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Embryogenesis requires cell-cell communication in which individual cells send and receive signals that determine their final fate. The transforming growth factor-β (TGF-β) superfamily of molecules encodes secreted factors which are capable of regulating cellular growth and differentiation. Recently, members of the TGF-β superfamily have emerged as candidates for many postulated embryonic inductive interactions. As a step towards understanding such interactions, this thesis investigates the hypothesis that TGF-β superfamily molecules may act as embryonic inducing factors in the mouse. The embryonic expression of a number of TGF-β superfamily members and a putative inhibitor of one of these, follistatin, were investigated. While activin (a mesoderm inducing factor in Xenopus animal caps) was not expressed in the mouse embryo, follistatin, BMP-7, BMP-2 and Vgr-2 were expressed during gastrulation and early organogenesis. Strategies were designed to ectopically express two of these molecules, BMP-7 and Vgr-2 in embryogenesis. Firstly, embryonic stem (ES) cells were used as a vehicle to secrete Vgr-2 throughout the embryo. No effect on embryonic morphology was detected, although conditioned medium from the\ud ES cells is capable of inducing mesoderm in Xenopus. Secondly, COS cells were used to deliver a localised source of BMP-7 to the cranial neural plate in cultured embryos. Such ectopic expression resulted in the induction of ectopic dorsal neural marker expression (Msx1 and AP-2), the diminished expression of a ventral marker (Shh), and a localised\ud expansion of neurectodermal tissue. The localisation of endogenous BMP-7 mRNA during formation and patterning of the neural axis, together with the activities shown in this assay, suggest that BMP-7 may direct one or more aspects of early central nervous system formation in the mouse.

Impaired wound healing and ulceration represent a serious complication of both type 1 and type 2 diabetes. Cytoskeletal protein Flightless I (Flii) is an important inhibitor of wound repair, and reduced Flii gene expression in fibroblasts increased migration, proliferation, and adhesion. As such it has the ability to influence all phases of wound healing including inflammation, remodelling and angiogenesis. Flii has the potential to modulate inflammation through its interaction with MyD88 which it an adaptor protein for TLR4. To assess the effect of Flii on the inflammatory response of diabetic wounds, we used a murine model of streptozocin-induced diabetes and Flii genetic mice. Increased levels of Flii were detected in Flii transgenic murine wounds resulting in impaired healing which was exacerbated when diabetes was induced. When Flii levels were reduced in diabetic wounds of Flii-deficient mice, healing was improved and decreased levels of TLR4 were observed. In contrast, increasing the level of Flii in diabetic mouse wounds led to increased TLR4 and NF-κB production. Treatment of murine diabetic wounds with neutralising antibodies to Flii led to an improvement in healing with decreased expression of TLR4. Decreasing the level of Flii in diabetic wounds may therefore reduce the inflammatory response and improve healing.

Flightless I (Flii) is an actin-remodeling protein that influences diverse processes including cell migration and gene transcription and links signal transduction with cytoskeletal regulation. Here, we show that Flii modulation of focal adhesions and filamentous actin stress fibers is Rac1-dependent. Using primary skin fibroblasts from Flii overexpressing (FliiTg/Tg), wild-type, and Flii deficient (Flii +/-) mice, we show that elevated expression of Flii increases stress fiber formation by impaired focal adhesion turnover and enhanced formation of fibrillar adhesions. Conversely, Flii knockdown increases the percentage of focal complex positive cells. We further show that a functional effect of Flii at both the cellular level and in in vivo mouse wounds is through inhibiting paxillin tyrosine phosphorylation and suppression of signaling proteins Src and p130Cas, both of which regulate adhesion signaling pathways. Flii is upregulated in response to wounding, and overexpression of Flii inhibits paxillin activity and reduces adhesion signaling by modulating the activity of the Rho family GTPases. Overexpression of constitutively active Rac1 GTPase restores the spreading ability of FliiTg/Tg fibroblasts and may explain the reduced adhesion, migration, and proliferation observed in FliiTg/Tg mice and their impaired wound healing, a process dependent on effective cellular motility and adhesion. Refereed/Peer-reviewed

