Stromal cells from bone marrow and adipose tissue are attractive sources of adult progenitors for cell-based therapy. However, whether those cell populations represent intrinsically different cell types is still largely under debate. The aim of this study was to systematically and quantitatively compare adipose-derived stromal cells (ADSC) and bone marrow-derived multipotent mesenchymal-stromal cells (BM-MSC). The quantitative comparison was realized using Taqman Low Density Array, 2D electrophoresis and differentiation functional assays in vitro. Furthermore, cells engineered to express TGFbeta1 were injected into the intra-articular space of mouse knee joints in order to determine whether they were able to form new differentiated tissues in vivo. Our data revealed cell specific differences at transcriptional and proteomic levels between both cell types according to their tissue origin as well as functional differences in their differentiation processes towards adipogenic, osteogenic and chondrogenic programs. Nevertheless, in vitro as well as in vivo ADSC displayed the same ability than MSC to differentiate towards chondrocytes/osteoblasts, comforting the status of both cell sources as promising regenerative cells. In summary, our observations indicate that ADSC and MSC are fundamentally different cell types and differently committed cells.

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1Cx36 is the predominant connexin isoform expressed by pancreatic ␤-cells. However, little is known about the role of this protein in the functioning of insulin-secreting cells. To address this question, we searched for a cell line expressing Cx36 and having glucose-induced insulin secretion comparable to that of primary ␤-cells. T he well coordinated functioning of cells within tissues is ensured by multiple mechanisms, including the direct exchange of ions, second messengers, and other metabolites through connexin channels, clustered at gap junctions (1,2). These channels connect almost all types of vertebrate cells, including those of pancreatic islets (3). Previous studies suggest that connexin-mediated communication between ␤-cells is required for the control of insulin secretion. Thus, glucose stimulation of single ␤-cells is reduced compared with that of cell clusters (4), pharmacological blockade of gap junction channels markedly decreases insulin release (5), and transgenic mice whose ␤-cells express Cx32 show altered insulin secretion in response to glucose (6). While these findings provide evidence that connexin-dependent communication contributes to the control of insulin release, they do not specifically address the function of native connexins expressed by pancreatic islet cells.We recently found that Cx36 is the predominant isoform expressed by ␤-cells (7). As yet, however, the specific role of this somewhat unusual connexin isoform (8,9) and, in particular, its possible contribution to insulin secretion have not been investigated. Moreover, no data are available to show how connexin-mediated signaling may influence ␤-cell function even though gap junctions have been implicated in the synchronization of [Ca 2ϩ ] i oscillations in ␤-cells (10 -13).To address these questions, we screened MIN6 cells, which, unlike some other cell lines, retain glucose-induced insulin secretion and express Cx36 like primary ␤-cells (14 -19). We decreased Cx36 expression via the stable transfection of an antisense construct. Here, we show that the loss of Cx36 resulted in impaired electrical coupling, desynchronization of [Ca 2ϩ ] i oscillations, and altered insulin release of MIN6 cells. These results support the hypothesis that Cx36 plays a critical role in glucoseinduced insulin secretion. RESEARCH DESIGN AND METHODSCell lines and tissues. RIN2A (14), INS1 (15), and HIT cells (16) were cultured in RPMI-1640 medium, whereas ␤TC3 (17) and MIN6 cells (18) were cultured in Dulbecco's modified Eagle's medium as indicated in the original reports. Control tissues were obtained from OFA rats (olfactory bulb) or C57BL/6 mice (liver and heart), which were frozen in liquid nitrogen and stored at Ϫ80°C until use. RNA analysis. Samples of total RNA were extracted, reverse-transcribed, and amplified as previously described (7). To detect native Cx36, we amplified either a 980-bp or a 559-bp fragment, using the oligonucleotide pairs 5Ј-CACAGCGATGGGGGAATGGA-3Ј/5Ј-TGCCCTTTCACACATAGGCA-3Ј and 5Ј-GAGCCCAGGCCAAGAGGAAGTC-3Ј/5Ј-GG...

Connexin channels clustered at gap junctions are obligatory attributes of all macroscopic endocrine and exocrine glands investigated so far and also connect most types of cells which produce secretory products in other tissues. Increasing evidence indicates that connexins, and the cell-to-cell communications that these proteins permit, contribute to control the growth of secretory cells, their expression of specific genes and their differentiated function, including their characteristic ability to biosynthetize and release secretory products in a regulated manner. Since the previous reviews which have been published on this topic, several lines of evidence have been added in support of multiple regulatory roles of gland connexins. Here, we review this novel evidence, point to the many questions which are still open and discuss some interesting perspectives of the field.