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Species-specific modifications of mandible shape reveal independent mechanisms for growth and initiation of the coronoid.

Anthwal N, Peters H, Tucker AS - Evodevo (2015)

Bottom Line: We also demonstrate that Sox9 plays a role independent of chondrogenesis in the growth of the coronoid process in response to muscle interaction.The mandibular coronoid process is initiated by intrinsic factors, but later growth is dependent on extrinsic signals from the muscle.These extrinsic influences are hypothesised to be the basis of the variation in coronoid length seen across the mammalian lineage.

View Article: PubMed Central - PubMed

Affiliation: Department of Craniofacial Development and Stem Cell Biology, Dental Institute, King's College London, London, SE1 9RT UK.

ABSTRACT

Background: The variation in mandibular morphology of mammals reflects specialisations for different diets. Omnivorous and carnivorous mammals posses large mandibular coronoid processes, while herbivorous mammals have proportionally smaller or absent coronoids. This is correlated with the relative size of the temporalis muscle that forms an attachment to the coronoid process. The role of this muscle attachment in the development of the variation of the coronoid is unclear.

Results: By comparative developmental biology and mouse knockout studies, we demonstrate here that the initiation and growth of the coronoid are two independent processes, with initiation being intrinsic to the ossifying bone and growth dependent upon the extrinsic effect of muscle attachment. A necessary component of the intrinsic patterning is identified as the paired domain transcription factor Pax9. We also demonstrate that Sox9 plays a role independent of chondrogenesis in the growth of the coronoid process in response to muscle interaction.

Conclusions: The mandibular coronoid process is initiated by intrinsic factors, but later growth is dependent on extrinsic signals from the muscle. These extrinsic influences are hypothesised to be the basis of the variation in coronoid length seen across the mammalian lineage.

No MeSH data available.


Related in: MedlinePlus

Deletion of Tbx1 in Mesp1 lineage mesoderm results in defect in coronoid process growth. a, b Sirius red/alcian blue trichrome staining of parasagittal section through E15.5 coronoid process of wildtype mouse (a) and residual coronoid process of Tbx1Mesp1Cre/− conditional mutant mouse (b). c, d Immunohistochemistry at E15.5 for muscle using muscle specific 12/101 antibody demonstrates a reduction in size of temporalis of mutant mice (d) compared to wildtype littermates (c) e Comparison of volume of temporalis muscle in µm3, estimated from histological staining (a, b), demonstrated that the temporalis muscle is significantly reduced in mesoderm specific Tbx1 mutants compared with wildtype littermates. f, g In situ hybridisation at E15.5 reveals expression of Pax9 around the coronoid process is unchanged in Tbx1Mesp1Cre/− (g) when compared with wildtype littermates (f). h–k At E15.5 Sox9 is detected by immunofluorescence around the E15.5 coronoid process in wildtype mice (h), whereas in situ hybridisation for Col2a shows that this expression is not associated with cartilage at the coronoid process (j). Sox9 expression is reduced in Tbx1Mesp1Cre/− mutant mouse coronoid process (i), and Col2a expression is not present (k), while expression of both is maintained in the condylar cartilage; cp coronoid process; Cdy mandibular condyle; temp temporalis muscle; Scale bar is 100 µm except c and d where bar is 1000 µm
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Fig4: Deletion of Tbx1 in Mesp1 lineage mesoderm results in defect in coronoid process growth. a, b Sirius red/alcian blue trichrome staining of parasagittal section through E15.5 coronoid process of wildtype mouse (a) and residual coronoid process of Tbx1Mesp1Cre/− conditional mutant mouse (b). c, d Immunohistochemistry at E15.5 for muscle using muscle specific 12/101 antibody demonstrates a reduction in size of temporalis of mutant mice (d) compared to wildtype littermates (c) e Comparison of volume of temporalis muscle in µm3, estimated from histological staining (a, b), demonstrated that the temporalis muscle is significantly reduced in mesoderm specific Tbx1 mutants compared with wildtype littermates. f, g In situ hybridisation at E15.5 reveals expression of Pax9 around the coronoid process is unchanged in Tbx1Mesp1Cre/− (g) when compared with wildtype littermates (f). h–k At E15.5 Sox9 is detected by immunofluorescence around the E15.5 coronoid process in wildtype mice (h), whereas in situ hybridisation for Col2a shows that this expression is not associated with cartilage at the coronoid process (j). Sox9 expression is reduced in Tbx1Mesp1Cre/− mutant mouse coronoid process (i), and Col2a expression is not present (k), while expression of both is maintained in the condylar cartilage; cp coronoid process; Cdy mandibular condyle; temp temporalis muscle; Scale bar is 100 µm except c and d where bar is 1000 µm

