An expression atlas of connexin genes in the mouse

Pathological mechanisms of connexin26-related hearing loss: Potassium recycling, ATP-calcium signaling, or energy supply?

Hereditary deafness is one of the most common human birth defects. GJB2 gene mutation is the most genetic etiology. Gap junction protein 26 (connexin26, Cx26) encoded by the GJB2 gene, which is responsible for intercellular substance transfer and signal communication, plays a critical role in hearing acquisition and maintenance. The auditory character of different Connexin26 transgenic mice models can be classified into two types: profound congenital deafness and late-onset progressive hearing loss. Recent studies demonstrated that there are pathological changes including endocochlear potential reduction, active cochlear amplification impairment, cochlear developmental disorders, and so on, in connexin26 deficiency mice. Here, this review summarizes three main hypotheses to explain pathological mechanisms of connexin26-related hearing loss: potassium recycling disruption, adenosine-triphosphate-calcium signaling propagation disruption, and energy supply dysfunction. Elucidating pathological mechanisms underlying connexin26-related hearing loss can help develop new protective and therapeutic strategies for this common deafness. It is worthy of further study on the detailed cellular and molecular upstream mechanisms to modify connexin (channel) function.

The Interplay of Cx26, Cx32, Cx37, Cx40, Cx43, Cx45, and Panx1 in Inner-Ear Development of Yotari (dab1−/−) Mice and Humans

We investigated DAB1-protein deficiency in the inner-ear development of yotari in comparison to humans and wild-type (wt) mice by immunofluorescence for the expression of connexins (Cxs) and the pannexin Panx1. The spatial and temporal dynamics of Cx26, Cx32, Cx37, Cx40, Cx43, Cx45, and Panx1 were determined in the sixth and eighth weeks of human development and at the corresponding mouse embryonic E13.5 and E15.5, in order to examine gap junction intercellular communication (GJIC) and hemichannel formation. The quantification of the area percentage covered by positive signal was performed for the epithelium and mesenchyme of the cochlear and semicircular ducts and is expressed as the mean ± SD. The data were analysed by one-way ANOVA. Almost all of the examined Cxs were significantly decreased in the cochlear and semicircular ducts of yotari compared to wt and humans, except for Cx32, which was significantly higher in yotari. Cx40 dominated in human inner-ear development, while yotari and wt had decreased expression. The Panx1 expression in yotari was significantly lower than that in the wt and human inner ear, except at E13.5 in the mesenchyme of the wt and epithelium and mesenchyme of humans. Our results emphasize the relevance of GJIC during the development of vestibular and cochlear functions, where they can serve as potential therapeutic targets in inner-ear impairments.

Role of Connexins 30, 36, and 43 in Brain Tumors, Neurodegenerative Diseases, and Neuroprotection

Gap junction (GJ) channels and their connexins (Cxs) are complex proteins that have essential functions in cell communication processes in the central nervous system (CNS). Neurons, astrocytes, oligodendrocytes, and microglial cells express an extraordinary repertory of Cxs that are important for cell to cell communication and diffusion of metabolites, ions, neurotransmitters, and gliotransmitters. GJs and Cxs not only contribute to the normal function of the CNS but also the pathological progress of several diseases, such as cancer and neurodegenerative diseases. Besides, they have important roles in mediating neuroprotection by internal or external molecules. However, regulation of Cx expression by epigenetic mechanisms has not been fully elucidated. In this review, we provide an overview of the known mechanisms that regulate the expression of the most abundant Cxs in the central nervous system, Cx30, Cx36, and Cx43, and their role in brain cancer, CNS disorders, and neuroprotection. Initially, we focus on describing the Cx gene structure and how this is regulated by epigenetic mechanisms. Then, the posttranslational modifications that mediate the activity and stability of Cxs are reviewed. Finally, the role of GJs and Cxs in glioblastoma, Alzheimer's, Parkinson's, and Huntington's diseases, and neuroprotection are analyzed with the aim of shedding light in the possibility of using Cx regulators as potential therapeutic molecules.

