The ob gene product, leptin, is an important circulating signal for the regulation of body weight. To identify high affinity leptin-binding sites, we generated a series of leptin-alkaline phosphatase (AP) fusion proteins as well as [125I]leptin. After a binding survey of cell lines and tissues, we identified leptin-binding sites in the mouse choroid plexus. A cDNA expression library was prepared from mouse choroid plexus and screened with a leptin-AP fusion protein to identify a leptin receptor (OB-R). OB-R is a single membrane-spanning receptor most related to the gp130 signal-transducing component of the IL-6 receptor, the G-CSF receptor, and the LIF receptor. OB-R mRNA is expressed not only in choroid plexus, but also in several other tissues, including hypothalamus. Genetic mapping of the gene encoding OB-R shows that it is within the 5.1 cM interval of mouse chromosome 4 that contains the db locus.

While many individual transcription factors are known to regulate hematopoietic differentiation, major aspects of the global architecture of hematopoiesis remain unknown. Here, we profiled gene expression in 38 distinct purified populations of human hematopoietic cells and used probabilistic models of gene expression and analysis of cis-elements in gene promoters to decipher the general organization of their regulatory circuitry. We identified modules of highly co-expressed genes, some of which are restricted to a single lineage, but most are expressed at variable levels across multiple lineages. We found densely interconnected cis-regulatory circuits and a large number of transcription factors that are differentially expressed across hematopoietic states. These findings suggest a more complex regulatory system for hematopoiesis than previously assumed.

Congenic breeding strategies are becoming increasingly important as a greater number of complex trait linkages are identified. Traditionally, the development of a congenic strain has been a time-consuming endeavour, requiring ten generations of backcrosses. The recent advent of a dense molecular genetic map of the mouse permits methods that can reduce the time needed for congenic-strain production by 18-24 months. We present a theoretical evaluation of marker-assisted congenic production and provide the empirical data that support it. We present this 'speed congenic' method in a user-friendly manner to encourage other investigators to pursue this or similar methods of congenic production.

No abstract

After antigen encounter, naive lymphocytes differentiate into populations of memory cells that share a common set of functions including faster response to antigen re-exposure and the ability to self-renew. However memory lymphocytes in different lymphocyte lineages are functionally and phenotypically diverse. It is not known whether discrete populations of T and B cells use similar transcriptional programs during differentiation into the memory state. We used cross-species genomic analysis to examine the pattern of genes upregulated during the differentiation of naive lymphocytes into memory cells in multiple populations of human CD4, CD8 and B cell lymphocytes as well as two mouse models of memory development. We identified and validated a signature of genes that was upregulated in memory cells compared to naive cells in both human and mouse CD8 memory differentiation, suggesting marked evolutionary conservation of this transcriptional program. Surprisingly, this conserved CD8 differentiation signature was also upregulated during memory differentiation in CD4 and B cell lineages. To validate the biologic significance of this signature we showed that alterations in this signature of genes could distinguish between functional and exhausted CD8 T cells from a mouse model of chronic viral infection. Finally, we generated genome-wide microarray data from tetramer-sorted human T cells and showed profound differences in this differentiation signature between T cells specific for HIV from those specific for influenza. Thus, our data suggest that in addition to lineage-specific differentiation programs, T and B lymphocytes employ a common transcriptional program during memory development that is disrupted in chronic viral infection.