Analysis of the GFP-labelled ß-dystroglycan interactome in HEK-293 transfected cells reveals novel intracellular networks.

Dystroglycan (DG) is a cell adhesion complex that is widely expressed in tissues. It is composed by two subunits, α-DG, a highly glycosylated protein that interacts with several extracellular matrix proteins, and transmembrane ß-DG whose, cytodomain binds to the actin cytoskeleton. Glycosylation of α-DG is crucial for functioning as a receptor for its multiple extracellular binding partners. Perturbation of α-DG glycosylation is the central event in the pathogenesis of severe pathologies such as muscular dystrophy and cancer. ß-DG acts as a scaffold for several cytoskeletal and nuclear proteins and very little is known about the fine regulation of some of these intracellular interactions and how they are perturbed in diseases. To start filling this gap by identifying uncharacterized intracellular networks preferentially associated with ß-DG, HEK-293 cells were transiently transfected with a plasmid carrying the ß-DG subunit with GFP fused at its C-terminus. With this strategy, we aimed at forcing ß-DG to occupy multiple intracellular locations instead of sitting tightly at its canonical plasma membrane milieu, where it is commonly found in association with α-DG. Immunoprecipitation by anti-GFP antibodies followed by shotgun proteomic analysis led to the identification of an interactome formed by 313 exclusive protein matches for ß-DG binding. A series of already known ß-DG interactors have been found, including ezrin and emerin, whilst significant new matches, which include potential novel ß-DG interactors and their related networks, were identified in diverse subcellular compartments, such as cytoskeleton, endoplasmic reticulum/Golgi, mitochondria, nuclear membrane and the nucleus itself. Of particular interest amongst the novel identified matches, Lamina-Associated Polypeptide-1B (LAP1B), an inner nuclear membrane protein, whose mutations are known to cause nuclear envelopathies characterized by muscular dystrophy, was found to interact with ß-DG in HEK-293 cells. This evidence was confirmed by immunoprecipitation, Western blotting and immunofluorescence experiments. We also found by immunofluorescence experiments that LAP1B looses its nuclear envelope localization in C2C12 DG-knock-out cells, suggesting that LAP1B requires ß-DG for a proper nuclear localization. These results expand the role of ß-DG as a nuclear scaffolding protein and provide novel evidence of a possible link between dystroglycanopathies and nuclear envelopathies displaying with muscular dystrophy.

TOR1AIP1-Associated Nuclear Envelopathies.

Human TOR1AIP1 encodes LAP1, a nuclear envelope protein expressed in most human tissues, which has been linked to various biological processes and human diseases. The clinical spectrum of diseases related to mutations in TOR1AIP1 is broad, including muscular dystrophy, congenital myasthenic syndrome, cardiomyopathy, and multisystemic disease with or without progeroid features. Although rare, these recessively inherited disorders often lead to early death or considerable functional impairment. Developing a better understanding of the roles of LAP1 and mutant TOR1AIP1-associated phenotypes is paramount to allow therapeutic development. To facilitate further studies, this review provides an overview of the known interactions of LAP1 and summarizes the evidence for the function of this protein in human health. We then review the mutations in the TOR1AIP1 gene and the clinical and pathological characteristics of subjects with these mutations. Lastly, we discuss challenges to be addressed in the future.

Loss of the Nuclear Envelope Protein LAP1B Disrupts the Myogenic Differentiation of Patient-Derived Fibroblasts.

Lamina-associated polypeptide 1 (LAP1) is a ubiquitously expressed inner nuclear membrane protein encoded by TOR1AIP1, and presents as two isoforms in humans, LAP1B and LAP1C. While loss of both isoforms results in a multisystemic progeroid-like syndrome, specific loss of LAP1B causes muscular dystrophy and cardiomyopathy, suggesting that LAP1B has a critical role in striated muscle. To gain more insight into the molecular pathophysiology underlying muscular dystrophy caused by LAP1B, we established a patient-derived fibroblast line that was transdifferentiated into myogenic cells using inducible MyoD expression. Compared to the controls, we observed strongly reduced myogenic differentiation and fusion potentials. Similar defects were observed in the C2C12 murine myoblasts carrying loss-of-function LAP1A/B mutations. Using RNA sequencing, we found that, despite MyoD overexpression and efficient cell cycle exit, transcriptional reprogramming of the LAP1B-deficient cells into the myogenic lineage is impaired with delayed activation of MYOG and muscle-specific genes. Gene set enrichment analyses suggested dysregulations of protein metabolism, extracellular matrix, and chromosome organization. Finally, we found that the LAP1B-deficient cells exhibit nuclear deformations, such as an increased number of micronuclei and altered morphometric parameters. This study uncovers the phenotypic and transcriptomic changes occurring during myoconversion of patient-derived LAP1B-deficient fibroblasts and provides a useful resource to gain insights into the mechanisms implicated in LAP1B-associated nuclear envelopathies.