Structure and Function of Cochlear Gap Junctions and Implications for the Translation of Cochlear Gene Therapies

Connexins (Cxs) are ubiquitous membrane proteins that are found throughout vertebrate organs, acting as building blocks of the gap junctions (GJs) known to play vital roles in the normal function of many organs. Mutations in Cx genes (particularly GJB2, which encodes Cx26) cause approximately half of all cases of congenital hearing loss in newborns. Great progress has been made in understanding GJ function and the molecular mechanisms for the role of Cxs in the cochlea. Data reveal that multiple types of Cxs work together to ensure normal development and function of the cochlea. These findings include many aspects not proposed in the classic K+ recycling theory, such as the formation of normal cochlear morphology (e.g., the opening of the tunnel of Corti), the fine-tuning of the innervation of nerve fibers to the hair cells (HCs), the maturation of the ribbon synapses, and the initiation of the endocochlear potential (EP). New data, especially those collected from targeted modification of major Cx genes in the mouse cochlea, have demonstrated that Cx26 plays an essential role in the postnatal maturation of the cochlea. Studies also show that Cx26 and Cx30 assume very different roles in the EP generation, given that only Cx26 is required for normal hearing. This article will review our current understanding of the molecular structure, cellular distribution, and major functions of cochlear GJs. Potential implications of the knowledge of cochlear GJs on the design and implementation of translational studies of cochlear gene therapies for Cx mutations are also discussed.

Inner Ear Connexin Channels: Roles in Development and Maintenance of Cochlear Function

Connexin 26 and connexin 30 are the prevailing isoforms in the epithelial and connective tissue gap junction systems of the developing and mature cochlea. The most frequently encountered variants of the genes that encode these connexins, which are transcriptionally coregulated, determine complete loss of protein function and are the predominant cause of prelingual hereditary deafness. Reducing connexin 26 expression by Cre/loxP recombination in the inner ear of adult mice results in a decreased endocochlear potential, increased hearing thresholds, and loss of >90% of outer hair cells, indicating that this connexin is essential for maintenance of cochlear function. In the developing cochlea, connexins are necessary for intercellular calcium signaling activity. Ribbon synapses and basolateral membrane currents fail to mature in inner hair cells of mice that are born with reduced connexin expression, even though hair cells do not express any connexin. In contrast, pannexin 1, an alternative mediator of intercellular signaling, is dispensable for hearing acquisition and auditory function.

Transplanting mouse induced pluripotent stem cells into mouse otocysts in vivo

The otocyst is an attractive target for studying treatment strategies for genetic hearing loss and for understanding inner ear development. We have previously reported that trans-uterine supplemental gene therapy in vivo into the otocysts of mice, which had a loss of function mutation in a causative gene of deafness, was able to prevent putative hearing loss. We herein set out to clarify the feasibility of allogenic cell transplantation into the mouse otocysts in vivo. We transplanted naive mouse-derived induced pluripotent stem cells (miPSCs) into the otocysts of wild type mice or connexin (Cx) 30 deficient mice, at embryonic day 11.5 (E11.5). The transplanted m-iPSCs survived in the lumens of the inner ears at E13.5 and E15.5 in wild type mice. In the Cx30 deficient mouse, the transplanted cells survived similarly, with some of the transplanted cells migrating into the lining cells of the lumens of the inner ears at E13.5 and showing tumorigenic cell proliferation at E15.5. In addition, engrafted cells appear to be able to differentiate after the cell transplantation. Our results suggest that otocyst transplanted cells survived and differentiated. A Cx30 deficiency may facilitate cell migration. These findings may offer some hope for cell transplantation therapy for profound genetic hearing loss caused by a Cxs deficiency.

Conserved glycine at position 45 of major cochlear connexins constitutes a vital component of the Ca²⁺ sensor for gating of gap junction hemichannels

Mutations in gap junction (GJ) family of proteins, especially in the connexin (Cx) 26, are responsible for causing severe congenital hearing loss in a significant portion of patients (30-50% in various ethnic groups). Substitution of glycine at the position 45 of Cx26 to glutamic acid (p.G45E mutation) causes the Keratitis-ichthyosis-deafness (KID) syndrome. Previous studies have suggested that this point mutation caused a gain-of-function defect. However, the molecular mechanism of KID syndrome remains unclear. Since glycine at this position is conserved in many Cxs expressed in the cochlea, we tested the hypothesis that glycine at position 45 is an important component of the sensor regulating the Ca(2+) gating of GJ hemichannels. Using reconstituted Cx30, 32 and 43 expressed in the HEK 293 cells, we compared the functions of wild type and p.G45E mutant Cxs. We found that G45E in Cx30 resulted in similar deleterious cellular effects as Cx26 did. Cell death occurred within 24h of transfection, which was rescued by increasing extracellular Ca(2+) concentration ([Ca(2+)]o). Dye loading assay showed that Cx30 G45E, similar to Cx26 G45E, had leaky hemichannels at physiological [Ca(2+)]o (1.2 mM). Higher [Ca(2+)]o reduced the dye loading in a dose-dependent manner. Whole cell membrane current recordings also indicated that G45E caused increased hemichannel activities. p.G45E mutations of Cx32 and 43 also resulted in leaky hemichannels compared to their respective wild types in lower [Ca(2+)]o. Our data in this study provided further support for the hypothesis that glycine at position 45 is a conserved Ca(2+) sensor for the gating of GJ hemichannels among multiple Cx subtypes expressed in the cochlea.

