The Novel Gene fad158, Having a Transmembrane Domain and Leucine-rich Repeat, Stimulates Adipocyte Differentiation

Genomic signatures of climate adaptation in bank voles

Evidence for divergent selection and adaptive variation across the landscape can provide insight into a species' ability to adapt to different environments. However, despite recent advances in genomics, it remains difficult to detect the footprints of climate-mediated selection in natural populations. Here, we analysed ddRAD sequencing data (21,892 SNPs) in conjunction with geographic climate variation to search for signatures of adaptive differentiation in twelve populations of the bank vole (Clethrionomys glareolus) distributed across Europe. To identify the loci subject to selection associated with climate variation, we applied multiple genotype-environment association methods, two univariate and one multivariate, and controlled for the effect of population structure. In total, we identified 213 candidate loci for adaptation, 74 of which were located within genes. In particular, we identified signatures of selection in candidate genes with functions related to lipid metabolism and the immune system. Using the results of redundancy analysis, we demonstrated that population history and climate have joint effects on the genetic variation in the pan-European metapopulation. Furthermore, by examining only candidate loci, we found that annual mean temperature is an important factor shaping adaptive genetic variation in the bank vole. By combining landscape genomic approaches, our study sheds light on genome-wide adaptive differentiation and the spatial distribution of variants underlying adaptive variation influenced by local climate in bank voles.

Physiological Functions of the Volume-Regulated Anion Channel VRAC/LRRC8 and the Proton-Activated Chloride Channel ASOR/TMEM206

Volume-regulated anion channels (VRACs) and the acid-sensitive outwardly rectifying anion channel (ASOR) mediate flux of chloride and small organic anions. Although known for a long time, they were only recently identified at the molecular level. VRACs are heteromers consisting of LRRC8 proteins A to E. Combining the essential LRRC8A with different LRRC8 paralogues changes key properties of VRAC such as conductance or substrate selectivity, which is how VRACs are involved in multiple physiological functions including regulatory volume decrease, cell proliferation and migration, cell death, purinergic signalling, fat and glucose metabolism, insulin signalling, and spermiogenesis. VRACs are also involved in pathological conditions, such as the neurotoxic release of glutamate and aspartate. Certain VRACs are also permeable to larger, organic anions, including antibiotics and anti-cancer drugs, making them an interesting therapeutic target. ASOR, also named proton-activated chloride channel (PAC), is formed by TMEM206 homotrimers on the plasma membrane and on endosomal compartments where it mediates chloride flux in response to extracytosolic acidification and plays a role in the shrinking and maturation of macropinosomes. ASOR has been shown to underlie neuronal swelling which causes cell death after stroke as well as promoting the metastasis of certain cancers, making them intriguing therapeutic targets as well.

Using QTL to Identify Genes and Pathways Underlying the Regulation and Production of Milk Components in Cattle

Milk is a complex liquid, and the concentrations of many of its components are under genetic control. Many genes and pathways are known to regulate milk composition, and the purpose of this review is to highlight how the discoveries of quantitative trait loci (QTL) for milk phenotypes can elucidate these pathways. The main body of this review focuses primarily on QTL discovered in cattle (Bos taurus) as a model species for the biology of lactation, and there are occasional references to sheep genetics. The following section describes a range of techniques that can be used to help identify the causative genes underlying QTL when the underlying mechanism involves the regulation of gene expression. As genotype and phenotype databases continue to grow and diversify, new QTL will continue to be discovered, and although proving the causality of underlying genes and variants remains difficult, these new data sets will further enhance our understanding of the biology of lactation.

Simple oligonucleotide-based multiplexing of single-cell chromatin accessibility

Microdroplet single-cell ATAC-seq is widely used to measure chromatin accessibility, however, highly scalable and simple sample multiplexing procedures are not available. Here, we present a transposome-assisted single nucleus barcoding approach for ATAC-seq (SNuBar-ATAC) that utilizes a single oligonucleotide adaptor for multiplexing samples during the existing tagmentation step and does not require a pre-labeling procedure. The accuracy and scalability of SNuBar-ATAC was evaluated using cell line mixture experiments. We applied SNuBar-ATAC to investigate treatment-induced chromatin accessibility dynamics by multiplexing 28 mice with lung tumors that received different combinations of chemo, radiation, and targeted immunotherapy. We also applied SNuBar-ATAC to study spatial epigenetic heterogeneity by multiplexing 32 regions from a human breast tissue. Additionally, we show that SNuBar can multiplex single cell ATAC and RNA multiomic assays in cell lines and human breast tissue samples. Our data show that SNuBar is a highly accurate, easy-to-use, and scalable system for multiplexing scATAC-seq and scATAC and RNA co-assay experiments.

Absolute Protein Amounts and Relative Abundance of Volume-regulated Anion Channel (VRAC) LRRC8 Subunits in Cells and Tissues Revealed by Quantitative Immunoblotting

The volume-regulated anion channel (VRAC) plays an important role in osmotic cell volume regulation. In addition, it is involved in various physiological processes such as insulin secretion, glia-neuron communication and purinergic signaling. VRAC is formed by hetero-hexamers of members of the LRRC8 protein family, which consists of five members, LRRC8A-E. LRRC8A is an essential subunit for physiological functionality of VRAC. Its obligate heteromerization with at least one of its paralogues, LRRC8B-E, determines the biophysical properties of VRAC. Moreover, the subunit composition is of physiological relevance as it largely influences the activation mechanism and especially the substrate selectivity. However, the endogenous tissue-specific subunit composition of VRAC is unknown. We have now developed and applied a quantitative immunoblot study of the five VRAC LRRC8 subunits in various mouse cell lines and tissues, using recombinant protein for signal calibration. We found tissue-specific expression patterns of the subunits, and generally relative low expression of the essential LRRC8A subunit. Immunoprecipitation of LRRC8A also co-precipitates an excess of the other subunits, suggesting that non-LRRC8A subunits present the majority in hetero-hexamers. With this, we can estimate that in the tested cell lines, the number of VRAC channels per cell is in the order of 10,000, which is in agreement with earlier calculations from the comparison of single-channel and whole-cell currents.