Mentions: To confirm that loss or reduction of cranial muscle is not sufficient to prevent the initiation of the mandibular coronoid process, mouse conditional knockouts for Tbx1 in mesoderm lineage cells (Mesp1Cre/+;Tbx1flox/flox, hence called Tbx1Mesp1Cre/−) were generated. This conditional knockout is known to have a variable level of penetrance, with low levels of Tbx1 being detected in some mesodermally derived tissues in mutant embryos [19]. To fully determine the level of muscle reduction, samples were collected at E15.5. Histology and immunohistochemistry showed that at E15.5 Tbx1Mesp1Cre/− mutant mice had a significantly reduced temporalis muscle, but still possessed a coronoid process, though it was of substantially reduced size when compared to wildtype (Tbx1Mesp1Cre/+) littermates (Fig. 4a, b, c, d, e). This rudimentary coronoid was lost later in development [19]. To determine if the expression of Pax9 and Sox9 in the developing coronoid was dependent upon interaction with the muscle in the mouse, in situ hybridisation for Pax9 and immunohistochemistry for Sox9 were carried out in Tbx1Mesp1Cre/− mutants with reduced temporalis muscle size. Pax9 expression was found in the condensed mesenchyme surrounding the rudimentary coronoid process of the Tbx1Mesp1Cre/−, in a similar pattern and intensity to that observed in Tbx1Mesp1Cre/+ littermates (Fig. 4f, g). However, compared with wildtype littermate, Tbx1Mesp1Cre/− mutant mice displayed a reduction in Sox9 expression around the vestigial coronoid process, with only a small number of weakly stained cells being present (Fig. 4h, i). As in the wildtype, no Col2a expressing cells were observed in the coronoid process (Fig. 4j, k), confirming the lack of secondary cartilage at the coronoid process. In contrast strong expression was observed as expected in the condylar cartilage (Fig. 4k). These data, along side the difference in Sox9 expression between mouse and guinea pig, imply a relationship between Sox9 expression and extrinsic muscle interactions.Fig. 4


Species-specific modifications of mandible shape reveal independent mechanisms for growth and initiation of the coronoid.

Anthwal N, Peters H, Tucker AS - Evodevo (2015)

Deletion of Tbx1 in Mesp1 lineage mesoderm results in defect in coronoid process growth. a, b Sirius red/alcian blue trichrome staining of parasagittal section through E15.5 coronoid process of wildtype mouse (a) and residual coronoid process of Tbx1Mesp1Cre/− conditional mutant mouse (b). c, d Immunohistochemistry at E15.5 for muscle using muscle specific 12/101 antibody demonstrates a reduction in size of temporalis of mutant mice (d) compared to wildtype littermates (c) e Comparison of volume of temporalis muscle in µm3, estimated from histological staining (a, b), demonstrated that the temporalis muscle is significantly reduced in mesoderm specific Tbx1 mutants compared with wildtype littermates. f, g In situ hybridisation at E15.5 reveals expression of Pax9 around the coronoid process is unchanged in Tbx1Mesp1Cre/− (g) when compared with wildtype littermates (f). h–k At E15.5 Sox9 is detected by immunofluorescence around the E15.5 coronoid process in wildtype mice (h), whereas in situ hybridisation for Col2a shows that this expression is not associated with cartilage at the coronoid process (j). Sox9 expression is reduced in Tbx1Mesp1Cre/− mutant mouse coronoid process (i), and Col2a expression is not present (k), while expression of both is maintained in the condylar cartilage; cp coronoid process; Cdy mandibular condyle; temp temporalis muscle; Scale bar is 100 µm except c and d where bar is 1000 µm
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4644282&req=5

