CSF-1 is broadly expressed and regulates macrophage and osteoclast development. The action and expression of IL-34, a novel CSF-1R ligand, were investigated in the mouse. As expected, huIL-34 stimulated macrophage proliferation via the huCSF-1R, equivalently to huCSF-1, but was much less active at stimulating mouse macrophage proliferation than huCSF-1. Like muCSF-1, muIL-34 and a muIL-34 isoform lacking Q81 stimulated mouse macrophage proliferation, CSF-1R tyrosine phosphorylation, and signaling and synergized with other cytokines to generate macrophages and osteoclasts from cultured progenitors. However, they respectively possessed twofold and fivefold lower affinities for the CSF-1R and correspondingly, lower activities than muCSF-1. Furthermore, muIL-34, when transgenically expressed in a CSF-1-dependent manner in vivo, rescued the bone, osteoclast, tissue macrophage, and fertility defects of Csf1(op)/(op) mice, suggesting similar regulation of CSF-1R-expressing cells by IL-34 and CSF-1. Whole-mount IL34 in situ hybridization and CSF-1 reporter expression revealed that IL34 mRNA was strongly expressed in the embryonic brain at E11.5, prior to the expression of Csf1 mRNA. QRT-PCR revealed that compared with Csf1 mRNA, IL34 mRNA levels were lower in pregnant uterus and in cultured osteoblasts, higher in most regions of the brain and heart, and not compensatorily increased in Csf1(op/op) mouse tissues. Thus, the different spatiotemporal expression of IL-34 and CSF-1 allows for complementary activation of the CSF-1R in developing and adult tissues.

Colony‐stimulating factor‐1 (CSF‐1), also known as macrophage colony‐stimulating factor, controls the survival, proliferation, and differentiation of mono‐nuclear phagocytes and regulates cells of the female reproductive tract. It appears to play an autocrine and/or paracrine role in cancers of the ovary, endometrium, breast, and myeloid and lymphoid tissues. Through alternative mRNA splicing and differential post‐translational proteolytic processing, CSF‐1 can either be secreted into the circulation as a glycoprotein or chondroitin sulfate‐containing proteoglycan or be expressed as a membrane‐spanning glycoprotein on the surface of CSF‐1‐producing cells. Studies with the op/op mouse, which possesses an inactivating mutation in the CSF‐1 gene, have established the central role of CSF‐1 in directly regulating osteoclastogenesis and macrophage production. CSF‐1 appears to preferentially regulate the development of macrophages found in tissues undergoing active morphogenesis and/or tissue remodeling. These CSF‐1 dependent macrophages may, via putative trophic and/or scavenger functions, regulate characteristics such as dermal thickness, male fertility, and neural processing. Apart from its expression on mononuclear phagocytes and their precursors, CSF‐1 receptor (CSF‐1R) expression on certain nonmononuclear phagocytic cells in the female reproductive tract and studies in the op/op mouse indicate that CSF‐1 plays important roles in female reproduction. Restoration of circulating CSF‐1 to op/op mice has preliminarily defined target cell populations that are regulated either humorally or locally by the synthesis of cell‐surface CSF‐1 or by sequestration of the CSF‐1 proteoglycan. The CSF‐1R is a tyrosine kinase encoded by the c‐fms proto‐oncogene product. Studies by several groups have used cells expressing either the murine or human CSF‐1R in fibroblasts to pinpoint the requirement of kinase activity and the importance of various receptor tyrosine phosphorylation sites for signaling pathways stimulated by CSF‐1. To investigate post‐CSF‐1R signaling in the macrophage, proteins that are rapidly phosphorylated on tyrosine in response to CSF‐1 have been identified, together with proteins associated with them. Studies on several of these proteins, including protein tyrosine phosphatase 1C, the c‐cbl proto‐oncogene product, and protein tyrosine phosphatase‐phi are discussed. Mol Reprod Dev 46:4–10, 1997. © 1997 Wiley‐Liss, Inc.

The cellular machinery promoting phagocytosis of corpses of apoptotic cells is well conserved from worms to mammals. An important component is the Caenorhabditis elegans engulfment receptor CED-1 (ref. 1) and its Drosophila orthologue, Draper 2 . The CED-1/Draper signalling pathway is also essential for the phagocytosis of other types of 'modified self' including necrotic cells 3 , developmentally pruned axons 4,5 and dendrites 6 , and axons undergoing Wallerian degeneration 7 . Here we show that Drosophila Shark, a non-receptor tyrosine kinase similar to mammalian Syk and Zap-70, binds Draper through an immunoreceptor tyrosine-based activation motif (ITAM) in the Draper intracellular domain. We show that Shark activity is essential for Draper-mediated signalling events in vivo, including the recruitment of glial membranes to severed axons and the phagocytosis of axonal debris and neuronal cell corpses by glia. We also show that the Src family kinase (SFK) Src42A can markedly increase Draper phosphorylation and is essential for glial phagocytic activity. We propose that ligand-dependent Draper receptor activation initiates the Src42A-dependent tyrosine phosphorylation of Draper, the association of Shark and the activation of the Draper pathway. These Draper-Src42A-Shark interactions are strikingly similar to mammalian immunoreceptor-SFK-Syk signalling events in mammalian myeloid and lymphoid cells 8,9 . Thus, Draper seems to be an ancient immunoreceptor with an extracellular domain tuned to modified self, and an intracellular domain promoting phagocytosis through an ITAM-domain-SFK-Syk-mediated signalling cascade.Developing tissues produce excessive numbers of cells and selectively destroy a subpopulation through programmed cell death to regulate growth. Rapid clearance of cell corpses is essential for maintaining tissue homeostasis and preventing the release of potentially cytotoxic or antigenic molecules from dying cells, and defects in cell corpse clearance are closely associated with autoimmune and inflammatory diseases 10-13 . In C. elegans the CED-1 receptor is expressed in engulfing cells, where it acts to recognize cell corpses and drive their phagocytosis 1 . CED-1 promotes engulfment through an intracellular NPXY motif, a binding site for proteins containing a phosphotyrosine-binding (PTB) domain, and a YXXL motif, a potential interaction site for proteins containing SH2 domains 1 . The PTB domain adaptor protein CED-6 can bind the NPXY motif of , is required for cell corpse Glia are the primary phagocytic cell type in the developing and mature brain. Glia rapidly engulf neuronal cell corpses produced during development, as well as neuronal debris generated during axon pruning 19,20 or during Wallerian degeneration in the adult brain 21 . In Drosophila, glial phagocytosis of these engulfment targets requires Draper, the fly orthologue of CED-1 (refs 2 , 4-6 ). Draper, like CED-1, contains 15 extracellular atypical epidermal growth factor (EGF) repeats, a single transmembrane domain, and NPXY an...

