Many biotypes of the northem-hemisphere Arctic-Alpine grass Poa alpina L. reproduce asexually via prolification of the spikelet axis to produce dehiscing shoots. Although such pseudoviviparous plantlets are capable of photosynthesis, the source-sink characteristics of these synflorescence systems are unknown, including the degree to which plantlets are capable of providing for their own carbon requirements, or contributing to parental sinks. An initial anatomical investigation of the culm revealed that transpiration flow, as delimited by Lucifer Yellow tracer dye, was maintained despite advanced senescence (as evidenced by loss of chlorophyll and chloroplasts), with plantlet leaves driving transpiration flow. Transpiration flow was not hindered by cavitation or tylosis in older culms, the low frequencies of these processes being bypassed via nodal plexi. Despite this, water content of plantlets declined over time and visual indications of water stress became apparent, suggesting that water supply via the determinate culm was not sufficient for the increasing transpirational demand of indeterminate plantlets. Photosynthetic rates within the paracladial zone, as determined by infrared gas analysis (IRGA), exceeded respiratory rates by 3-4 fold, indicating that plantlets were sources of carbon. 14C tracer studies determined that the paracladial zone was not only as efficient at fixing carbon as the youngest fully expanded leaf, but that both organs exported carbon basipetally (c.f acropetal export from this leaf in seminiferous grasses). Distal plantlets fixed approx. 20% more 14C than proximal plantlets, by virtue of greater dry weight. Manipulative growth analysis of the paracladial zone suggests the operation of a system of apical dominance, with distal plantlets becoming dominant over proximal plantlets. At dehiscence, distal plantlets were more likely to become established, and possessed relative growth rates more than ten times those of proximal plantlets. Paracladial heterogeneity was also apparent as an increased proportion of aborted spikelets on proximal paracladia. Data indicate that this abortion was, at least in part, a result of constraint imposed by the pseudostem on the developing synflorescence. When grown in conditions of differing resource availability (altered nutrient supply and atmospheric C02 concentration), low nutrient availability in concert with elevated C02 concentration induced particularly low photosynthetic nitrogen and phosphorus use efficiencies in both parent and plantlet tissues. This occurred in concert with acclimatory loss of photosynthetic capacity leading to a decreased reproductive response of the plant; a product of the number of tillers in flower and the subsequent growth of attached plantlets. lt is predicted that in future climatic conditions Poa alpina will decline in habitats that include species which exhibit less acclimatory loss, no change, or an increase in photosynthetic capacity. These experiments also rule out resource availability as a cause of heterogeneity within the paracladial zone. A direct study of the phytohormonal characteristics of the pseudoviviparous system is therefore proposed in order to elucidate the mechanism of control within the paracladial zone.

Comprehensive in vitro modelling of inflammatory human skin conditions is an essential first step in the development and assessment of potential therapeutic approaches. Mouse models or monolayer keratinocyte cultures come with distinct limitations which might be complimented or overcome by the use of human-specific organotypic 3D culture models. Over the course of this thesis, an organotypic culture system, based on patientderived immortalised keratinocyte cell lines on a dermal equivalent collagen 1 gel, was established and used to recapitulate phenotypical features for two hereditary skin diseases, Harlequin ichthyosis and Tylosis with oesophageal cancer. Small molecular compounds, supplied via the medium, or RNA interference were used to modulate disease-specific changes in histology and marker expression of the skin equivalent. Since hyperproliferative skin conditions can be associated with an aberrant wound healing phenotype, the organotypic system was manipulated to obtain a basic in vitro wound healing model. This model displays typical features of re-epithelialisation over time (both normal and disease-specific) which can further be manipulated via shRNAmediated knockdown or the exogenous supply of compounds. In parallel, a non-disease model was used to assess the topical application of novel nanopolymeric drug delivery systems in regard to their ability to penetrate across the permeability barrier. Penetrance profiles for the organotypic model (in dependence of co-application with chemical enhancers) showed a similar pattern as for topical applications performed in parallel on explant skin. In conclusion, a highly adaptable human organotypic keratinocyte culture model was developed and used to recapitulate (and manipulate) skin disease phenotypes and epidermal wound healing in vitro, as well as perform first essential assessments of novel drug delivery systems.

This thesis describes investigations into the genetic basis and pathophysiology of three distinct inherited diseases in humans, two of which are strongly associated to the function of the ectodomain sheddase enzyme ADAM17. The first of these is a novel inherited syndrome of neonatal onset inflammatory skin and bowel disease, which is associated in a consanguineous family with homozygous loss-offunction mutations in ADAM17. This thesis describes investigations of the expression and function of ADAM17 – and downstream proteins it regulates – in an individual affected by this disease. This is accompanied by genetic investigations into other individuals suspected of suffering from the same syndrome. The second investigated disease is Tylosis with Oesophageal Cancer (TOC), an inherited cutaneous disease which represents the only known syndrome of familial oesophageal cancer susceptibility. This disease was associated to dominantly inherited mutations in the Rhomboid protein iRHOM2. This work describes investigations of immortalised keratinocyte cell lines and tissues derived from TOC-affected individuals, and illustrates that the pathogenesis of TOC is characterised by increased iRHOM2-dependent activation and activity of ADAM17, and upregulation of the shedding of ADAM17 substrates, particularly in the EGFR ligand family, accompanied by increased desmosome turnover and transglutaminase 1 activity. This pattern of upregulation results in attendant increases in growth factor signalling, proliferation and motility in TOC keratinocytes, dependent on ADAM17. The third focus of this thesis is a life-threatening inherited gastrointestinal disease (accompanied by severe extraintestinal complications) whose symptoms correspond to Cryptogenic Multifocal Ulcerative Stenosing Enteritis. This work describes the identification of mutations in cytosolic phospholipase A2-α (cPLA2α) – an enzyme responsible for arachidonic acid production, the first step in the eicosanoid synthesis pathway – as associated with this condition in a single affected family. The expression and function of cPLA2α in this disease was investigated, using platelet aggregation stimulated by a downstream product of cPLA2α (Thromboxane A2) as a model.