More than just a pressure relief valve: physiological roles of volume-regulated LRRC8 anion channels

The volume-regulated anion channel (VRAC) is a key player in the volume regulation of vertebrate cells. This ubiquitously expressed channel opens upon osmotic cell swelling and potentially other cues and releases chloride and organic osmolytes, which contributes to regulatory volume decrease (RVD). A plethora of studies have proposed a wide range of physiological roles for VRAC beyond volume regulation including cell proliferation, differentiation and migration, apoptosis, intercellular communication by direct release of signaling molecules and by supporting the exocytosis of insulin. VRAC was additionally implicated in pathological states such as cancer therapy resistance and excitotoxicity under ischemic conditions. Following extensive investigations, 5 years ago leucine-rich repeat-containing family 8 (LRRC8) heteromers containing LRRC8A were identified as the pore-forming components of VRAC. Since then, molecular biological approaches have allowed further insight into the biophysical properties and structure of VRAC. Heterologous expression, siRNA-mediated downregulation and genome editing in cells, as well as the use of animal models have enabled the assessment of the proposed physiological roles, together with the identification of new functions including spermatogenesis and the uptake of antibiotics and platinum-based cancer drugs. This review discusses the recent molecular biological insights into the physiology of VRAC in relation to its previously proposed roles.

LRRC8A Expression Influences Growth of Esophageal Squamous Cell Carcinoma

The volume-regulated anion channel is composed of leucine-rich repeat-containing protein A (LRRC8A) and is activated by hypotonic conditions to implement the process of regulatory volume decrease. The role of LRRC8A in regulating genes related to progression of esophageal squamous cell carcinoma (ESCC) was investigated, as well as the prognostic significance of LRRC8A expression in this tumor. Knockdown experiments were conducted using ESCC cell lines and LRRC8A siRNA to assess the influence of this protein on tumor function. In addition, the gene expression profile of ESCC was determined by microarray analysis. Immunohistochemistry was performed on 64 primary tumor samples from ESCC patients receiving radical esophagectomy. It was found that depletion of LRRC8A decreased cell proliferation and migration and also promoted apoptosis. Microarray data demonstrated G₁/S checkpoint regulation and up-regulation or down-regulation of phosphatidylinositol 3-kinase/AKT signaling, matrix metalloproteinase, and integrin signaling-related genes (including p21, p27, MMP1, and ITGAV) in LRRC8A-depleted cells. Immunohistochemistry showed that LRRC8A expression was related to the pathologic N and T stage categories, and strong LRRC8A expression was correlated with a worse prognosis of ESCC. These findings indicate that LRRC8A modulates tumor progression by influencing cell cycle, apoptosis, and migration, providing new insights into its function as an effector or biomarker of ESCC.

Molecular Biology and Physiology of Volume-Regulated Anion Channel (VRAC)

The Volume-Regulated Anion Channel (VRAC) is activated by cell swelling and plays a key role in cell volume regulation. VRAC is ubiquitously expressed in vertebrate cells and also implicated in many other physiological and cellular processes including fluid secretion, glutamate release, membrane potential regulation, cell proliferation, migration, and apoptosis. Although its biophysical properties have been well characterized, the molecular identity of VRAC remained a mystery for almost three decades. The field was transformed by recent discoveries showing that the leucine-rich repeat-containing protein 8A (LRRC8A, also named SWELL1) and its four other homologs form heteromeric VRAC channels. The composition of LRRC8 subunits determines channel properties and substrate selectivity of a large variety of different VRACs. Incorporating purified SWELL1-containing protein complexes into lipid bilayers is sufficient to reconstitute channel activities, a finding that supports the decrease in intracellular ionic strength as the mechanism of VRAC activation during cell swelling. Characterization of Swell1 knockout mice uncovers the important role of VRAC in T cell development, pancreatic β-cell glucose-stimulated insulin secretion, and adipocyte metabolic function. The ability to permeate organic osmolytes and metabolites is a major feature of VRAC. The list of VRAC substrates is expected to grow, now also including some cancer drugs and antibiotics even under non-cell swelling conditions. Therefore, a critical role of VRAC in drug resistance and cell-cell communication is emerging. This review summarizes the exciting recent progress on the structure-function relationship and physiology of VRAC and discusses key future questions to be solved.

Space microgravity drives transdifferentiation of human bone marrow-derived mesenchymal stem cells from osteogenesis to adipogenesis

Bone formation is linked with osteogenic differentiation of mesenchymal stem cells (MSCs) in the bone marrow. Microgravity in spaceflight is known to reduce bone formation. In this study, we used a real microgravity environment of the SJ-10 Recoverable Scientific Satellite to examine the effects of space microgravity on the osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hMSCs). hMSCs were induced toward osteogenic differentiation for 2 and 7 d in a cell culture device mounted on the SJ-10 satellite. The satellite returned to Earth after going through space experiments in orbit for 12 d, and cell samples were harvested and analyzed for differentiation potentials. The results showed that space microgravity inhibited osteogenic differentiation and resulted in adipogenic differentiation, even under osteogenic induction conditions. Under space microgravity, the expression of 10 genes specific for osteogenesis decreased, including collagen family members, alkaline phosphatase ( ALP), and runt-related transcription factor 2 ( RUNX2), whereas the expression of 4 genes specific for adipogenesis increased, including adipsin ( CFD), leptin ( LEP), CCAAT/enhancer binding protein β ( CEBPB), and peroxisome proliferator-activated receptor-γ ( PPARG). In the analysis of signaling pathways specific for osteogenesis, we found that the expression and activity of RUNX2 was inhibited, expression of bone morphogenetic protein-2 ( BMP2) and activity of SMAD1/5/9 were decreased, and activity of focal adhesion kinase (FAK) and ERK-1/2 declined significantly under space microgravity. These data indicate that space microgravity plays a dual role by decreasing RUNX2 expression and activity through the BMP2/SMAD and integrin/FAK/ERK pathways. In addition, we found that space microgravity increased p38 MAPK and protein kinase B (AKT) activities, which are important for the promotion of adipogenic differentiation of hMSCs. Space microgravity significantly decreased the expression of Tribbles homolog 3 ( TRIB3), a repressor of adipogenic differentiation. Y15, a specific inhibitor of FAK activity, was used to inhibit the activity of FAK under normal gravity; Y15 decreased protein expression of TRIB3. Therefore, it appears that space microgravity decreased FAK activity and thereby reduced TRIB3 expression and derepressed AKT activity. Under space microgravity, the increase in p38 MAPK activity and the derepression of AKT activity seem to synchronously lead to the activation of the signaling pathway specifically promoting adipogenesis.-Zhang, C., Li, L., Jiang, Y., Wang, C., Geng, B., Wang, Y., Chen, J., Liu, F., Qiu, P., Zhai, G., Chen, P., Quan, R., Wang, J. Space microgravity drives transdifferentiation of human bone marrow-derived mesenchymal stem cells from osteogenesis to adipogenesis.

