5 - Too Close for Comfort: Role of Fibronectin Matrix in Suture Development and Disease

Poster Board Number: 5
There are separate poster presentation times for odd and even posters.
Odd poster #s – first hour
Even poster #s – second hour

Co-authors:

Megan Gregory, B.A - Masters Student, Case Western Reserve Univ; Xiaotian Feng - Case Western Reserve Univ; Matthew Harris, Ph.D. - Primary Investigator, Genetics, Orthopedics, Harvard Medical School, Bs; Gregory Holmes, Ph.D. - Primary Investigator, Dept of Genetics and Genome sciences, Ichan School of Medicine, Mt. Sinai Hospital; Radhika Atit, Ph.D. - Primary Investigator, Biology, Case Western Reserve Univ

Abstract Body :
The roof of the mammalian skull is composed of calvarial bones that abut at fibrous sutures to form an expandable and protective case for the brain as it grows to adult size. Premature fusion, or synostosis, of these cranial sutures results in the reduced growth of these bones, limiting brain growth and development. Craniosynostosis (CS), a prevalent condition affecting 1 in every 2500 live births worldwide, is associated with mutations in over 79 different genes. This genetic heterogeneity with common phenotypic output suggests that these genetic determinants alter common downstream processes of skeletal development – a convergence point among their varied functions. Here, we look to common biological mechanisms of calvarial growth as potential shared etiologies of CS. Recently, we found polarized extracellular matrix as a key factor regulating calvarial growth in development. Fibronectin (FN1) expression in particular is predominantly polarized along anterior – basal axes coincident with migration of calvarial progenitors. Furthermore, dysregulation of FN1 expression has been identified in 2 different human CS syndromes. We hypothesize that dysregulated FN1 expression is a shared etiology of CS, and that FN1 is required to prevent premature ossification of the suture space to maintain suture patency. To test this hypothesis, we visualized FN1 expression in the cranial mesenchyme and measured apical extension of frontal bone primordia across four different mouse mutants of CS. We found FN1 expression and calvarial growth were dysregulated in each of these models. Next, we generated conditional Fn1-deleted mouse mutants in the mouse cranial mesenchyme starting at E10.5 (CM-Fnfl/fl). Control mice have sutures that remain patent and free of osteoblast gene expression during embryonic development. In contrast, the CM-Fnfl/fl mutants had CS of the coronal suture with approximately 81% penetrance as early as E16.5. At E15.5, CM-Fnfl/fl embryos show ectopic mineralization and diminished or absent Six2, a marker for suture mesenchyme in coronal sutures. Consistently, our conditional mutant had ectopic expression of Osterix (Osx), a marker for bone progenitors, and a diminished proliferation index when compared to controls as early as E14.5. These data suggest that FN1 regulates cell differentiation in the suture space to maintain suture patency. Our research suggests that FN1 dysregulation can be the downstream convergence point altering cellular behavior to cause CS. Further studies could develop the efficacy of FN1 matrix modulation as a new non-invasive therapeutic target for CS.