Ermap, a gene coding for a novel erythroid specific adhesion/receptor membrane protein

Towards reliable quantification of cell state velocities

A few years ago, it was proposed to use the simultaneous quantification of unspliced and spliced messenger RNA (mRNA) to add a temporal dimension to high-throughput snapshots of single cell RNA sequencing data. This concept can yield additional insight into the transcriptional dynamics of the biological systems under study. However, current methods for inferring cell state velocities from such data (known as RNA velocities) are afflicted by several theoretical and computational problems, hindering realistic and reliable velocity estimation. We discuss these issues and propose new solutions for addressing some of the current challenges in consistency of data processing, velocity inference and visualisation. We translate our computational conclusion in two velocity analysis tools: one detailed method κ-velo and one heuristic method eco-velo, each of which uses a different set of assumptions about the data.

ERMAP is a B7 family-related molecule that negatively regulates T cell and macrophage responses

T cell activation and tolerance are tightly regulated by costimulatory and coinhibitory molecules. B7 family members play a crucial role in regulating immune responses. In this study, we identified erythroid membrane-associated protein (ERMAP) as a novel T cell inhibitory molecule. ERMAP shares significant sequence and structural homology with existing B7 family members in its extracellular domain. The ERMAP protein is expressed on the cell surface of resting and activated antigen-presenting cells (APCs) and in some tumor tissues. The putative ERMAP receptor is expressed on activated CD4 and CD8 T cells and macrophages. Both mouse and human ERMAP-IgG2a Fc (ERMAP-Ig) fusion proteins inhibit T cell functions in vitro. Administration of ERMAP-Ig protein ameliorates autoimmune diseases, including experimental autoimmune encephalomyelitis and type 1 diabetes, in mice. Anti-ERMAP antibody enhances macrophage phagocytosis of cancer cells in vitro. Furthermore, administration of an anti-ERMAP antibody inhibits tumor growth in mice likely by blocking the inhibitory effects of ERMAP on T cells and macrophages. Our results suggest that therapeutic interaction with the ERMAP inhibitory pathway may represent a novel strategy for treating patients with autoimmune disease or cancer.

Development of IFN-Stimulated Gene Expression from Embryogenesis through Adulthood, with and without Constitutive MDA5 Pathway Activation

Pathogen-associated molecular patterns (e.g., dsRNA) activate expression of IFN-stimulated genes (ISGs), which protect hosts from infection. Although transient ISG upregulation is essential for effective innate immunity, constitutive activation typically causes harmful autoimmunity in mice and humans, often including severe developmental abnormalities. We have shown that transgenic mice expressing a picornavirus RNA-dependent RNA polymerase (RdRP) outside the viral context (RdRP mice) exhibit constitutive, MDA5-dependent, and quantitatively dramatic upregulation of many ISGs, which confers broad viral infection resistance. Remarkably, RdRP mice never develop autoinflammation, interferonopathy, or other discernible abnormalities. In this study, we used RNA sequencing and other methods to analyze ISG expression across five time points from fetal development to adulthood in wild-type and RdRP mice. In RdRP mice, the proportion of upregulated ISGs increased during development, with the most dramatic induction occurring 2 wk postnatally. The amplified ISG profile is then maintained lifelong. Molecular pathways and biological functions associated with innate immune and IFN signaling are only activated postnatally, suggesting constrained fetal responsiveness to innate immune stimuli. Biological functions supporting replication of viruses are only inhibited postnatally. We further determined that the RdRP is expressed at low levels and that blocking Ifnar1 reverses the amplified ISG transcriptome in adults. In conclusion, the upregulated ISG profile of RdRP mice is mostly triggered early postnatally, is maintained through adulthood, and requires ongoing type I IFN signaling to maintain it. The model provides opportunities to study the systems biology of innate immunity and to determine how sustained ISG upregulation can be compatible with robust health.

The phylogeny of 48 alleles, experimentally verified at 21 kb, and its application to clinical allele detection

Background

Sequence information generated from next generation sequencing is often computationally phased using haplotype-phasing algorithms. Utilizing experimentally derived allele or haplotype information improves this prediction, as routinely used in HLA typing. We recently established a large dataset of long ERMAP alleles, which code for protein variants in the Scianna blood group system. We propose the phylogeny of this set of 48 alleles and identify evolutionary steps to derive the observed alleles.

