Foregut mesenchyme contributes cells to pancreatic acini during embryonic development in a chick-quail chimera model.

To understand causes of developmental abnormalities of the pancreas, it is essential to understand its normal embryonic development. Current understanding of the development of pancreatic exocrine tissue is that it develops solely from embryonic epithelium, while the role of the surrounding mesenchyme is to signal to this epithelium and form connective tissue. Recent work in our laboratory has shown that pancreatic bud mesenchyme can contribute cells to islets during embryonic development. However, no published studies have investigated in detail whether mesenchyme contributes cells to the exocrine structures of the pancreas. The aim of this study was to investigate whether cells from foregut mesenchyme can contribute to pancreatic acini during embryonic development. Chick-quail chimera recombinant organs were constructed using pancreatic epithelium and mesenchyme from either the pancreas (n=12) or stomach (n=25). These were cultured for 7 days in 3-D collagen gels. The resulting specimens were analysed using morphological criteria and fluorescent immunocytochemistry against pancreatic amylase, insulin, and the quail-specific nucleolar antigen QCPN. Two independent observers determined the origins of acini as either solely epithelial, solely mesenchymal, or of mixed origin. Results are expressed as percentages of total acini identified in each group. Statistical analysis was performed using chi(2) tests (P<0.01 was considered statistically significant). Recombinations of pancreatic epithelium and pancreatic mesenchyme yielded 11 acini, of which 45% were derived from epithelium only, 45% from mesenchyme only, and 10% of mixed origin. Recombinations of pancreatic epithelium and stomach mesenchyme yielded 78 acini, of which 40% were derived from epithelium only, 32% from mesenchyme only, and 28% of mixed origin. When acini with any mesenchymal cellular contribution were considered as a group, there was no significant difference between stomach and pancreatic mesenchymal contribution (P=0.72). This is the first study to demonstrate the cellular contribution of mesenchyme to pancreatic exocrine structures. Our data show that mesenchyme contributes cells to pancreatic acini during development in this model and that mesenchyme derived from stomach and pancreatic sources are both able to form acini

The importance of pancreatic embryonic epithelium for mesenchyme-to-epithelial transition during islet development.

Stem or progenitor cells are a promising potential alternative source of pancreatic islets for transplantation in the treatment of juvenile-onset diabetes. However, to derive islets from such cells, it is important to elucidate the mechanisms of normal pancreatic development. Previous work in our laboratory has shown that, contrary to previous thinking, pancreatic mesenchyme when combined with pancreatic epithelium can contribute cells to islets. However, the signals and role of individual tissues involved in this mesenchyme-to-epithelial transition (MET) have yet to be elucidated. The aim of this study was to investigate whether MET can occur in the absence of pancreatic epithelium. Chick and quail eggs were incubated for 4 days and the dorsal pancreatic buds and stomach rudiments were microdissected. Mesenchyme and epithelium of the organ rudiments were separated after collagenase treatment. Separated pancreatic mesenchyme were cultured alone and in combination with stomach (nonpancreatic). After 7 days of culture, the specimens were analysed using immunohistochemistry for quail-specific nucleolar antigen (QCPN), insulin, and islet precursor cell marker (ISL-1). Pancreatic mesenchyme when cultured in the absence of epithelium did not differentiate into islets, but differentiated into fibroblast-like cells. When pancreatic mesenchyme were cultured in combination with stomach epithelium, there was no evidence of mesenchymally derived islets. We have demonstrated that pancreatic mesenchyme require pancreatic epithelium to differentiate into islet cells. These findings further increase our understanding of normal pancreatic islet development and may help to elucidate the molecular mechanisms of MET in islet development

The competency of foregut mesenchyme in islet mesenchyme-to-epithelial transition during embryonic development.

BACKGROUND/PURPOSE: Potential for curative stem-cell treatments of juvenile-onset diabetes has focussed research into pancreatic islet development. Islets were previously thought to originate solely from embryonic pancreatic epithelium, but we have demonstrated that islets can originate from mesenchyme, that is, islet mesenchyme-to-epithelial transition. The aim of this study was to establish the competence of foregut mesenchyme during mesenchymal islet development. METHODS: Embryonic chick pancreatic epithelium of gestational stage Hamburger-Hamilton (HH) 22 (J Morphol. 1951;88:49-92) was combined with quail stomach mesenchyme of increasing gestation (stage HH22 [n = 6], HH26 [n = 6], HH28 [n = 4], or HH31 [n = 6]). Recombinants were cultured and analysed by immunocytochemistry for coexpression of insulin and quail-specific antigen to determine the embryonic origin of islets. RESULTS: Recombinants constructed using stage HH22 mesenchyme yielded 34 islets, of which 35% were mesenchymal. However, when recombinants were constructed using stage HH26 mesenchyme, 24% of 25 islets were mesenchymal. When using mesenchyme, 13% of 15 islets were mesenchymal. All islets (n = 35) in recombinants constructed using stage HH31 mesenchyme were epithelial derived. Islet mesenchyme-to-epithelial transition diminished significantly with increasing mesenchymal gestational stage (P = .002). CONCLUSIONS: These data show foregut mesenchyme is competent to form islets between stages HH22 and HH28. Developmental competence of foregut mesenchyme in islet mesenchyme-to-epithelial transition diminishes as gestation increases. This may have important implications for identifying stem cells to treat juvenile-onset diabetes

Intraosseous vascular access in adults using the EZ-IO in an emergency department

10.1007/s12245-009-0116-9International Journal of Emergency Medicine23155-16