FAD104, a regulator of adipogenesis, is a novel suppressor of TGF-β-mediated EMT in cervical cancer cells

Epithelial-to-mesenchymal transition (EMT) is a biological process in which epithelial cells translate into a mesenchymal phenotype with invasive capacities, contributing to tumour progression, metastasis, and the acquisition of chemotherapy resistance. To identify new therapeutic targets for cancers, it is important to clarify the molecular mechanism of induction of EMT. We have previously reported that fad104, a positive regulator of adipocyte differentiation, suppressed the invasion and metastasis of melanoma and breast cancer cells. In this study, we showed that FAD104 functions as a novel suppressor of transforming growth factor-β (TGF-β)–mediated EMT in cervical cancer cells. Expression of FAD104 is upregulated during TGF-β–mediated EMT in human cervical cancer HeLa cells. Reduction of fad104 expression enhanced TGF-β–mediated EMT and migration in HeLa cells. Conversely, overexpression of FAD104 suppressed TGF-β–induced EMT. In addition, we showed that FAD104 negatively regulated phosphorylation of Smad2 and Smad3 but positively regulated phosphorylation of Smad1/5/8 via treatment with TGF-β. These findings demonstrate that FAD104 is a novel suppressor of TGF-β signalling and represses TGF-β–mediated EMT in cervical cancer cells.

Leucine-rich repeat containing protein LRRC8A is essential for swelling-activated Cl- currents and embryonic development in zebrafish

A volume‐regulated anion channel (VRAC) has been electrophysiologically characterized in innumerable mammalian cell types. VRAC is activated by cell swelling and mediates the volume regulatory efflux of Cl⁻ and small organic solutes from cells. Two groups recently identified the mammalian leucine‐rich repeat containing protein LRRC8A as an essential VRAC component. LRRC8A must be coexpressed with at least one of the other four members of this gene family, LRRC8B‐E, to reconstitute VRAC activity in LRRC8^−/− cells. LRRC8 genes likely arose with the origin of chordates. We identified LRRC8A and LRRC8C‐E orthologs in the zebrafish genome and demonstrate that zebrafish embryo cells and differentiated adult cell types express a swelling‐activated Cl⁻ current indistinguishable from mammalian VRAC currents. Embryo cell VRAC currents are virtually eliminated by morpholino knockdown of the zebrafish LRRC8A ortholog lrrc8aa. VRAC activity is fully reconstituted in LRRC8^−/− human cells by coexpression of zebrafish lrrc8aa and human LRRC8C cDNAs. lrrc8aa expression varies during zebrafish embryogenesis and lrrc8aa knockdown causes pericardial edema and defects in trunk elongation and somatogenesis. Our studies provide confirmation of the importance of LRRC8A in VRAC activity and establish the zebrafish as a model system for characterizing the molecular regulation and physiological roles of VRAC and LRRC8 proteins.

Leucine-rich repeat-containing 8B protein is associated with the endoplasmic reticulum Ca2+ leak in HEK293 cells

Leucine-rich repeat-containing 8 (LRRC8) proteins have been proposed to evolutionarily originate from the combination of the channel protein pannexin, and a leucine-rich repeat (LRR) domain. Five paralogs of LRRC8, namely LRRC8A, LRRC8B, LRRC8C, LRRC8D and LRRC8E have been reported. LRRC8A has been shown to be instrumental in cell swelling. Here, we identify LRRC8B as a key player in the cellular Ca²⁺ signaling network. Overexpression of human LRRC8B in HEK293 cells reduced the Ca²⁺ level in the endoplasmic reticulum (ER). LRRC8B-overexpressing cells exhibited a lesser release of Ca²⁺ from the ER in response to ATP, carbachol and intracellular administration of inositol (1,4,5)-trisphosphate (IP₃). LRRC8B-knockdown cells showed a slower depletion of the ER Ca²⁺ stores when sarco-endoplasmic reticulum Ca²⁺-ATPase was blocked with thapsigargin (TG), while overexpression of LRRC8B had the opposite effect. LRRC8B-overexpressing cells exhibited a higher level of store-operated Ca²⁺ entry following store-depletion by TG. Collectively, LRRC8B participates in intracellular Ca²⁺ homeostasis by acting as a leak channel in the ER. This study gives a fundamental understanding of the role of a novel protein in the elemental cellular process of ER Ca²⁺ leak and expands the known roles for LRRC8 proteins.This article has an associated First Person interview with the first author of the paper.

SWELL1 is a regulator of adipocyte size, insulin signalling and glucose homeostasis

Adipocytes undergo considerable volumetric expansion in the setting of obesity. It has been proposed that such marked increases in adipocyte size may be sensed via adipocyte-autonomous mechanisms to mediate size-dependent intracellular signalling. Here, we show that SWELL1 (LRRC8a), a member of the Leucine-Rich Repeat Containing protein family, is an essential component of a volume-sensitive ion channel (VRAC) in adipocytes. We find that SWELL1-mediated VRAC is augmented in hypertrophic murine and human adipocytes in the setting of obesity. SWELL1 regulates adipocyte insulin-PI3K-AKT2-GLUT4 signalling, glucose uptake and lipid content via SWELL1 C-terminal leucine-rich repeat domain interactions with GRB2/Cav1. Silencing GRB2 in SWELL1 KO adipocytes rescues insulin-pAKT2 signalling. In vivo, shRNA-mediated SWELL1 knockdown and adipose-targeted SWELL1 knockout reduce adiposity and adipocyte size in obese mice while impairing systemic glycaemia and insulin sensitivity. These studies identify SWELL1 as a cell-autonomous sensor of adipocyte size that regulates adipocyte growth, insulin sensitivity and glucose tolerance.