Methods

The nucleotide sequence of > 21 kb each was used for all physically confirmed 48 ERMAP alleles that we previously published. Full-length sequences were aligned and variant sites were extracted manually. The Bayesian coalescent algorithm implemented in BEAST v1.8.3 was used to estimate a coalescent phylogeny for these variants and the allelic ancestral states at the internal nodes of the phylogeny.

Results

The phylogenetic analysis allowed us to identify the evolutionary relationships among the 48 ERMAP alleles, predict 4243 potential ancestral alleles and calculate a posterior probability for each of these unobserved alleles. Some of them coincide with observed alleles that are extant in the population.

Conclusions

Our proposed strategy places known alleles in a phylogenetic framework, allowing us to describe as-yet-undiscovered alleles. In this new approach, which relies heavily on the accuracy of the alleles used for the phylogenetic analysis, an expanded set of predicted alleles can be used to infer alleles when large genotype data are analyzed, as typically generated by high-throughput sequencing. The alleles identified by studies like ours may be utilized in designing of microarray technologies, imputing of genotypes and mapping of next generation sequencing data.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1791-9) contains supplementary material, which is available to authorized users.

Developments beyond blood group serology in the genomics era

Blood group serology and single nucleotide polymorphism-based genotyping platforms are accurate but do not provide a comprehensive cover for all 36 blood group systems and do not cover the antigen diversity observed among population groups. This review examines the extent to which genomics is shaping blood group serology. Resources for genomics include the Human Reference Genome Sequence assembly; curated blood group tables listing variants; public databases providing information on genetic variants from world-wide studies; and massively parallel sequencing technologies. Blood group genomic studies span the spectrum, from bioinformatic data mining of huge data sets containing whole genome and whole exome information to laboratory investigations utilising targeted sequencing approaches. Blood group predictions based on genome sequencing and genomic studies are proving accurate, and have shown utility in both research and reference settings. Overall, studies confirm the potential for blood group genomics to reshape donor and patient transfusion management strategies to provide more compatible blood transfusions.

Prediction of Disordered Regions and Their Roles in the Anti-Pathogenic and Immunomodulatory Functions of Butyrophilins

Butyrophilins (BTNs) are a group of the moonlighting proteins, some members of which are secreted in milk. They constitute a large family of structurally similar type 1 transmembrane proteins from the immunoglobulin superfamily. Although the founding member of this family is related to lactation, participating in the secretion, formation and stabilization of milk fat globules, it may also have a cell surface receptor function. Generally, the BTN family members are known to modulate co-stimulatory responses, T cell selection, differentiation, and cell fate determination. Polymorphism of these genes was shown to be associated with the pathology of several human diseases. Despite their biological significance, structural information on human butyrophilins is rather limited. Based on their remarkable multifunctionality, butyrophilins seem to belong to the category of moonlighting proteins, which are known to contain intrinsically disordered protein regions (IDPRs). However, the disorder status of human BTNs was not systematically investigated as of yet. The goal of this study is to fill this gap and to evaluate peculiarities of intrinsic disorder predisposition of the members of human BTN family, and to find if they have IDPRs that can be attributed to the multifunctionality of these important proteins.

Krüppel-like factors compete for promoters and enhancers to fine-tune transcription

Krüppel-like factors (KLFs) are a family of 17 transcription factors characterized by a conserved DNA-binding domain of three zinc fingers and a variable N-terminal domain responsible for recruiting cofactors. KLFs have diverse functions in stem cell biology, embryo patterning, and tissue homoeostasis. KLF1 and related family members function as transcriptional activators via recruitment of co-activators such as EP300, whereas KLF3 and related members act as transcriptional repressors via recruitment of C-terminal Binding Proteins. KLF1 directly activates the Klf3 gene via an erythroid-specific promoter. Herein, we show KLF1 and KLF3 bind common as well as unique sites within the erythroid cell genome by ChIP-seq. We show KLF3 can displace KLF1 from key erythroid gene promoters and enhancers in vivo. Using 4sU RNA labelling and RNA-seq, we show this competition results in reciprocal transcriptional outputs for >50 important genes. Furthermore, Klf3-/- mice displayed exaggerated recovery from anemic stress and persistent cell cycling consistent with a role for KLF3 in dampening KLF1-driven proliferation. We suggest this study provides a paradigm for how KLFs work in incoherent feed-forward loops or networks to fine-tune transcription and thereby control diverse biological processes such as cell proliferation.