Anthocyanin pigmentation as a quantitative visual marker for arbuscular mycorrhizal fungal colonization of Medicago truncatula roots.

Visualization of root colonization by arbuscular mycorrhizal fungi (AMF) is the most elementary experiment in the field of mycorrhizal symbiosis. The most widely used approach for evaluating levels of AMF colonization is staining with trypan blue or ink, which is scored using the time-consuming grid intersection method. Here we demonstrate the use of an anthocyanin-based visual marker system for visualizing AMF colonization of Medicago truncatula roots. Expression of MtLAP1, a transcription factor which regulates the production of anthocyanins, from the AMF-induced Kunitz Protease Inhibitor 106 promoter, allowed the visualization of arbuscules in live plant tissues without microscopy or staining. This marker system allowed straightforward qualitative evaluation of the ram1, vpy and dmi3 AMF phenotypes using Agrobacterium rhizogenes hairy-root transformation. For the strigolactone biosynthesis mutant carotenoid cleavage dioxygenase 8a and a novel mutant scooby, which show quantitative AMF symbiotic phenotypes, the amount of anthocyanins in the roots estimated by spectrophotometry correlated very well with colonization levels estimated by staining and scoring using the grid intersection method. The LAP1-based marker system therefore provides a highly efficient approach for mutant screening and monitoring of AMF colonization in live tissues by eye, or for quantitative assessment using a simple and quick photometric assay.

MtGSTF7, a TT19-like GST gene, is essential for accumulation of anthocyanins, but not proanthocyanins in Medicago truncatula.

Anthocyanins and proanthocyanins (PAs) are two end products of the flavonoid biosynthesis pathway. They are believed to be synthesized in the endoplasmic reticulum and then sequestered into the vacuole. In Arabidopsis thaliana, TRANSPARENT TESTA 19 (TT19) is necessary for both anthocyanin and PA accumulation. Here, we found that MtGSTF7, a homolog of AtTT19, is essential for anthocyanin accumulation but not required for PA accumulation in Medicago truncatula. MtGSTF7 was induced by the anthocyanin regulator LEGUME ANTHOCYANIN PRODUCTION 1 (LAP1), and its tissue expression pattern correlated with anthocyanin deposition in M. truncatula. Tnt1-insertional mutants of MtGSTF7 lost anthocyanin accumulation in vegetative organs, and introducing a genomic fragment of MtGSTF7 could complement the mutant phenotypes. Additionally, the accumulation of anthocyanins induced by LAP1 was significantly reduced in mtgstf7 mutants. Yeast-one-hybridization and dual-luciferase reporter assays revealed that LAP1 could bind to the MtGSTF7 promoter to activate its expression. Ectopic expression of MtGSTF7 in tt19 mutants could rescue their anthocyanin deficiency, but not their PA defect. Furthermore, PA accumulation was not affected in the mtgstf7 mutants. Taken together, our results show that the mechanism of anthocyanin and PA accumulation in M. truncatula is different from that in A. thaliana, and provide a new target gene for engineering anthocyanins in plants.

Nuclear Envelope Alterations in Myotonic Dystrophy Type 1 Patient-Derived Fibroblasts.

Myotonic dystrophy type 1 (DM1) is a hereditary and multisystemic disease characterized by myotonia, progressive distal muscle weakness and atrophy. The molecular mechanisms underlying this disease are still poorly characterized, although there are some hypotheses that envisage to explain the multisystemic features observed in DM1. An emergent hypothesis is that nuclear envelope (NE) dysfunction may contribute to muscular dystrophies, particularly to DM1. Therefore, the main objective of the present study was to evaluate the nuclear profile of DM1 patient-derived and control fibroblasts and to determine the protein levels and subcellular distribution of relevant NE proteins in these cell lines. Our results demonstrated that DM1 patient-derived fibroblasts exhibited altered intracellular protein levels of lamin A/C, LAP1, SUN1, nesprin-1 and nesprin-2 when compared with the control fibroblasts. In addition, the results showed an altered location of these NE proteins accompanied by the presence of nuclear deformations (blebs, lobes and/or invaginations) and an increased number of nuclear inclusions. Regarding the nuclear profile, DM1 patient-derived fibroblasts had a larger nuclear area and a higher number of deformed nuclei and micronuclei than control-derived fibroblasts. These results reinforce the evidence that NE dysfunction is a highly relevant pathological characteristic observed in DM1.

