We are currently working on knock-in and conditional mouse variants that express fibronectin with cellular adhesion problems. We use these mice to know how essential are proteins and sequences related to adhesion in vivo to define the pathologies produced due to deficiency.
FN is secreted as a dimer and polymerises in a shape decided by the cell, since uniting integrines activates and stimulates the contractility of cytoskeleton (stress fibers) to apply traction on the FN and allow deployment and self-polymerisation. We want to know what adhesions are limiting and how each of them influences in cell behaviour and ECM secretion, structure and rigidity; determining factors in formation and regeneration of tissues. We are analysing three FN regions:

1. The variable of the C-terminal end of FN uniting the α4β1/β7 integrines, related in maturity and movement of hematopoietic cells.
2. The RGD motif of the FNIII10 module is the main integrin-binding sequence. FN-RGD binding is very complex: it has been said to be the only one that allows the formation of FN polymers; it binds two different groups of integrines, α5β1 and αIIbβ3 (exclusive of platelets) and dimers with αv, with different but in many tissues complementary functions; and in addition in the first group it seems that adhesion is reinforced, under conditions of increased tension, by binding of the so-called synergistic site that is located in the FNIII module9. To study this we have the following lines of mice: A) The strain of mice where we substituted the RGD sequence for RGE and showed that only α5β1 binding was inhibited leading to embryonic lethality in which in addition to cardiovascular problems truncated trunk elongation and the process of somitogenesis. We are currently working with RGE conditional mutants in cartilage to study their influence on cartilage regeneration in a model of induced osteoarthritis. B) The FN-delta-RGD strain that lacks the three amino acids and is helping us to establish that RGD is critical, as FNΔRGD mice show an embryonic lethal phenotype similar to that of FN-deficient mice. C) The strain with the non-functional synergistic site (FNSyn) that develop normally but have blood clotting problems. We are now focused on the in-depth analysis of these mice on processes that are closely linked to the cell's perception of mechanical signals: C1) skin wound healing; C2) the development of malignant tumours; C3) haemostasis processes; and C4) muscle regeneration after injury.
3. The generation of two mouse variant with mutation in Type 2 heparin (FNIII12-14 modules) region to unite another cell receptor, Syndecan-4, and various growth factors. Hypothetically, this region could allow signaling by growth factors cooperatively with the RGD adhesion. This region is particularly interesting in the area of tissue regeneration. We aim to study muscle regeneration