KLF1-null neonates display hydrops fetalis and a deranged erythroid transcriptome

We describe a case of severe neonatal anemia with kernicterus caused by compound heterozygosity for null mutations in KLF1, each inherited from asymptomatic parents. One of the mutations is novel. This is the first described case of a KLF1-null human. The phenotype of severe nonspherocytic hemolytic anemia, jaundice, hepatosplenomegaly, and marked erythroblastosis is more severe than that present in congenital dyserythropoietic anemia type IV as a result of dominant mutations in the second zinc-finger of KLF1. There was a very high level of HbF expression into childhood (>70%), consistent with a key role for KLF1 in human hemoglobin switching. We performed RNA-seq on circulating erythroblasts and found that human KLF1 acts like mouse Klf1 to coordinate expression of many genes required to build a red cell including those encoding globins, cytoskeletal components, AHSP, heme synthesis enzymes, cell-cycle regulators, and blood group antigens. We identify novel KLF1 target genes including KIF23 and KIF11 which are required for proper cytokinesis. We also identify new roles for KLF1 in autophagy, global transcriptional control, and RNA splicing. We suggest loss of KLF1 should be considered in otherwise unexplained cases of severe neonatal NSHA or hydrops fetalis.

Genome-wide identification of TAL1's functional targets: insights into its mechanisms of action in primary erythroid cells

Coordination of cellular processes through the establishment of tissue-specific gene expression programs is essential for lineage maturation. The basic helix-loop-helix hemopoietic transcriptional regulator TAL1 (formerly SCL) is required for terminal differentiation of red blood cells. To gain insight into TAL1 function and mechanisms of action in erythropoiesis, we performed ChIP-sequencing and gene expression analyses from primary fetal liver erythroid cells. We show that TAL1 coordinates expression of genes in most known red cell-specific processes. The majority of TAL1's genomic targets require direct DNA-binding activity. However, one-fifth of TAL1's target sequences, mainly among those showing high affinity for TAL1, can recruit the factor independently of its DNA binding activity. An unbiased DNA motif search of sequences bound by TAL1 identified CAGNTG as TAL1-preferred E-box motif in erythroid cells. Novel motifs were also characterized that may help distinguish activated from repressed genes and suggest a new mechanism by which TAL1 may be recruited to DNA. Finally, analysis of recruitment of GATA1, a protein partner of TAL1, to sequences occupied by TAL1 suggests that TAL1's binding is necessary prior or simultaneous to that of GATA1. This work provides the framework to study regulatory networks leading to erythroid terminal maturation and to model mechanisms of action of tissue-specific transcription factors.

A global role for KLF1 in erythropoiesis revealed by ChIP-seq in primary erythroid cells

KLF1 regulates a diverse suite of genes to direct erythroid cell differentiation from bipotent progenitors. To determine the local cis-regulatory contexts and transcription factor networks in which KLF1 operates, we performed KLF1 ChIP-seq in the mouse. We found at least 945 sites in the genome of E14.5 fetal liver erythroid cells which are occupied by endogenous KLF1. Many of these recovered sites reside in erythroid gene promoters such as Hbb-b1, but the majority are distant to any known gene. Our data suggests KLF1 directly regulates most aspects of terminal erythroid differentiation including production of alpha- and beta-globin protein chains, heme biosynthesis, coordination of proliferation and anti-apoptotic pathways, and construction of the red cell membrane and cytoskeleton by functioning primarily as a transcriptional activator. Additionally, we suggest new mechanisms for KLF1 cooperation with other transcription factors, in particular the erythroid transcription factor GATA1, to maintain homeostasis in the erythroid compartment.

Gatekeepers of intestinal inflammation

The intestine is subjected to a barrage of insults from food, bacterial flora, and pathogens. Despite this constant antigenic challenge, the mucosal tissues lining the intestinal tract remain largely under control. The mechanisms regulating the homeostatic balance in the gut have been investigated for many years by many groups, but the precise nature of the regulatory control remains elusive. In this review, we provide an overview of pathways proposed to be involved in dampening the inflammatory response and maintaining the homeostatic balance in the intestine, and how these pathways may be disrupted in ulcerative colitis and Crohn's disease.

