We have used in situ hybridization histochemistry to examine the cellular sites of synthesis of two major nervous tissue proteoglycans, neurocan and phosphacan, in embryonic and postnatal rat brain and spinal cord. Both proteoglycans were detected only in nervous tissue. Neurocan mRNA was evident in neurons, including cerebellar granule cells and Purkinje cells, and in neurons of the hippocampal formation and cerebellar nuclei. In contrast, phosphacan message was detected only in astroglia, such as the Golgi epithelial cells of the cerebellum. At embryonic day 13-16, phosphacan mRNA is largely confined to areas of active cell proliferation (e.g., the ventricular zone of the ganglionic eminence and septal area of the brain and the ependymal layer surrounding the central canal of the spinal cord) as well as being present in the roof plate. The distribution of neurocan message is more widespread, extending to the cortex, hippocampal formation, caudate putamen, and basal telencephalic neuroepithelium, and neurocan mRNA is present in both the ependymal and mantle layers of the spinal cord but not in the roof plate. The presence of neurocan mRNA in areas where the proteoglycan is not expressed suggests that the short open reading frame in the 5'-leader of neurocan may function as a cis-acting regulatory signal for the modulation of neurocan expression in the developing central nervous system.

Tomato yields from fields and greenhouses are often reduced due to virus infection. In a number of cases, geminiviruses have been identified as the disease-causing agents. Geminiviruses are small plant viruses with circular single-stranded DNA (ssDNA) genomes encapsidated in twinned (geminate) particles (Harrison, 1985). Members have been divided into three subgroups on the basis of their genome organization and host range (Murphy et al., 1995). Members of the genus Begomovirus (previously known as subgroup III)

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The production of pseudorecombinant viruses following exchange of cloned genomic components of the distinct geminiviruses Sida golden mosaic virus (SiGMV-Co) and Abutilon mosaic virus (AbMV) has been investigated. The pseudorecombinant virus produced by DNA A of AbMV and DNA B of SiGMV-Co was infectious in various host plants, although showing a limited host range compared with the two parental viruses. The reciprocal exchange of genomic components did not result in an infectious pseudorecombinant virus. However, in leaf disks SiGMV-Co DNA A was able to trans-replicate the heterogenomic AbMV DNA B component.