Twist1 and Twist2 are major regulators of embryogenesis. Twist1 has been shown to favor the metastatic dissemination of cancer cells through its ability to induce an epithelial-mesenchymal transition (EMT). Here, we show that a large fraction of human cancers overexpress Twist1 and/or Twist2. Both proteins override oncogene-induced premature senescence by abrogating key regulators of the p53- and Rb-dependent pathways. Twist1 and Twist2 cooperate with Ras to transform mouse embryonic fibroblasts. Interestingly, in epithelial cells, the oncogenic cooperation between Twist proteins and activated mitogenic oncoproteins, such as Ras or ErbB2, leads to complete EMT. These findings suggest an unanticipated direct link between early escape from failsafe programs and the acquisition of invasive features by cancer cells.

Microelectrode recordings were used to investigate the tonotopic organization of auditory cortex of macaque monkeys and guide the placement of injections of wheat germ agglutinin-horse radish peroxidase (WGA-HRP) and fluorescent dyes. Anatomical and physiological results were later related to histological distinctions in the same brains after sections were processed for cytoarchitecture, myeloarchitecture, acetylcholinesterase (AchE), or cytochrome oxidase (CO). The experiments produced several major findings. (1) Neurons throughout a broad expanse of cortex were highly responsive to pure tones, and best frequencies could be determined for neurons in arrays of recording sites. (2) The microelectrode recordings revealed two systematic representations of tone frequencies, the primary area (AI) and a primary-like rostral field (R) as previously described. The representation of high to low frequency tones in A1 was largely caudorostral along the plane of the sulcus. A reversal of the order of representation of frequencies occurred in R. (3) AI and R together were coextensive with a koniocellular, densely myelinated zone that expressed high levels of AchE and CO. These architectonic features were somewhat less pronounced in R than AI, but a clear border between the two areas was not apparent. (4) Cortex bordering AI and R was less responsive to tones, but when best frequencies for neurons could be determined, they matched those for adjoining parts of AI and R. (5) Architectonically distinct regions were apparent within some of the cortex bordering AI and R. (6) The major ipsilateral cortical connections of AI were with R and cortex immediately lateral and medial to AI. (7) Callosal connections of AI were predominantly with matched locations in the opposite AI, but they also included adjoining fields. (8) Neurons in the ventral (MGV), medial (MGM), and dorsal (MGD) nuclei of the medial geniculate complex projected to AI and cortex lateral to AI. (9) Injections in cortex responsive to high frequency tones labeled more dorsal parts of MGV than injections in cortex responsive to low frequency tones.

The primate visual system consists of at least two processing streams, one passing ventrally into temporal cortex that is responsible for object vision, and the other running dorsally into parietal cortex that is responsible for spatial vision. How information from these two streams is combined for perception and action is not understood. Visually guided eye movements require information about both feature identity and location, so we investigated the topographic organization of visual cortex connections with frontal eye field (FEF), the final stage of cortical processing for saccadic eye movements. Multiple anatomical tracers were placed either in parietal and temporal cortex or in different parts of FEF in individual macaque monkeys. Convergence from the dorsal and ventral processing streams occurred in lateral FEF but not in medial FEF. Certain extrastriate areas with retinotopic visual field organizations projected topographically onto FEF. The dorsal bank of the superior temporal sulcus projected to medial FEF; the ventral bank, to lateral FEF, and the fundus, throughout FEF. Thus, lateral FEF, which is responsible for generating short saccades, receives visual afferents from the foveal representation in retinotopically organized areas, from areas that represent central vision in inferotemporal cortex and from other areas having no retinotopic order. In contrast, medial FEF, which is responsible for generating longer saccades, is innervated by the peripheral representation of retinotopically organized areas, from areas that emphasize peripheral vision or are multimodal and from other areas that have no retinotopic order or are auditory.

To improve anatomical definition and stereotactic precision of thalamic targets in neurosurgical treatments of chronic functional disorders, a new atlas of the human thalamus has been developed. This atlas is based on multiarchitectonic parcellation in sections parallel or perpendicular to the standard intercommissural reference plane. The calcium-binding proteins parvalbumin (PV), calbindin D-28K (CB), and calretinin (CR) were used as neurochemical markers to further characterize thalamic nuclei and delimit subterritories of functional significance for stereotactic explorations. Their overall distribution reveals a subcompartmentalization of thalamic nuclei into several groups. Predominant PV immunostaining characterizes primary somatosensory, visual and auditory nuclei, the ventral lateral posterior nucleus, reticular nucleus (R), and to a lesser degree also, lateral part of the centre median nucleus, and anterior, lateral, and inferior divisions of the pulvinar complex. In contrast, CB immunoreactivity is prevalent in medial thalamic nuclei (intralaminar and midline), the posterior complex, ventral posterior inferior nucleus, the ventral lateral anterior nucleus, ventral anterior, and ventral medial nuclei. The complementary distributions of PV and CB appear to correlate with distinct lemniscal and spinothalamic somatosensory pathways and to cerebellar and pallidal motor territories, respectively. Calretinin, while overlapping with CB in medial thalamic territories, is also expressed in R and limbic associated anterior group nuclei that contain little or no CB. Preliminary analysis indicates that interindividual nuclear variations cannot easily be taken into account by standardization procedures. Nevertheless, some corrections in antero-posterior coordinates in relation to different intercommissural distances are proposed.

No abstract

Ribosomes are specialized entities that participate in regulation of gene expression through their rRNAs carrying ribozyme activity. Ribosome biogenesis is overactivated in p53-inactivated cancer cells, although involvement of p53 on ribosome quality is unknown. Here, we show that p53 represses expression of the rRNA methyl-transferase fibrillarin (FBL) by binding directly to FBL. High levels of FBL are accompanied by modifications of the rRNA methylation pattern, impairment of translational fidelity, and an increase of internal ribosome entry site (IRES)-dependent translation initiation of key cancer genes. FBL overexpression contributes to tumorigenesis and is associated with poor survival in patients with breast cancer. Thus, p53 acts as a safeguard of protein synthesis by regulating FBL and the subsequent quality and intrinsic activity of ribosomes.

No abstract

(2009