Signals from the brain and olfactory epithelium control shaping of the mammalian nasal capsule cartilage

Abstract

Facial shape is the basis for facial recognition and categorization. Facial features reflect the underlying geometry of the skeletal structures. Here, we reveal that cartilaginous nasal capsule (corresponding to upper jaw and face) is shaped by signals generated by neural structures: brain and olfactory epithelium. Brain-derived Sonic Hedgehog (SHH) enables the induction of nasal septum and posterior nasal capsule, whereas the formation of a capsule roof is controlled by signals from the olfactory epithelium. Unexpectedly, the cartilage of the nasal capsule turned out to be important for shaping membranous facial bones during development. This suggests that conserved neurosensory structures could benefit from protection and have evolved signals inducing cranial cartilages encasing them. Experiments with mutant mice revealed that the genomic regulatory regions controlling production of SHH in the nervous system contribute to facial cartilage morphogenesis, which might be a mechanism responsible for the adaptive evolution of animal faces and snouts.

Sculpting the skull through neurosensory epithelial–mesenchymal signaling

“…Consistent with this idea, experiments in which the OE was blocked from forming or arrested at very early stages also led to malformed nasal cavity and surrounding craniofacial structures. This was observed in Fgf8 ‐conditional null (Kawauchi et al, ), Foxg1 ‐null (Duggan et al, ; Kawauchi et al, ), Six1/4 ‐double null (Kaucka et al, ; Laclef et al, ), Dlx5/6 ‐double null (Gitton et al, ), and Dicer1 ‐conditional null (Kersigo et al, ) mice. Up until recently, however, an epithelial–mesenchymal signal regulating OE and olfactory structure development has remained elusive (Adameyko and Fried, ; Van Valkenburgh et al, ).…”

Phosphotungstic acid‐enhanced microCT: Optimized protocols for embryonic and early postnatal mice

“…Furthermore, the majority of published protocols provide only minimal details, requiring extensive experimentation to reach an optimized protocol, particularly if using a different model organism, specimen age, or tissue type. One research group has published detailed PTA protocols for use in embryonic mice from E12.5 to 18.5 . The Kaucka and Tesařová protocols added several significant steps to Metscher's original PTA staining method: a slow graded ethanol and methanol dehydration series, different suggested staining times for several ages of embryonic mice, and a final graded methanol rehydration series.…”

“…The Kaucka and Tesařová protocols added several significant steps to Metscher's original PTA staining method: a slow graded ethanol and methanol dehydration series, different suggested staining times for several ages of embryonic mice, and a final graded methanol rehydration series. The slow dehydration and rehydration steps were added to help minimize soft tissue shrinkage, addressing many of the concerns with iodine staining. With these modifications, the Kaucka and Tesařová protocols provided excellent contrast enhancement, particularly for embryonic murine cranial soft tissues and cartilage .…”

“…The slow dehydration and rehydration steps were added to help minimize soft tissue shrinkage, addressing many of the concerns with iodine staining. With these modifications, the Kaucka and Tesařová protocols provided excellent contrast enhancement, particularly for embryonic murine cranial soft tissues and cartilage . However, these protocols vary between publications, making it difficult to elect an optimum method.…”

“…However, these protocols vary between publications, making it difficult to elect an optimum method. For example, E15.5 embryos were either stained for 6 days with 0.7% PTA solution or 3 weeks with 1.0% to 1.5% PTA solution . These differences may reflect differences in the specific research goals for the stained specimens.…”