Cytokines manifest their function through alteration of gene expression. However, target genes for signals from cytokine receptors are largely unknown. We therefore searched for immediate‐early cytokine‐responsive genes and isolated a novel gene, CIS (cytokine inducible SH2‐containing protein) which is induced in hematopoietic cells by a subset of cytokines including interleukin 2 (IL2), IL3, granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) and erythropoietin (EPO), but not by stem cell factor, granulocyte colony‐stimulating factor and IL6. The CIS message encodes a polypeptide of 257 amino acids that contains an SH2 domain of 96 amino acids in the middle. To clarify the function of CIS in cytokine signal transduction, we expressed CIS in IL3‐dependent hematopoietic cell lines under the control of a steroid‐inducible promoter. The CIS product stably associated with the tyrosine‐phosphorylated beta chain of the IL3 receptor as well as the tyrosine‐phosphorylated EPO receptor. Forced expression of CIS by steroid reduced the growth rate of these transformants, suggesting a negative role of CIS in signal transduction. CIS induction requires the membrane‐proximal region of the cytoplasmic domain of the EPO receptor as well as that of the common beta chain of the IL3, IL5 and GM‐CSF receptor, whereas CIS binds to the receptor that is tyrosine phosphorylated by cytokine stimulation. Thus CIS appears to be a unique regulatory molecule for cytokine signal transduction.

Observations of rapid shifts in mitochondrial DNA (mtDNA) variants between generations prompted the creation of the bottleneck theory. A prevalent hypothesis is that a massive reduction in mtDNA content during early oogenesis leads to the bottleneck. To test this, we estimated the mtDNA copy number in single germline cells and in single somatic cells of early embryos in mice. Primordial germ cells (PGCs) show consistent, moderate mtDNA copy numbers across developmental stages, whereas primary oocytes demonstrate substantial mtDNA expansion during early oocyte maturation. Some somatic cells possess a very low mtDNA copy number. We also demonstrated that PGCs have more than 100 mitochondria per cell. We conclude that the mitochondrial bottleneck is not due to a drastic decline in mtDNA copy number in early oogenesis but rather to a small effective number of segregation units for mtDNA in mouse germ cells. These results provide new information for mtDNA segregation models and for understanding the recurrence risks for mtDNA diseases.

Post-translational protein modifications are systems designed to expand restricted genomic information through functional conversion of target molecules. Ubiquitin-like post-translational modifiers regulate numerous cellular events through their covalent linkages to target protein(s) by an enzymatic cascade analogous to ubiquitylation consisting of E1 (activating), E2 (conjugating) and E3 (ligating) enzymes. In this study, we report the essential role of Uba5, a specific activating enzyme for the ubiquitin-like modifier, Ufm1, in erythroid development. Mice lacking Uba5 exhibited severe anaemia, followed by death in utero. Although Uba5 was dispensable for the production of erythropoietin, its genetic loss led to impaired development of megakaryocyte and erythroid progenitors from common myeloid progenitors. Intriguingly, transgenic expression of Uba5 in the erythroid lineage rescued the Uba5-deficient embryos from anaemia and prolonged their survival, demonstrating the importance of Uba5 in cell-autonomous erythroid differentiation. Our results suggest that one of the ubiquitin-like protein modification systems, the Ufm1 system, is involved in the regulation of haematopoiesis.

Oncostatin M (OSM) is a member of the interleukin‐6 (IL6)‐related cytokine subfamily that includes IL6, IL11, leukemia inhibitory factor (LIF), ciliary neurotrophic factor and cardiotrophin‐1. While human OSM has been characterized and the bovine OSM gene was recently cloned, the murine counterpart had not been identified. Here we describe molecular cloning of murine OSM as an immediate early gene induced by a subset of cytokines including IL2, IL3 and erythropoietin (EPO) in myeloid and lymphoid cell lines. The induction kinetics of OSM are rapid and transient, reaching a maximal level within 30–60 min and decreasing thereafter. Induction of OSM depends on the signals generated by the membrane‐proximal region of the EPO receptor as well as that of the beta chain of the IL3/GM‐CSF receptor, which activate JAK2 and STAT5. About 100 bases upstream of the transcription initiation site of the OSM gene contains a possible STAT5 binding site which is essential for IL2, IL3 and EPO‐dependent promoter activity of the OSM gene. Expression of STAT5 and the EPO receptor in COS cells conferred EPO‐dependent activation of the OSM promoter. Moreover, the mutant IL2 receptor lacking the ability to activate STAT5 induced c‐myc but failed to induce OSM. Thus OSM is one of the common targets of a subset of cytokines that activate STAT5. The murine OSM gene is located near to the LIF gene, expressed at high levels in bone marrow and possesses similar biological activity to human OSM. Identification of murine OSM as a cytokine‐inducible immediate early gene provides a new insight into the physiological function of this unique cytokine.

In obese individuals, white adipose tissue (WAT) is infiltrated by large numbers of macrophages, resulting in enhanced inflammatory responses that contribute to insulin resistance. Here we show that expression of the CXC motif chemokine ligand-14 (CXCL14), which targets tissue macrophages, is elevated in WAT of obese mice fed a high fat diet (HFD) compared with lean mice fed a regular diet. We found that HFD-fed CXCL14-deficient mice have impaired WAT macrophage mobilization and improved insulin responsiveness. Insulin-stimulated phosphorylation of Akt kinase in skeletal muscle was severely attenuated in HFD-fed CXCL14 ؉/؊ mice but not in HFD-fed CXCL14؊/؊ mice. The insulin-sensitive phenotype of CXCL14 ؊/؊ mice after HFD feeding was prominent in female mice but not in male mice. HFD-fed CXCL14 ؊/؊ mice were protected from hyperglycemia, hyperinsulinemia, and hypoadiponectinemia and did not exhibit increased levels of circulating retinol-binding protein-4 and increased expression of interleukin-6 in WAT. Transgenic overexpression of CXCL14 in skeletal muscle restored obesityinduced insulin resistance in CXCL14 ؊/؊ mice. CXCL14 attenuated insulin-stimulated glucose uptake in cultured myocytes and to a lesser extent in cultured adipocytes. These results demonstrate that CXCL14 is a critical chemoattractant of WAT macrophages and a novel regulator of glucose metabolism that functions mainly in skeletal muscle.