A TOR1AIP1 variant segregating with an early onset limb girdle myasthenia-Support for the role of LAP1 in NMJ function and disease.

Rare pathogenic variants in TOR1AIP1 (OMIM 614512), coding the inner nuclear membrane protein lamin-associated protein 1 (LAP1), have been associated with a spectrum of disorders including limb girdle muscular dystrophy with cardiac involvement and a severe multisystem phenotype. Recently, Cossins et al reported two siblings with limb girdle muscular dystrophy and impaired transmission of the neuromuscular synapse, demonstrating that defective LAP1 may lead to a congenital myasthenic syndrome. Herein, we describe the association of TOR1AIP1 deficiency with congenital myasthenic syndrome in three siblings.

Selective loss of a LAP1 isoform causes a muscle-specific nuclear envelopathy.

The nuclear envelope (NE) separates the nucleus from the cytoplasm in all eukaryotic cells. A disruption of the NE structure compromises normal gene regulation and leads to severe human disorders collectively classified as nuclear envelopathies and affecting skeletal muscle, heart, brain, skin, and bones. The ubiquitous NE component LAP1B is encoded by TOR1AIP1, and the use of an alternative start codon gives rise to the shorter LAP1C isoform. TOR1AIP1 mutations have been identified in patients with diverging clinical presentations such as muscular dystrophy, progressive dystonia with cerebellar atrophy, and a severe multi-systemic disorder, but the correlation between the mutational effect and the clinical spectrum remains to be determined. Here, we describe a novel TOR1AIP1 patient manifesting childhood-onset muscle weakness and contractures, and we provide clinical, histological, ultrastructural, and genetic data. We demonstrate that the identified TOR1AIP1 frameshift mutation leads to the selective loss of the LAP1B isoform, while the expression of LAP1C was preserved. Through comparative review of all previously reported TOR1AIP1 cases, we delineate a genotype/phenotype correlation and conclude that LAP1B-specific mutations cause a progressive skeletal muscle phenotype, while mutations involving a loss of both LAP1B and LAP1C isoforms induce a syndromic disorder affecting skeletal muscle, brain, eyes, ear, skin, and bones.

Torsin ATPases influence chromatin interaction of the Torsin regulator LAP1.

The inner nuclear membrane is functionalized by diverse transmembrane proteins that associate with nuclear lamins and/or chromatin. When cells enter mitosis, membrane-chromatin contacts must be broken to allow for proper chromosome segregation; yet how this occurs remains ill-understood. Unexpectedly, we observed that an imbalance in the levels of the lamina-associated polypeptide 1 (LAP1), an activator of ER-resident Torsin AAA+-ATPases, causes a failure in membrane removal from mitotic chromatin, accompanied by chromosome segregation errors and changes in post-mitotic nuclear morphology. These defects are dependent on a hitherto unknown chromatin-binding region of LAP1 that we have delineated. LAP1-induced NE abnormalities are efficiently suppressed by expression of wild-type but not ATPase-deficient Torsins. Furthermore, a dominant-negative Torsin induces chromosome segregation defects in a LAP1-dependent manner. These results indicate that association of LAP1 with chromatin in the nucleus can be modulated by Torsins in the perinuclear space, shedding new light on the LAP1-Torsin interplay.

The Nuclear Envelope in Lipid Metabolism and Pathogenesis of NAFLD.

Nonalcoholic fatty liver disease (NAFLD) is a burgeoning public health problem worldwide. Despite its tremendous significance for public health, we lack a comprehensive understanding of the pathogenic mechanisms of NAFLD and its more advanced stage, nonalcoholic steatohepatitis (NASH). Identification of novel pathways or cellular mechanisms that regulate liver lipid metabolism has profound implications for the understanding of the pathology of NAFLD and NASH. The nuclear envelope is topologically connected to the ER, where protein synthesis and lipid synthesis occurs. Emerging evidence points toward that the nuclear lamins and nuclear membrane-associated proteins are involved in lipid metabolism and homeostasis. We review published reports that link these nuclear envelope proteins to lipid metabolism. In particular, we focus on the recent work demonstrating the essential roles for the nuclear envelope-localized torsinA/lamina-associated polypeptide (LAP1) complex in hepatic steatosis, lipid secretion, and NASH development. We also discuss plausible pathogenic mechanisms by which the loss of either protein in hepatocytes leads to hepatic dyslipidemia and NASH development.