Fig4: Deletion of Tbx1 in Mesp1 lineage mesoderm results in defect in coronoid process growth. a, b Sirius red/alcian blue trichrome staining of parasagittal section through E15.5 coronoid process of wildtype mouse (a) and residual coronoid process of Tbx1Mesp1Cre/− conditional mutant mouse (b). c, d Immunohistochemistry at E15.5 for muscle using muscle specific 12/101 antibody demonstrates a reduction in size of temporalis of mutant mice (d) compared to wildtype littermates (c) e Comparison of volume of temporalis muscle in µm3, estimated from histological staining (a, b), demonstrated that the temporalis muscle is significantly reduced in mesoderm specific Tbx1 mutants compared with wildtype littermates. f, g In situ hybridisation at E15.5 reveals expression of Pax9 around the coronoid process is unchanged in Tbx1Mesp1Cre/− (g) when compared with wildtype littermates (f). h–k At E15.5 Sox9 is detected by immunofluorescence around the E15.5 coronoid process in wildtype mice (h), whereas in situ hybridisation for Col2a shows that this expression is not associated with cartilage at the coronoid process (j). Sox9 expression is reduced in Tbx1Mesp1Cre/− mutant mouse coronoid process (i), and Col2a expression is not present (k), while expression of both is maintained in the condylar cartilage; cp coronoid process; Cdy mandibular condyle; temp temporalis muscle; Scale bar is 100 µm except c and d where bar is 1000 µm
Mentions: To confirm that loss or reduction of cranial muscle is not sufficient to prevent the initiation of the mandibular coronoid process, mouse conditional knockouts for Tbx1 in mesoderm lineage cells (Mesp1Cre/+;Tbx1flox/flox, hence called Tbx1Mesp1Cre/−) were generated. This conditional knockout is known to have a variable level of penetrance, with low levels of Tbx1 being detected in some mesodermally derived tissues in mutant embryos [19]. To fully determine the level of muscle reduction, samples were collected at E15.5. Histology and immunohistochemistry showed that at E15.5 Tbx1Mesp1Cre/− mutant mice had a significantly reduced temporalis muscle, but still possessed a coronoid process, though it was of substantially reduced size when compared to wildtype (Tbx1Mesp1Cre/+) littermates (Fig. 4a, b, c, d, e). This rudimentary coronoid was lost later in development [19]. To determine if the expression of Pax9 and Sox9 in the developing coronoid was dependent upon interaction with the muscle in the mouse, in situ hybridisation for Pax9 and immunohistochemistry for Sox9 were carried out in Tbx1Mesp1Cre/− mutants with reduced temporalis muscle size. Pax9 expression was found in the condensed mesenchyme surrounding the rudimentary coronoid process of the Tbx1Mesp1Cre/−, in a similar pattern and intensity to that observed in Tbx1Mesp1Cre/+ littermates (Fig. 4f, g). However, compared with wildtype littermate, Tbx1Mesp1Cre/− mutant mice displayed a reduction in Sox9 expression around the vestigial coronoid process, with only a small number of weakly stained cells being present (Fig. 4h, i). As in the wildtype, no Col2a expressing cells were observed in the coronoid process (Fig. 4j, k), confirming the lack of secondary cartilage at the coronoid process. In contrast strong expression was observed as expected in the condylar cartilage (Fig. 4k). These data, along side the difference in Sox9 expression between mouse and guinea pig, imply a relationship between Sox9 expression and extrinsic muscle interactions.Fig. 4

Bottom Line: We also demonstrate that Sox9 plays a role independent of chondrogenesis in the growth of the coronoid process in response to muscle interaction.The mandibular coronoid process is initiated by intrinsic factors, but later growth is dependent on extrinsic signals from the muscle.These extrinsic influences are hypothesised to be the basis of the variation in coronoid length seen across the mammalian lineage.

View Article: PubMed Central - PubMed

Affiliation: Department of Craniofacial Development and Stem Cell Biology, Dental Institute, King's College London, London, SE1 9RT UK.

ABSTRACT

Background: The variation in mandibular morphology of mammals reflects specialisations for different diets. Omnivorous and carnivorous mammals posses large mandibular coronoid processes, while herbivorous mammals have proportionally smaller or absent coronoids. This is correlated with the relative size of the temporalis muscle that forms an attachment to the coronoid process. The role of this muscle attachment in the development of the variation of the coronoid is unclear.

Results: By comparative developmental biology and mouse knockout studies, we demonstrate here that the initiation and growth of the coronoid are two independent processes, with initiation being intrinsic to the ossifying bone and growth dependent upon the extrinsic effect of muscle attachment. A necessary component of the intrinsic patterning is identified as the paired domain transcription factor Pax9. We also demonstrate that Sox9 plays a role independent of chondrogenesis in the growth of the coronoid process in response to muscle interaction.

Conclusions: The mandibular coronoid process is initiated by intrinsic factors, but later growth is dependent on extrinsic signals from the muscle. These extrinsic influences are hypothesised to be the basis of the variation in coronoid length seen across the mammalian lineage.

No MeSH data available.


Related in: MedlinePlus