Ephrin-as guide the formation of functional maps in the visual cortex

Ephrin-As and their receptors, EphAs, are expressed in the developing cortex where they may act to organize thalamic inputs. Here, we map the visual cortex (V1) in mice deficient for ephrin-A2, -A3, and -A5 functionally, using intrinsic signal optical imaging and microelectrode recording, and structurally, by anatomical tracing of thalamocortical projections. V1 is shifted medially, rotated, and compressed and its internal organization is degraded. Expressing ephrin-A5 ectopically by in utero electroporation in the lateral cortex shifts the map of V1 medially, and expression within V1 disrupts its internal organization. These findings indicate that interactions between gradients of EphA/ephrin-A in the cortex guide map formation, but that factors other than redundant ephrin-As are responsible for the remnant map. Together with earlier work on the retinogeniculate map, the current findings show that the same molecular interactions may operate at successive stages of the visual pathway to organize maps.

Ephrin-As and neural activity are required for eye-specific patterning during retinogeniculate mapping

In mammals, retinal ganglion cell (RGC) projections initially intermingle and then segregate into a stereotyped pattern of eye-specific layers in the dorsal lateral geniculate nucleus (dLGN). Here we found that in mice deficient for ephrin-A2, ephrin-A3 and ephrin-A5, eye-specific inputs segregated but the shape and location of eye-specific layers were profoundly disrupted. In contrast, mice that lacked correlated retinal activity did not segregate eye-specific inputs. Inhibition of correlated neural activity in ephrin mutants led to overlapping retinal projections that were located in inappropriate regions of the dLGN. Thus, ephrin-As and neural activity act together to control patterning of eye-specific retinogeniculate layers.

Ephrin-A2 and -A5 influence patterning of normal and novel retinal projections to the thalamus: Conserved mapping mechanisms in visual and auditory thalamic targets

Sensory axons are targeted to modality-specific nuclei in the thalamus. Retinal ganglion cell axons project retinotopically to their principal thalamic target, the dorsal lateral geniculate nucleus (LGd), in a pattern likely dictated by the expression of molecular gradients in the LGd. Deafferenting the auditory thalamus induces retinal axons to innervate the medial geniculate nucleus (MGN). These retino-MGN projections also show retinotopic organization. Here we show that ephrin-A2 and -A5, which are expressed in similar gradients in the MGN and LGd, can be used to pattern novel retinal projections in the MGN. As in the LGd, retinal axons from each eye terminate in discrete eye-specific zones in the MGN of rewired wild-type and ephrin-A2/A5 knockout mice. However, ipsilateral eye axons, which arise from retinal regions of high EphA5 receptor expression and represent central visual field, terminate in markedly different ways in the two mice. In rewired wild-type mice, ipsilateral axons specifically avoid areas of high ephrin expression in the MGN. In rewired ephrin knockout mice, ipsilateral projections shift in location and spread more broadly, leading to an expanded representation of the ipsilateral eye in the MGN. Similarly, ipsilateral projections to the LGd in ephrin knockout mice are shifted and are more widespread than in the LGd of wild-type mice. In the MGN, as in the LGd, terminations from the two eyes show little overlap even in the knockout mice, suggesting that local interocular segregation occurs regardless of other patterning determinants. Our data demonstrate that graded topographic labels, such as the ephrins, can serve to shape multiple related aspects of afferent patterning, including topographic mapping and the extent and spread of eye-specific projections. Furthermore, when mapping labels and other cues are expressed in multiple target zones, novel projections are patterned according to rules that operate in their canonical targets.

Defective production of functional 98-kDa form of Elf-1 is responsible for the decreased expression of TCR zeta-chain in patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE), the prototypic autoimmune disease, is characterized by defective expression of TCR zeta-chain. Elf-1 (E-74-like factor) is a member of the Ets (E-26-specific) family and is crucial for the basal transcription of TCR zeta-chain in Jurkat cells. We previously demonstrated that Elf-1 exists in the cytoplasm mainly as 80-kDa form and after phosphorylation and O-glycosylation it moves to the nucleus as a 98-kDa which binds DNA. We now demonstrate that Elf-1 is crucial for the transactivation of TCR zeta-chain promoter in normal and SLE T cells. Defective expression of TCR zeta-chain in SLE T cells is associated with two distinct molecular defects in the generation of the 98-kDa DNA binding Elf-1 form. In the first, the levels of the 98-kDa form were either decreased or absent. In the second, the apparent levels of the nuclear Elf-1 form were normal but included only two of the three bands into which the nuclear Elf-1 form separated in isoelectric focusing gels. Because both the transcription and the translation processes of Elf-1 gene are normal in SLE T cells, our data demonstrate that abnormal posttranslational mechanisms of the Elf-1 protein result in defective expression of functional Elf-1, and consequently, the transcriptional defect of TCR zeta-chain in patients of SLE.