Expression Profiling Using Microfluidic Living Cell Arrays

Abstract

The cellular microenvironment is remarkably complex. In the small space near each cell, growth factors are liberated from extracellular matrix, cytokines are secreted by neighboring cells, and hormones arrive from distant endocrine organs through the circulation. These soluble cues are detected by surface or cytoplasmic receptors and integrated using complex signal transduction cascades to modulate the activity of transcription factors (TFs), the primary regulators of gene expression. Transcription factors serve as points of convergence between the vast number of extracellular signaling molecules and the equally vast number of target genes. For perspective, the human genome contains approximately 1500 identified transcription factors regulating more than 20,000 target genes [1]. Adding further complexity to the picture, transcription factors often cooperate, compete, and regulate each other, forming transcriptional regulatory networks with rich possibilities to control cell behavior. Under normal conditions, network regulators are activated in a defined temporal sequence and function as a transcriptional regulatory program to coordinate physiological adaptations to changes in the external cellular microenvironment. When transcriptional programs are dysregulated, they can lead to inappropriate pathological responses that result in clinical disease. One example of such a transcriptional regulatory network is that which regulates insulin secretion by hepatocyte nuclear factors (HNFs; [2]). The expression of 3 HNFs—HNF-1alpha, HNF-4alpha, and HNF-3alpha—are positively regulated by HNF-3beta. However, HNF-3alpha also acts as a negative regulator of HNF-1alpha and HNF-4alpha, which has been attributed to competition for the