A new Cys2/His2 zinc finger gene, rKr1, expressed in oligodendrocytes and neurons

Induction of zinc-finger proliferation 1 expression in non-myelinating Schwann cells after denervation

Terminal Schwann cells (tSCs) are non-myelinating glia that wrap the nerve terminal at the neuromuscular junction. They are required for the maintenance of the neuromuscular synapse and are likely to play essential roles in the restoration of synaptic connections after nerve injury. tSCs acquire a reactive phenotype after nerve damage characterized by the extension of cellular processes that may facilitate reinnervation. The molecular signaling events underpinning the tSC reactive state remain elusive, in particular, little is known about transcription factors involved in the transcriptional reprogramming during tSC activation. Prior research implicated nine members of the zinc-finger transcription factor family in Schwann cell (SC) development and myelination, and levels of one such protein were reported increased in other non-myelinating SCs after denervation. We hypothesize that zinc-finger transcription factors could play a role during tSC activation. Because of their relative paucity, tSCs are difficult to study molecularly. Here, we used the rat cervical sympathetic trunk (CST), an autonomic nerve in which non-myelinating SCs are the predominant cell type, to isolate zinc-finger protein (ZFP) cDNAs by reverse transcriptase-polymerase chain reaction. We isolated 29 unique ZFP sequences of which zinc proliferation 1 (Zipro1) was the most abundant. We found that after CST transection, levels for Zipro1 mRNA doubled and that Zipro1 protein expression increased in non-myelinating CST SCs. We also determined that Zipro1 is expressed in tSCs and its levels increased following skeletal muscle denervation. Thus, Zipro1 is a good candidate for a transcription factor involved in activation of non-myelinating SCs in general, and tSCs in particular.

AP-1 activity during the growth, differentiation, and death of O-2A lineage cells

Oligodendrocyte differentiation has been correlated with AP-1 activity, being low in progenitors and high in differentiated cells. In this study we have carried out a detailed temporal analysis of AP-1 activity in oligodendrocyte-type-2 astrocyte (O-2A) lineage cells. We show that low AP-1 activity in progenitor cells depended on the application of growth factors. Treatment of cells with B104-conditioned medium induced high AP-1 activity, increased process length, and improved growth. The role of AP-1 in proliferation and process extension was emphasized when progenitor cells overexpressing a c-Jun dominant-negative mutant had impaired growth and shortened processes. AP-1 DNA-binding activity during O-2A differentiation in vitro showed an initial down-regulation followed by up-regulation after 2 days. Increased AP-1 levels in oligodendrocytes were inhibited by overexpression of bcl-2, indicating that AP-1 in mature oligodendrocytes is involved in the regulation of apoptosis. Prevention of cell death by bcl-2 in oligodendrocytes was accompanied by progressive differentiation and expression of MOG and PLP.

Chromosomal, in silico and in vitro expression analysis of cardiovascular-based genes encoding zinc finger proteins

Three hundred and sixty expressed sequence tags (ESTs) from human heart cDNA libraries corresponding to one hundred and twenty six unique zinc finger proteins (ZFPs) were annotated and classified into seven types of ZFPs as reported previously. Among these 126 cvbZFPs (cardiovascular-based ZFPs), the C(2)H(2)-type and the C(2)C(2)-type are the two major ZFP types which account for more than 80% of ZFP genes present in the cardiovascular system. The expression patterns of 11 randomly selected ZFP genes (at least one for each type) in normal fetal, adult and hypertrophic adult hearts, respectively, were determined using reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. The results suggest that ZFPs may be involved in the processes of either developmental control (downregulated or upregulated expression) or basic cellular functional regulation (constant expression). Interestingly, PAF-1 (peroxisome assembly factor-1), a C(3)HC(4)-type ZFP (RING domain-containing ZFP) showing a downregulated expression pattern in normal tissues was found to be upregulated in hypertrophic adult heart, suggesting a possible role for this fetal gene in the pathogenesis of cardiac hypertrophy. In silico Northern analysis of 15 tissues showed that over 90% of cvbZFPs demonstrate widespread tissue distribution, suggesting the vast majority of ZFPs are functionally shared among tissues. The potential importance of transcriptional repressors in cardiovascular development and disease, such as HFHZ, was supported by the observation that one-third (39 of 126) of cvbZFPs possess this function. Of these, 26 are C(2)H(2)-type and the remaining 13 included 8 C(2)C(2)-type, 1 C(3)HC(4)-type, 1 C(2)HC(4)C(HD)-type, 2 C(3)H-type and 1 combination type. Of particular interest was the observation that ZFPs which contain a KRAB domain are the major subtype present (51. 3% of the total repressors in cvbZFPs). Chromosomal distribution analysis showed that mapping loci of cvbZFP genes are concentrated on chromosomes 1, 3, 6, 8, 10, 11, 12, 19 and X. In particular, chromosome 19 appears to be enriched in ZFP genes with C(2)H(2)-type as the predominant type present. Overall, this report provides a fundamental initial step toward understanding the potential role of ZFPs in regulating cadiac development and disease.

Signals that initiate myelination in the developing mammalian nervous system

The myelination of axons by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system is essential for the establishment of saltatory conduction. In the absence or destruction of the myelin sheath, as seen in demyelinating diseases, impulse conduction is impeded resulting in severe sensory and motor deficits. Axon myelination is the culmination of a sequence of events that begins with the differentiation of glial cells and proceeds to the transcription and translation of myelin genes, the elaboration of a myelin sheath, and the recognition and ensheathment of axons. This review examines the regulatory mechanisms for each of these steps and compares and contrasts the role of the axon in initiating myelination in the central and peripheral nervous system.

Transcription of a new zinc finger gene, rKr1, is localized to subtypes of neurons in the adult rat CNS

Proteins which share zinc finger DNA binding motifs comprise one of the main families of transcription factors. We have previously described rKr1, a new rat Cys2/Hys2 zinc finger gene of the Krüppel gene family. This gene is predominantly expressed in the nervous system, with highest abundance in neurons and with lower abundance in developing oligodendrocytes of the CNS. Here, we have undertaken a detailed anatomical analysis of rKr1 expression in the adult brain of the rat using in situ hybridization. Our results show that rKr1 is expressed in a specific manner in defined subpopulations of neurons in many regions of the adult brain. Moderate levels of rKr1 mRNA were detectable in some structures of the telencephalon (e.g. cerebral cortex and hippocampus) and a few nuclei of the thalamus. The highest degree of labelling was seen in both upper and lower motor neurons of the mesencephalon and rhombencephalon (e.g. red nucleus, gigantocellular reticular nuclei, motor nuclei of the cranial nerves). High levels of rKr1 expression were also present in spinal motoneurons and dorsal root ganglion cells. In order to determine if rKr1 gene expression can be regulated, we have examined the expression pattern of rKr1 in the facial nucleus in response to facial nerve lesion. The expression of rKr1 in the facial nucleus showed a differential downregulation, reaching lowest levels 1 week after transection of the facial nerve. By 3 weeks after lesion, expression of rKr1 on the operated side of the brain reached normal levels and was identical to that of the unoperated side. These data suggest that rKr1 could be involved in the maintenance of the phenotypic differentiation of specific neuronal subtypes including motoneurons.