Andrew B. Leiter

Transplantation studies and cell lineage analyses require the ability to explicitly distinguish morphologically identical cells that have an identifiable marker indicating their origin in vivo. Several reporter mouse strains have been generated for such studies, but pancellular detection of the marker in all tissues has not been achieved. In this report, we describe the generation of transgenic mice that express enhanced green fluorescent protein (EGFP) under control of a 187 kb bacterial artificial chromosome (BAC) containing the murine ROSA26 locus, and show several advantages over existing EGFP reporter lines. It is demonstrated that EGFP is ubiquitously and reproducibly expressed from the murine BAC transgene in all organs and tissues analyzed, including the hematolymphoid compartment. Using this new reporter strain in hematopoietic cell transplantation studies, it is demonstrated that leukocytes in recipients maintain uniform transgene expression and are easily distinguished by flow cytometric analysis of live cells. The results suggest that the ROSA26 BAC is an efficient strategy for expressing complex transgene cassettes in vivo. genesis 45:83–89, 2007. Published 2007 Wiley‐Liss, Inc.

The gastrointestinal hormone peptide YY is a potent inhibitor of food intake and is expressed early during differentiation of intestinal and pancreatic endocrine cells. In order to better understand the role of peptide YY in energy homeostasis and development, we created mice with a targeted deletion of the peptide YY gene. All intestinal and pancreatic endocrine cells developed normally in the absence of peptide YY with the exception of pancreatic polypeptide (PP) cells, indicating that peptide YY expression was not required for terminal differentiation. We used recombination-based cell lineage trace to determine if peptide YY cells were progenitors for gastrointestinal endocrine cells. Peptide YY⁺ cells gave rise to all L-type enteroendocrine cells and to islet ∂ and PP cells. In the pancreas, approximately 40% of pancreatic α and rare β cells arose from peptide YY⁺ cells, suggesting that most β cells and surprisingly the majority of α cells are not descendants of peptide YY⁺/glucagon-positive/insulin-positive cells that appear during early pancreagenesis. Despite the anorectic effects of exogenous peptide YY_3-36 following intraperitoneal administration, mice lacking peptide YY showed normal growth, food intake, energy expenditure, and responsiveness to peptide YY_3-36. These observations suggest that targeted disruption of the peptide YY gene does not perturb terminal endocrine cell differentiation or the control of food intake and energy homeostasis.

The gut-derived hormones peptide YY[3-36] (PYY[3-36]) and ghrelin are believed to influence similar hypothalamic circuits, albeit with opposing actions on energy balance. Thus, we carried out a series of studies to evaluate the interaction of these hormones on short-term food intake responses in mice. Intraperitoneal PYY[3-36] injection reduced short-term food intake by up to 50% in overnight-fasted mice and in postabsorptive animals during the early and late light cycle. This effect was not sensitive to the prevailing endogenous plasma acyl-ghrelin concentrations, which ranged from high physiological (overnight-fasted, 1252 +/- 108 pg/ml) to low levels (late light cycle, 402 +/- 33 pg/ml). PYY[3-36] administration did not reduce plasma total or acyl-ghrelin concentration in conjunction with its anorexigenic actions. Ghrelin increased short-term food intake by up to 1.8-fold in mice treated ip in the early light cycle, but was ineffective in animals treated after an overnight fast or during the late light cycle. Ghrelin did not increase food intake or GH secretion unless plasma levels were increased above high physiological fasting values. The anorexigenic effect of PYY[3-36] over a range of doses was not compromised by coinjection of ghrelin, and PYY[3-36] reduced food intake in agouti mice, which lack fully functional melanocortin signaling. These results in mice support a model in which 1) PYY[3-36] diminishes short-term food intake at least in part through mechanisms distinct from the neuropeptide Y/proopiomelanocortin neural circuits engaged by ghrelin; and 2) a reduction in circulating ghrelin is not requisite for the anorexigenic effects of PYY[3-36].