Claudin-11 in health and disease: implications for myelin disorders, hearing, and fertility.

Claudin-11 plays a critical role in multiple physiological processes, including myelination, auditory function, and spermatogenesis. Recently, stop-loss mutations in CLDN11 have been identified as a novel cause of hypomyelinating leukodystrophy (HLD22). Understanding the multifaceted roles of claudin-11 and the potential pathogenic mechanisms in HLD22 is crucial for devising targeted therapeutic strategies. This review outlines the biological roles of claudin-11 and the implications of claudin-11 loss in the context of the Cldn11 null mouse model. Additionally, HLD22 and proposed pathogenic mechanisms, such as endoplasmic reticulum stress, will be discussed.

An inducible Cldn11-CreERT2 mouse line for selective targeting of lymphatic valves.

Luminal valves of collecting lymphatic vessels are critical for maintaining unidirectional flow of lymph and their dysfunction underlies several forms of primary lymphedema. Here, we report on the generation of a transgenic mouse expressing the tamoxifen inducible CreERT2 under the control of Cldn11 promoter that allows, for the first time, selective and temporally controlled targeting of lymphatic valve endothelial cells. We show that within the vasculature CLDN11 is specifically expressed in lymphatic valves but is not required for their development as mice with a global loss of Cldn11 display normal valves in the mesentery. Tamoxifen treated Cldn11-CreERT2 mice also carrying a fluorescent Cre-reporter displayed reporter protein expression selectively in lymphatic valves and, to a lower degree, in venous valves. Analysis of developing vasculature further showed that Cldn11-CreERT2 -mediated recombination is induced during valve leaflet formation, and efficient labeling of valve endothelial cells was observed in mature valves. The Cldn11-CreERT2 mouse thus provides a valuable tool for functional studies of valves.

Author Correction: Onecut-dependent Nkx6.2 transcription factor expression is required for proper formation and activity of spinal locomotor circuits.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Onecut-dependent Nkx6.2 transcription factor expression is required for proper formation and activity of spinal locomotor circuits.

In the developing spinal cord, Onecut transcription factors control the diversification of motor neurons into distinct neuronal subsets by ensuring the maintenance of Isl1 expression during differentiation. However, other genes downstream of the Onecut proteins and involved in motor neuron diversification have remained unidentified. In the present study, we generated conditional mutant embryos carrying specific inactivation of Onecut genes in the developing motor neurons, performed RNA-sequencing to identify factors downstream of Onecut proteins in this neuron population, and employed additional transgenic mouse models to assess the role of one specific Onecut-downstream target, the transcription factor Nkx6.2. Nkx6.2 expression was up-regulated in Onecut-deficient motor neurons, but strongly downregulated in Onecut-deficient V2a interneurons, indicating an opposite regulation of Nkx6.2 by Onecut factors in distinct spinal neuron populations. Nkx6.2-null embryos, neonates and adult mice exhibited alterations of locomotor pattern and spinal locomotor network activity, likely resulting from defective survival of a subset of limb-innervating motor neurons and abnormal migration of V2a interneurons. Taken together, our results indicate that Nkx6.2 regulates the development of spinal neuronal populations and the formation of the spinal locomotor circuits downstream of the Onecut transcription factors.

Age-related murine hippocampal CA1 laminae oxidative stress measured in vivo by QUEnch-assiSTed (QUEST) MRI: impact of isoflurane anesthesia.

Age-related impairments in spatial learning and memory often precede non-familial neurodegenerative disease. Ex vivo studies suggest that physiologic age-related oxidative stress in hippocampus area CA1 may contribute to prodromal spatial disorientation and to morbidity. Yet, conventional blood or cerebrospinal fluid assays appear insufficient for early detection or management of oxidative stress within CA1 sub-regions in vivo. Here, we address this biomarker problem using a non-invasive MRI index of CA1 laminae oxidative stress based on reduction in R1 (= 1/T1) after anti-oxidant administration. An R1 reduction reflects quenching of continuous and excessive production of endogenous paramagnetic free radicals. Careful motion-correction image acquisition, and avoiding repeated exposure to isoflurane, facilitates detection of hippocampus CA1 laminae oxidative stress with QUEnch-assiSTed (QUEST) MRI. Intriguingly, age- and isoflurane-related oxidative stress is localized to the stratum lacunosum of the CA1 region. Our data raise the possibility of using QUEST MRI and FDA-approved anti-oxidants to remediate spatial disorientation and later neurodegeneration with age in animals and humans.

