Expression of carbonic anhydrase II (CA II) promoter-reporter fusion genes in multiple tissues of transgenic mice does not replicate normal patterns of expression indicating complexity of CA II regulation in vivo

Acinar cells in the neonatal pancreas grow by self-duplication and not by neogenesis from duct cells

Pancreatic acinar cells secrete digestive enzymes necessary for nutrient digestion in the intestine. They are considered the initiating cell type of pancreatic cancer and are endowed with differentiation plasticity that has been harnessed to regenerate endocrine beta cells. However, there is still uncertainty about the mechanisms of acinar cell formation during the dynamic period of early postnatal development. To unravel cellular contributions in the exocrine acinar development we studied two reporter mouse strains to trace the fate of acinar and duct cells during the first 4 weeks of life. In the acinar reporter mice, the labelling index of acinar cells remained unchanged during the neonatal pancreas growth period, evidencing that acinar cells are formed by self-duplication. In line with this, duct cell tracing did not show significant increase in acinar cell labelling, excluding duct-to-acinar cell contribution during neonatal development. Immunohistochemical analysis confirms massive levels of acinar cell proliferation in this early period of life. Further, also increase in acinar cell size contributes to the growth of pancreatic mass.We conclude that the growth of acinar cells during physiological neonatal pancreas development is by self-duplication (and hypertrophy) rather than neogenesis from progenitor cells as was suggested before.

The use of stem cells for pancreatic regeneration in diabetes mellitus

The endocrine pancreas represents an interesting arena for regenerative medicine and cell therapeutics. One of the major pancreatic diseases, diabetes mellitus is a metabolic disorder caused by having an insufficient number of insulin-producing β cells. Replenishment of β cells by cell transplantation can restore normal metabolic control. The shortage in donor pancreata has meant that the demand for transplantable β cells has outstripped the supply, which could be met by using alternative sources of stem cells. This situation has opened up new areas of research, such as cellular reprogramming and in vivo β-cell regeneration. Pluripotent stem cells seem to be the best option for clinical applications of β-cell regeneration in the near future, as these cells have been demonstrated to represent an unlimited source of functional β cells. Although compelling evidence shows that the adult pancreas retains regenerative capacity, it remains unclear whether this organ contains stem cells. Alternatively, specialized cell types within or outside the pancreas retain plasticity in proliferation and differentiation. Cellular reprogramming or transdifferentiation of exocrine cells or other types of endocrine cells in the pancreas could provide a long-term solution.

Lineage tracing of pancreatic stem cells and beta cell regeneration

Restoring a functional β cell mass in diabetes patients by β cell transplantation or stimulation of β cell regeneration are promising approaches. It requires knowledge on the mechanisms of β cell neogenesis, an issue that is still quite controversial. Postnatal islet regeneration may or may not depend on an influx of new islet cells from adult progenitors. To solve this issue in animal models, genetic lineage tracing has become a crucial research method. This method allows to test the various hypotheses that have been proposed concerning β cell neogenesis and regeneration.

Timing and expression pattern of carbonic anhydrase II in pancreas

In the search for genetic markers for assessing the role of duct cells in pancreas growth, we examined whether carbonic anhydrase II (CAII) has ductal cell specificity. We determined the distribution and timing of CAII expression in mouse pancreas from embryonic stage to adult. The pancreatic ducts only start expressing CAII at embryonic day (E) 18.5, with increases after birth. Around E15.5, glucagon-positive cells, but not insulin-positive cells, also express CAII, with further increases by adult. CAII expression was restricted to cells within ductal structures and glucagon-positive cells with no colocalization with any insulin-positive cells at any time. In the human pancreas, CAII expression is restricted to the ducts. Furthermore, the activity of a 1.6-kb fragment of the human promoter with Luciferase assays was moderately strong compared with the cytomegalovirus promoter in human pancreatic duct cell line (PANC-1). Thus, we believe that the CAII gene could serve as a useful pancreatic duct cell marker.

Müller cell differentiation in the zebrafish neural retina: evidence of distinct early and late stages in cell maturation

The vertebrate neural retina is mainly composed of cells of neuroectodermal origin. The primary cell types found in all vertebrate retinas are several categories of neurons and the archetypical retina glial cell the Müller cell. Although the neurons and the single glial cell type of the retina are specialized for very distinct functions, they all have a common developmental origin within the tissue. How the distinctions between cell types, in particular between neurons and glia, arise during embryonic development remains a central issue in neurobiology. In this report, we examine the genesis of Müller glial cells during zebrafish (Danio rerio) eye development. Particular emphasis is placed on the expression of the Müller cell maturation markers carbonic anhydrase and glutamine synthetase. In addition, we report that the HNK-1 monoclonal antibody, which identifies a particular glycoconjugate frequently found on cell surface recognition molecules, also identifies zebrafish retina Müller cells early in development. The expression patterns of these three markers clearly show that the Müller cells mature in stages: HNK-1 labeling and glutamine synthetase arise earlier than carbonic anhydrase expression. In addition, the embryonic zebrafish neural retina is characterized by the presence of amoeboid, carbonic anhydrase-positive microglial cells even before the genesis of retinal neuroectodermal glia. The stepwise maturation of the glia is likely to be indicative of an overall retinal maturational program in which cell differentiation and the expression of certain phenotype-defining gene products may be separately regulated.

Characterization of the rat carbonic anhydrase II gene structure: sequence analysis of the 5' flanking region and 3' UTR

The rat carbonic anhydrase II gene was characterized and found to be approximately 15.5 kb in length and to contain 7 exons and 6 introns. All intron/exon junction and branch point sequences conform to consensus sequences, and the overall rat CA II genomic structure appears to be conserved upon comparison with mouse, human, and chicken CA II genes. The putative cis-acting elements within the analyzed 1014 bp 5' flanking region include: TATA box, 4 Sp1 binding sites, 2 AP2 sites and putative tissue-specific beta-globin-like repeat elements. A CpG island of approximately 800 bp was identified that begins about 600 bp upstream of exon 1 and extends about 200 bp into intron 1. In the 3' UTR, two polyadenylation signals (AATAAA) are present, the second of which is believed to be utilized. Northern blot analysis reveals that the 1.7 kb rat CA II mRNA is abundantly expressed in adult male brain and kidney, while negligible amounts are detected in heart and liver.