Lrrc75b is a novel negative regulator of C2C12 myogenic differentiation

Many transcription factors and signaling molecules involved in the guidance of myogenic differentiation have been investigated in previous studies. However, the precise molecular mechanisms of myogenic differentiation remain largely unknown. In the present study, by performing a meta-analysis of C2C12 myogenic differentiation microarray data, we found that leucine-rich repeat-containing 75B (Lrrc75b), also known as AI646023, a molecule of unknown biological function, was downregulated during C2C12 myogenic differentiation. The knockdown of Lrrc75b using specific siRNA in C2C12 myoblasts markedly enhanced the expression of muscle-specific myogenin and increased myoblast fusion and the myotube diameter. By contrast, the adenovirus-mediated overexpression of Lrrc75b in C2C12 cells markedly inhibited myoblast differentiation accompanied by a decrease in myogenin expression. In addition, the phosphorylation of extracellular signal-regulated kinase 1/2 (Erk1/2) was suppressed in the cells in which Lrrc75b was silenced. Taken together, our results demonstrate that Lrrc75b is a novel suppressor of C2C12 myogenic differentiation by modulating myogenin and Erk1/2 signaling.

Characterization of Somatically-Eliminated Genes During Development of the Sea Lamprey (Petromyzon marinus)

The sea lamprey (Petromyzon marinus) is a basal vertebrate that undergoes developmentally programmed genome rearrangements (PGRs) during early development. These events facilitate the elimination of ∼20% of the genome from the somatic cell lineage, resulting in distinct somatic and germline genomes. Thus far only a handful of germline-specific genes have been definitively identified within the estimated 500 Mb of DNA that is deleted during PGR, although a few thousand germline-specific genes are thought to exist. To improve our understanding of the evolutionary/developmental logic of PGR, we generated computational predictions to identify candidate germline-specific genes within a new transcriptomic dataset derived from adult germline and the early embryonic stages during which PGR occurs. Follow-up validation studies identified 44 germline-specific genes and further characterized patterns of transcription and DNA loss during early embryogenesis. Expression analyses reveal that many of these genes are differentially expressed during early embryogenesis and presumably function in the early development of the germline. Ontology analyses indicate that many of these germline-specific genes play known roles in germline development, pluripotency, and oncogenesis (when misexpressed). These studies provide support for the theory that PGR serves to segregate molecular functions related to germline development/pluripotency in order to prevent their potential misexpression in somatic cells. This larger set of eliminated genes also allows us to extend the evolutionary/developmental breadth of this theory, as some deleted genes (or their gnathostome homologs) appear to be associated with the early development of somatic lineages, perhaps through the evolution of novel functions within gnathostome lineages.

LRRC8 Proteins Form Volume-Regulated Anion Channels that Sense Ionic Strength

The volume-regulated anion channel (VRAC) is activated when a cell swells, and it plays a central role in maintaining cell volume in response to osmotic challenges. SWELL1 (LRRC8A) was recently identified as an essential component of VRAC. However, the identity of the pore-forming subunits of VRAC and how the channel is gated by cell swelling are unknown. Here, we show that SWELL1 and up to four other LRRC8 subunits assemble into heterogeneous complexes of ∼800 kDa. When reconstituted into bilayers, LRRC8 complexes are sufficient to form anion channels activated by osmolality gradients. In bilayers, as well as in cells, the single-channel conductance of the complexes depends on the LRRC8 composition. Finally, low ionic strength (Γ) in the absence of an osmotic gradient activates the complexes in bilayers. These data demonstrate that LRRC8 proteins together constitute the VRAC pore and that hypotonic stress can activate VRAC through a decrease in cytoplasmic Γ.

FAD104, a Regulator of Adipogenesis and Osteogenesis, Interacts with the C-Terminal Region of STAT3 and Represses Malignant Transformation of Melanoma Cells

Anchorage-independent growth is one of the defining characteristics of cancer cells. Many oncogenes and tumor suppressor genes are involved in regulating this type of growth. Factor for adipocyte differentiation 104 gene (fad104) is a regulator of adipogenesis and osteogenesis. Previously, we reported that fad104 suppressed metastasis as well as invasion of melanoma cells. However, it is unclear whether fad104 is involved in malignant transformation, which is associated with metastasis. In this study, we revealed that fad104 negatively regulated the colony forming activity of melanoma cells. The presence of the N-terminal region of FAD104 was required for the regulation of malignant transformation of melanoma cells. In addition, the deletion mutant of FAD104 that contained the N-terminal region and transmembrane domain interacted with signal transducer and activator of transcription 3 (STAT3) and suppressed STAT3 activity. However, the deletion mutant of FAD104 lacking the N-terminal region did not influence the interaction with STAT3 or suppress the STAT3 activity. Moreover, FAD104 interacted with the C-terminal region of STAT3. In summary, we demonstrated that fad104 suppressed anchorage-independent growth of melanoma cells, and that the N-terminal region of FAD104 is essential for inhibiting malignant transformation and STAT3 activity.

[Molecular Mechanisms of Early-stage Adipocyte Differentiation and Multi-functional Roles of Newly Isolated Adipogenic Factors]

Obesity is a major risk factor for diabetes, hypertension, hyperlipidemia, and arteriosclerosis. Although the middle and late stages of adipocyte differentiation are well characterized, the earliest step in the differentiation process has remained largely unknown. We isolated 102 genes expressed at the beginning of the differentiation of a mouse preadipocyte cell line, 3T3-L1 cells. Because approximately half of these genes were unknown, we named them factor for adipocyte differentiation (fad) genes. I first show how these genes regulate the early stage of adipocyte differentiation. We next generated fad104-deficient mice, and demonstrated that fad104-deficient mice died due to cyanosis-associated lung dysplasia with atelectasis. We also found that fad104 positively regulated adipocyte differentiation and negatively regulated osteoblast differentiation. We then demonstrated that fad24-knockdown inhibited mitotic clonal expansion (MCE) and that FAD24 contributed to the regulation of DNA replication by recruiting histone acetyltransferase binding to ORC1 (HBO1) to DNA replication origins. In vitro culture experiments revealed that fad24-null embryos developed normally to the morula stage, but acquired growth defects in subsequent stages. These results strongly suggest that fad24 is essential for pre-implantation in embryonic development, particularly for progression to the blastocyst stage. These findings together indicate that both fad104 and fad24 contribute not only to adipogenesis but also to other physiological events. The multi-functional roles of these genes are discussed.

