In Caenorhabditis elegans, body muscles extend muscle arms in a chemotropic fashion to the nearest nerve cord and serves as a model for the investigation of guided cell migration. I found that the transmembrane receptor UNC-40/DCC is required, and functions cell-autonomously to regulate muscle arm extension. Surprisingly, both the canonical ligand of UNC-40 (UNC-6/Netrin) and the extracellular domains of UNC-40 are dispensable, suggesting that UNC-40 relies on a co-receptor or other polarizing pathways to direct muscle arm extension. Furthermore, through double mutant analyses and the use of a neomorphic phenotype induced by UNC-40 over-expression, I define a distinct UNC-40 pathway in which UNC-73/Trio, the WAVE actin polymerization complex, and components of the dense body likely act downstream of UNC-40 to regulate muscle arm extension. Distinct modes of UNC-40’s function in muscle arm extension compared to its role in neurons provide a more complete understanding of how this conserved guidance receptor functions.

In Caenorhabditis elegans, body muscles extend muscle arms in a chemotropic fashion to the nearest nerve cord and serves as a model for the investigation of guided cell migration. I found that the transmembrane receptor UNC-40/DCC is required, and functions cell-autonomously to regulate muscle arm extension. Surprisingly, both the canonical ligand of UNC-40 (UNC-6/Netrin) and the extracellular domains of UNC-40 are dispensable, suggesting that UNC-40 relies on a co-receptor or other polarizing pathways to direct muscle arm extension. Furthermore, through double mutant analyses and the use of a neomorphic phenotype induced by UNC-40 over-expression, I define a distinct UNC-40 pathway in which UNC-73/Trio, the WAVE actin polymerization complex, and components of the dense body likely act downstream of UNC-40 to regulate muscle arm extension. Distinct modes of UNC-40’s function in muscle arm extension compared to its role in neurons provide a more complete understanding of how this conserved guidance receptor functions.

Une réponse immunitaire efficace repose sur un recrutement rapide de leucocytes du sang au tissu enflammé ou endommagé. Pendant ce processus, les leucocytes sont capturés par l'endothélium et migrent le long de la paroi pour atteindre les sites de transmigration. Ces processus sont médiés par des signaux externes parmi lesquels le rôle des molécules d’adhésion reste flou. L’haptotaxie adhésive a été décrite pour les cellules mésenchymateuses qui s’orientent via un mécanisme de tir à la corde - une compétition entre les bords adhérents des cellules. Pour les cellules amiboïdes, l'existence d'une haptotaxie adhésif n'a jamais été observée. Ici, nous avons étudié la migration des lymphocytes T humains sur des substrats dont l’adhérence est spatialement modulée et avons observé une haptotaxie robuste. Mécanistiquement, nous montrons que l'haptotaxie adhésive diffère à la fois de la chimiotaxie, car aucune mécanotransduction n'a été détectée, et du mécanisme de tir à la corde passif, car différentes intégrines induisent des phénotypes opposés. Les cellules ont favorisé des zones plus adhérentes avec VLA-4 et, contre-intuitivement, des zones moins adhérentes avec LFA-1. Ces résultats révèlent que les intégrines contrôlent les comportements différentiels d'haptotaxie adhésive sans mécanotransduction. Nous avons également étudié le mécanisme à l'origine de ce phénotype induit par LFA-1 et avons découvert que la dynamique du lamellipode plutôt que le niveau d'expression de l'intégrine, était impliquée. Les résultats préliminaires avec des lymphocytes T déficients en VASP indiquent également que la protéine VASP pourrait jouer un rôle important dans l'haptotaxie adhésive. / An efficient immune response relies on a rapid recruitment of leukocytes from blood to the inflamed or damaged tissue. During this process, leukocytes are captured by the endothelium and migrate along the vessel wall to reach permissive transmigration sites. These processes are mediated by multiple external cues among which the role of adhesion molecules remains unclear. Adhesive haptotaxis has been described for mesenchymal cells that develop strong pulling forces with their substrates and orient via a tug of war mechanism – a competition between cells’ adherent pulling edges. In the case of amoeboid cells that migrate with minimal interaction with their substrate, the existence of adhesive haptotaxis has yet to be evidenced. Here, we studied the crawling of human T lymphocytes on substrates with spatially modulated adhesion. and observed robust adhesive haptotaxis. Mechanistically, we show that integrin-mediated adhesive haptotaxis of lymphocytes differs both from active chemotaxis, because no mechanotransduction was detected, and from the passive tug of war mechanism, because different integrins support opposite phenotypes. Cells favored more adherent zones with VLA-4 and, counterintuitively, less adherent zones with LFA-1. These results reveal that integrins control differential adhesive haptotaxis behaviors without mechanotransduction. We further investigated the mechanism behind this specific haptotactic phenotype mediated by LFA-1 and find that the lamellipodial dynamics, rather than the integrin expression level, is involved. Preliminary findings with VASP deficient T cells indicate also that VASP protein may play an important role in T cell adhesive haptotaxis.

Yes / Cell behavior in terms of adhesion, orientation and guidance, on extracellular matrix (ECM) molecules including collagen, fibronectin and laminin can be examined using micro contact printing (MCP). These cell adhesion proteins can direct cellular adhesion, migration, differentiation and network formation in-vitro. This study investigates the effect of microcontact printed ECM protein, namely fibronectin, on alignment and morphology of HeLa cells cultured in-vitro. Fibronectin was stamped on plain glass cover slips to create patterns of 25μm, 50μm and 100μm width. However, HeLa cells seeded on 50μm induced the best alignment on fibronectin pattern (7.66° ±1.55SD). As a consequence of this, 50μm wide fibronectin pattern was used to see how fibronectin induced cell guidance of HeLa cells was influenced by 100μs and single pulse electric fields (PEF) of 1kV/cm. The results indicates that cells aligned more under pulse electric field exposure (2.33° ±1.52SD) on fibronectin pattern substrate. Thus, PEF usage on biological cells would appear to enhance cell surface attachment and cell guidance. Understanding this further may have applications in enhancing tissue graft generation and potentially wound repair. / Ministry of Higher Education Malaysia and UTHM Tier 1 Research Grant (U865)