The CMV enhancer-promoter sequence is often used as a transcriptional regulatory element in vector systems. We have used this control element to drive expression of GFP in a lentivirus vector transgene in pigs and chickens. Promoted as a 'universal' enhancer/promoter element capable of transcriptional activity in a number of cells in vitro, CMV-GFP transgene expression in vivo is preferentially observed in exocrine cells. This expression profile validates the use of this transcriptional control sequence to target expression to exocrine cells in gene transfer strategies.

Throughout development cells make the decision to proliferate, arrest or die. Control of this process is essential for normal development, with unrestrained cell proliferation and cell death underlying the origin and progression of disease. The cell-cycle is tightly regulated by a number of factors including the cyclin-dependent kinase inhibitor 1A (Cdkn1a), termed p21 (or Cip1 or WAF1). p21 acts as a negative regulator of cell-cycle progression by binding and inhibiting complexes formed between the cyclin-dependent kinases and their catalytic partners the cyclins. In this report we identify the temporal spatial expression profile of p21 in the developing mid-term mouse embryo using a p21-LacZ reporter mouse line. Expression of p21 was restricted to specific regions with a correspondence to both areas of terminal differentiation and active remodelling. A complex temporal and spatial relationship between p21 expression and regions of apoptosis was evident. A protective role with regard to apoptosis for p21 is proposed.