Craniofacial Biology

This project investigates different aspects of craniofacial phenotypes exhibited in individuals with Down syndrome (DS), siblings of individuals with DS, and typically developing sibling pairs. A human sample (4-12 yrs.) consisting of 3D facial surface images (n = 55 for four separate samples: i.e. n = 220 overall) was used to explore developmental instability of the face and patterns of facial covariation between individuals with DS, their siblings, and typically developing sibling pairs. Morphometric analyses were used to infer how gene-dosage imbalance, caused by trisomy 21, is affecting DS craniofacial development. Overall we found increased fluctuating asymmetry in the faces of individuals with DS, which provides evidence for the "amplified developmental instability" model put forth by Shapiro (1975, 1983). However, the patterns of differences that we found suggest specific disruptions to regions of the face during craniofacial development rather than the generalized disruptions described by Shapiro under the amplified developmental instability model. Additionally, the results of our investigation found that covariation of facial metrics is different in DS individuals and in DS siblings relative to typically developing siblings. Based on differences in the pattern and strength of integration within and between facial regions in the DS and DS sibling samples, we put forth an "aneuploid conception model" to explain why facial integration is lowest in DS siblings and strengthened in DS relative to DS siblings.

In addition to the human-based analyses, micro-computed tomography (µCT) scans and morphometric analysis were employed to evaluate a complete genetic mouse model for DS - the Ts1Yey mouse. Morphometric comparison of craniofacial measures for Ts1Yey mice and euploid littermates (n = 12 for each sample) was done to determine if this model exhibits craniofacial differences similar to differences seen in humans with DS and in previously established DS mouse models. Overall, our results validate this mouse model for use in craniofacial DS investigations.

Today, and looking to the future, scientific discoveries from cellular, developmental and molecular biology inform our understanding of cell, tissue and organ morphogenesis as exemplified in skin, bone, cartilage, dentine, enamel, muscle, nerve and many organs such as salivary glands and teeth. Present day biomedical science yields principles for the biomi-metic design and fabrication of cells, tissues and organs. Bioengineering has become a strategy that can 'mimic' biological processes, and inform clinical procedures for tissue and organ replacements. The future of regenerative craniofacial biology holds enormous promise for the diagnosis and treatment of congenital birth defects, traumatic injuries, degenera-tive chronic diseases as well as for Mendelian single gene and complex multigene diseases and disorders. The past 50 years have heralded the completion of the human genome and the introduction of 'personalized medicine and den-tistry', the utilization of stem cell therapy for an array of diseases and disorders, the 'proof of principle' to reverse select inherited diseases such as anhidrotic ectodermal dysplasia (ED), and the fruits from interdisciplinary research drawn from the diverse biomedical sciences. Looking to the future, we can readily anticipate as major goals to emphasize the clinician's role in identifying clinical phenotypes that can lead to differential diagnosis, and rejuvenate missing or damaged tissues by establishing processes for the utilization of gene, cell and/or protein therapies. The future is replete with remarkable opportunities to enhance clinical outcomes for congenital as well as acquired craniofacial malformations. Cli-nicians play a pivotal role because critical thinking and sound clinical acumen substantially improve diagnostic precision and thereby clinical health outcomes. Abbreviations and acronyms: ED = ectodermal dysplasia; FGFR2 = fibroblast growth factor receptor 2; iPS = induced pluripotent cell; SNP = single nucleotide polymorphisms.

Background: The developmental basis of craniofacial morphology hinges on interactions of numerous signalling systems. Extensive craniofacial variation in the polymorphic Arctic charr, a member of the salmonid family, from Lake Thingvallavatn (Iceland), offers opportunities to find and study such signalling pathways and their key regulators, thereby shedding light on the developmental pathways, and the genetics of trophic divergence. Results: To identify genes involved in the craniofacial differences between benthic and limnetic Arctic charr, we used transcriptome data from different morphs, spanning early development, together with data on craniofacial expression patterns and skeletogenesis in model vertebrate species. Out of 20 genes identified, 7 showed lower gene expression in benthic than in limnetic charr morphs. We had previously identified a conserved gene network involved in extracel-lular matrix (ECM) organization and skeletogenesis, showing higher expression in developing craniofacial elements of benthic than in limnetic Arctic charr morphs. The present study adds a second set of genes constituting an expanded gene network with strong, benthic–limnetic differential expression. To identify putative upstream regulators, we performed knowledge-based motif enrichment analyses on the regulatory sequences of the identified genes which yielded potential binding sites for a set of known transcription factors (TFs). Of the 8 TFs that we examined using qPCR, two (Ahr2b and Ap2) were found to be differentially expressed between benthic and limnetic charr. Expression analysis of several known AhR targets indicated higher activity of the AhR pathway during craniofacial development in benthic charr morphotypes. Conclusion: These results suggest a key role of the aryl hydrocarbon receptor (AhR) pathway in the observed crani-ofacial differences between distinct charr morphotypes.

Typological classification of human zygomaticomaxillary suture (ZMS) shape is often used in forensic assessment of ancestry, following earlier studies reporting higher frequencies of ‘‘angled’’ sutures among American Indians and higher frequencies of ‘‘curved’’ sutures among Caucasians. In this paper we present a new method of digital morphometrics to quantify and compare ZMS shape in 60 American Indian and 60 European crania. Suture outlines were recorded as three-dimensional (3D) contours on digital models of adult male and female crania created with a portable 3D laser scanner. Each contour was represented by about four hundred point coordinates, which were transformed via Fourier analysis into amplitude coefficients suitable for use in linear discriminant analysis. Discriminant functions were created that accurately predicted group membership for 83% of the crania in the sample, after leave-oneout cross-validation. The results were compared with traditional typological classifications based on visual evaluation of ZMS shape, and the contour-based method was found to be more effective than the typological approach. However, the distribution of ZMS types within the two sample groups did not conform to previously reported patterns. This discrepancy indicates that ZMS shape may reflect not only genetic factors, but also environmental factors such as diet and stress. In addition, some evidence for sexual dimorphism in the zygomaticomaxillary complex was observed. Based on these findings, we recommend caution when using ZMS shape analysis in forensic ancestry determination.

La transformación morfológica extrínseca del neurocráneo se produce no por la retracción pasiva de los tejidos cefálicos sino por su expansión compensatoria. Durante este proceso, el cerebro y la bóveda craneal se expanden hacia las zonas no oprimidas. Este capítulo examinaalgunas nociones básicas de la expansión neuro- y craneológica humanadurante el crecimiento infantil natural. Igualmente recurrimos a la información anatómica y fisiopatológica para explicar luego las alteraciones operantes en la dinámica del creciemiento cefálico durante el proceso de compression externa. Especialmente la embriología craneana y lafisiología del desarrollo postnatal proporcionan valiosos puntos de partida para explorar y discutir las limitaciones naturales en los cambios inducidos ala forma de la bóveda craneal y sus efectos secundarios en la base y en la cara. Llegamos a confirmar que el modelado cefálico solo es posible durante los primeros años de vida y que los cambios en la formación del basi-y esplacnocráneovan en función del momento postnatal, del grado, la duración y de las técnicas del modelado. Su implementación cultural también puede tener implicaciones estéticas para el portador, como son la asimetríacefálicaconcomitante a la compression en cuna y una serie de riesgos para la saluden formade hemorragias, hipertensiónintracraneana, infecciones locales o la necrosis del tejido comprimido.