Amalgam plays a dual role in controlling the number of leg muscle progenitors and regulating their interactions with the developing Drosophila tendon.

Formation of functional organs requires cell-cell communication between different cell lineages and failure in this communication can result in severe developmental defects. Hundreds of possible interacting pairs of proteins are known, but identifying the interacting partners that ensure a specific interaction between 2 given cell types remains challenging. Here, we use the Drosophila leg model and our cell type-specific transcriptomic data sets to uncover the molecular mediators of cell-cell communication between tendon and muscle precursors. Through the analysis of gene expression signatures of appendicular muscle and tendon precursor cells, we identify 2 candidates for early interactions between these 2 cell populations: Amalgam (Ama) encoding a secreted protein and Neurotactin (Nrt) known to encode a membrane-bound protein. Developmental expression and function analyses reveal that: (i) Ama is expressed in the leg myoblasts, whereas Nrt is expressed in adjacent tendon precursors; and (ii) in Ama and Nrt mutants, myoblast-tendon cell-cell association is lost, leading to tendon developmental defects. Furthermore, we demonstrate that Ama acts downstream of the FGFR pathway to maintain the myoblast population by promoting cell survival and proliferation in an Nrt-independent manner. Together, our data pinpoint Ama and Nrt as molecular actors ensuring early reciprocal communication between leg muscle and tendon precursors, a prerequisite for the coordinated development of the appendicular musculoskeletal system.

An adherent-invasive Escherichia coli-colonized mouse model to evaluate microbiota-targeting strategies in Crohn's disease.

Adherent-invasive Escherichia coli (AIEC) were investigated for their involvement in the induction/chronicity of intestinal inflammation in Crohn's disease (CD). AIEC gut establishment is favoured by overexpression of the glycoprotein CEACAM6 in the ileal epithelium. We generated a transgenic mouse model, named 'Vill-hCC6', in which the human CEACAM6 gene was under the control of the villin promoter, conditioning expression in the small intestine. We demonstrated that CEACAM6 is strongly expressed in the small intestine mucosa and is correlated with numerous glycosylations displayed at the brush border of enterocytes. Ex vivo, the AIEC-enterocyte interaction was enhanced by CEACAM6 expression and necessitated the presence of the bacterial adhesive factor FimH. Finally, AIEC bacteria preferentially persisted in a FimH-dependent manner in the ileal mucosa of Vill-hCC6 mice compared to wild-type mice. This preclinical model opens new perspectives in the mechanistic study of the AIEC pathobiont and represents a valuable tool to evaluate the efficacy of new strategies to eliminate AIEC implanted in the ileal mucosa, such as phages, inhibitory and/or anti-virulence molecules, or CRISPR-based strategies targeting virulence or fitness factors of AIEC bacteria.