Volume-regulated anion channel--a frenemy within the brain

The volume-regulated anion channel (VRAC) is a ubiquitously expressed yet highly enigmatic member of the superfamily of chloride/anion channels. It is activated by cellular swelling and mediates regulatory cell volume decrease in a majority of vertebrate cells, including those in the central nervous system (CNS). In the brain, besides its crucial role in cellular volume regulation, VRAC is thought to play a part in cell proliferation, apoptosis, migration, and release of physiologically active molecules. Although these roles are not exclusive to the CNS, the relative significance of VRAC in the brain is amplified by several unique aspects of its physiology. One important example is the contribution of VRAC to the release of the excitatory amino acid neurotransmitters glutamate and aspartate. This latter process is thought to have impact on both normal brain functioning (such as astrocyte-neuron signaling) and neuropathology (via promoting the excitotoxic death of neuronal cells in stroke and traumatic brain injury). In spite of much work in the field, the molecular nature of VRAC remained unknown until less than 2 years ago. Two pioneer publications identified VRAC as the heterohexamer formed by the leucine-rich repeat-containing 8 (LRRC8) proteins. These findings galvanized the field and are likely to result in dramatic revisions to our understanding of the place and role of VRAC in the brain, as well as other organs and tissues. The present review briefly recapitulates critical findings in the CNS and focuses on anticipated impact on the LRRC8 discovery on further progress in neuroscience research.

Fad104, a positive regulator of adipocyte differentiation, suppresses invasion and metastasis of melanoma cells by inhibition of STAT3 activity

Metastasis is the main cause of death in patients with cancer, and understanding the mechanisms of metastatic processes is essential for the development of cancer therapy. Although the role of several cell adhesion, migration or proliferation molecules in metastasis is established, a novel target for cancer therapy remains to be discovered. Previously, we reported that fad104 (factor for adipocyte differentiation 104), a regulatory factor of adipogenesis, regulates cell adhesion and migration. In this report, we clarify the role of fad104 in the invasion and metastasis of cancer cells. The expression level of fad104 in highly metastatic melanoma A375SM cells was lower than that in poorly metastatic melanoma A375C6 cells. Reduction of fad104 expression enhanced the migration and invasion of melanoma cells, while over-expression of FAD104 inhibited migration and invasion. In addition, melanoma cells stably expressing FAD104 showed a reduction in formation of lung colonization compared with control cells. FAD104 interacted with STAT3 and down-regulated the phosphorylation level of STAT3 in melanoma cells. These findings together demonstrate that fad104 suppressed the invasion and metastasis of melanoma cells by inhibiting activation of the STAT3 signaling pathway. These findings will aid a comprehensive description of the mechanism that controls the invasion and metastasis of cancer cells.

The protein synthesis inhibitor blasticidin s enters mammalian cells via leucine-rich repeat-containing protein 8D

Leucine-rich repeat-containing 8 (LRRC8) proteins have been identified as putative receptors involved in lymphocyte development and adipocyte differentiation. They remain poorly characterized, and no specific function has been assigned to them. There is no consensus on how this family of proteins might function because homology searches suggest that members of the LRRC8 family act not as plasma membrane receptors, but rather as channels that mediate cell-cell signaling. Here we provide experimental evidence that supports a role for LRRC8s in the transport of small molecules. We show that LRRC8D is a mammalian protein required for the import of the antibiotic blasticidin S. We characterize localization and topology of LRRC8A and LRRC8D and demonstrate that LRRC8D interacts with LRRC8A, LRRC8B, and LRRC8C. Given the suggested involvement in solute transport, our results support a model in which LRRC8s form one or more complexes that may mediate cell-cell communication by transporting small solutes.

FAD104, a regulatory factor of adipogenesis, acts as a novel regulator of calvarial bone formation

Osteogenesis is a complex process that is orchestrated by several growth factors, extracellular cues, signaling molecules, and transcriptional factors. Understanding the mechanisms of bone formation is pivotal for clarifying the pathogenesis of bone diseases. Previously, we reported that fad104 (factor for adipocyte differentiation 104), a novel positive regulator of adipocyte differentiation, negatively regulated the differentiation of mouse embryonic fibroblasts into osteocytes. However, the physiological role of fad104 in bone formation has not been elucidated. Here, we clarified the role of fad104 in bone formation in vivo and in vitro. fad104 disruption caused craniosynostosis-like premature ossification of the calvarial bone. Furthermore, analyses using primary calvarial cells revealed that fad104 negatively regulated differentiation and BMP/Smad signaling pathway. FAD104 interacted with Smad1/5/8. The N-terminal region of FAD104, which contains a proline-rich motif, was capable of binding to Smad1/5/8. We demonstrated that down-regulation of Smad1/5/8 phosphorylation by FAD104 is dependent on the N-terminal region of FAD104 and that fad104 functions as a novel negative regulator of BMP/Smad signaling and is required for proper development for calvarial bone. These findings will aid a comprehensive description of the mechanism that controls normal and premature calvarial ossification.

A reporter screen in a human haploid cell line identifies CYLD as a constitutive inhibitor of NF-κB

The development of forward genetic screens in human haploid cells has the potential to transform our understanding of the genetic basis of cellular processes unique to man. So far, this approach has been limited mostly to the identification of genes that mediate cell death in response to a lethal agent, likely due to the ease with which this phenotype can be observed. Here, we perform the first reporter screen in the near-haploid KBM7 cell line to identify constitutive inhibitors of NF-κB. CYLD was the only currently known negative regulator of NF-κB to be identified, thus uniquely distinguishing this gene. Also identified were three genes with no previous known connection to NF-κB. Our results demonstrate that reporter screens in haploid human cells can be applied to investigate the many complex signaling pathways that converge upon transcription factors.