Headbobber: a combined morphogenetic and cochleosaccular mouse model to study 10qter deletions in human deafness

The recessive mouse mutant headbobber (hb) displays the characteristic behavioural traits associated with vestibular defects including headbobbing, circling and deafness. This mutation was caused by the insertion of a transgene into distal chromosome 7 affecting expression of native genes. We show that the inner ear of hb/hb mutants lacks semicircular canals and cristae, and the saccule and utricle are fused together in a single utriculosaccular sac. Moreover, we detect severe abnormalities of the cochlear sensory hair cells, the stria vascularis looks severely disorganised, Reissner's membrane is collapsed and no endocochlear potential is detected. Myo7a and Kcnj10 expression analysis show a lack of the melanocyte-like intermediate cells in hb/hb stria vascularis, which can explain the absence of endocochlear potential. We use Trp2 as a marker of melanoblasts migrating from the neural crest at E12.5 and show that they do not interdigitate into the developing strial epithelium, associated with abnormal persistence of the basal lamina in the hb/hb cochlea. We perform array CGH, deep sequencing as well as an extensive expression analysis of candidate genes in the headbobber region of hb/hb and littermate controls, and conclude that the headbobber phenotype is caused by: 1) effect of a 648 kb deletion on distal Chr7, resulting in the loss of three protein coding genes (Gpr26, Cpmx2 and Chst15) with expression in the inner ear but unknown function; and 2) indirect, long range effect of the deletion on the expression of neighboring genes on Chr7, associated with downregulation of Hmx3, Hmx2 and Nkx1.2 homeobox transcription factors. Interestingly, deletions of the orthologous region in humans, affecting the same genes, have been reported in nineteen patients with common features including sensorineural hearing loss and vestibular problems. Therefore, we propose that headbobber is a useful model to gain insight into the mechanisms underlying deafness in human 10qter deletion syndrome.

The role of connexins in ear and skin physiology - functional insights from disease-associated mutations

Defects in several different connexins have been associated with several different diseases. The most common of these is deafness, where a few mutations in connexin (Cx) 26 have been found to contribute to over 50% of the incidence of non-syndromic deafness in different human populations. Other mutations in Cx26 or Cx30 have also been associated with various skin phenotypes linked to deafness (palmoplanta keratoderma, Bart-Pumphrey syndrome, Vohwinkel syndrome, keratitis-ichthyosis-deafness syndrome, etc.). The large array of disease mutants offers unique opportunities to gain insights into the underlying function of gap junction proteins and their channels in the normal and pathogenic physiologies of the cochlea and epidermis. This review focuses on those mutants where the impact on channel function has been assessed, and correlated with the disease phenotype, or organ function in knock-out mouse models. These approaches have provided evidence supporting a role of gap junctions and hemichannels in K(+) removal and recycling in the ear, as well as possible roles for nutrient passage, in the cochlea. In contrast, increases in hemichannel opening leading to increased cell death, were associated with several keratitis-ichthyosis-deafness syndrome skin disease/hearing mutants. In addition to providing clues for therapeutic strategies, these findings allow us to better understand the specific functions of connexin channels that are important for normal tissue function. This article is part of a Special Issue entitled: The communicating junctions, roles and dysfunctions.

