The post-natal dental pulp tissue contains a population of multipotent mesenchymal progenitor cells known as dental pulp stromal/stem cells (DPSCs), with high proliferative potential for self-renewal. In this investigation, we explored the potential of DPSCs to differentiate into pancreatic cell lineage resembling islet-like cell aggregates (ICAs). We isolated, propagated, and characterized DPSCs and demonstrated that these could be differentiated into adipogenic, chondrogenic, and osteogenic lineage upon exposure to an appropriate cocktail of differentiating agents. Using a three-step protocol reported previously by our group, we succeeded in obtaining ICAs from DPSCs. The identity of ICAs was confirmed as islets by dithiozone-positive staining, as well as by expression of C-peptide, Pdx-1, Pax4, Pax6, Ngn3, and Isl-1. There were several-fold up-regulations of these transcription factors proportional to days of differentiation as compared with undifferentiated DPSCs. Day 10 ICAs released insulin and C-peptide in a glucose-dependent manner, exhibiting in vitro functionality. Our results demonstrated for the first time that DPSCs could be differentiated into pancreatic cell lineage and offer an unconventional and non-controversial source of human tissue that could be used for autologous stem cell therapy in diabetes.

The mammalian pancreas is known to show a remarkable degree of regenerative ability. Several studies until now have demonstrated that the mammalian pancreas can regenerate in normal as well as diabetic conditions. These studies illustrate that pancreatic transcription factors that are seen to be expressed in a temporal fashion during development are re-expressed during regeneration. The only known exception to this is Neurogenin3 (NGN3). Though NGN3 protein, which marks all the pro-endocrine cells during development, is not seen during mouse pancreas regeneration, functional neo-islets are generated by 4 weeks after 70% pancreatectomy. We observed that pancreatic transcription factors upstream of ngn3 showed similar gene expression patterns during development and regeneration. However, gene transcripts of transcription factors immediately downstream of ngn3 (neuroD and nkx2.2) did not show such similarities in expression. Since NGN3 protein was not detected at any time point during regeneration, we reasoned that post-transcriptional silencing of ngn3 by microRNAs may be a possible mechanism. We carried out microRNA analysis of 283 known and validated mouse microRNAs during different stages of pancreatic development and regeneration and identified that 4 microRNAs; miR-15a, miR-15b, miR-16 and miR-195, which can potentially bind to ngn3 transcript, are expressed at least 200-fold higher in the regenerating mouse pancreas as compared to embryonic day (e) 10.5 or e 16.5 developing mouse pancreas. Inhibition of these miRNAs in regenerating pancreatic cells using anti-sense miRNA-specific inhibitors, induces expression of NGN3 and its downstream players: neuroD and nkx2.2. Similarly, overexpression of miRNAs targeting ngn3 during pancreas development shows reduction in the number of hormone-producing cells. It appears that during pancreatic regeneration in mice, increased expression of these microRNAs allows endocrine regeneration via an alternate pathway that does not involve NGN3 protein. Our studies on microRNA profiling of developing and regenerating pancreas provide us with better understanding of mechanisms that regulate post-natal islet neogenesis.

Putative stem cells have been isolated from various tissue fluids such as synovial fluid, amniotic fluid, menstrual blood, etc. Recently the presence of nestin positive putative mammary stem cells has been reported in human breast milk. However, it is not clear whether they demonstrate multipotent nature. Since human breast milk is a non-invasive source of mammary stem cells, we were interested in examining the nature of these stem cells. In this pursuit, we could succeed in isolating and expanding a mesenchymal stem cell-like population from human breast milk. These cultured cells were examined by immunofluorescent labeling and found positive for mesenchymal stem cell surface markers CD44, CD29, SCA-1 and negative for CD33, CD34, CD45, CD73 confirming their identity as mesenchymal stem cells. Cytoskeletal protein marker analysis revealed that these cells expressed mesenchymal stem cells markers, namely, nestin, vimentin, smooth muscle actin and also manifests presence of E-Cadherin, an epithelial to mesenchymal transition marker in their early passages. Further we tested the multipotent differentiation potential of these cells and found that they can differentiate into adipogenic, chondrogenic and oesteogenic lineage under the influence of specific differentiation cocktails. This means that these mesenchymal stem cells isolated from human breast milk could potentially be "reprogrammed" to form many types of human tissues. The presence of multipotent stem cells in human milk suggests that breast milk could be an alternative source of stem cells for autologous stem cell therapy although the significance of these cells needs to be determined.

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Two new cell lines, SIMH and SIGE, were derived from the heart of milkfish (Chanos chanos), a euryhaline teleost, and from the eye of grouper (Epinephelus coioides), respectively. These cell lines were maintained in Leibovitz's L-15 supplemented with 20% fetal bovine serum (FBS). The SIMH cell line was subcultured more than 50 times over a period of 210 days and SIGE cell line has been subcultured 100 times over a period of 1 1/2 years. The SIMH cell line consists predominantly of fibroblastic-like cells. The SIGE cell line consists predominantly of epithelial cells. Both the cell lines were able to grow at temperatures between 25 and 32 degrees C with an optimum temperature of 28 degrees C. The growth rate of these cells increased as the proportion of FBS increased from 2% to 20% at 28 degrees C with optimum growth at the concentrations of 15% or 20% FBS. Seven marine fish viruses were tested to determine the susceptibility of these cell lines. The SIGE cell line was found to be susceptible to nodavirus, MABV NC-1 and Y6, and the infection was confirmed by cytopathic effect (CPE) and reverse transcriptase-polymerase chain reaction. When these cells were transfected with pEGFP-N1 vector DNA, significant fluorescent signals were observed, suggesting that these cell lines can be a useful tool for transgenic and genetic manipulation studies. Further, these cell lines are characterized by immunocytochemistry using confocal laser scanning microscopy (CFLSM).