Influence of maternal low protein diet during pregnancy on hepatic gene expression signature in juvenile female porcine offspring

SCOPE

Epidemiological and experimental evidence indicates that maternal nutrition status contributes to long-term changes in the metabolic phenotype of the offspring, a process known as fetal programming.

METHODS AND RESULTS

We have used a swine model (Sus scrofa) to analyze consequences of a maternal low protein diet (about 50% of control) during pregnancy on hepatic lipid metabolism and genome-wide hepatic gene expression profile of juvenile female offspring (mean age 85 days). We found 318 S. scrofa genes to be differentially expressed in the liver at age 85 days. In the low protein offspring group key genes of fatty acid de novo synthesis were downregulated whereas several genes of lipolysis and phospholipid biosynthesis were upregulated. qRT-PCR analysis of selected genes verified microarray data and revealed linear correlations between gene expression levels and slaughter weight. Hepatic cholesterol 7α hydroxylase protein expression tended to be lower in the low protein group. Total lipid and triglyceride content and fatty acid composition of total lipids were not different between groups.

CONCLUSION

A maternal low protein diet during pregnancy induces a distinct hepatic gene expression signature in juvenile female pigs which was not translated into phenotypical changes of liver lipid metabolism.

Indispensable role of factor for adipocyte differentiation 104 (fad104) in lung maturation

Factor for adipocyte differentiation 104 (fad104) is a regulator of adipogenesis and osteogenesis. Our previous study showed that fad104-deficient mice died immediately after birth, suggesting fad104 to be essential for neonatal survival. However, the cause of this rapid death is unclear. Here, we demonstrate the role of fad104 in neonatal survival. Phenotypic and morphological analyses showed that fad104-deficient mice died due to cyanosis-associated lung dysplasia including atelectasis. Furthermore, immunohistochemistry revealed that FAD104 was strongly expressed in ATII cells in the developing lung. Most importantly, the ATII cells in lungs were immature, and impaired the expression of surfactant-associated proteins. Collectively, these results indicate that fad104 has an indispensable role in lung maturation, especially the maturation and differentiation of ATII cells.

Fad104, a positive regulator of adipogenesis, negatively regulates osteoblast differentiation

Fad104 (factor for adipocyte differentiation 104) is a novel gene expressed temporarily in the early stages of adipocyte differentiation. Previously, we showed that fad104 promotes adipocyte differentiation in mouse 3T3-L1 cells and mouse embryonic fibroblasts (MEFs). Furthermore, we reported that implanted wild-type MEFs could develop into adipocytes, whereas fad104-deficient MEFs could not. Interestingly, bone-like tissues were only observed in the implants derived from fad104-deficient MEFs. This result implies that fad104 is involved in osteoblast differentiation. However, the functions of fad104 during osteogenesis are unknown. In this paper, we show that fad104 negatively regulates osteoblast differentiation. During the differentiation process, the level of fad104 expression decreased. Deletion of fad104 facilitated osteoblast differentiation in MEFs, and elevated the level of runx2, a master regulator of osteoblast differentiation. Disruption of fad104 suppressed BMP-2-mediated adipocyte differentiation in MEFs. In conclusion, we demonstrate that fad104 reciprocally regulates differentiation of adipocytes and osteoblast; functions as a positive regulator in adipocyte differentiation and as a negative regulator in osteoblast differentiation.

Disruption of the novel gene fad104 causes rapid postnatal death and attenuation of cell proliferation, adhesion, spreading and migration

The molecular mechanisms at the beginning of adipogenesis remain unknown. Previously, we identified a novel gene, fad104 (factor for adipocyte differentiation 104), transiently expressed at the early stage of adipocyte differentiation. Since the knockdown of the expression of fad104 dramatically repressed adipogenesis, it is clear that fad104 plays important roles in adipocyte differentiation. However, the physiological roles of fad104 are still unknown. In this study, we generated fad104-deficient mice by gene targeting. Although the mice were born in the expected Mendelian ratios, all died within 1 day of birth, suggesting fad104 to be crucial for survival after birth. Furthermore, analyses of mouse embryonic fibroblasts (MEFs) prepared from fad104-deficient mice provided new insights into the functions of fad104. Disruption of fad104 inhibited adipocyte differentiation and cell proliferation. In addition, cell adhesion and wound healing assays using fad104-deficient MEFs revealed that loss of fad104 expression caused a reduction in stress fiber formation, and notably delayed cell adhesion, spreading and migration. These results indicate that fad104 is essential for the survival of newborns just after birth and important for cell proliferation, adhesion, spreading and migration.

The role of C/EBPdelta in the early stages of adipogenesis

Adipocyte differentiation is a complex process triggered and facilitated by transcription factors such as peroxisome proliferator-activated receptor gamma (PPARgamma) and CCAAT/enhancer-binding protein (C/EBP) alpha. Most about the cascade underlying the differentiation process, especially events in the early stages, remain to be elucidated. Early on in adipocyte differentiation, the C/EBPbeta and C/EBPdelta genes are rapidly induced to express and later activate PPARgamma and C/EBPalpha expression. C/EBPbeta also plays a crucial role in mitotic clonal expansion (MCE), the approximately two rounds of mitosis which occurs soon after preadipocytes are stimulated by differentiation inducers and a necessary step for adipocyte differentiation. However, the effect of C/EBPdelta, another member of the C/EBP family, on MCE remains unclear. In the present study, we investigated the role of C/EBPdelta in the early stages of adipogenesis. A remarkable induction of C/EBPdelta gene expression after the initiation of differentiation was observed not in proliferating preadipocytes, but in growth-arrested, differentiable cells. RNAi-mediated knockdown of C/EBPdelta dramatically suppressed cell growth after differentiation was induced, and inhibited conversion into lipid-laden adipocytes. Furthermore, silencing of C/EBPdelta impaired the expression of factor for adipocyte differentiation (fad) 49, which is up-regulated and plays a crucial role early in adipogenesis. Taken together, these findings show that C/EBPdelta is involved in MCE and gene expression in the early stages of adipocyte differentiation.