Gap junctions/hemichannels modulate interkinetic nuclear migration in the forebrain precursors

During mitotic division in the telencephalic proliferative ventricular zone (VZ), the nuclei of the neural precursors move basally away from the ventricular surface for DNA synthesis, and apically return to the surface for mitotic division; a process known as interkinetic migration or "to-and-fro" nuclear translocation. The cell, which remains attached to the ventricular surface, either continues cycling, or exits the cycle and migrates to the subventricular zone or the developing cortical plate. Although gap junctions/hemichannels are known to modulate DNA synthesis via Ca(2+) waves, the role of Ca(+) oscillations and the mechanism of nuclear translocation in the VZ precursors are unclear. Here, we provide evidence that, during apical nuclear migration, VZ precursors display dynamic spontaneous Ca(2+) transients, which depend on functional gap junctions/hemichannels via ATP release and Ca(2+)-mobilizing messenger diffusion. Furthermore, we found that blocking gap junctions/hemichannels or short hairpin RNA-mediated knockdown of Cx43 (connexin 43) retards the apically directed interkinetic nuclear migration accompanied with changes in the nuclear length/width ratio. In addition, we demonstrated that blocking functional gap junctions/hemichannels induces phosphorylation of small GTPase cdc42 in the VZ precursors. The basal phase of interkinetic migration is much slower and appears to be mediated passively by mechanical forces after cell division. Our findings indicate that functional interference with gap junctions/hemichannels during embryonic development may lead to abnormal corticogenesis and dysfunction of the cerebral cortex in adult organisms.

Diverse deafness mechanisms of connexin mutations revealed by studies using in vitro approaches and mouse models

Mutations in connexins (Cxs), the constitutive protein subunits of gap junction (GJ) intercellular channels, are one of the most common human genetic defects that cause severe prelingual non-syndromic hearing impairments. Many subtypes of Cxs (e.g., Cxs 26, 29, 30, 31, 43) and pannexins (Panxs) are expressed in the cochlea where they contribute to the formation of a GJ-based intercellular communication network. Cx26 and Cx30 are the predominant cochlear Cxs and they co-assemble in most GJ plaques to form hybrid GJs. The cellular localization of specific Cx subtypes provides a basis for understanding the molecular structure of GJs and hemichannels in the cochlea. Information about the interactions among the various co-assembled Cx partners is critical to appreciate the functional consequences of various types of genetic mutations. In vitro studies of reconstituted GJs in cell lines have yielded surprisingly heterogeneous mechanisms of dysfunction caused by various Cx mutations. Availability of multiple lines of Cx-mutant mouse models has provided some insight into the pathogenesis processes in the cochlea of deaf mice. Here we summarize recent advances in understanding the structure and function of cochlear GJs and give a critical review of current findings obtained from both in vitro studies and mouse models on the mechanisms of Cx mutations that lead to cell death in the cochlea and hearing loss.

Charcot-Marie-Tooth disease: a clinico-genetic confrontation

Charcot-Marie-Tooth disease (CMT) is the most common neuromuscular disorder. It represents a group of clinically and genetically heterogeneous inherited neuropathies. Here, we review the results of molecular genetic investigations and the clinical and neurophysiological features of the different CMT subtypes. The products of genes associated with CMT phenotypes are important for the neuronal structure maintenance, axonal transport, nerve signal transduction and functions related to the cellular integrity. Identifying the molecular basis of CMT and studying the relevant genes and their functions is important to understand the pathophysiological mechanisms of these neurodegenerative disorders, and the processes involved in the normal development and function of the peripheral nervous system. The results of molecular genetic investigations have impact on the appropriate diagnosis, genetic counselling and possible new therapeutic options for CMT patients.

Mutations in splicing factor PRPF3, causing retinal degeneration, form detrimental aggregates in photoreceptor cells

PRPF3 is an element of the splicing machinery ubiquitously expressed, yet mutations in this gene are associated with a tissue-specific phenotype: autosomal dominant retinitis pigmentosa (RP). Here, we studied the subcellular localization of endogenous- and mutant-transfected PRPF3. We found that (i) subcellular distribution of the endogenous wild-type protein co-localizes with small nuclear ribonucleoproteins, partially with a nucleolar marker and accumulates in speckles labeled by SC35; (ii) in human retinas, PRPF3 does not show a distinctive abundance in photoreceptors, the cells affected in RP and (iii) the RP causing mutant PRPF3, differently from the wild-type protein, forms abnormally big aggregates in transfected photoreceptor cells. Aggregation of T494M mutant PRPF3 inside the nucleus triggers apoptosis only in photoreceptor cells. On the basis of the observation that mutant PRPF3 accumulates in the nucleolus and that transcriptional, translational and proteasome inhibition can induce this phenomenon in non-photoreceptor cells, we hypothesize that mutation affects splicing factor recycling. Noteworthy, accumulation of the mutant protein in big aggregates also affects distribution of some other splicing factors. Our data suggest that the mutant protein has a cell-specific dominant effect in rod photoreceptors while appears not to be harmful to epithelial and fibroblast cells.