Easy identification of antibodies to high-prevalence Scianna antigens and detection of admixed alloantibodies using soluble recombinant Scianna protein

BACKGROUND

Identification of antibodies against high-prevalence Scianna (Sc; ERMAP) antigens, like Sc1 and Sc5, is difficult and may incur delays in blood procurement and costs. The detection of additional clinically significant alloantibodies is hampered in the presence of anti-Scianna. Soluble recombinant Scianna protein is demonstrated to facilitate antibody diagnostics in both cases.

STUDY DESIGN AND METHODS

Soluble recombinant Scianna protein (Sc:1,-2,3,-4,5,6,7) was produced comprising the antigenic extracellular domain fused to a V5-His tag. The protein was isolated from eukaryotic cell culture supernatants of stably transfected HEK293 cells. Seven serum samples with anti-Sc1, anti-Sc2, and anti-Sc5 and 30 serum samples with antibodies to other blood group antigens were evaluated in hemagglutination inhibition assays. Antisera with mixed antibody specificities and autoantibodies were also tested.

RESULTS

Soluble Scianna protein inhibited specifically antibodies to the high-prevalence Scianna antigens Sc1 and Sc5. No antibodies were neutralized that were directed to the low-prevalence Sc2 antigen or to a large representative set of antigens from other blood group systems. Clinically relevant antibodies could be identified despite being masked by anti-Sc1 and anti-Sc5. A mixture of Scianna and JMH proteins allowed detecting a common antibody despite the presence of antibodies to high-prevalence antigens of the Scianna or JMH blood group systems.

CONCLUSION

Antibody detection systems comprising soluble recombinant Scianna protein provide an easy single-step method for detection and identification of antibodies to high-prevalence Scianna antigens. Reagents with Scianna and other recombinant blood group proteins and mixtures of such proteins would be useful routine reagents in immunohematology.

A global role for EKLF in definitive and primitive erythropoiesis

Erythroid Kruppel-like factor (EKLF, KLF1) plays an important role in definitive erythropoiesis and beta-globin gene regulation but failure to rectify lethal fetal anemia upon correction of globin chain imbalance suggested additional critical EKLF target genes. We employed expression profiling of EKLF-null fetal liver and EKLF-null erythroid cell lines containing an inducible EKLF-estrogen receptor (EKLF-ER) fusion construct to search for such targets. An overlapping list of EKLF-regulated genes from the 2 systems included alpha-hemoglobin stabilizing protein (AHSP), cytoskeletal proteins, hemesynthesis enzymes, transcription factors, and blood group antigens. One EKLF target gene, dematin, which encodes an erythrocyte cytoskeletal protein (band 4.9), contains several phylogenetically conserved consensus CACC motifs predicted to bind EKLF. Chromatin immunoprecipitation demonstrated in vivo EKLF occupancy at these sites and promoter reporter assays showed that EKLF activates gene transcription through these DNA elements. Furthermore, investigation of EKLF target genes in the yolk sac led to the discovery of unexpected additional defects in the embryonic red cell membrane and cytoskeleton. In short, EKLF regulates global erythroid gene expression that is critical for the development of primitive and definitive red cells.