Muscular involvement and tendon contracture in limb-girdle muscular dystrophy 2Y: a mild adult phenotype and literature review.

BACKGROUND: Limb girdle muscular dystrophy type 2Y (LGMD2Y) is a rare subgroup of limb girdle muscular dystrophy featuring limb-girdle weakness, tendon contracture and cardiac involvement. It is caused by the mutation of TOR1AIP1, which encodes nuclear membrane protein LAP1 (lamina-associated polypeptide 1) and comprises heterogeneous phenotypes. The present study reported a patient with a novel homozygous TOR1AIP1 mutation that presented with selective muscle weakness, which further expanded the phenotype of LGMD2Y- and TOR1AIP1-associated nuclear envelopathies. CASE PRESENTATION: A 40-year-old male presented with Achilles tendon contracture and muscle weakness that bothered him from 8 years old. While the strength of his distal and proximal upper limbs was severely impaired, the function of his lower limbs was relatively spared. Muscle pathology showed dystrophic features, and electron microscopy showed ultrastructural abnormalities of disrupted muscle nuclei envelopes. Whole-exome sequencing showed a frameshift mutation in TOR1AIP1 (c.98dupC). CONCLUSION: We reported a novel mild phenotype of LGMD2Y with relatively selective distal upper limb weakness and joint contracture and revealed the heterogeneity of LGDM2Y and the role of the LAP1 isoform by literature review.

Nuclear Accumulation of LAP1:TRF2 Complex during DNA Damage Response Uncovers a Novel Role for LAP1.

Lamina-associated polypeptide 1 (LAP1) is a nuclear envelope (NE) protein whose function remains poorly characterized. In a recent LAP1 protein interactome study, a putative regulatory role in the DNA damage response (DDR) has emerged and telomeric repeat-binding factor 2 (TRF2), a protein intimately associated with this signaling pathway, was among the list of LAP1 interactors. To gain insights into LAP1's physiological properties, the interaction with TRF2 in human cells exposed to DNA-damaging agents was investigated. The direct LAP1:TRF2 binding was validated in vitro by blot overlay and in vivo by co-immunoprecipitation after hydrogen peroxide and bleomycin treatments. The regulation of this protein interaction by LAP1 phosphorylation was demonstrated by co-immunoprecipitation and mass spectrometry following okadaic acid exposure. The involvement of LAP1 and TRF2 in the DDR was confirmed by their increased nuclear protein levels after bleomycin treatment, evaluated by immunoblotting, as well as by their co-localization with DDR factors at the NE and within the nucleoplasm, assessed by immunocytochemistry. Effectively, we showed that the LAP1:TRF2 complex is established during a cellular response against DNA damage. This work proposes a novel functional role for LAP1 in the DDR, revealing a potential biological mechanism that may be disrupted in LAP1-associated pathologies.

CD8 Treg Cells Inhibit B-Cell Proliferation and Immunoglobulin Production.

AIM: The role of CD4+ Treg in immune responses has been well established. More recently, a role of CD8+ T regulatory cells (CD8 Treg) in the regulation of immune responses in health and autoimmune diseases has been investigated. Furthermore, different investigators have used different markers to define CD8 Treg. Finally, regulatory effects of CD8 Treg have been studied against T-cell responses; however, their role in regulating B-cell proliferation and immunoglobulin production has not been evaluated. Therefore, in this study we examined the effect of two types of CD8 Treg on B-cell proliferation and immunoglobulin production. METHODS: Purified CD8+ T cells were activated with anti-CD3/CD28 for 48 h and then sorted into two different types of CD8 Treg as defined by two different sets of markers, CD8+CD183+CD197+CD45RA- and CD8+CD183+CD25highCD278+. Purified B cells were cocultured with sorted CD8 Treg at 1:1, 1:1/2, and 1:1/4 ratios and activated with anti-CD40 and CpG. B-cell proliferation was assessed by the CFSE dye dilution assay and immunoglobulin production by the ELISA assay. RESULTS: Our data show CD183+CD197+CD45RA-CD8 Treg significantly inhibited B-cell proliferation and inhibited IgM and IgG production but not IgA production at 1:1 ratio only. However, CD183+CD25highCD278+CD8 Treg inhibited significantly B-cell proliferation at 1:1 and 1:1/2 ratios and IgM, IgG, and IgA production at all ratios. CONCLUSION: CD8 Treg regulate B-cell responses, and CD183+CD25highCD278+CD8 Treg are more powerful regulators of B-cell proliferation and immunoglobulin production than CD183+CD197+CD45RA-CD8 Treg and, therefore, may be used as preferred markers for CD8 Treg.

