Ph.D.: Université Paris VI (France)
During development, extensive cell movements change the shape the embryo from a sphere with a radial symmetry to an elongated, multilayered and asymmetric organism. The first morphogenetic movement occurs at gastrulation, when the mesoderm (that gives rise to the muscles, heart and blood vessels) and the endoderm (that gives rise to the gut, liver, pancreas etc…) are internalized. During neurulation, the neural tissue “rolls up” into a tube and the somitic mesoderm (future muscles) undergoes segmentation and rotation. After neurulation is complete, the dorsal most cells called neural crest cells undergo extensive migrations in the embryos and give rise to the melanocytes, and ganglia in the trunk and to most of the facial structures in the head. All these cell movements require the extracellular matrix (ECM) and transmembrane proteins capable of mediating cell-matrix (like integrin) and cell-cell (like cadherins) adhesion. These transmembrane proteins can also activate or be activated by intracellular signals to direct or modulate these events.
Cell movement during frog embryonic development.
We are investigating the mechanisms that control the morphogenetic movements with a particular emphasis on Cranial Neural Crest cell (CNC) migration in the frog Xenopus laevis. So far, we have identified the ECM protein fibronectin and the transmembrane proteins integrin α5β1, the ADAM metalloproteases as key players during CNC migration. We are currently studying the exact role of each of these ADAMs during CNC migration in vivo using classical embryology approaches such as grafts (Figure 1) combined with the latest molecular biology tools available (knock down, microarray etc…). We are also searching for the physiological substrates of these ADAMs and their involvement during these processes. In parallel, we are exploring the potential roleof these ADAMs during other morphogenetic movements. We are also studying the peculiar role of their cytoplasmic domain during these events. The cytoplasmic domain of ADAM13 is cleaved by the protease gamma secretase, and is transported into the nucleus where it regulate the transcription of genes involved in CNC migration, including the protease Calpain8b. We are currently investigating the mechanisms that control each of these steps.
ADAMs function during Zebrafish development.
While the frog system allowed us to decipher previously unknown function of ADAM during CNC migration, a few observations suggest that this function may have diverged in other vertebrates. First, the Xenopus CNC migration assay shows that while the cytoplasmic domain of C.elegans, zebrafish and opposum ADAM13 is functionally equivalent to Xenopus ADAM13, the mouse ADAM13 (aka ADAM33) is not (Cousin et al., 2011). Second, Xenopus CNC migration is very particular among the vertebrates. While most other species’ crest delaminates from the neural tube and migrate as a single cells from throughout the entire migration, Xenopus CNC migrate first as a cohesive sheet of cells before undergoing EMT and migrating as single cells. Since we showed that meltrin are necessary for the initiation of CNC migration, it is possible its function is only required for the “sheet” migration but not the single cell migration. The absence of effect of ADAM13 and 19 knock down on CNC migration in vitro seems to support this hypothesis (Cousin et al, submitted).Therefore, we are investigating the function of meltrins in a specie whose CNC migrate in a fashion that reflect mammalian CNC migration. The Zebrafish model is ideal for various reasons: 1- the embryos are readily amenable to microinjection (mRNA, morpholino), 2- the availability of many strain where GFP is expressed in specific tissues (ex: Sox10::GFP line express GFP in neural crest) allows a quick identification of phenotype by simple live imaging (Figure 2). The inhibition of the ADAM expression using antisens morpholino technology will answers two of fundamental questions: 1- Are ADAM involved in CNC migration in vertebrates other than Xenopus? 2- Are ADAM involved at a later stage of craniofacial development?
Cousin H, Abbruzzese G, McCusker C, Alfandari D. 2012. ADAM13 function is required in the 3 dimensional context of the embryo during cranial neural crest cell migration in Xenopus laevis.. Developmental biology.
Cousin H, Abbruzzese G, Kerdavid E, Gaultier A, Alfandari D. 2011. Translocation of the cytoplasmic domain of ADAM13 to the nucleus is essential for Calpain8-a expression and cranial neural crest cell migration.. Developmental cell. 20(2):256-63.
Cousin H, Alfandari D. 2011. ADAM and cell migration: the unexpected role of the cytoplasmic domain. Médecine sciences : M/S. 27(12):1069-71.
Alfandari D, Cousin H, Marsden M. 2010. Mechanism of Xenopus cranial neural crest cell migration.. Cell adhesion & migration. 4(4):553-60.
Coyne MJ, Cousin H, Loftus JP, Johnson PJ, Belknap JK, Gradil CM, Black SJ, Alfandari D. 2009. Cloning and expression of ADAM-related metalloproteases in equine laminitis.. Veterinary immunology and immunopathology. 129(3-4):231-41.
Neuner R, Cousin H, McCusker C, Coyne M, Alfandari D. 2009. Xenopus ADAM19 is involved in neural, neural crest and muscle development.. Mechanisms of development. 126(3-4):240-55.
McCusker C, Cousin H, Neuner R, Alfandari D. 2009. Extracellular cleavage of cadherin-11 by ADAM metalloproteases is essential for Xenopus cranial neural crest cell migration.. Molecular biology of the cell. 20(1):78-89.
Alfandari D, McCusker C, Cousin H. 2009. ADAM function in embryogenesis.. Seminars in cell & developmental biology. 20(2):153-63.
Cousin H, Desimone DW, Alfandari D. 2008. PACSIN2 regulates cell adhesion during gastrulation in Xenopus laevis.. Developmental biology. 319(1):86-99.
Cousin H, Alfandari D. 2004. A PTP-PEST-like protein affects alpha5beta1-integrin-dependent matrix assembly, cell adhesion, and migration in Xenopus gastrula.. Developmental biology. 265(2):416-32.
Cousin H, Gaultier A, Bleux C, Darribère T, Alfandari D. 2000. PACSIN2 is a regulator of the metalloprotease/disintegrin ADAM13.. Developmental biology. 227(1):197-210.