A Mathematical Model of Liver Cell Aggregation In Vitro

The behavior of mammalian cells within three-dimensional structures is an area of intense biological research and underpins the efforts of tissue engineers to regenerate human tissues for clinical applications. In the particular case of hepatocytes (liver cells), the formation of spheroidal multicellular aggregates has been shown to improve cell viability and functionality compared to traditional monolayer culture techniques. We propose a simple mathematical model for the early stages of this aggregation process, when cell clusters form on the surface of the extracellular matrix (ECM) layer on which they are seeded. We focus on interactions between the cells and the viscoelastic ECM substrate. Governing equations for the cells, culture medium, and ECM are derived using the principles of mass and momentum balance. The model is then reduced to a system of four partial differential equations, which are investigated analytically and numerically. The model predicts that provided cells are seeded at a suitable density, aggregates with clearly defined boundaries and a spatially uniform cell density on the interior will form. While the mechanical properties of the ECM do not appear to have a significant effect, strong cell-ECM interactions can inhibit, or possibly prevent, the formation of aggregates. The paper concludes with a discussion of our key findings and suggestions for future work

A Triassic spider from Italy

A new fossil spider from the Triassic (Norian) Dolomia di Forni Formation of Friuli, Italy, is described as Friularachne rigoi gen. et sp. nov. This find brings the number of known Triassic spider species to four. The specimen is an adult male, and consideration of various features, including enlarged, porrect chelicerae, subequal leg length, and presence of a dorsal scutum, point to its identity as a possible member of the mygalomorph superfamily Atypoidea. If correct, this would extend the geological record of the superfamily some 98–115 Ma from the late Early Cretaceous (?Albian, c. 100–112 Ma) to the late middle–early late Norian (c. 210–215 Ma)

Effect of Invivo Administration of An Antibody to Epidermal Growth-Factor On the Rapid Increase in Dna-Synthesis Induced by Partial-Hepatectomy in the Rat

Recent reports indicate that transforming growth factor alpha (TGF-alpha) is produced within the fiver and acts as the natural ligand of the epidermal growth factor (EGF) receptor causing the EGF receptor down regulation and the hepatocyte proliferation observed after partial hepatectomy. The reported phenomenon that an antibody to EGF inhibits the regenerative response to partial hepatectomy was therefore re-investigated. The IgG fraction of an anti-rat EGF antibody was injected intravenously at the time of partial hepatectomy, and its effects on regenerative DNA synthesis were compared with those of non-immune IgG. Injection of IgG reduced the DNA synthetic response to partial hepatectomy, assessed 24 hours after resection by H-3-thymidine incorporation, but the effects of normal and anti-EGF IgG were not statistically different, despite the presence of excess anti-EGF IgG in the circulation throughout the experimental period. However, anti-EGF IgG could completely block the proliferative response of hepatocytes in culture to EGF. These results support the suggestion that EGF is not the major mediator of hepatocyte DNA synthesis in the early stages of liver regeneration

Microanatomy of Early Devonian book lungs

The book lungs of an exceptionally preserved fossil arachnid (Trigonotarbida) from the Early Devonian (approx. 410 Myr ago) Rhynie cherts of Scotland were studied using a non-destructive imaging technique. Our three-dimensional modelling of fine structures, based on assembling successive images made at different focal planes through the translucent chert matrix, revealed for the first time fossil trabeculae: tiny cuticular pillars separating adjacent lung lamellae and creating a permanent air space. Trabeculae thus show unequivocally that trigonotarbids were fully terrestrial and that the microanatomy of the earliest known lungs is indistinguishable from that in modern Arachnida. A recurrent controversy in arachnid evolution is whether the similarity between the book lungs of Pantetrapulmonata (i.e. spiders, trigonotarbids, etc.) and those of scorpions is a result of convergence. Drawing on comparative studies of extant taxa, we have identified explicit characters (trabeculae, spines on the lamellar edge) shared by living and fossil arachnid respiratory organs, which support the hypothesis that book lungs were derived from a single, common, presumably terrestrial, ancestor