Regeneration of cells, tissues, and organs has long captured the attention of researchers for its obvious potential benefits in biomedical applications. Although mammals are notoriously poor at regeneration compared with many lower-order species, the hair follicle, paradoxically a defining characteristic of mammals, is capable of regeneration following partial amputation. To investigate the role of a negative regulator of wound healing, flightless I (Flii), on hair follicle regeneration, the bulbar region of vibrissae from rats as well as strains of mice expressing low (Flii þ/ ), normal (Flii þ/þ), and high (FLIITg/Tg) levels of Flii were surgically amputated, and then allowed to regenerate in vivo. Macroscopic and histological assessment of the regeneration process revealed impaired or delayed regenerative potential in Flii þ/ follicles. Regenerated follicles expressing high levels of Flii (FLIITg/Tg) produced significantly longer terminal hair fibers. Immunohistochemical analysis was used to characterize the pattern of expression of Flii, as well as markers of hair follicle development and wound healing-associated factors during hair follicle regeneration. These studies confirmed that Flii appears to have a positive role in the regeneration of hair follicles, contrary to its negative influence on wound healing in skin. Refereed/Peer-reviewed

Up until late in the third trimester of gestation and through to adulthood, the healing response acts more to regenerate than to repair a wound. The mechanisms underlying this "scar-free" healing remain unknown although the actin cytoskeleton has a major role. Flightless I (Flii), an actin-remodelling protein and essential developmental regulator, negatively affects wound repair but its effect on scar-free fetal healing is unknown. Using fetal skin explants from E17 (regenerate) and E19 (repair) rats, the function of Flii in fetal wound repair was determined. Expression of Flii increased between E17 and E19 days of gestation and wounding transiently increased Flii expression in E17 but not E19 wounds. However, both confocal and immunofluorescent analysis showed E17 keratinocytes immediately adjacent to the wounds downregulated Flii. As a nuclear coactivator and inhibitor of proliferation and migration, the absence of Flii in cells at the edge of the wound could be instrumental in allowing these cells to proliferate and migrate into the wound deficit. In contrast, Flii was strongly expressed within the cytoplasm and nucleus of keratinocytes within epidermal cells at the leading edge of E19 wounded fetal skin explants. This increase in Flii expression in E19 wounds could affect the way these cells migrate into the wound space and contribute to impaired wound healing. Neutralising Flii protein improved healing of early- but not late-gestation wounds. Flii did not colocalise with actin cables formed around E17 wounds suggesting an independent mechanism of action distinct from its actin-binding function in scar-free wound repair. Refereed/Peer-reviewed

The cytoskeletal protein Flightless (Flii) is a negative regulator of wound healing. Upregulation of Flii is associated with impaired migration, proliferation and adhesion of both fibroblasts and keratinocytes. Importantly, Flii translocates from the cytoplasm to the nucleus in response to wounding in fibroblasts but not keratinocytes. This cell-specific nuclear translocation of Flii suggests that Flii may directly regulate gene expression in fibroblasts, providing one potential mechanism of action for Flii in the wound healing response. To determine whether the tissue-specific upregulation of Flii in fibroblasts was important for the observed inhibitory effects of Flii on wound healing, an inducible fibroblast-specific Flii overexpressing mouse model was generated. The inducible ROSA26 system allowed the overexpression of Flii in a temporal and tissue-specific manner in response to tamoxifen treatment. Wound healing in the inducible mice was impaired, with wounds at day 7 postwounding significantly larger than those from non-inducible controls. There was also reduced collagen maturation, increased myofibroblast infiltration and elevated inflammation. The impaired healing response was similar in magnitude to that observed in mice with non-tissue-specific upregulation of Flii suggesting that fibroblast-derived Flii may have an important role in the wound healing response.

Flightless I (Flii), a highly conserved member of the gelsolin family of actin-remodelling proteins associates with actin structures and is involved in cellular motility and adhesion. Our previous studies have shown that Flii is an important negative regulator of wound repair. Here, we show that Flii affects hemidesmosome formation and integrin-mediated keratinocyte adhesion and migration. Impaired hemidesmosome formation and sparse arrangements of keratin cytoskeleton tonofilaments and actin cytoskeleton anchoring fibrils were observed in Flii(Tg/+) and Flii(Tg/Tg) mice with their skin being significantly more fragile than Flii(+/-) and WT mice. Flii(+/-) primary keratinocytes showed increased adhesion on laminin and collagen I than WT and Flii(Tg/Tg) primary keratinocytes. Decreased expression of CD151 and laminin-binding integrins alpha3, beta1, alpha6 and beta4 were observed in Flii overexpressing wounds, which could contribute to the impaired wound re-epithelialization observed in these mice. Flii interacts with proteins directly linked to the cytoplasmic domain of integrin receptors suggesting that it may be a mechanical link between ligand-bound integrin receptors and the actin cytoskeleton driving adhesion-signaling pathways. Therefore Flii may regulate wound repair through its effect on hemidesmosome formation and integrin-mediated cellular adhesion and migration.