Liver-enriched activator protein 1 as an isoform of CCAAT/enhancer-binding protein beta suppresses stem cell features of hepatocellular carcinoma.

PURPOSE: Liver cancer stem cells (CSCs) are known to be associated with the development, survival, proliferation, metastasis, and recurrence of liver tumors. The aim of this study was to investigate the association of liver-enriched activator protein 1 (LAP1) with hepatocellular carcinoma (HCC) and liver CSCs (LCSCs) and explore the impact of LAP1 on LCSCs. MATERIALS AND METHODS: Differences in LAP1 expression in liver cancer tissues versus matched para-tumoral liver tissues and LCSCs versus non-CSCs were analyzed by Western blotting, real-time polymerase chain reaction, immunohistochemistry, and flow cytometry. The effect of LAP1 on liver cancer cells was evaluated by the expression of CSC markers, oncosphere formation, proliferation, migration, and invasion in vitro. Cell cycle distribution and the number of apoptotic cells were analyzed to assess cell cycle and cell apoptosis. Furthermore, a mouse subcutaneous tumor implant model was established to explore the role of LAP1 in the development of HCC in vivo. Finally, the expression of CSC markers in paraffin-embedded sections was evaluated by immunofluorescence. RESULTS: LAP1 was weakly expressed in HCC tumors and cell lines and even weaker in LCSCs. LAP1 inhibited the expression of stem cell-associated genes and reduced the abilities of oncosphere formation, proliferation, migration, and invasion in vitro. Cell cycle assay revealed that LAP1 induced G1/G0 arrest. Furthermore, LAP1 decreased subcutaneous tumor-formation ability and the expression of CSC markers and Ki67 in vivo. CONCLUSION: LAP1 suppressed the stem cell features of HCC, indicating that it possessed an antitumor effect in liver cancer, both in vitro and in vivo; therefore, LAP1 may prove to be a potential target in liver CSC-targeted therapy.

Torsins: not your typical AAA+ ATPases.

Torsin ATPases (Torsins) belong to the widespread AAA+ (ATPases associated with a variety of cellular activities) family of ATPases, which share structural similarity but have diverse cellular functions. Torsins are outliers in this family because they lack many characteristics of typical AAA+ proteins, and they are the only members of the AAA+ family located in the endoplasmic reticulum and contiguous perinuclear space. While it is clear that Torsins have essential roles in many, if not all metazoans, their precise cellular functions remain elusive. Studying Torsins has significant medical relevance since mutations in Torsins or Torsin-associated proteins result in a variety of congenital human disorders, the most frequent of which is early-onset torsion (DYT1) dystonia, a severe movement disorder. A better understanding of the Torsin system is needed to define the molecular etiology of these diseases, potentially enabling corrective therapy. Here, we provide a comprehensive overview of the Torsin system in metazoans, discuss functional clues obtained from various model systems and organisms and provide a phylogenetic and structural analysis of Torsins and their regulatory cofactors in relation to disease-causative mutations. Moreover, we review recent data that have led to a dramatically improved understanding of these machines at a molecular level, providing a foundation for investigating the molecular defects underlying the associated movement disorders. Lastly, we discuss our ideas on how recent progress may be utilized to inform future studies aimed at determining the cellular role(s) of these atypical molecular machines and their implications for dystonia treatment options.

Development of a novel multiplexed assay for quantification of transforming growth factor-ß (TGF-ß).

Changes in activity or levels of transforming growth factor-ß (TGF-ß) are associated with a variety of diseases; however, measurement of TGF-ß in biological fluids is highly variable. TGF-ß is biologically inert when associated with its latency-associated peptide (LAP). Most available immunoassays require exogenous activation by acid/heat to release TGF-ß from the latent complex. We developed a novel electrochemiluminescence-based multiplexed assay on the MesoScale Discovery® platform that eliminates artificial activation, simultaneously measures both active TGF-ß1 and LAP1 and includes an internal control for platelet-derived TGF-ß contamination in blood specimens. We optimized this assay to evaluate plasma levels as a function of activation type and clinical specimen preparation. We determined that breast cancer patients' plasma have higher levels of circulating latent TGF-ß (LTGF-ß) as measured by LAP1 than healthy volunteers (p < 0.0001). This assay provides a robust tool for correlative studies of LTGF-ß levels with disease, treatment outcomes and toxicity with a broad clinical applicability.