Novel Role for Claudin-11 in the Regulation of Osteoblasts via Modulation of ADAM10-Mediated Notch Signaling.

The claudin (Cldn) family comprises 27 members of 20 to 34 kDa transmembrane tight junction proteins. In addition to Cldns' established canonical role as barriers controlling paracellular flow of molecules, a distinct noncanonical role for them as mediators of cell signaling is now emerging. In our studies evaluating Cldn family expression levels during osteoblast differentiation, Cldn-11 showed the largest increase (60-fold). Immunohistochemistry studies revealed high Cldn-11 expression in trabecular (Tb) bone lining cells. Micro-CT analysis of femurs and vertebrae of Cldn-11 knock-out (KO) mice at 12 weeks of age exhibited a 40% (p < 0.01) reduction in Tb bone volume adjusted for tissue volume compared with control mice, a change caused by significant reductions in Tb number and thickness and increase in Tb separation. Histomorphometry and serum biomarker studies revealed that reduced bone formation, not increased resorption, is the cause for reduced Tb bone volume in the Cldn-11 KO mice. Cldn-11 KO osteoblasts expressed reduced ALP and BSP, whereas Cldn-11 overexpression in MC3T3-E1 cells increased expression of ALP and BSP. Mechanistically, Cldn-11 interacted with tetraspanin (Tspan)3 in osteoblasts, and Tspan3 knockdown reduced osteoblast differentiation. Because members of the Tspan family regulate cell functions via Notch signaling, we evaluated whether Cldn-11/Tspan3 regulates Notch signaling in osteoblasts. Accordingly, Notch targets Hey1 and Hey2 were significantly upregulated in Cldn-11 overexpressing cultures but downregulated in both Cldn-11 KO and Tspan3 knockdown osteoblasts. Because ADAM10 has been shown to interact with Tspan family members to regulate Notch signaling, we evaluated whether Cldn-11 regulates ADAM10 expression. Cldn-11 overexpressing cells express more mature ADAM10, and an ADAM10 inhibitor blocked the Cldn-11 effect on osteoblast differentiation. Based on these data, we propose Cldn-11 as a novel component of an osteoblast cell surface protein complex, comprising Tspan3 and ADAM10, which regulates Notch signaling and cell differentiation. © 2019 American Society for Bone and Mineral Research.

Corticohippocampal Dysfunction In The OBiden Mouse Model Of Primary Oligodendrogliopathy.

Despite concerted efforts over decades, the etiology of multiple sclerosis (MS) remains unclear. Autoimmunity, environmental-challenges, molecular mimicry and viral hypotheses have proven equivocal because early-stage disease is typically presymptomatic. Indeed, most animal models of MS also lack defined etiologies. We have developed a novel adult-onset oligodendrogliopathy using a delineated metabolic stress etiology in myelinating cells, and our central question is, "how much of the pathobiology of MS can be recapitulated in this model?" The analyses described herein demonstrate that innate immune activation, glial scarring, cortical and hippocampal damage with accompanying electrophysiological, behavioral and memory deficits naturally emerge from disease progression. Molecular analyses reveal neurofilament changes in normal-appearing gray matter that parallel those in cortical samples from MS patients with progressive disease. Finally, axon initial segments of deep layer pyramidal neurons are perturbed in entorhinal/frontal cortex and hippocampus from OBiden mice, and computational modeling provides insight into vulnerabilities of action potential generation during demyelination and early remyelination. We integrate these findings into a working model of corticohippocampal circuit dysfunction to predict how myelin damage might eventually lead to cognitive decline.

Absence of Claudin 11 in CNS Myelin Perturbs Behavior and Neurotransmitter Levels in Mice.

Neuronal origins of behavioral disorders have been examined for decades to construct frameworks for understanding psychiatric diseases and developing useful therapeutic strategies with clinical application. Despite abundant anecdotal evidence for white matter etiologies, including altered tractography in neuroimaging and diminished oligodendrocyte-specific gene expression in autopsy studies, mechanistic data demonstrating that dysfunctional myelin sheaths can cause behavioral deficits and perturb neurotransmitter biochemistry have not been forthcoming. At least in part, this impasse stems from difficulties in identifying model systems free of degenerative pathology to enable unambiguous assessment of neuron biology and behavior in a background of myelin dysfunction. Herein we examine myelin mutant mice lacking expression of the Claudin11 gene in oligodendrocytes and characterize two behavioral endophenotypes: perturbed auditory processing and reduced anxiety/avoidance. Importantly, these behaviors are associated with increased transmission time along myelinated fibers as well as glutamate and GABA neurotransmitter imbalances in auditory brainstem and amygdala, in the absence of neurodegeneration. Thus, our findings broaden the etiology of neuropsychiatric disease to include dysfunctional myelin, and identify a preclinical model for the development of novel disease-modifying therapies.

