Cell adhesion molecules in the cadherin family have been implicated in histogenesis and maintenance of cellular structure and function in several organs. Zebrafish have emerged as an important new developmental model, but only three zebrafish cadherin molecules have been identified to date (N‐cadherin, paraxial protocadherin, and VN‐cadherin). We began a systematic study to identify other zebrafish cadherins by screening zebrafish cDNA libraries using an antibody raised to the cytoplasmic domain of mouse E‐cadherin. Here, we report a partial cDNA with extensive sequence homology to R‐cadherin. Spatial and temporal expression of this putative zebrafish R‐cadherin was examined in embryos and adults by Northern analysis, RNase protection, and in situ hybridization. R‐cadherin message increased during embryogenesis up to 80 hours postfertilization (hpf) and persisted in adults. In the embryonic brain, R‐cadherin was first expressed in groups of cells in the diencephalon and pretectum. In adult zebrafish brain, R‐cadherin continued to be expressed in several specific regions including primary visual targets. In the retina, R‐cadherin was first detected at about 33 hours postfertilization in the retinal ganglion cell layer and the inner part of the inner nuclear layer. Expression levels were highest during periods of axon outgrowth and synaptogenesis. Retrograde labeling of the optic nerve with 1,1′‐dioctadecyl‐3,3,3′,3′, tetramethylindocarbocyanine perchlorate (DiI) followed by in situ hybridization confirmed that a subset of retinal ganglion cells in the embryo expressed R‐cadherin message. In the adult, R‐cadherin expression continued in a subpopulation of retinal ganglion cells. These results suggest that R‐cadherin‐mediated adhesion plays a role in development and maintenance of neuronal connections in zebrafish visual system. J. Comp. Neurol. 410:303–319, 1999. © 1999 Wiley‐Liss, Inc.

Mechanisms underlying axonal pathfinding have been investigated for decades, and numerous molecules have been shown to play roles in this process, including members of the cadherin family of cell adhesion molecules. We showed in the companion paper that a member of the cadherin family (zebrafish R‐cadherin) is expressed in retinal ganglion cells, and in presumptive visual structures in zebrafish brain, during periods when the axons were actively extending toward their targets. The present study extends the earlier work by using 1,1′‐dioctadecyl‐3,3,3′,3′, tetramethylindocarbocyanine perchlorate (DiI) anterograde tracing techniques to label retinal ganglion cell axons combined with R‐cadherin in situ hybridization to explicitly examine the association of retinal axons and brain regions expressing R‐cadherin message. We found that in zebrafish embryos at 46–54 hours postfertilization, DiI‐labeled retinal axons were closely associated with cells expressing R‐cadherin message in the hypothalamus, the pretectum, and the anterolateral optic tectum. These results demonstrate that R‐cadherin is appropriately distributed to play a role in regulating development of the zebrafish visual system, and in particular, pathfinding and synaptogenesis of retinal ganglion cell axons. J. Comp. Neurol. 410:290–302, 1999. © 1999 Wiley‐Liss, Inc.

This article investigates the spatial poetics of disruption in Ubah Cristina Ali Farah's second novel Il comandante del fiume. The book sets a unique stage around fragmented flashbacks to resignify the configuration of Afro-Italian urban identity and community. These flashbacks are rendered through a complicated recoding of Rome's urbanscape by its protagonist, Yabar, a young Somali immigrant who experiences a mysterious disfigurement of his body and narrates his past as he recuperates in the hospital. The Black body thus becomes the primary shifting site through which new paradigms of spatial arrangements against power and authority are articulated. This article argues that, by having Yabar fantasize, observe, and live through Rome's urban physicality, Ali Farah delineates a poetics of disruption that functions to redraw the conceptual boundaries of Blackness and postcoloniality in contemporary Italy. Ali Farah's experiment with the city as an actual character de-romanticizes it as a historical fixed site, and instead displays the possibility of plurality in the shape of Black corporeal relationality in determined stances. In this novel, not as observed objects, the protagonists remap Rome as a Black city and carry forward a Benjaminian mode of flâneur to observe the city's fragmented and chaotic arrangements, demystifying its undercurrent construction of racial exclusion.