Blood monocytes are well-characterized precursors for macrophages and dendritic cells. Subsets of human monocytes with differential representation in various disease states are well known. In contrast, mouse monocyte subsets have been characterized minimally. In this study we identify three subpopulations of mouse monocytes that can be distinguished by differential expression of Ly-6C, CD43, CD11c, MBR, and CD62L. The subsets share the characteristics of extensive phagocytosis, similar expression of M-CSF receptor (CD115), and development into macrophages upon M-CSF stimulation. By eliminating blood monocytes with dichloromethylene-bisphosphonate-loaded liposomes and monitoring their repopulation, we showed a developmental relationship between the subsets. Monocytes were maximally depleted 18 h after liposome application and subsequently reappeared in the circulation. These cells were exclusively of the Ly-6Chigh subset, resembling bone marrow monocytes. Serial flow cytometric analyses of newly released Ly-6Chigh monocytes showed that Ly-6C expression on these cells was down-regulated while in circulation. Under inflammatory conditions elicited either by acute infection with Listeria monocytogenes or chronic infection with Leishmania major, there was a significant increase in immature Ly-6Chigh monocytes, resembling the inflammatory left shift of granulocytes. In addition, acute peritoneal inflammation recruited preferentially Ly-6Cmed-high monocytes. Taken together, these data identify distinct subpopulations of mouse blood monocytes that differ in maturation stage and capacity to become recruited to inflammatory sites.

Neuronal information processing requires a large amount of energy, indicating that sugars and other metabolites must be efficiently delivered. However, reliable neuronal function also depends on the maintenance of a constant microenvironment in the brain. Therefore, neurons are efficiently separated from circulation by the blood-brain barrier, and their long axons are insulated by glial processes. At the example of the Drosophila brain, we addressed how sugar is shuttled across the barrier to nurture neurons. We show that glial cells of the blood-brain barrier specifically take up sugars and that their metabolism relies on glycolysis, which, surprisingly, is dispensable in neurons. Glial cells secrete alanine and lactate to fuel neuronal mitochondria, and lack of glial glycolysis specifically in the adult brain causes neurodegeneration. Our work implies that a global metabolic compartmentalization and coupling of neurons and glial cells is a conserved, fundamental feature of bilaterian nervous systems independent of their size.

Endothelial sprouting and proliferation are tightly coordinated processes mediating the formation of new blood vessels during physiological and pathological angiogenesis. Endothelial tip cells lead sprouts and are thought to suppress tip-like behaviour in adjacent stalk endothelial cells by activating Notch. Here, we show with genetic experiments in postnatal mice that the level of active Notch signalling is more important than the direct Dll4-mediated cell-cell communication between endothelial cells. We identify endothelial expression of VEGF-A and of the chemokine receptor CXCR4 as key processes controlling Notch-dependent vessel growth. Surprisingly, genetic experiments targeting endothelial tip cells in vivo reveal that they retain their function without Dll4 and are also not replaced by adjacent, Dll4-positive cells. Instead, activation of Notch directs tip-derived endothelial cells into developing arteries and thereby establishes that Dll4-Notch signalling couples sprouting angiogenesis and artery formation.

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Mouse and human stem cells with features similar to those of embryonic stem cells have been derived from testicular cells. Although pluripotent stem cells have been obtained from defined germline stem cells (GSCs) of mouse neonatal testis, only multipotent stem cells have been obtained so far from defined cells of mouse adult testis. In this study we describe a robust and reproducible protocol for obtaining germline-derived pluripotent stem (gPS) cells from adult unipotent GSCs. Pluripotency of gPS cells was confirmed by in vitro and in vivo differentiation, including germ cell contribution and transmission. As determined by clonal analyses, gPS cells indeed originate from unipotent GSCs. We propose that the conversion process requires a GSC culture microenvironment that depends on the initial number of plated GSCs and the length of culture time.