Brown dwarfs: At last filling the gap between stars and planets

Until the mid-1990s a person could not point to any celestial object and say with assurance that “here is a brown dwarf.” Now dozens are known, and the study of brown dwarfs has come of age, touching upon major issues in astrophysics, including the nature of dark matter, the properties of substellar objects, and the origin of binary stars and planetary systems.

A computer-based systematic survey reveals the predominance of small inverted-repeat elements in wild-type rice genes.

Several recent reports indicate that mobile elements are frequently found in and flanking many wild-type plant genes. To determine the extent of this association, we performed computer-based systematic searches to identify mobile elements in the genes of two "model" plants, Oryza sativa (domesticated rice) and Arabidopsis thaliana. Whereas 32 common sequences belonging to nine putative mobile element families were found in the noncoding regions of rice genes, none were found in Arabidopsis genes. Five of the nine families (Gaijin, Castaway, Ditto, Wanderer, and Explorer) are first described in this report, while the other four were described previously (Tourist, Stowaway, p-SINE1, and Amy/LTP). Sequence similarity, structural similarity, and documentation of past mobility strongly suggests that many of the rice common sequences are bona fide mobile elements. Members of four of the new rice mobile element families are similar in some respects to members of the previously identified inverted-repeat element families, Tourist and Stowaway. Together these elements are the most prevalent type of transposons found in the rice genes surveyed and form a unique collection of inverted-repeat transposons we refer to as miniature inverted-repeat transposable elements or MITEs. The sequence and structure of MITEs are clearly distinct from short or long interspersed nuclear elements (SINEs or LINEs), the most common transposable elements associated with mammalian nuclear genes. Mobile elements, therefore, are associated with both animal and plant genes, but the identity of these elements is strikingly different.

Learning and recall of form discriminations during reversible cooling deactivation of ventral-posterior suprasylvian cortex in the cat.

Extrastriate visual cortex of the ventral-posterior suprasylvian gyrus (vPS cortex) of freely behaving cats was reversibly deactivated with cooling to determine its role in performance on a battery of simple or masked two-dimensional pattern discriminations, and three-dimensional object discriminations. Deactivation of vPS cortex by cooling profoundly impaired the ability of the cats to recall the difference between all previously learned pattern and object discriminations. However, the cats' ability to learn or relearn pattern and object discriminations while vPS was deactivated depended upon the nature of the pattern or object and the cats' prior level of exposure to them. During cooling of vPS cortex, the cats could neither learn the novel object discriminations nor relearn a highly familiar masked or partially occluded pattern discrimination, although they could relearn both the highly familiar object and simple pattern discriminations. These cooling-induced deficits resemble those induced by cooling of the topologically equivalent inferotemporal cortex of monkeys and provides evidence that the equivalent regions contribute to visual processing in similar ways.