Neuregulin1 modulation of experimental autoimmune encephalomyelitis (EAE).

Neuregulin1 (NRG1) is a differentiation factor that regulates glial development, survival, synaptogenesis, axoglial interactions, and microglial activation. We previously reported that a targeted NRG1 antagonist (HBD-S-H4) given intrathecally, reduces inflammatory microglial activation in a spinal cord pain model and a neurodegenerative disease mouse model in vivo, suggesting that it may have effects in neuroninflammatory and neuronal disorders. We hypothesized that expression of HBD-S-H4 in the central nervous system (CNS) could reduce disease severity in experimental autoimmune encephalomyelitis (EAE), a widely used animal model for multiple sclerosis (MS). In the present study, we generated tetO-HBD-S-H4, a single transgenic (Tg) mouse line in, which the fusion protein in expressed in the brain, resulting in reduction of disease severity in both male and female mice when compared to sex- and age-matched wild type littermates. We also generated GFAP-tTA:tetO-HBD-S-H4 double Tg mice, which express this fusion protein in the brain and the spinal cord, they displayed sex differences in the reduction of disease severity. In healthy mice, expression of HBD-S-H4 in the CNS does not result in any significant neurological or other overt phenotypes. In myelin oligodendrocyte glycoprotein (MOG)-induced EAE, female double Tg mice show delayed disease onset and reduced disease severity compared to male double Tg as well as wild type littermates. In male double Tg mice, the levels of HBD-S-H4 gene expression negatively correlates with disease severity and increased microglia associated genes' expression. In conclusion, expression of neuregulin antagonist in the brain and spinal cord protects females but not males, suggesting a complex interplay between NRG1 and sex difference in EAE that may be associated with microglia-mediated inflammation. This study provides important information for understanding the heterogeneity of disease pathology and the therapeutic potential of targeting microglial activation in male and female MS patients.

Developmental window of sensorineural deafness in biotinidase-deficient mice.

Biotinidase deficiency is an autosomal recessively inherited disorder that results in the inability to recycle the vitamin, biotin. If untreated, the disorder can result in a range of neurological and cutaneous symptoms, including sensorineural deficits and deafness. To understand early mechanistic abnormalities that may precede more generalized and nonspecific effects of metabolic deficits such as weight loss and acidosis, we have analyzed auditory brainstem responses (ABRs) in biotinidase-deficient knockout (Btd -/- ) mice in the periweaning period with or without dietary biotin supplementation. We find significant increases in the latency of wave V of the ABR elicited by pure tone stimuli at one octave intervals, which precede substantial increases in ABR thresholds. Finer interpeak latency analyses of these changes indicate they are confined to the latter ABR waves associated with the CNS and likely reflect slowed brainstem transmission time. In contrast, peripheral nervous system conduction velocity appears normal. Further, we find that biotin-supplementation after the onset of symptoms reverses the latency shifts, which has significant relevance for early treatment in patients. Finally, ABR latencies in Btd -/- mice fed a biotin-supplemented diet for the first month of life appear refractory to transmission time slowing during a subsequent bout of biotin deficiency. These data suggest a transient vulnerability window for biotin deficiency in the auditory brainstem. Finally, we also observe a developmental vulnerability window involving follicular melanosome production or melanocyte survival. Sensorineural deafness precedes peripheral hearing loss in developmental biotinidase deficiency and is transient if rescued by dietary biotin within a short developmental window.

Dimethyl fumarate ameliorates myoclonus stemming from protein misfolding in oligodendrocytes.