A novel gene, fad49, plays a crucial role in the immediate early stage of adipocyte differentiation via involvement in mitotic clonal expansion

Adipogenesis is accomplished via a complex series of steps, and the events at the earliest stage remain to be elucidated. To clarify the molecular mechanisms of adipocyte differentiation, we previously isolated 102 genes expressed early in mouse 3T3-L1 preadipocyte cells using a PCR subtraction system. About half of the genes isolated appeared to be unknown. After isolating full-length cDNAs of the unknown genes, one of them, named factor for adipocyte differentiation 49 (fad49), appeared to be a novel gene, as the sequence of this clone showed no identity to known genes. FAD49 contains a phox homology (PX) domain and four Src homology 3 (SH3) domains, suggesting that it may be a novel scaffold protein. We found that the PX domain of FAD49 not only has affinity for phosphoinositides, but also binds to its third SH3 domain. Expression of fad49 was transiently elevated 3 h after differentiation was induced, and diminished 24 h after induction. Induction of the fad49 gene was observed in adipocyte differentiable 3T3-L1 cells, but not in non-adipogenic NIH-3T3 cells. RNAi-mediated knockdown of fad49 significantly impaired adipocyte differentiation. Moreover, the knockdown of fad49 by RNAi inhibited mitotic clonal expansion, and reduced the expression of CCAAT/enhancer-binding protein beta (C/EBPbeta) and C/EBPdelta at the immediate early phase. Taken together, these results show that fad49, a novel gene, plays a crucial role in the immediate early stage of adipogenesis.

A novel method of differential gene expression analysis using multiple cDNA libraries applied to the identification of tumour endothelial genes

Background

In this study, differential gene expression analysis using complementary DNA (cDNA) libraries has been improved. Firstly by the introduction of an accurate method of assigning Expressed Sequence Tags (ESTs) to genes and secondly, by using a novel likelihood ratio statistical scoring of differential gene expression between two pools of cDNA libraries. These methods were applied to the latest available cell line and bulk tissue cDNA libraries in a two-step screen to predict novel tumour endothelial markers. Initially, endothelial cell lines were in silico subtracted from non-endothelial cell lines to identify endothelial genes. Subsequently, a second bulk tumour versus normal tissue subtraction was employed to predict tumour endothelial markers.

Results

From an endothelial cDNA library analysis, 431 genes were significantly up regulated in endothelial cells with a False Discovery Rate adjusted q-value of 0.01 or less and 104 of these were expressed only in endothelial cells. Combining the cDNA library data with the latest Serial Analysis of Gene Expression (SAGE) library data derived a complete list of 459 genes preferentially expressed in endothelium. 27 genes were predicted tumour endothelial markers in multiple tissues based on the second bulk tissue screen.

Conclusion

This approach represents a significant advance on earlier work in its ability to accurately assign an EST to a gene, statistically measure differential expression between two pools of cDNA libraries and predict putative tumour endothelial markers before entering the laboratory. These methods are of value and available to researchers that are interested in the analysis of transcriptomic data.

Crucial roles of D-type cyclins in the early stage of adipocyte differentiation

Cyclin D2 was isolated as one of the genes expressed early in adipogenesis. The expression of cyclin D2 increased temporarily early on and then again late in the differentiation process. The expression of cyclin D1 and cyclin D3, the other D-type cyclins, was also transiently induced early during adipocyte differentiation. RNAi (RNA interference)-mediated knockdown of cyclin D1, D2, or D3 inhibited the differentiation of 3T3-L1 cells into lipid-laden adipocytes. Moreover, the knockdown of cyclin D1 or D3 significantly inhibited mitotic clonal expansion (MCE), while silencing of the cyclin D2 gene had a milder effect on MCE. Each of the D-type cyclins seems to play a crucial role in adipocyte differentiation by regulating MCE.

Different Isoforms of HPV-16 E7 Protein are Present in Cytoplasm and Nucleus

The E7 protein of high risk HPV types has been found with different molecular weights, mainly because of phosphorylation, an event that changes protein charge and mobility in SDS-PAGE. Distribution of E7 protein in the cellular compartments has also been subject of debate as some groups report the protein in nucleus and others in cytoplasm. The different subcellular distribution and molecular weights reported for the E7 protein suggest the presence of isoforms. We examined this possibility by using several antibodies that recognize different epitopes on the HPV-16 E7 protein. We showed that E7 is processed in 3 isoforms with different molecular weights and isoelectric points (IEP), and described as E7a1 (17.5 kDa, IEP 4.68), E7a (17 kDa, IEP 6.18) and E7b (16 kDa, IEP 6.96). The immunofluorescense results also showed that E7 is distributed into different compartments (ER, Golgi and nucleus), which suggest the presence of other posttranslational modifications, besides phosphorylation.

FAD24 acts in concert with histone acetyltransferase HBO1 to promote adipogenesis by controlling DNA replication

Preadipocytes differentiate into adipocytes through approximately two rounds of mitosis, referred to as mitotic clonal expansion (MCE), but the events early in the differentiation process are not fully understood. Previously, we identified and characterized a novel gene, fad24 (factor for adipocyte differentiation 24), induced to express at the early stages of adipocyte differentiation. Although fad24 clearly has crucial roles in adipogenesis, its precise functions remain unknown. Here we show that the knockdown of fad24 by RNAi in 3T3-L1 preadipocytes repressed MCE. Moreover, FAD24 interacts with HBO1, a histone acetyltransferase and positive regulator of DNA replication initiation. The knockdown of hbo1 repressed MCE and adipogenesis, indicating that FAD24 acts in concert with HBO1 to promote adipogenesis by controlling DNA replication. Regarding the molecular mechanisms behind the regulation of DNA replication by fad24, we revealed that FAD24 co-localizes with HBO1 to chromatin during late mitosis, which is when the prereplication initiation complex is assembled. Furthermore, chromatin immunoprecipitation experiments indicated that FAD24 localizes to origins of DNA replication with HBO1. When fad24 expression was inhibited during adipocyte differentiation, the recruitment of HBO1 to origins of DNA replication was reduced. Thus, FAD24 controls DNA replication by recruiting HBO1 to origins of DNA replication and is required for MCE during adipocyte differentiation.

peg10, an imprinted gene, plays a crucial role in adipocyte differentiation

An imprinted gene, paternally expressed gene (peg) 10, was isolated as one of the genes expressed early in adipogenesis. The expression of peg10 was elevated after the addition of inducers, and was detected in adipocyte differentiable 3T3-L1 cells, but not observed in the non-adipogenic cell line NIH-3T3. Moreover, the knockdown of peg10 by RNA interference (RNAi) inhibited the differentiation of 3T3-L1 cells into lipid-laden adipocytes. Interestingly, peg10 RNAi-treatment reduced the expressions of C/EBPbeta and C/EBPdelta, and inhibited mitotic clonal expansion. These findings strongly indicate that peg10 plays a crucial role at the immediate early stage of adipocyte differentiation.

