Independent component analysis using Potts models

We explore the extending application of Potts encoding to the task of independent component analysis, which primarily deals with the problem of minimizing the Kullback-Leibler divergence between the joint distribution and the product of all marginal distributions of output components. The competitive mechanism of Potts neurons is used to encode the overlapping projections from observations to output components. Based on these projections, the marginal distributions and the entropy of output components are made tractable for computation and the adaptation of the de-mixing matrix toward independent output components is obtained. The Potts model for ICA is well formulated by an objective function subject to a set of constraints, which leads to a novel energy function. A hybrid of the mean field annealing and the gradient descent method is applied to the energy function. Our approach to independent component analysis presents a new criterion for ICA. The performance of the Potts model for ICA given by our numerical simulations is encouraging.

Role of alpha(3)beta(1) integrin in tubulogenesis of Madin-Darby canine kidney cells

BACKGROUND

We isolated several Madin-Darby canine kidney (MDCK) subclones that exhibit different degrees of branching tubulogenesis in lower concentrations of collagen gel. The M634 clone formed cell aggregates in 0.3% collagen gel, but developed branching tubules vigorously in 0.1% collagen gel. In contrast, the Y224 clone formed cysts in 0.3% collagen gel and displayed fewer branching structures in 0.1% collagen gel. Morphologically, M634 cells exhibited higher levels of cell scattering as well as collagen-induced cell migration than Y224. We conducted this study to delineate the underlying mechanism of branching tubulogenesis in M634 cells.

METHODS

Components of the focal contact machinery were analyzed in both cell lines, including the extracellular matrix glycoproteins fibronectin, laminin, and vitronectin; cytoskeleton-associated elements alpha-actinin, talin, and vinculin; and receptors for extracellular matrix and alpha(2), alpha(3), alpha(5), alpha(v), beta(1), and beta(3) integrins. Furthermore, we established several stable transfectants of alpha(3) integrin antisense RNA in M634 cells to examine the role of alpha(3)beta(1) integrin in branching morphogenesis directly.

RESULTS

There were no obvious differences in levels of the focal adhesion complex proteins between M634 and Y224 cells, except that the content of the alpha(3) and beta1 integrins were 1.2- and 0.6-fold higher in M634 cells, respectively. The expression of alpha(3) integrin antisense RNA significantly lowered the levels of alpha(3) integrin mRNA and protein. The potential of cell scattering, migration, and branching tubulogenesis in M634 cells was inhibited according to the decrease in alpha(3) integrin expression.

CONCLUSION

Our data indicate that expression of alpha(3)beta(1) integrin regulates cell scattering, migration, and branching tubulogenesis of MDCK cells, possibly via adhesion to or serving as a signaling molecule for type I collagen.