The effects of a dominant connexin32 mutant in myelinating Schwann cells

Mutations in GJB1, the gene encoding the gap junction protein connexin32 (Cx32), cause X-linked Charcot-Marie-Tooth disease, an inherited demyelinating peripheral neuropathy. We generated transgenic mice that express the R142W mutation in myelinating Schwann cells. The R142W mutant protein was aberrantly localized to the Golgi, indicating that it does not traffic properly, but the molecular organization of the myelin sheath, including the localization of Cx29, another connexin expressed by myelinating Schwann cells, was not disrupted. In a wild type background, this mutation dramatically decreased the level of wild type mouse Cx32 in immunoblots of sciatic nerve and caused demyelination. The expression of wild type human Cx32 with the same transgenic construct had different effects-increased amounts of Cx32, normal localization of Cx32 at nodes and incisures, and split myelin sheaths. Thus, the R142W mutant protein has dominant effects that are distinct from overexpression.

Molecular characterization of a t(2;6) balanced translocation that is associated with a complex phenotype and leads to truncation of the TCBA1 gene

The molecular characterization of balanced chromosomal rearrangements has often been a powerful tool for the positional identification of genes associated with specific diseases. In some instances, these rearrangements may be associated with a variety of different phenotypes, and thus establishing a genotype-phenotype correlation may be a complex process. However, molecular characterization of the rearrangement remains a useful tool for diagnoses or prognoses, or for identifying new genes and establishing a gene-to-function relationship. In this work we describe the characterization of a de novo balanced translocation t(2;6)(q24.3;q22.31) found in a patient with a complex phenotype. The major clinical finding was a severe neurological involvement. Thanks to the molecular characterization of this translocation we found that the rearrangement led to the truncation of the TCBA1 gene on chromosome 6q. We found that the gene is transcribed in different splice variants and is highly specific for the central nervous system. TCBA1 does not show any similarity with other known genes, and no information is available about its function. However, the gene appears to be well conserved among species, and we were able to infer the sequence of a putative mouse homolog of TCBA1. This allowed us to perform a more detailed expression study in mice, thus confirming its specificity for the nervous system. This finding is of particular interest because it suggests that TCBA1 may be correlated with the neurological phenotype of our patient, and possibly mutated in genetic diseases with a neurological phenotype.

Cord blood in vitro expanded CD41 cells: identification of novel components of megakaryocytopoiesis

BACKGROUND

Megakaryopoiesis represents a multi-step, often unclear, process leading to commitment, differentiation, and maturation of megakaryocytes (MKs) that release platelets.

AIM

To identify the novel genes that might help to clarify the molecular mechanisms of megakaryocytopoiesis and be regarded as potential candidates of inherited platelet defects, global gene expression of hematopoietic lineages was carried out.

METHODS

Human cord blood was used to purify CD34+ stem cells and in vitro expand CD41+ cells and burst-forming unit-erythroid (BFU-E). We investigated the expression profiles of these three hematopoietic lineages in the Affymetrix system and selected genes specifically expressed in MKs by comparing transcripts of the different lineages using the dchip and pam algorithms.

RESULTS

A detailed characterization of MK population showed that 99% of cells expressed the CD41 antigen whereas 73% were recognizable as terminally differentiated fetal MKs. The profile of these cells was compared with that of CD34+ cells and BFU-E allowing us to select 70 transcripts (MK-core), which represent not only the genes with a well-known function in MKs, but also novel genes never detected or characterized in these cells. Moreover, the specific expression was confirmed at both RNA and protein levels, thus validating the 'MK-core' isolated by informatics tools.

CONCLUSIONS

This is a global gene expression that for the first time depicts a well-characterized population of cord blood-derived fetal MKs. Novel genes have been detected, such as those encoding components of the extracellular matrix and basal membrane, which have been found in the cytoplasm of Mks, suggesting that new physiological aspects of MKs should be studied.

