Neural regeneration and neuronal migration following injury. I. The endocrine hypothalamus and neurohypophyseal system

Central to this investigation are several basic hypotheses that are designed to test the role of nitric oxide (NO) in the complex process of central regeneration and plasticity in a well established model system of the mammalian brain. We have employed histochemical techniques at the light and ultrastructural level coupled with correlative scanning electron microscopy, immunoelectron microscopy, and in situ hybridization in order to determine the functional significance of the increased expression of nitric oxide synthase (NOS) in neurons of the supraoptic (SON) and paraventricular (PVN) nuclei which accompanies regeneration of their axotomized neurites following hypophysectomy, The aim of this investigation was to determine the potential role and temporal up-regulation of NOS in this basic regenerative process and to establish the ultrastructural and neuroanatomical correlates during critical periods of regeneration and regrowth of SON and PVN axons following hypophysectomy in the endocrine hypothalamus of the rat. Our data support the hypothesis that NO may serve as a second messenger molecule that may act in some fashion to govern not only the process of central regeneration and regrowth of magnocellular (SON/PVN) axons into the median eminence, neural stem, and neural lobe (the neurohypophyseal system) but may also influence the regeneration of neurites into new neuroanatomical domains such as the adjacent lumen of the third cerebral ventricle. We have demonstrated a distinct temporal relationship between injury (axotomy) of SON/PVN axons and the establishment of new neurovascular zones following hypophysectomy with the up-regulation of NOS. This up-regulation appears to correlate well with successful regeneration in the mammalian neurohypophyseal system. We have also successfully inhibited axonal regeneration with the use of nitroarginine, a competitive antagonist of NO. NOS up-regulation attendant to regeneration of SON and PVN axons may have inestimable clinical implications, particularly with respect to closed head injury and cerebral contusion that involves the mechanical shearing of the infundibular stalk. In addition, this investigation has reaffirmed that large numbers of bona fide neurons migrate and emerge upon the floor of the adjacent third cerebral ventricle shortly following hypophysectomy (within 2 weeks). The origin and mechanisms of neuronal migration and plasticity following hypophysectomy are the subject of interpretation and discussion in this investigation.link_to_subscribed_fulltex

Direct interaction of the human cytomegalovirus IE86 protein with the cis repression signal does not preclude TBP from binding to the TATA box.

The human cytomegalovirus major immediate-early gene encodes several protein isoforms which autoregulate the major immediate-early promoter (MIEP). One of these isoforms, the IE86 protein, represses the MIEP through a DNA sequence located between the TATA box and the transcription initiation site, designated the cis repression signal (crs). Through mutational analysis, amino acid domains within IE86 responsible for binding the crs element were located at the C terminus. Mutation of the putative zinc finger domain, which precluded IE86 from binding DNA, converted the protein from a repressor of MIEP transcription into an activator. DNase I protection analysis demonstrated that the IE86 footprint overlapped the sequence protected by the TATA-binding protein (TBP). Investigation of whether IE86 was able to displace TBP from DNA revealed that both proteins could bind DNA simultaneously. However, higher concentrations of IE86 were required to obtain protection of the crs element in the presence of prebound TBP. Similarly, higher concentrations of TBP were required to obtain protection in the presence of prebound IE86. These observations indicate that steric hinderance impairs but does not prevent both proteins from binding DNA synchronously