The Interaction of Genetic Background and Mutational Effects in Regulation of Mouse Craniofacial Shape.

Inbred genetic background significantly influences the expression of phenotypes associated with known genetic perturbations and can underlie variation in disease severity between individuals with the same mutation. However, the effect of epistatic interactions on the development of complex traits, such as craniofacial morphology, is poorly understood. Here, we investigated the effect of three inbred backgrounds (129X1/SvJ, C57BL/6J, and FVB/NJ) on the expression of craniofacial dysmorphology in mice (Mus musculus) with loss of function in three members of the Sprouty family of growth factor negative regulators (Spry1, Spry2, or Spry4) in order to explore the impact of epistatic interactions on skull morphology. We found that the interaction of inbred background and the Sprouty genotype explains as much craniofacial shape variation as the Sprouty genotype alone. The most severely affected genotypes display a relatively short and wide skull, a rounded cranial vault, and a more highly angled inferior profile. Our results suggest that the FVB background is more resilient to Sprouty loss of function than either C57 or 129, and that Spry4 loss is generally less severe than loss of Spry1 or Spry2 While the specific modifier genes responsible for these significant background effects remain unknown, our results highlight the value of intercrossing mice of multiple inbred backgrounds to identify the genes and developmental interactions that modulate the severity of craniofacial dysmorphology. Our quantitative results represent an important first step toward elucidating genetic interactions underlying variation in robustness to known genetic perturbations in mice

Meeting report: a hard look at the state of enamel research.

The Encouraging Novel Amelogenesis Models and Ex vivo cell Lines (ENAMEL) Development workshop was held on 23 June 2017 at the Bethesda headquarters of the National Institute of Dental and Craniofacial Research (NIDCR). Discussion topics included model organisms, stem cells/cell lines, and tissues/3D cell culture/organoids. Scientists from a number of disciplines, representing institutions from across the United States, gathered to discuss advances in our understanding of enamel, as well as future directions for the field

On the trail of the 'new head' in Les Treilles

The vertebrate brain develops in association with neighboring tissues: neural crest, placodes, mesoderm and endoderm. The molecular and evolutionary relationships between the forming nervous system and the other craniofacial structures were at the focus of a recent meeting at the Fondation des Treilles in France. Entitled 'Relationships between Craniofacial and Neural Development', the meeting brought together researchers working on diverse species, the findings of whom provide clues as to the origin and diversity of the brain and facial regions that are involved in forming the 'new head' of vertebrates

Genetic architecture of craniofacial shape in the house mouse: a genetic and morphological perspective

Morphological diversity in nature is astounding. A remarkable example of such diversity is the vertebrate cranium. This structure is developmentally, anatomically, and functionally integrated with the many other tissues and sensory systems of the head. Because of this, it is under strong constrains to achieve an adult form (size and shape) compatible with the functional requirements of the individual. The genetic basis of craniofacial diversity has been traditionally studied from a macro-evolutionary perspective (i.e. at the between-species level), with special focus on adaptive radiation and domestication. The work presented in this thesis is an attempt to understand the genetic basis of craniofacial shape variation in the house mouse. By using between-subspecies and within population variation, I address the question from a micro-evolutionary perspective. In this thesis I also explore the genetic architecture of the traits (i.e. number, effect size, and genomic distribution of the causal loci), and the extent to which phenotypic variation can be explained by genetic variation – i.e. heritability of the traits. The first two chapters of this thesis are the first genome-wide approximation to the genetic architecture of craniofacial shape and size in mice. I combine highly recombinant mouse populations –wild hybrid mice and outbred lab mice- with dense marker coverage of the genome to map the loci underlying phenotypic variation. I identify genes previously known to be involved in craniofacial formation, and provide a list of genomic regions that contain new candidate genes for craniofacial development. Regarding the genetic architecture, I show that craniofacial traits are highly polygenic and highly heritable, with many loci of very small effect distributed uniformly along the genome. The last chapter of the thesis is an assessment of the morphological transition associated with the degree of admixture between two subspecies of the house mouse, Mus musculus musculus and Mus musculus domesticus. I show that craniofacial shape changes, but not size changes, are correlated with the level of admixture. The transition from M. m. musculus to M. m. domesticus is continuous, such mode would be expected from a trait with polygenic architecture, and therefore these results are in line with the genetic results obtained in previous chapters. Overall the work presented in this thesis is the first genome-wide analyses of the genetic basis and genetic architecture of craniofacial shape variation in the house mouse. It is also the first time shape variation is explored in a close-to-natural context; previous work used crosses between inbred 10 mouse strains. Therefore, the results reported here are directly relevant to the understanding of complex traits evolution

Use of a natural hybrid zone for genome-wide association mapping of craniofacial traits in the house mouse