Gap junctions and cochlear homeostasis

Gap junctions play a critical role in hearing and mutations in connexin genes cause a high incidence of human deafness. Pathogenesis mainly occurs in the cochlea, where gap junctions form extensive networks between non-sensory cells that can be divided into two independent gap junction systems, the epithelial cell gap junction system and the connective tissue cell gap junction system. At least four different connexins have been reported to be present in the mammalian inner ear, and gap junctions are thought to provide a route for recycling potassium ions that pass through the sensory cells during the mechanosensory transduction process back to the endolymph. Here we review the cochlear gap junction networks and their hypothesized role in potassium ion recycling mechanism, pharmacological and physiological gating of cochlear connexins, animal models harboring connexin mutations and functional studies of mutant channels that cause human deafness. These studies elucidate gap junction functions in the cochlea and also provide insight for understanding the pathogenesis of this common hereditary deafness induced by connexin mutations.

Molecular genetics of X-linked Charcot-Marie-Tooth disease

The X-linked form of Charcot-Marie-Tooth disease (CMT1X) is the second most common molecularly designated form of hereditary motor and sensory neuropathy. The clinical phenotype is characterized by progressive distal muscle atrophy and weakness, areflexia, and variable sensory abnormalities. Affected males have moderate-to-severe symptoms, whereas heterozygous females are usually mildly affected or even asymptomatic. Several patients also have manifestations of central nervous system involvement or hearing impairment. Electrophysiological and pathological studies of peripheral nerves show evidence of demyelinating neuropathy with prominent axonal degeneration. A large number of mutations in the GJB1 gene encoding the gap junction (GJ) protein connexin32 (Cx32) cause CMT1X. Cx32 is expressed by Schwann cells and oligodendrocytes, as well as by other tissues, and the GJ formed by Cx32 play an important role in the homeostasis of myelinated axons. The reported CMT1X mutations are diverse and affect both the promoter region as well as the coding region of GJB1. Many Cx32 mutants fail to form functional GJ, or form GJ with abnormal biophysical properties. Furthermore, Cx32 mutants are often retained intracellularly either in the endoplasmic reticulum or Golgi in which they could potentially have additional dominant-negative effects. Animal models of CMT1X demonstrate that loss of Cx32 in myelinating Schwann cells causes a demyelinating neuropathy. No definite phenotype-genotype correlation has yet been established for CMT1X and effective molecular based therapeutics for this disease, remain to be developed.

Connexins in hearing loss: a comprehensive overview

Connexins are a family of transmembrane proteins that form gap junctions between adjacent cells and allow intercellular communication. Connexin proteins are involved in pathological conditions in humans, mainly in hearing loss, neurodegenerative disorders and skin diseases. The association between connexin proteins and the inner ear is well established. The abundant expression of connexins in the auditory system of the inner ear demonstrates their importance in inner ear development and the hearing process. Most compelling, there are over 100 mutations in genes encoding connexins that are associated with deafness. Most prominent is the remarkable involvement of connexin 26 in hearing loss. Mutations in the gene GJB2, encoding connexin 26, are responsible for around 50% of genetic cases of severe to profound non-syndromic hearing loss in some parts of the world. Learning more about the connexin family in general and about connexin 26 in particular can shed light on the pathogenesis of the inner ear and bring us closer to finding clinical solutions for the hearing impaired.

Simian immunodeficiency virus disrupts extended lengths of the blood-brain barrier

It is known that there is disruption of the blood-brain barrier during terminal AIDS encephalitis in both human immunodeficiency virus (HIV)-infected humans and simian immunodeficiency virus (SIV)-infected rhesus macaques. Much, although by no means all, of the neuropathological findings of HIV and SIV infection involves accumulation of monocytes/macrophages that have likely crossed the blood-brain barrier (BBB). There is no convincing, rigorous, demonstration of HIV (or SIV) infecting endothelial cells in vivo. However, this is not to say that HIV infection would not have any effects on the physiology of microvascular brain endothelial cells. Because of the elaborate nature of cerebral microvessels, previous studies of cerebral endothelial cells have been constrained by sectioning artifacts. Examination of freshly isolated cerebral microvessels allows investigation of extended lengths of vessels (>150 mum) without sectioning artifacts. These studies determine the changes in the expression of the tight junction protein zo-1 protein on the endothelial cells of cerebral capillaries at terminal acquired immune deficiency syndrome, demonstrating that there is a decreased expression of zo-1 protein over extended lengths of microvessels.