Depletion of lamina-associated polypeptide 1 from cardiomyocytes causes cardiac dysfunction in mice.

We previously showed that striated muscle-selective depletion of lamina-associated polypeptide 1 (LAP1), an integral inner nuclear membrane protein, leads to profound muscular dystrophy with premature death in mice. As LAP1 is also depleted in hearts of these mice, we examined their cardiac phenotype. Striated muscle-selective LAP1 knockout mice display ventricular systolic dysfunction with abnormal induction of genes encoding cardiomyopathy related proteins. To eliminate possible confounding effects due to skeletal muscle pathology, we generated a new mouse line in which LAP1 is deleted in a cardiomyocyte-selective manner. These mice had no skeletal muscle pathology and appeared overtly normal at 20 weeks of age. However, cardiac echocardiography revealed that they developed left ventricular systolic dysfunction and cardiac gene expression analysis revealed abnormal induction of cardiomyopathy-related genes. Our results demonstrate that LAP1 expression in cardiomyocytes is required for normal left ventricular function, consistent with a report of cardiomyopathy in a human subject with mutation in the gene encoding LAP1.

Mutation in TOR1AIP1 encoding LAP1B in a form of muscular dystrophy: a novel gene related to nuclear envelopathies.

We performed genome-wide homozygosity mapping and mapped a novel myopathic phenotype to chromosomal region 1q25 in a consanguineous family with three affected individuals manifesting proximal and distal weakness and atrophy, rigid spine and contractures of the proximal and distal interphalangeal hand joints. Additionally, cardiomyopathy and respiratory involvement were noted. DNA sequencing of torsinA-interacting protein 1 (TOR1AIP1) gene encoding lamina-associated polypeptide 1B (LAP1B), showed a homozygous c.186delG mutation that causes a frameshift resulting in a premature stop codon (p.E62fsTer25). We observed that expression of LAP1B was absent in the patient skeletal muscle fibres. Ultrastructural examination showed intact sarcomeric organization but alterations of the nuclear envelope including nuclear fragmentation, chromatin bleb formation and naked chromatin. LAP1B is a type-2 integral membrane protein localized in the inner nuclear membrane that binds to both A- and B-type lamins, and is involved in the regulation of torsinA ATPase. Interestingly, luminal domain-like LAP1 (LULL1)-an endoplasmic reticulum-localized partner of torsinA-was overexpressed in the patient's muscle in the absence of LAP1B. Therefore, the findings suggest that LAP1 and LULL1 might have a compensatory effect on each other. This study expands the spectrum of genes associated with nuclear envelopathies and highlights the critical function for LAP1B in striated muscle.

Histone variant selectivity at the transcription start site: H2A.Z or H2A.Lap1.

Considerable attention has been given to the understanding of how nucleosomes are altered or removed from the transcription start site of RNA polymerase II genes to enable transcription to proceed. This has led to the view that for transcriptional activation to occur, the transcription start site (TSS) must become depleted of nucleosomes. However, we have shown that this is not the case with different unstable histone H2A variant-containing nucleosomes occupying the TSS under different physiological settings. For example, during mouse spermatogenesis we found that the mouse homolog of human H2A.Bbd, H2A.Lap1, is targeted to the TSS of active genes expressed during specific stages of spermatogenesis. On the other hand, we observed in trophoblast stem cells, a H2A.Z-containing nucleosome occupying the TSS of genes active in the G 1 phase of the cell cycle. Notably, this H2A.Z-containing nucleosome was different compared with other promoter specific H2A.Z nucleosomes by being heterotypic rather than being homotypic. In other words, it did not contain the expected two copies of H2A.Z per nucleosome but only one (i.e., H2A.Z/H2A rather than H2A.Z/H2A.Z). Given these observations, we wondered whether the histone variant composition of a nucleosome at an active TSS could in fact vary in the same cell type. To investigate this possibility, we performed H2A.Z ChIP-H2A reChIP assays in the mouse testis and compared this data with our testis H2A.Lap1 ChIP-seq data. Indeed, we find that different promoters involved in the expression of genes involved in distinct biological processes can contain either H2A.Z/H2A or H2A.Lap1. This argues that specific mechanisms exist, which can determine whether H2A.Z or H2A.Lap1 is targeted to the TSS of an active gene.