Turner syndrome and the evolution of human sexual dimorphism

Turner syndrome is caused by loss of all or part of an X chromosome in females. A series of recent studies has characterized phenotypic differences between Turner females retaining the intact maternally inherited versus paternally inherited X chromosome, which have been interpreted as evidence for effects of X-linked imprinted genes. In this study I demonstrate that the differences between Turner females with a maternal X and a paternal X broadly parallel the differences between males and normal females for a large suite of traits, including lipid profile and visceral fat, response to growth hormone, sensorineural hearing loss, congenital heart and kidney malformations, neuroanatomy (sizes of the cerebellum, hippocampus, caudate nuclei and superior temporal gyrus), and aspects of cognition. This pattern indicates that diverse aspects of human sex differences are mediated in part by X-linked genes, via genomic imprinting of such genes, higher rates of mosaicism in Turner females with an intact X chromosome of paternal origin, karyotypic differences between Turner females with a maternal versus paternal X chromosome, or some combination of these phenomena. Determining the relative contributions of genomic imprinting, karyotype and mosaicism to variation in Turner syndrome phenotypes has important implications for both clinical treatment of individuals with this syndrome, and hypotheses for the evolution and development of human sexual dimorphism

ECM Degradation, Matricryptic Peptides, and Stem Cell Recruitment

Biologic scaffolds composed of extracellular matrix (ECM) have been used to promote site-specific, functional remodeling of tissue in both preclinical animal models and human clinical applications. Although the mechanisms of action of ECM scaffolds are not completely understood, proteolytic degradation of the ECM scaffold and subsequent progenitor cell recruitment are thought to be important mediators of the constructive remodeling process.Proteolytic degradation of the ECM scaffolds results in the generation and release of cryptic peptides with novel bioactive properties not associated with their parent molecules such as angiogenic, antimicrobial, mitogenic, and chemotactic properties. While previous studies have suggested that degradation products of ECM scaffolds are chemotactic for progenitor cells in vitro, the present thesis expands upon these findings in vivo.In a non-regenerating model of mid-second phalanx digit amputation, treatment with ECM degradation rpodcuts resulted in the accumulation of a heterogeneous population of cells with in vitro differentiation potential along osteogenic, adipogenic, and neuroectodermal lineages. Focusing specifically on the Sox2+ population of cells found at the site of injury, work in the present thesis showed that Sox2+ cells co-express bone marrow and periosteal stem cell markers CD90 and Sca1, but not dermal stem cell marker CD133 or circulating stem cell marker c-kit (CD117). Additionally, bone marrow chimeric studies utilizing wild type C57/BL6 and Sox2 eGFP/+ mice showed that the Sox2+ cells are not derived from the bone marrow, but more likely from a local tissue source such as the periosteum. Fractionation of the ECM degradation products resulted in the identification of a highly conserved cryptic peptide derived from the C-terminal telopeptide of the collagen type IIIα molecule with chemotactic activity for multiple progenitor cells in vitro, IAGVGGEKSGGF. Administration of the cryptic peptide in a model of digit amputation resulted in the accumulation of Sox2+, Sca1+, Lin- cells at the site of amputation. Peptide treatment also resulted in the formation of a bone nodule at the site that coincided with the spatial location of Sox2+ cells. In vitro, the peptide accelerated osteogenesis of mesenchymal stem cells and increased the expression of osteogenic and chondrogenic genes.The result of this body of work shows that degradation products of ECM scaffolds contain cryptic peptides with the ability to influence chemotaxis and differentiation of progenitor cells in vitro and in vivo. The ability to influence stem cell phenotype and fate may be useful in designing new therapies for regenerative medicine approaches to complex, composite tissue reconstruction. Additionally, the findings of the present thesis may serve as the basis for future studies investigating the importance of ECM degradation in the downstream constructive remodeling events at a site of ECM implantation in soft tissue models of injury