Multiple sclerosis (MS) is considered a primary autoimmune disease; however, this view is increasingly being challenged in basic and clinical science arenas because of the growing body of clinical trials' data showing that exclusion of immune cells from the CNS only modestly slows disease progression to disability. Accordingly, there is significant need for expanding the scope of potential disease mechanisms to understand the etiology of MS. Concomitantly, the use of a broader range of pre-clinical animal models for characterizing existing efficacious clinical treatments may elucidate additional or unexpected mechanisms of action for these drugs that augment insight into MS etiology. Herein, we explore the in vivo mechanism of action of dimethyl fumarate, which has been shown to suppress oxidative stress and immune cell responses in psoriasis and MS. Rather than studying this compound in the context of an experimental autoimmune-induced attack on the CNS, we have used a genetic model of hypomyelination, male rumpshaker (rsh) mice, which exhibit oligodendrocyte metabolic stress and startle-induced subcortical myoclonus during development and into adulthood. We find that myoclonus is reduced 30-50% in treated mutants but we do not detect substantial changes in metabolic or oxidative stress response pathways, cytokine modulation, or myelin thickness (assessed by anova). All procedures involving vertebrate animals in this study were reviewed and approved by the IACUC committee at Wayne State University.

Ranking Novel Regulatory Genes in Gene Expression Profiles using NetExpress.

Understanding gene regulation by identifying gene products and determining their roles in regulatory networks is a complex process. A common computational method is to reverse engineer a regulatory network from gene expression profile, and sanitize the network using known information about the genes, their interactions and other properties to filter out unlikely interactors. Unfortunately, due to limited resources most gene expression studies have a limited and small number of time points, and most reverse engineering tools are unable to handle large numbers of genes. Both of these factors play significant roles in influencing the accuracy of the process. In this paper, we present a new gene ranking algorithm from gene expression profiles with a small number of time points so that the most relevant genes can be selected for reverse engineering. We also present a graphical interface called NetExpress, which adopts this algorithm and allows users to set control parameters to effect the desired outcome, and visualize the analysis for iterative fine tuning.

Overexpression of CHOP in Myelinating Cells Does Not Confer a Significant Phenotype under Normal or Metabolic Stress Conditions.

UNLABELLED: The PKR-like endoplasmic reticulum kinase (PERK) pathway of the unfolded protein response (UPR) is protective against toxic accumulations of misfolded proteins in the endoplasmic reticulum, but is thought to drive cell death via the transcription factor, CHOP. However, in many cell types, CHOP is an obligate step in the PERK pathway, which frames the conundrum of a prosurvival pathway that kills cells. Our laboratory and others have previously demonstrated the prosurvival activity of the PERK pathway in oligodendrocytes. In the current study, we constitutively overexpress CHOP in myelinating cells during development and into adulthood under normal or UPR conditions. We show that this transcription factor does not drive apoptosis. Indeed, we observe no detriment in mice at multiple levels from single cells to mouse behavior and life span. In light of these data and other studies, we reinterpret PERK pathway function in the context of a stochastic vulnerability model, which governs the likelihood that cells undergo cell death upon cessation of UPR protection and while attempting to restore homeostasis. SIGNIFICANCE STATEMENT: Herein, we tackle the biggest controversy in the UPR literature: the function of the transcription factor CHOP as a protective or a prodeath factor. This manuscript is timely in light of the 2014 Lasker award for the UPR. Our in vivo data show that CHOP is not a prodeath protein, and we demonstrate that myelinating glial cells function normally in the presence of high CHOP expression from development to adulthood. Further, we propose a simplified view of UPR-mediated cell death after CHOP induction. We anticipate our work may turn the tide of the dogmatic view of CHOP and cause a reinvestigation of its function in different cell types. Accordingly, we believe our work will be a watershed for the UPR field.

Claudin-11 Tight Junctions in Myelin Are a Barrier to Diffusion and Lack Strong Adhesive Properties.

The radial component is a network of interlamellar tight junctions (TJs) unique to central nervous system myelin. Ablation of claudin-11, a TJ protein, results in the absence of the radial component and compromises the passive electrical properties of myelin. Although TJs are known to regulate paracellular diffusion, this barrier function has not been directly demonstrated for the radial component, and some evidence suggests that the radial component may also mediate adhesion between myelin membranes. To investigate the physical properties of claudin-11 TJs, we compared fresh, unfixed Claudin 11-null and control nerves using x-ray and neutron diffraction. In Claudin 11-null tissue, we detected no changes in myelin structure, stability, or membrane interactions, which argues against the notion that myelin TJs exhibit significant adhesive properties. Moreover, our osmotic stressing and D2O-H2O exchange experiments demonstrate that myelin lacking claudin-11 is more permeable to water and small osmolytes. Thus, our data indicate that the radial component serves primarily as a diffusion barrier and elucidate the mechanism by which TJs govern myelin function.