The identification of the genes involved in morphological variation in nature is still a major challenge. Here we explore a new approach: we combine 178 samples from a natural hybrid zone between two subspecies of the house mouse (Mus musculus domesticus and Mus musculus musculus), and high coverage of the genome (~145K SNPs) to identify loci underlying craniofacial shape variation. Due to the long history of recombination in the hybrid zone, high mapping resolution is anticipated. The combination of genomes from subspecies allows the mapping of both, variation within subspecies and intersubspecific differences, thereby increasing the overall amount of causal genetic variation than can be detected. Skull and mandible shape were measured using 3D landmarks and geometric morphometrics. Using principle component axes as phenotypes, and a linear mixed model accounting for genetic relatedness in the mapping populations, we identified 9 genomic regions associated with skull and 10 with mandible shape. High mapping resolution (median size of significant regions = 148 kb) enabled identification of single or few candidate genes in most cases. Some of the genes act as regulators or modifiers of signaling pathways relevant for morphological development and bone formation, including several with known craniofacial phenotypes in mice and humans. The significant associations combined explain 13% and 7% of the skull and mandible shape variation. In addition, a positive correlation was found between chromosomal length and proportion of variation explained. Our results suggest a complex genetic architecture for shape traits, and support a polygenic model

Molecular and cellular mechanisms underlying the evolution of form and function in the amniote jaw.

The amniote jaw complex is a remarkable amalgamation of derivatives from distinct embryonic cell lineages. During development, the cells in these lineages experience concerted movements, migrations, and signaling interactions that take them from their initial origins to their final destinations and imbue their derivatives with aspects of form including their axial orientation, anatomical identity, size, and shape. Perturbations along the way can produce defects and disease, but also generate the variation necessary for jaw evolution and adaptation. We focus on molecular and cellular mechanisms that regulate form in the amniote jaw complex, and that enable structural and functional integration. Special emphasis is placed on the role of cranial neural crest mesenchyme (NCM) during the species-specific patterning of bone, cartilage, tendon, muscle, and other jaw tissues. We also address the effects of biomechanical forces during jaw development and discuss ways in which certain molecular and cellular responses add adaptive and evolutionary plasticity to jaw morphology. Overall, we highlight how variation in molecular and cellular programs can promote the phenomenal diversity and functional morphology achieved during amniote jaw evolution or lead to the range of jaw defects and disease that affect the human condition

A Cross-Species Analysis of MicroRNAs in the Developing Avian Face

Higher vertebrates use similar genetic tools to derive very different facial features. This diversity is believed to occur through temporal, spatial and species-specific changes in gene expression within cranial neural crest (NC) cells. These contribute to the facial skeleton and contain species-specific information that drives morphological variation. A few signaling molecules and transcription factors are known to play important roles in these processes, but little is known regarding the role of micro-RNAs (miRNAs). We have identified and compared all miRNAs expressed in cranial NC cells from three avian species (chicken, duck, and quail) before and after species-specific facial distinctions occur. We identified 170 differentially expressed miRNAs. These include thirty-five novel chicken orthologs of previously described miRNAs, and six avian-specific miRNAs. Five of these avian-specific miRNAs are conserved over 120 million years of avian evolution, from ratites to galliforms, and their predicted target mRNAs include many components of Wnt signaling. Previous work indicates that mRNA gene expression in NC cells is relatively static during stages when the beak acquires species-specific morphologies. However, miRNA expression is remarkably dynamic within this timeframe, suggesting that the timing of specific developmental transitions is altered in birds with different beak shapes. We evaluated one miRNA:mRNA target pair and found that the cell cycle regulator p27KIP1 is a likely target of miR-222 in frontonasal NC cells, and that the timing of this interaction correlates with the onset of phenotypic variation. Our comparative genomic approach is the first comprehensive analysis of miRNAs in the developing facial primordial, and in species-specific facial development

Insights into vertebrate head development: From cranial neural crest to the modelling of neurocristopathies

Although the vertebrate head has evolved to a wide collection of adaptive shapes, the fundamental signalling pathways and cellular events that outline the head skeleton have proven to be highly conserved. This conservation suggests that major morphological differences are due to changes in differentiation and morphogenetic programs downstream of a well-maintained developmental prepattern. Here we provide a brief examination of the mechanisms and pathways responsible for vertebrate head development, as well as an overview of the animal models suitable for studying face development. In addition, we describe the criteria for neurocristopathy classifica-tion, highlighting the contribution of zebrafish to the modelling of Treacher Collins/Franceschetti Syndrome, an emblematic neurocristopathy. The contributions from our laboratory reveal that proper zebrafish head development depends on the fine-tuning of developmental-gene expression mediated by nucleic acid binding proteins able to regulate DNA conformation and / or the neuroepithelium redox state.Fil: Weiner, Andrea Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Coux, Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Armas, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Calcaterra, Nora Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; Argentin