Modeling of mosaic patterns in chimeric liver and adrenal cortex: algorithmic organogenesis?

If organogenesis were a completely deterministic process, then the amount of information required to store the spatial position and fate of every cell in vertebrate organisms would be larger than the total information that could be contained in their genomes. This suggests that the instructions of developmental mechanisms involved in organogenesis, coded in DNA, must be at least in part procedural or algorithmically based. Chimeric mosaic patterns in rat livers have been shown to be isotropic and to have fractal profiles (D approximately 1.3) whereas adrenal gland mosaics show a less irregular radial pattern, with lower fractal dimension (D approximately 1.2) than in the liver. These findings suggested a possible model of parenchyma generation. We propose that during organogenesis in both liver and adrenal cortex, the same basic mechanism is directed to organ mass enlargement, whereas the differences observed in mosaic patterns between the organs could be due to the control of a single parameter, namely, a form of contact inhibition. Computer simulations in two dimensions returned comparable results in both the fractal dimension value of mosaic patches and appearance of the mosaic 'tissues', as observed histologically in chimeras. This suggests that position information and locomotion of cells would not be required to produce the mosaic pattern observed in chimeras.     

Fluid-Structure Interaction Simulation of Prosthetic Aortic Valves: Comparison between Immersed Boundary and Arbitrary Lagrangian-Eulerian Techniques for the Mesh Representation

In recent years the role of FSI (fluid-structure interaction) simulations in the analysis of the fluid-mechanics of heart valves is becoming more and more important, being able to capture the interaction between the blood and both the surrounding biological tissues and the valve itself. When setting up an FSI simulation, several choices have to be made to select the most suitable approach for the case of interest: in particular, to simulate flexible leaflet cardiac valves, the type of discretization of the fluid domain is crucial, which can be described with an ALE (Arbitrary Lagrangian-Eulerian) or an Eulerian formulation. The majority of the reported 3D heart valve FSI simulations are performed with the Eulerian formulation, allowing for large deformations of the domains without compromising the quality of the fluid grid. Nevertheless, it is known that the ALE-FSI approach guarantees more accurate results at the interface between the solid and the fluid. The goal of this paper is to describe the same aortic valve model in the two cases, comparing the performances of an ALE-based FSI solution and an Eulerian-based FSI approach. After a first simplified 2D case, the aortic geometry was considered in a full 3D set-up. The model was kept as similar as possible in the two settings, to better compare the simulations’ outcomes. Although for the 2D case the differences were unsubstantial, in our experience the performance of a full 3D ALE-FSI simulation was significantly limited by the technical problems and requirements inherent to the ALE formulation, mainly related to the mesh motion and deformation of the fluid domain. As a secondary outcome of this work, it is important to point out that the choice of the solver also influenced the reliability of the final results.     

A probabilistic model of mosaicism based on the histological analysis of chimaeric rat liver

The analysis of pattern development in mosaic and chimaeric animals has provided insight into a number of developmental problems. In order to aid the understanding of the dynamics of the development of mosaic tissues, a computer simulation of the generation of a mosaic tissue was created using simple probabilistic decisions. Results of quantitative analysis of the simulated mosaicism were compared with chimaeric liver. Chimaeric animals were produced by morula aggregation between histologically distinguishable strains of congenic rats. The livers of these animals revealed a pattern of patchy mosaicism unrelated to either acinar or lobular architecture of the organ. Independent quantifiable parameters were correlated and compared between the simulation and chimaeric liver tissue. This analysis showed that extensive cell migration is not required to develop finely variegated mosaic tissue and that the patterns of mosaicism observed could have resulted from tissue development in which as few as three reiterated decisions were required. First, the simulation established anlagen of two cell types of various specified proportions with randomly chosen placement. Second, in each generation of the simulation the order in which the cells divided was established randomly. Third, there was a random choice of the direction of placement of the daughter cell. The quantitative relationships between the proportion of cell types, the area of patches and the number of patches per unit area was consistent between the simulation and the chimaeric tissue.     

Pattern of steroid interaction with inducers of aryl hydrocarbon hydroxylase activity in several cloned estradiol-responsive stromal cell strains from mouse endometrium

Several steroid responsive stromal cell strains were isolated from normal mouse endometrium. Both estrogen responsive and progesterone responsive strains were obtained. The estrogen responsive cells were also responsive to diethylstilbestrol (DES). The progesterone responsive strains were inhibited by estrone and estriol. One of the estrogen responsive cell strains, E041, was cloned in the presence and absence of 17-beta-estradiol (E2). Of 14 clones developed in the absence of E2 and screened for responsivity of growth, six were significantly responsive to E2. Six of 26 clones developed in the presence of E2 were responsive to E2. Microsomes isolated from these clones were shown to have aryl hydrocarbon hydroxylase (AHH) activity which was inducible with either benzanthracene (BA) or 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD). The basal levels of AHH activity were significantly reduced by E2 in E2 responsive clones. The TCDD induced levels of AHH activity in the E2 responsive and E2 non-responsive clones were significantly reduced by E2. The BA induced levels of AHH were significantly increased by E2 in one of the clones. These results show that mouse endometrial stroma consists of a number of populations of cells with different specific proliferative and metabolic responses to steroids.     

Erratum to: An in silico biomechanical analysis of the stent–esophagus interaction

Biomechanics and Modeling in Mechanobiology - In the original publication of the article, Tables 2 and 3 were published with error. The correct tables are provided below (Tables 2, 3). The...