Male Drosophila reproductive glands secrete exosomes in a BMP-dependent manner that fuse with sperm after mating and suppress female remating.

The Groucho (Gro)/TLE/Grg family of corepressors operates in many signaling pathways (including Notch and Wnt). Gro/TLE proteins recognize a wide range of transcriptional repressors by binding to divergent short peptide sequences, including a C-terminal WRPW/Y motif (Hairy/Hes/Runx) and internal eh1 motifs (FxIxxIL; Engrailed/Goosecoid/Pax/Nkx). Here, we identify several missense mutations in Drosophila Gro, which demonstrate peptide binding to the central pore of the WD (WD40) beta propeller domain in vitro and in vivo. We define these interactions at the molecular level with crystal structures of the WD domain of human TLE1 bound to either WRPW or eh1 peptides. The two distinct peptide motifs adopt markedly different bound conformations but occupy overlapping sites across the central pore of the beta propeller. Our structural and functional analysis explains the rigid conservation of the WRPW motif, the sequence flexibility of eh1 motifs, and other aspects of repressor recognition by Gro in vivo.

Exosomes are secreted extracellular vesicles carrying diverse molecular cargos, which can modulate recipient cell behaviour. They are thought to derive from intraluminal vesicles formed in late endosomal multivesicular bodies ( MVB s). An alternate exosome formation mechanism, which is conserved from fly to human, is described here, with exosomes carrying unique cargos, including the GTP ase Rab11, generated in Rab11‐positive recycling endosomal MVB s. Release of Rab11‐positive exosomes from cancer cells is increased relative to late endosomal exosomes by reducing growth regulatory Akt/mechanistic Target of Rapamycin Complex 1 ( mTORC 1) signalling or depleting the key metabolic substrate glutamine, which diverts membrane flux through recycling endosomes. Vesicles produced under these conditions promote tumour cell proliferation and turnover and modulate blood vessel networks in xenograft mouse models in vivo . Their growth‐promoting activity, which is also observed in vitro , is Rab11a‐dependent, involves ERK ‐ MAPK ‐signalling and is inhibited by antibodies against amphiregulin, an EGFR ligand concentrated on these vesicles. Therefore, glutamine depletion or mTORC 1 inhibition stimulates release from Rab11a compartments of exosomes with pro‐tumorigenic functions, which we propose promote stress‐induced tumour adaptation.

The evolutionarily conserved Ras/mitogen-activated protein kinase (MAPK) cascade is an integral part of the processes of cell division, differentiation, movement and death. Signals received at the cell surface are relayed into the nucleus, where MAPK phosphorylates and thereby modulates the activities of a subset of transcription factors. Here we report the cloning and characterization of a new component of this signal transduction pathway called Mae (for modulator of the activity of Ets). Mae is a signalling intermediate that directly links the MAPK signalling pathway to its downstream transcription factor targets. Phosphorylation by MAPK of the critical serine residue (Ser 127) of the Drosophila transcription factor Yan depends on Mae, and is mediated by the binding of Yan to Mae through their Pointed domains. This phosphorylation is both necessary and sufficient to abrogate transcriptional repression by Yan. Mae also regulates the activity of the transcriptional activator Pointed-P2 by a similar mechanism. Mae is essential for the normal development and viability of Drosophila, and is required in vivo for normal signalling of the epidermal growth factor receptor. Our study indicates that MAPK signalling specificity may depend on proteins that couple specific substrates to the kinase.