Using a mouse model in which Vascular Endothelial Growth Factor (VEGF) was inactivated specifically in stratified squamous epithelia (which include skin) by means of the keratin5-Cre/LoxP system, we initially examined wound healing and epidermal tumor formation. The early healing phase of full-thickness wounds progressed normally. However, crust shedding was significantly retarded, suggesting a delay in the later phase of healing. Immunohistochemical investigation of the wounded skin revealed a blood vessel-free zone underneath the epidermis, which presumably prevented an adequate supply of nutrients reaching the epidermis, resulting in the delayed healing. Surprisingly tumor formation, induced by the carcinogen 9,12-dimethyl 1,2-benzanthracene (DMBA) was completely abrogated in these mutant mice, and investigations are currently underway to identify the mechanism(s) underlying this observation. VEGF is also inactivated in other tissues in this mouse model, and we have been able to show that this factor is critical in mammary gland development and milk secretion.
Furthermore, mutant pups are somewhat smaller than their control littermates, suggesting that nutrient uptake may be impaired in these mice, possibly because of defective vascularization to the stomach and small intestine. Finally, mutant females experienced great difficulty in becoming pregnant, despite normal copulation activity. The few pups born to these females were wild type with respect to VEGF expression, suggesting that the cre enzyme contained in their oocytes was activated by global gene activation, leading to generalized VEGF inactivation, and death of the cre-transgene bearing pups. Our studies therefore demonstrate firstly, the importance of VEGF for effective angiogenesis in the adult, and secondly, that the keratin5-Cre/LoxP system is not specific to the skin, but affects all tissues in which the keratin5 promoter is expressed.