Expression of nestin-green fluorescent protein transgene marks oval cells in the adult liver

Oval cells, which become apparent in the liver after chronic injury, serve as bipotent progenitors for differentiated hepatocytes and cholangiocytes. We found that, in the liver of adult transgenic mice in which expression of green fluorescent protein (GFP) is driven by regulatory elements of the nestin gene, the GFP signal marks a subpopulation of small epithelial cells that meet the criteria for oval cells, including morphology, localization, antigenic profile, and reactivity in response to injury. In the regenerating and developing liver, we also found nestin-GFP-positive cells that express hepatocyte markers; such cells may correspond to transiently appearing differentiating progeny of oval cells. During development, GFP-expressing cells in the liver emerge relatively late, after the appearance of differentiated hepatocytes and cholangiocytes. Our results suggest that nestin-GFP cells in the liver correspond to a specialized cell type whose primary function may be to serve as a reserve for adult liver epithelial cell types

Zebrafish KLF4 is essential for hatching and haematopoiesis

Shvartsman et al. [1] have recently proposed a mathematical model of the EGF receptor pathway activation in the predevelopment of dorsal appendages (DA) in Drosophila. In particular, a one-dimensional model for the interaction of the ligands: Gurken, Rhomboid, Spitz, and Argos, was presented, with a predefined Gurken shape and evolution. With their model, they were able to reproduce many of the observed behaviors of these ligands about the midline of the anterior – dorsal region of the oocyte, and even predict mutations. A subsequent experimental study [2] showed that the number of DA varies between species of Drosophila and is related to differences in the expression of Argos and Rhomboid. This is a startling demonstration of the power of mathematics for predicting the range of states available to a biological system. Here, we present results of a 2-dimensional (2D) extension to the above model. With an axisymmetric concentration of Gurken, the 2D model predicts the possibility of concentric rings of DA. Indeed concentric rings have been observed in experiments in which the oocyte nucleus was (abnormally) localized in the posterior region [3]. By including an additional morphogen, Decapentaplegic (Dpp), which is known to display an anterior – posterior gradient in anterior – dorsal follicle cells, we demonstrate that Dpp can determine the anterior – posterior extent of the DA follicle cell patterning

Genetic approaches identify adult pituitary stem cells

Adult tissues undergo continuous cell turnover in response to stress, damage, or physiological demand. New differentiated cells are generated from dedicated or facultative stem cells or from self-renewing differentiated cells. Here we describe a different stem cell strategy for tissue maintenance, distinct from that observed for dedicated or facultative stem cells. We report the presence of nestin-expressing adult stem cells in the perilumenal region of the mature anterior pituitary and, using genetic inducible fate mapping, demonstrate that they serve to generate subsets of all six terminally differentiated endocrine cell types of the pituitary gland. These stem cells, while not playing a significant role in organogenesis, undergo postnatal expansion and start producing differentiated progeny, which colonize the organ that initially entirely consisted of differentiated cells derived from embryonic precursors. This generates a mosaic organ with two phenotypically similar subsets of endocrine cells that have different origins and different life histories. These parallel but distinct lineages of differentiated cells in the gland may help the maturing organism adapt to changes in the metabolic regulatory landscape