Neuroradiologic correlates of clinical disability and progression in the X-linked leukodystrophy Pelizaeus-Merzbacher disease.

OBJECTIVE: To determine whether quantitative measure of magnetic resonance imaging data from patients with the inherited leukodystrophy, Pelizaeus-Merzbacher disease (PMD) correlates with clinical severity or progression. METHODS: In our current work we have analyzed the clinical phenotypes and MRI scans of 51 male patients with PMD and 10 female carriers for whom the PLP1 genotype had been determined. In addition, we developed a 32-point functional disability scoring (FDS) system for PMD, and validated it for inter-rater reliability. Using conventional T1- and T2-weighted MRI images of the whole brain, we measured white matter and total brain volume (WMV and TBV), inter-caudate ratio (ICR), and corpus callosum area. RESULTS: There was a significant positive correlation of FDS with white matter fraction (WMV/TBV) and corpus callosum area. Also, when applying a median split based on FDS, patients with lower FDS showed reduced white matter fraction and corpus callosum area, and increased ICR compared to patients with relatively higher FDS, regardless of age. CONCLUSION: Although this patient population is heterogeneous, with multiple genetic and molecular mechanisms causing PMD, these data imply that white matter atrophy is a major pathological determinant of the clinical disability in most patients. Development of reliable non-invasive quantitative biomarkers of disease activity would be useful not only for following the natural history of the disease, but also raising the potential for evaluating future therapies.

Increased anesthesia time using 2,2,2-tribromoethanol-chloral hydrate with low impact on mouse psychoacoustics.

BACKGROUND: To examine psychoacoustics in mice, we have used 2,2,2-tribromoethanol anesthesia in multiple studies. We find this drug is fast-acting and yields consistent results, providing 25-30 min of anesthesia. Our recent studies in binaural hearing prompted development of a regimen to anesthesia time to 1h. We tested a novel cocktail using 2,2,2-tribromoethanol coupled with low dose chloral hydrate to extend the effective anesthesia time. NEW METHOD: We have established an intraperitoneal dosing regimen for 2,2,2-tribromoethanol-chloral hydrate anesthesia. To measure efficacy of the drug cocktail, we measured auditory brainstem responses (ABRs) at 10 min intervals to determine the effects on hearing thresholds and wave amplitudes and latencies. RESULTS: This novel drug combination increases effective anesthesia to 1h. ABR Wave I amplitudes, but not latencies, are marginally suppressed. Additionally, amplitudes of the centrally derived Waves III and V show significant inter-animal variability that is independent of stimulus intensity. These data argue against the systematic suppression of ABRs by the drug cocktail. COMPARISON WITH EXISTING METHODS: Using 2,2,2-tribromoethanol-chloral hydrate combination in psychoacoustic studies has several advantages over other drug cocktails, the most important being preservation of latencies from centrally- and peripherally-derived ABR waves. In addition, hearing thresholds are unchanged and wave amplitudes are not systematically suppressed, although they exhibit greater variability. CONCLUSIONS: We demonstrate that 375 mg/kg 2,2,2-tribromoethanol followed after 5 min by 200mg/kg chloral hydrate provides an anesthesia time of 60 min, has negligible effects on ABR wave latencies and thresholds and non-systematic effects on amplitudes.

Potential For Cell-mediated Immune Responses In Mouse Models Of Pelizaeus-Merzbacher Disease.

Although activation of the innate and adaptive arms of the immune system are undoubtedly involved in the pathophysiology of neurodegenerative diseases, it is unclear whether immune system activation is a primary or secondary event. Increasingly, published studies link primary metabolic stress to secondary inflammatory responses inside and outside of the nervous system. In this study, we show that the metabolic stress pathway known as the unfolded protein response (UPR) leads to secondary activation of the immune system. First, we observe innate immune system activation in autopsy specimens from Pelizaeus-Merzbacher disease (PMD) patients and mouse models stemming from PLP1 gene mutations. Second, missense mutations in mildly- and severely-affected Plp1-mutant mice exhibit immune-associated expression profiles with greater disease severity causing an increasingly proinflammatory environment. Third and unexpectedly, we find little evidence for dysregulated expression of major antioxidant pathways, suggesting that the unfolded protein and oxidative stress responses are separable. Together, these data show that UPR activation can precede innate and/or adaptive immune system activation and that neuroinflammation can be titrated by metabolic stress in oligodendrocytes. Whether-or-not such activation leads to autoimmune disease in humans is unclear, but the case report of steroid-mitigated symptoms in a PMD patient initially diagnosed with multiple sclerosis lends support.

