Mononuclear phagocytes are classified as macrophages or dendritic cells (DCs) based on cell morphology, phenotype, or select functional properties. However, these attributes are not absolute and often overlap, leading to difficulties in cell-type identification. To circumvent this issue, we describe a mouse model to define DCs based on their ontogenetic descendence from a committed precursor. We show that precursors of mouse conventional DCs, but not other leukocytes, are marked by expression of DNGR-1. Genetic tracing of DNGR-1 expression history specifically marks cells traditionally ascribed to the DC lineage, and this restriction is maintained after inflammation. Notably, in some tissues, cells previously thought to be monocytes/macrophages are in fact descendants from DC precursors. These studies provide an in vivo model for fate mapping of DCs, distinguishing them from other leukocyte lineages, and thus help to unravel the functional complexity of the mononuclear phagocyte system.

Hox genes are essential for the patterning of the axial skeleton. Hox group 10 has been shown to specify the lumbar domain by setting a rib-inhibiting program in the presomitic mesoderm (PSM). We have now produced mice with ribs in every vertebra by ectopically expressing Hox group 6 in the PSM, indicating that Hox genes are also able to specify the thoracic domain. We show that the information provided by Hox genes to specify rib-containing and rib-less areas is first interpreted in the myotome through the regional-specific control of Myf5 and Myf6 expression. This information is then transmitted to the sclerotome by a system that includes FGF and PDGF signaling to produce vertebrae with or without ribs at different axial levels. Our findings offer a new perspective of how Hox genes produce global patterns in the axial skeleton and support a redundant nonmyogenic role of Myf5 and Myf6 in rib formation.

hematopoiesis ͉ HOX genes ͉ microarray ͉ self-renewal ͉ embryoid bodies

The transcriptional regulatory network that controls the determination and differentiation of skeletal muscle cells in the embryo has at its core the four myogenic regulatory factors (MRFs) Myf5, MyoD, Mrf4 and MyoG. These basic helix-loop-helix transcription factors act by binding, as obligate heterodimers with the ubiquitously expressed E proteins, to the E-box sequence CANNTG. While all skeletal muscle cells have the same underlying function their progenitors arise at many sites in the embryo and it has become apparent that the upstream activators of the cascade differ in these various populations so that it can be switched on by a variety of inductive signals, some of which act by initiating transcription, some by maintaining it. The application of genome-wide approaches has provided important new information as to how the MRFs function to activate the terminal differentiation programme and some of these data provide significant mechanistic insights into questions which have exercised the field for many years. We also consider the emerging roles played by micro-RNAs in the regulation of both upstream activators and terminal differentiation genes.

Highlights d Secreted gelsolin (sGSN) inhibits DNGR-1 binding to F-actin d sGSN dampens DNGR-1-dependent cross-presentation of dead cell-associated antigens d sGSN impairs DNGR-1-dependent cDC1-mediated antitumor immunity d Low sGSN expression and mutations in FABPs correlate with cancer patient survival