Lee Niswander for the use of her confocal microscope and allowing KRA to work in her lab space. are also misexpressed in the Nkx2.2-/-pancreas. == Conclusions == Expression profiling of Nkx2.2-/-mice Rabbit polyclonal to ABHD12B during embryogenesis has allowed us to identify known and novel pancreatic genes that function downstream of Nkx2.2 to regulate pancreas development. Several of the newly identified signaling factors and transmembrane proteins may function to influence islet cell fate decisions. These studies have also (4R,5S)-nutlin carboxylic acid revealed a novel function for (4R,5S)-nutlin carboxylic acid Nkx2.2 in maintaining appropriate exocrine gene expression. Most importantly, Nkx2.2 appears to function within a complex regulatory loop with Ngn3 at a key endocrine differentiation step. == Background == The pancreas is a multifunctional organ that is critical for maintaining glucose homeostasis and for producing many of the enzymes required for digestion of carbohydrates, lipids and proteins. To carry out these diverse functions, the pancreas contains three major tissue types: the exocrine acinar cells, the endocrine cells that comprise the islet of Langerhans, and the ductal epithelial cells. Although each of these pancreatic components performs unique functions, all are derived from a defined set of endodermally-derived progenitors [1]. Subsequent pancreatic morphogenesis and differentiation of these progenitor populations is dependent on the concerted action of multiple transcriptional regulators. Early during pancreatic bud evagination, Pancreatic duodenal homeobox 1 (Pdx1) and Pancreatic transcription factor 1a (Ptf1a) are co-expressed in the pancreatic progenitor population [1,2]. Ptf1a, a basic helix-loop-helix (bHLH) transcription factor, becomes restricted to the exocrine cell population, where it is essential for exocrine cell formation and function [2,3]. Pdx1 expression is maintained throughout the early pancreatic epithelium and becomes mostly restricted (4R,5S)-nutlin carboxylic acid to and cells after the secondary transition, although low levels of Pdx1 persist in some (4R,5S)-nutlin carboxylic acid acinar cells into adulthood [4-6]. Pdx1 has distinct functions at each developmental stage and in each of the cell types where it is expressed, and itself is critically dependent on the winged helix transcription factors Foxa1 and Foxa2 [7-9]. Ngn3, a bHLH transcription factor, is required downstream of Pdx1 to activate the endocrine differentiation program [10-13]. Further islet cell fate determination in the Ngn3+cells then depends on a number of additional transcription factors including Pdx1, Nkx2.2, (4R,5S)-nutlin carboxylic acid Pax4, Pax6, Isl1, NeuroD1, Arx, and Nkx6.1, each of which has been identified and characterized through genetic deletion or overexpression studies [14-19]. These and other transcription factors are then necessary for appropriate neogenesis, differentiation, and maturation of the five islet cell types (recently reviewed in [5,20-22]). Although much is known about the identity, expression and function of many of the intrinsic regulatory proteins involved in pancreatic development and differentiation, the identification of downstream targets of these transcription factors to mediate these developmental events has proven to be more challenging. In efforts to identify downstream functional players during pancreagenesis, multiple groups have determined pancreatic gene expression profiles of wild type and transcription factor knockout models, including Pdx1, Ngn3, NeuroD1, and FoxA2 [23-30]. Alternatively, temporal comparisons between transcription factor positive cell populations, such as Pdx1+or Ngn3+[31,32], by microarray analysis have also uncovered important downstream factors. Here we present the first study comparing gene expression alterations between wild type and Nkx2.2-/-mouse pancreata at e12.5 and e13.5, the stages marking the onset of the secondary transition when the major wave of islet cell type specification events occur for both endocrine and exocrine pancreas. Nkx2.2 is a homeodomain containing transcription factor critical for endocrine pancreas specification [19]. Prior to e15.5, the pancreas of Nkx2.2-/-mice appears overtly normal and contains wild type numbers of undifferentiated Pdx1+ pancreatic epithelium and Ngn3+ endocrine progenitor cells [12,19,33]. As development proceeds, the Nkx2.2-/-mice form the normal numbers of total endocrine and exocrine cells; however, within the endocrine compartment all.