N-cadherin and ß1-integrins cooperate during the development of the enteric nervous system.

Cell adhesion controls various embryonic morphogenetic processes, including the development of the enteric nervous system (ENS). Ablation of ß1-integrin (ß1-/-) expression in enteric neural crest cells (ENCC) in mice leads to major alterations in the ENS structure caused by reduced migration and increased aggregation properties of ENCC during gut colonization, which gives rise to a Hirschsprung's disease-like phenotype. In the present study, we examined the role of N-cadherin in ENS development and the interplay with ß1 integrins during this process. The Ht-PA-Cre mouse model was used to target gene disruption of N-cadherin and ß1 integrin in migratory NCC and to produce single- and double-conditional mutants for these two types of adhesion receptors. Double mutation of N-cadherin and ß1 integrin led to embryonic lethality with severe defects in ENS development. N-cadherin-null (Ncad-/-) ENCC exhibited a delayed colonization in the developing gut at E12.5, although this was to a lesser extent than in ß1-/- mutants. This delay of Ncad-/- ENCC migration was recovered at later stages of development. The double Ncad-/-; ß1-/- mutant ENCC failed to colonize the distal part of the gut and there was more severe aganglionosis in the proximal hindgut than in the single mutants for N-cadherin or ß1-integrin. This was due to an altered speed of locomotion and directionality in the gut wall. The abnormal aggregation defect of ENCC and the disorganized ganglia network in the ß1-/- mutant was not observed in the double mutant. This indicates that N-cadherin enhances the effect of the ß1-integrin mutation and demonstrates cooperation between these two adhesion receptors during ENS ontogenesis. In conclusion, our data reveal that N-cadherin is not essential for ENS development but it does modulate the modes of ENCC migration and acts in concert with ß1-integrin to control the proper development of the ENS.

Mechanosensitive shivering of model tissues under controlled aspiration.

During embryonic development and wound healing, the mechanical signals transmitted from cells to their neighbors induce tissue rearrangement and directional movements. It has been observed that forces exerted between cells in a developing tissue under stress are not always monotonically varying, but they can be pulsatile. Here we investigate the response of model tissues to controlled external stresses. Spherical cellular aggregates are subjected to one-dimensional stretching forces using micropipette aspiration. At large enough pressures, the aggregate flows smoothly inside the pipette. However, in a narrow range of moderate aspiration pressures, the aggregate responds by pulsed contractions or "shivering." We explain the emergence of this shivering behavior by means of a simple analytical model where the uniaxially stretched cells are represented by a string of Kelvin-Voigt elements. Beyond a deformation threshold, cells contract and pull on neighboring cells after a time delay for cell response. Such an active behavior has previously been found to cause tissue pulsation during dorsal closure of Drosophila embryo.