical vertebra (C9) (figure 2f). HoxC-5 is expressed at the last two cervical vertebrae (figure 2e).Figure 2.


Correlation between Hox code and vertebral morphology in archosaurs.

Böhmer C, Rauhut OW, Wörheide G - Proc. Biol. Sci. (2015)

WISH results. Hox gene expression in the somites (so) of Nile crocodile embryos (ED 10–14). Arrowheads indicate the anterior and posterior expression boundary. (a) HoxB-4 has an anterior limit at C3 (so 7/8) and extends to C6 (so 10/11). (b) HoxD-4 expression starts at C3 (so 7/8) and fades out posteriorly at D1 (so 14/15). (c) HoxA-4 is expressed from C5 (so 9/10) to D3 (so 16/17). (d) HoxC-4 has an anterior boundary at C5 (so 9/10) and extends to C9 (so 13/14). (e) HoxC-5 expression starts at C8 (so 12/13) and fades out posteriorly at D1 (so 14/15). (f) HoxA-5 is expressed from C9 (so 13/14) to D4 (so 17/18).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4590465&req=5

RSPB20150077F2: WISH results. Hox gene expression in the somites (so) of Nile crocodile embryos (ED 10–14). Arrowheads indicate the anterior and posterior expression boundary. (a) HoxB-4 has an anterior limit at C3 (so 7/8) and extends to C6 (so 10/11). (b) HoxD-4 expression starts at C3 (so 7/8) and fades out posteriorly at D1 (so 14/15). (c) HoxA-4 is expressed from C5 (so 9/10) to D3 (so 16/17). (d) HoxC-4 has an anterior boundary at C5 (so 9/10) and extends to C9 (so 13/14). (e) HoxC-5 expression starts at C8 (so 12/13) and fades out posteriorly at D1 (so 14/15). (f) HoxA-5 is expressed from C9 (so 13/14) to D4 (so 17/18).
Mentions: The gene expression analysis (figure 2) showed that C. niloticus expresses the same Hox genes (HoxA-4, B-4, C-4, D-4 as well as A-5, C-5) found in the neck of other tetrapods [22,23,29–32,50,51]. In crocodiles, which generally have nine cervicals, the anterior expression limit of HoxA-4 and C-4 is at the fifth cervical vertebra (C5), extending to the thoracic region (figure 2c,d). The expression of HoxB-4 and D-4 begins at the third cervical vertebra (figure 2a,b). HoxB-4 is only active until C6, whereas HoxD-4 is expressed to the end of the neck. Whereas the expression of HoxB-5 already starts at C2 [23], the anterior expression boundary of HoxA-5 is at the last cervical vertebra (C9) (figure 2f). HoxC-5 is expressed at the last two cervical vertebrae (figure 2e).Figure 2.

Bottom Line: By using geometric morphometrics, we demonstrate a correlation between vertebral Hox code and quantifiable vertebral morphology in modern archosaurs, in which the boundaries between morphological subgroups of vertebrae can be linked to anterior Hox gene expression boundaries.Our findings reveal homologous units of cervical vertebrae in modern archosaurs, each with their specific Hox gene pattern, enabling us to trace these homologies in the extinct sauropodomorph dinosaurs, a group with highly variable vertebral counts.Based on the quantifiable vertebral morphology, this allows us to infer the underlying genetic mechanisms in vertebral evolution in fossils, which represents not only an important case study, but will lead to a better understanding of the origin of morphological disparity in recent archosaur vertebral columns.

View Article: PubMed Central - PubMed

Affiliation: Department für Geo- und Umweltwissenschaften und GeoBio-Center, Ludwig-Maximilians-Universität München, Richard-Wagner-Strasse 10, München 80333, Deutschland SNSB - Bayerische Staatssammlung für Paläontologie und Geologie, Richard-Wagner-Strasse 10, München 80333, Deutschland boehmer@vertevo.de.

ABSTRACT
The relationship between developmental genes and phenotypic variation is of central interest in evolutionary biology. An excellent example is the role of Hox genes in the anteroposterior regionalization of the vertebral column in vertebrates. Archosaurs (crocodiles, dinosaurs including birds) are highly variable both in vertebral morphology and number. Nevertheless, functionally equivalent Hox genes are active in the axial skeleton during embryonic development, indicating that the morphological variation across taxa is likely owing to modifications in the pattern of Hox gene expression. By using geometric morphometrics, we demonstrate a correlation between vertebral Hox code and quantifiable vertebral morphology in modern archosaurs, in which the boundaries between morphological subgroups of vertebrae can be linked to anterior Hox gene expression boundaries. Our findings reveal homologous units of cervical vertebrae in modern archosaurs, each with their specific Hox gene pattern, enabling us to trace these homologies in the extinct sauropodomorph dinosaurs, a group with highly variable vertebral counts. Based on the quantifiable vertebral morphology, this allows us to infer the underlying genetic mechanisms in vertebral evolution in fossils, which represents not only an important case study, but will lead to a better understanding of the origin of morphological disparity in recent archosaur vertebral columns.

No MeSH data available.