The androgen receptor (AR) is a nuclear hormone receptor superfamily member that conveys both trans repression and ligand-dependent trans-activation function. Activation of the AR by dihydrotestosterone (DHT) regulates diverse physiological functions including secondary sexual differentiation in the male and the induction of apoptosis by the JNK kinase, MEKK1. The AR is posttranslationally modified on lysine residues by acetylation and sumoylation. The histone acetylases p300 and P/CAF directly acetylate the AR in vitro at a conserved KLKK motif. To determine the functional properties governed by AR acetylation, point mutations of the KLKK motif that abrogated acetylation were engineered and examined in vitro and in vivo. Steroid receptors, including the androgen receptor (AR), are members of the nuclear receptor (NR) superfamily which generally function as ligand-dependent transcriptional regulators (9, 31, 84). The AR is expressed in a variety of cell types and plays an important role in development, male sexual differentiation, and prostate cellular proliferation. The functional domains of the AR (termed A to F) are conserved with other members of the classical receptor subclass. The C-terminal region of the AR, including the hinge region and ligand-binding domain (LBD), is responsible for ligand binding and dimerization. The well-conserved DNA binding domain consists of 68 amino acids with two zinc finger structures. The N-terminal region contributes to transcriptional activation through its activation function 1 (AF-1) (5). In contrast to several other hormone-regulated NRs, the AR lacks an intrinsic AF-2 function in the LBD. The LBD, which consists of 12 ␣ helices projecting away from the hormone-binding pocket in the absence of ligand, undergoes substantial conformational changes in the presence of ligand. The folding of the most carboxyl-terminal helix 12 over the ligand-binding pocket in turn creates new structural surfaces that bind coactivators required for efficient transactivation.Several AR coactivators have been identified, including the p160 proteins, the p300/CREB-binding protein (CBP) family, Ubc9, ARA70, ARA55, and TIP60 (1,5,15,68,92). The efficient recruitment of coactivators to the AR involves an association between both the AR amino terminus and the LBD (5, 34). The coactivator proteins regulate gene expression through several distinct mechanisms. CBP and the related functional homologue p300 (CBP/p300) convey a bridging function between the DNA-bound transcription factor and the basal apparatus and provide a scaffold to assemble high-molecular-weight enhanceosomes (reviewed in reference 26). In addition, the cointegrator proteins p300/CBP share the capacity to acetylate histones, which correlates, under certain circumstances, with their transcriptional coactivator function (54,87). Acetylation facilitates binding of transcription factors to * Corresponding author. Mailing address: The Albert Einstein Can-

Tubular damage following ischemic renal injury is often reversible, and tubular epithelial cell (TEC) proliferation is a hallmark of tubular repair. Macrophages have been implicated in tissue repair, and CSF-1, the principal macrophage growth factor, is expressed by TECs. We therefore tested the hypothesis that CSF-1 is central to tubular repair using an acute renal injury and repair model, ischemia/reperfusion (I/R). Mice injected with CSF-1 following I/R exhibited hastened healing, as evidenced by decreased tubular pathology, reduced fibrosis, and improved renal function. Notably, CSF-1 treatment increased TEC proliferation and reduced TEC apoptosis. Moreover, administration of a CSF-1 receptor-specific (CSF-1R-specific) antibody after I/R increased tubular pathology and fibrosis, suppressed TEC proliferation, and heightened TEC apoptosis. To determine the contribution of macrophages to CSF-1-dependent renal repair, we assessed the effect of CSF-1 on I/R in mice in which CD11b + cells were genetically ablated and determined that macrophages only partially accounted for CSF-1-dependent tubular repair. We found that TECs expressed the CSF-1R and that this receptor was upregulated and coexpressed with CSF-1 in TECs following renal injury in mice and humans. Furthermore, signaling via the CSF-1R stimulated proliferation and reduced apoptosis in human and mouse TECs. Taken together, these data suggest that CSF-1 mediates renal repair by both a macrophage-dependent mechanism and direct autocrine/paracrine action on TECs.