Tissue-restricted transcription from a conserved intragenic CpG island in the Klf1 gene in mice.

Beyond Mendelian inheritance, an understanding of the complexities and consequences of the transfer of nonhereditary information to successive generations is at an early stage. Such epigenetic functionality is exemplified by DNA methylation and, as genome-wide high-throughput methodologies emerge, is increasingly being considered in the context of conserved intragenic and intergenic CpG islands that function as alternate sites of transcription initiation. Here we characterize an intragenic CpG island in exon 2 of the protein-coding mouse Klf1 gene, from which clustered transcription initiation sites yield positive-strand, severely truncated, capped and spliced RNAs. Expression from this CpG island in the testis begins between Postnatal Days 14-20, increases during development, and is temporally correlated with the maturation of secondary spermatocytes as they become the dominant cell population in the seminiferous epithelium. Only full-length KLF1-encoding mRNAs are detected in the hematopoietic tissue, spleen; thus, expression from the exon 2 CpG island is both developmentally regulated and tissue restricted. DNA methylation analysis indicates that spatiotemporal expression from the Klf1 CpG island is not associated with hypermethylation. Finally, our computational analysis from multiple species confirms intragenic transcription initiation and indicates that the KLF1 CpG island is evolutionarily conserved. Currently we have no evidence that these truncated RNAs can be translated via nonconventional mechanisms such as in-frame, conserved non-AUG-dependent Kozak consensus sequences; however, high-quality carboxyl-terminal antibodies will more effectively address this issue.

MpzR98C arrests Schwann cell development in a mouse model of early-onset Charcot-Marie-Tooth disease type 1B.

Mutations in myelin protein zero (MPZ) cause Charcot-Marie-Tooth disease type 1B. Many dominant MPZ mutations, including R98C, present as infantile onset dysmyelinating neuropathies. We have generated an R98C 'knock-in' mouse model of Charcot-Marie-Tooth type 1B, where a mutation encoding R98C was targeted to the mouse Mpz gene. Both heterozygous (R98C/+) and homozygous (R98C/R98C) mice develop weakness, abnormal nerve conduction velocities and morphologically abnormal myelin; R98C/R98C mice are more severely affected. MpzR98C is retained in the endoplasmic reticulum of Schwann cells and provokes a transitory, canonical unfolded protein response. Ablation of Chop, a mediator of the protein kinase RNA-like endoplasmic reticulum kinase unfolded protein response pathway restores compound muscle action potential amplitudes of R98C/+ mice but does not alter the reduced conduction velocities, reduced axonal diameters or clinical behaviour of these animals. R98C/R98C Schwann cells are developmentally arrested in the promyelinating stage, whereas development is delayed in R98C/+ mice. The proportion of cells expressing c-Jun, an inhibitor of myelination, is elevated in mutant nerves, whereas the proportion of cells expressing the promyelinating transcription factor Krox-20 is decreased, particularly in R98C/R98C mice. Our results provide a potential link between the accumulation of MpzR98C in the endoplasmic reticulum and a developmental delay in myelination. These mice provide a model by which we can begin to understand the early onset dysmyelination seen in patients with R98C and similar mutations.

Transgene-mediated rescue of spermatogenesis in Cldn11-null mice.

Claudins comprise a large family of tight junction (TJ) proteins that are often expressed broadly during development and in adult tissues and constitute the physical barriers that occlude the paracellular space in polarized epithelia. In mouse testis, the integrity of TJs is critical to normal spermatogenesis and is dependent on CLDN11 expression. In the current study, we have generated multiple transgenic mouse lines in which steady-state levels of transgene-derived Cldn11 mRNA are up to fourfold greater than endogenous gene expression. Spermatogenesis in all founder mice harboring two copies of the endogenous Cldn11 gene is normal. These animals breed well, indicating that transgene overexpression, at least at the level of mRNA, is well tolerated by Sertoli cells. In addition, we demonstrate that the promoter/enhancer of the transgene, comprising 5 kb of genomic sequence upstream of exon 1 of the mouse Cldn11 gene, is sufficient to rescue azoospermia in Cldn11-null mice. Finally, using transient transgenic mice, we narrow the location of Sertoli cell-specific cis regulatory elements to a 2-kb region upstream of the Cldn11 transcription start site. Together, these data provide essential information for further investigation of the biological regulation of CLDN11 TJs in the testis.