Mapping genetic loci that regulate lipid levels in a NZB/B1NJxRF/J intercross and a combined intercross involving NZB/B1NJ, RF/J, MRL/MpJ, and SJL/J mouse strains

The NZB/B1NJ (NZB) mouse strain exhibits high cholesterol and HDL levels in blood compared with several other strains of mice. To study the genetic regulation of blood lipid levels, we performed a genome-wide linkage analysis in 542 chow-fed F2 female mice from an NZBxRF/J (RF) intercross and in a combined data set that included NZBxRF and MRL/MpJxSJL/J intercrosses. In the NZBxRF F2 mice, the cholesterol and HDL concentrations were influenced by quantitative trait loci (QTL) on chromosome (Chr) 5 [logarithm of odds (LOD) 17-19; D5Mit10] that was in the region identified earlier in crosses involving NZB mice, but two QTLs on Chr 12 (LOD 4.7; D12Mit182) and Chr 19 (LOD 5.7; D19Mit1) were specific to the NZBxRF intercross. Triglyceride levels were affected by two novel QTLs at D12Mit182 (LOD 8.7) and D15Mit13 (LOD 3.5). The combined-cross linkage analysis (1,054 mice, 231 markers) 1) identified four shared QTLs (Chrs 5, 7, 14, and 17) that were not detected in one of the parental crosses and 2) improved the resolution of two shared QTLs. In summary, we report additional loci regulating lipid levels in NZB mice that had not been identified earlier in crosses involving the NZB strain of mice. The identification of shared loci from multiple crosses increases confidence toward finding the QTL gene.

Characterization of Novel Genes Regulating Adipocyte Differentiation

The mid- and late stages of adipocyte differentiation are known to be regulated by transcription factors such as peroxisome proliferator-activated receptor (PPAR)gamma and CCAAT-box/enhancer binder protein (C/EBP) families. However, events in the early stage of adipocyte differentiation remain largely unknown. To gain insights into the molecular mechanisms underlying the beginning of adipocyte differentiation, we have isolated 102 genes, which are induced at the beginning of the differentiation of mouse 3T3-L1 preadipocytes, using the polymerase chain reaction (PCR)-subtraction method. Of these, 46 appear to be unknown genes. Since rapid amplification of cDNA end (RACE), cDNA library screening, and a genome database search have revealed that two of these genes are novel, we have named them factor for adipocyte differentiation (fad) 24 and fad158. The database research of amino acid sequences revealed that fad24 has a basic leucine zipper motif and an NOC domain, and fad158 has four transmembrane domains and eight leucine-rich repeats. The expression of fad24 and fad158 transiently increased after the addition of adipogenic inducers [insulin, dexamethasone, 3-isobutyl-1-methylxanthine, fetal bovine serum (FBS)]. RNAi-mediated knockdown of fad24 or antisense fad158 inhibited adipogenesis of 3T3-L1 preadipocytes and decreased expressions of PPARgamma and C/EBPalpha. Furthermore, the constitutive overexpression of fad24 or fad158 in the mouse fibroblast cell line NIH-3T3 resulted in adipocyte conversion when stimulated with adipogenic inducers and PPARgamma ligand BRL49653. Moreover, it was found that FAD24 localizes in the nucleus, especially within nuclear speckles and nucleolus, and FAD158 localizes to the endoplasmic reticulum (ER). Taken together, fad24 and fad158 appear to regulate adipocyte differentiation by activating the PPARgamma pathway.

Up-regulation of adipogenin, an adipocyte plasma transmembrane protein, during adipogenesis

Until now, the various proteins highly expressed in adipose tissues have been identified and characterized by traditional gene cloning techniques. However, methods of computer analysis have been developed to compare the levels of expression among various tissues, and genes whose expression levels differ significantly between tissues have been found. Among these genes, we report on the possible function of a new adipose-specific gene, showed higher expression in adipose tissue through 'Search Expression' on Genome Institute of Norvartis Research Foundation (GNF) SymAtlas v0.8.0. This database has generated and analyzed gene expression of each gene in diverse samples of normal tissues, organs, and cell lines. This newly discovered gene product was named adipogenin because of its role in stimulating adipocyte differentiation and development. Adipogenin mRNA was highly expressed in four different fat depots, and exclusively expressed in adipocytes isolated from adipose tissues. The level of adipogenin mRNA was up-regulated in the subcutaneous and visceral adipose tissues of mice fed a high-fat diet compared to those on the control diet. The expression of adipogenin mRNA is dramatically elevated during adipocyte differentiation of 3T3-L1 cells. Troglitazone, which up-regulated peroxisome proliferators-activated receptor gamma2 (PPAR-gamma2) expression, increased adipogenin mRNA expression, although this gene was down-regulated by retinoic acid. Confocal image analyses of green-fluorescent protein-adipogenin (pEGFP-adipogenin) transiently expressed in 3T3-L1 adipocytes showed that adipogenin was strictly localized to membranes and was absent from the cytosol. Moreover, small interfering RNA (siRNA) mediated a reduction of adipogenin mRNA in 3T3-L1 cells and blocked the process of adipocyte differentiation. These results indicate that adipogenin, an adipocyte-specific membrane protein, may be involved with adipogenesis, as one of the regulators of adipose tissue development.