MicroRNAs Modulate Hematopoietic Lineage Differentiation

MicroRNAs (miRNAs), an abundant class of ~22 nucleotide non-coding RNAs, are thought to play an important regulatory role in animal and plant development at the posttranscriptional level. Many miRNAs cloned from mouse bone marrow cells are differentially regulated in various hematopoietic lineages, suggesting that they might influence hematopoietic lineage differentiation. Some human miRNAs are linked to leukemias: the miR-15a/miR-16 locus is frequently deleted or down-regulated in patients with B-cell chronic lymphocytic leukemia and miR-142 is at a translocation site found in a case of aggressive B-cell leukemia. miR-181, a miRNA upregulated only in the B cell lineage of mouse bone marrow cells, promotes B cell differentiation and inhibits production of CD8⁺ T cells when expressed in hematopoietic stem/progenitor cells. In contrast miR-142s inhibits production of both CD4⁺ and CD8⁺ T cells and does not affect B cells. Collectively, these results indicate that microRNAs are components of the molecular circuitry controlling mouse hematopoiesis and suggest that other microRNAs have similar regulatory roles during other facets of vertebrate development.

Dissociated Dipoles: Image representation via non-local comparisons

A fundamental question in visual neuroscience is how to represent image structure. The most common representational schemes rely on differential operators that compare adjacent image regions. While well-suited to encoding local relationships, such operators have significant drawbacks. Specifically, each filter's span is confounded with the size of its sub-fields, making it difficult to compare small regions across large distances. We find that such long-distance comparisons are more tolerant to common image transformations than purely local ones, suggesting they may provide a useful vocabulary for image encoding. . We introduce the "Dissociated Dipole," or "Sticks" operator, for encoding non-local image relationships. This operator de-couples filter span from sub-field size, enabling parametric movement between edge and region-based representation modes. We report on the perceptual plausibility of the operator, and the computational advantages of non-local encoding. Our results suggest that non-local encoding may be an effective scheme for representing image structure.