Drosophila melanogaster is a leading genetic model system in nervous system development and disease research. Using the power of fly genetics in traumatic axonal injury research will significantly speed up the characterization of molecular processes that control axonal regeneration in the CNS. We developed a versatile and physiologically robust preparation for the long-term culture of the whole Drosophila brain. We use this method to develop a novel Drosophila model for CNS axonal injury and regeneration. We first show that, similar to mammalian CNS axons, injured adult wild-type fly CNS axons fail to regenerate, whereas adult-specific enhancement of protein kinase A activity increases the regenerative capacity of lesioned neurons. Combined, these observations suggest conservation of neuronal regeneration mechanisms after injury. We next exploit this model to explore pathways that induce robust regeneration and find that adultspecific activation of c-Jun N-terminal protein kinase signaling is sufficient for de novo CNS axonal regeneration injury, including the growth of new axons past the lesion site and into the normal target area.

The precise number and pattern of axonal connections generated during brain development regulates animal behavior. Therefore, understanding how developmental signals interact to regulate axonal extension and retraction to achieve precise neuronal connectivity is a fundamental goal of neurobiology. We investigated this question in the developing adult brain of Drosophila and find that it is regulated by crosstalk between Wnt, fibroblast growth factor (FGF) receptor, and Jun N-terminal kinase (JNK) signaling, but independent of neuronal activity. The Rac1 GTPase integrates a Wnt-Frizzled-Disheveled axon-stabilizing signal and a Branchless (FGF)-Breathless (FGF receptor) axon-retracting signal to modulate JNK activity. JNK activity is necessary and sufficient for axon extension, whereas the antagonistic Wnt and FGF signals act to balance the extension and retraction required for the generation of the precise wiring pattern.

The N-terminal fragment of prolactin (16K PRL) inhibits tumor growth by impairing angiogenesis, but the underlying mechanisms are unknown. Here, we found that 16K PRL binds the fibrinolytic inhibitor plasminogen activator inhibitor-1 (PAI-1), which is known to contextually promote tumor angiogenesis and growth. Loss of PAI-1 abrogated the antitumoral and antiangiogenic effects of 16K PRL. PAI-1 bound the ternary complex PAI-1-urokinase-type plasminogen activator (uPA)-uPA receptor (uPAR), thereby exerting antiangiogenic effects. By inhibiting the antifibrinolytic activity of PAI-1, 16K PRL also protected mice against thromboembolism and promoted arterial clot lysis. Thus, by signaling through the PAI-1-uPA-uPAR complex, 16K PRL impairs tumor vascularization and growth and, by inhibiting the antifibrinolytic activity of PAI-1, promotes thrombolysis.

SUMMARYCognate interactions between CD154 (CD40 ligand, CD40L) on activated T cells and its receptor CD40 on various antigen-presenting cells are involved in thymus-dependent humoral immune responses and multiple other cell-mediated immune responses. We have studied the regulation of CD154 expression in human T cells after activation with anti-CD3 and anti-CD28 antibodies or after pharmacological activation of protein kinase C with phorbol 12-myristate 13-acetate, and the calcium ionophore ionomycin. Under these conditions, transcription of the CD154 gene was rapidly induced without requiring de novo protein synthesis. Pharmacological inhibitors of NF-kB activation down-regulated CD154 mRNA and protein levels. Cyclosporin A, an inhibitor of NF-AT activation, acted similarly, and the effects of both inhibitors were additive. A potential NF-kB binding site is present within the CD154 promoter at positions 21190 to 2 1181. In electrophoretic mobility shift assays, this sequence was specifically bound by NF-kB present in nuclear extracts from activated T cells. Furthermore, in transient co-transfection of Jurkat T cells, p65 activated the transcription of a reporter construct containing a multimer of this NF-kB binding site. These observations demonstrate a role of NF-kB transcription factors in the regulation of CD40L expression in activated primary human T cells.