Biomedical subjects

L Hou

Publications and source records attributed to L Hou.

93 records · Page 6Linked to original sources

PubMed1990

Tracer diffusion in F-actin and Ficoll mixtures. Toward a model for cytoplasm.

We have previously reported that self-diffusion of inert tracer particles in the cytoplasm of living Swiss 3T3 cells is hindered in a size-dependent manner (Luby-Phelps, K., D.L. Taylor, and F. Lanni. 1986. J. Cell Biol. 102:2015-2022; Luby-Phelps, K., P.E. Castle, D.L. Taylor, and F. Lanni. 1987. Proc Natl. Acad. Sci. USA. 84:4910-4913). Lacking a theory that completely explains our data, we are attempting to understand the molecular architecture responsible for this phenomenon by studying tracer diffusion in simple, reconstituted model systems. This report contains our findings on tracer diffusion in concentrated solutions of Ficoll 70 or Ficoll 400, in solutions of entangled F-actin filaments, and in solutions of entangled F-actin containing a background of concentrated Ficoll particles or concentrated bovine serum albumin (BSA). A series of size-fractionated fluorescein-Ficolls were used as tracer particles. By fluorescence recovery after photobleaching (FRAP), we obtained the mean diffusion coefficients in a dilute, aqueous reference phase (Do), the mean diffusion coefficients in the model matrices (D), and the mean hydrodynamic radii (RH) for selected tracer fractions. For each model matrix, the results were compared with similar data obtained from living cells. As in concentrated solutions of globular proteins (Luby-Phelps et al., 1987), D/Do was not significantly size-dependent in concentrated solutions of Ficoll 400 or Ficoll 70. In contrast, D/Do decreased monotonically with increasing RH in solutions of F-actin ranging in concentration from 1 to 12 mg/ml. This size dependence was most pronounced at higher F-actin concentrations. However, the shape of the curve and the extrapolated value of D/Do in the limit, RH----O did not closely resemble the cellular data for tracers in the same size range (3 less than RH less than 30 nm). In mixtures of F-actin and Ficoll or F-actin and BSA, D/Do was well approximated by D/Do for the same concentration of F-actin alone multiplied by D/Do for the same concentrations of Ficoll or BSA alone. Based on these results, it is possible to model the submicroscopic architecture of cytoplasm in living cells as a densely entangled filament network (perhaps made up of F-actin and other filamentous structures) interpenetrated by a fluid phase crowded with globular macromolecules, which in cytoplasm would be primarily proteins.

Actins↗

PubMed1990

Brownian motion of inert tracer macromolecules in polymerized and spontaneously bundled mixtures of actin and filamin.

By use of light microscopy and fluorescence photobleaching recovery, we have studied (a) structures that form in a system composed of copolymerized rabbit muscle actin and chicken gizzard filamin and (b) the Brownian motion of inert tracer macromolecules in this matrix. We have used as tracers size-fractionated fluorescein-labeled ficoll and submicron polystyrene latex particles. In F-actin solutions, the relative diffusion coefficient of the tracer was a decreasing function of both tracer size and actin concentration. Also, a percolation transition for latex particle mobility was found to follow a form suggested by Ogston (Ogston, A. G. 1958. Trans. Faraday Soc. 54:1754-1757) for random filament matrices. The inclusion of filamin before polymerization resulted in increased tracer mobility. Below a filamin dimer-to-actin monomer ratio of 1:140, no structural features were observed in the light microscope. At or above this ratio for all actin concentrations tested, a three-dimensional network of filament bundles was clearly discriminated. Latex particles were always excluded from the bundles. By use of a dialysis optical cell in which polymerization could be initiated with very little hydrodynamic stress, we found that filamin can spontaneously bundle F-actin. A simple physical picture explains how dynamics can affect the structural result of coassembly and provides a further hypothesis on the balance between random filament cross-linking and large-scale bundling. Control of this balance may be important in cytoplasmic motile events.

Actins↗

PubMedDate not supplied

Dinosaur's feather and chicken's tooth? Tissue engineering of the integument.

The integument forms the interface between animals and the environment. During evolution, diverse integument and integument appendages have evolved to adapt animals to different niches. The formation of these different integument forms is based on the acquisition of novel developmental mechanisms. This is the way Nature does her tissue/organ engineering and experiments. To do tissue engineering of the integument in the new century for medical applications, we need to learn more principles from developmental and evolutionary studies. A novel diagram showing the evolution and development of integument complexity is presented, and the molecular pathways involved discussed. We then discuss two examples in which the gain and loss of appendages are modulated: transformation of avian scale epidermis into feathers with mutated beta catenin, and induction of chicken tooth like appendages with FGF, BMP and feather mesenchyme.

Animals↗