bloodthirsty, an RBCC/TRIM gene required for erythropoiesis in zebrafish

The Antarctic icefishes (family Channichthyidae, suborder Notothenioidei) constitute the only vertebrate taxon that fails to produce red blood cells. These fishes can be paired with closely related, but erythrocyte-producing, notothenioids to discover erythropoietic genes via representational difference analysis. Using a B30.2-domain-encoding DNA probe so derived from the hematopoietic kidney (pronephros) of a red-blooded Antarctic rockcod, Notothenia coriiceps, we discovered a related, novel gene, bloodthirsty (bty), that encoded a 547-residue protein that contains sequential RING finger, B Box, coiled-coil, and B30.2 domains. bty mRNA was expressed by the pronephric kidney of N. coriiceps at a steady-state level 10-fold greater than that found in the kidney of the icefish Chaenocephalus aceratus. To test the function of bty, we cloned the orthologous zebrafish gene from a kidney cDNA library. Whole-mount in situ hybridization of zebrafish embryos showed that bty mRNA was present throughout development and, after the mid-blastula transition, was expressed in the head and in or near the site of primitive erythropoiesis in the tail just prior to red cell production. One- to four-cell embryos injected with two distinct antisense morpholino oligonucleotides (MOs) targeted to the 5'-end of the bty mRNA failed to develop red cells, whereas embryos injected with 4- and 5-bp mismatch control MOs produced wild-type quantities of erythrocytes. The morphant phenotype was rescued by co-injection of synthetic bty mRNA containing an artificial 5'-untranslated region (UTR) with the antisense MO that bound the 5'-UTR of the wild-type bty transcript. Furthermore, the expression of genes that mark terminal erythroid differentiation was greatly reduced in the antisense-MO-treated embryos. We conclude that bty is likely to play a role in differentiation of the committed red cell progenitor.

Systematic identification of immunoreceptor tyrosine-based inhibitory motifs in the human proteome

Immunoreceptor tyrosine-based inhibitory motifs (ITIMs) are short sequences of the consensus (ILV)-x-x-Y-x-(LV) in the cytoplasmic tail of immune receptors. The phosphorylation of tyrosines in ITIMs is known to be an important signalling mechanism regulating the activation of immune cells. The shortness of the motif makes it difficult to predict ITIMs in large protein databases. Simple pattern searches find ITIMs in approximately 30% of the protein sequences in the RefSeq database. The majority are false positive predictions. We propose a new database search strategy for ITIM-bearing transmembrane receptors based on the use of sequence context, i.e. the predictions of signal peptides, transmembrane helices (TMs) and protein domains. Our new protocol allowed us to narrow down the number of potential human ITIM receptors to 109 proteins (0.7% of RefPep). Of these, 36 have been described as ITIM receptors in the literature before. Many ITIMs are conserved between orthologous human and mouse proteins which represent novel ITIM receptor candidates. Publicly available DNA array expression data revealed that ITIM receptors are not exclusively expressed in blood cells. We hypothesise that ITIM signalling is not restricted to immune cells, but also functions in diverse solid organs of mouse and man.

Genetic basis of blood group diversity

In the last 18 years the genes that encode all but one of the 29 blood group systems present on red blood cells (RBCs) have been identified. This body of knowledge has permitted the application of molecular techniques to characterize the common blood group antigens and to elucidate the background for some of the variant phenotypes. Just as the RBC was used as a model for the biochemical characterization of cell membranes, so the genes encoding blood groups provide a readily accessible model for the study of gene expression and diversity. The application of genotyping techniques to identify fetuses at risk of haemolytic disease of the newborn is now the standard of care, and the expansion of nucleic acid testing platforms to include both disease testing and blood typing in the blood centre is on the horizon. This review summarizes the molecular basis of blood groups and illustrates the mechanisms that generate diversity through specific examples.

Expression of butyrophilin (Btn1a1) in lactating mammary gland is essential for the regulated secretion of milk-lipid droplets

Butyrophilin 1a1 (Btn1a1), which is a member of the Ig superfamily, is highly expressed in the lactating mammary gland and is secreted into milk in association with lipid droplets. To determine the potential function of Btn1a1 in milk secretion, we ablated Btn1a1 in mice and analyzed the lactation phenotype of homozygous (Btn1a1(-/-)) animals. Two mutant mouse lines were generated in which expression of Btn1a1 was either disrupted or eliminated, respectively. The regulated secretion of milk-lipid droplets was severely compromised in both mutant mouse lines in comparison to wild-type animals. Large pools of triacylglycerol accumulated in the cytoplasm of secretory cells, and lipid droplets escaped from the apical surface with disrupted outer membranes. Luminal spaces became engorged with unstable lipid droplets, which coalesced to form large aggregates. The amount of lipid (wt/vol) was elevated, on average by 50%, during the first 10 days of lactation, and the diameter of the droplets was up to seven times larger than the normal diameter. In contrast, there was no significant difference between wild-type and null animals in the relative amounts of skim-milk proteins secreted from Golgi-derived secretory vesicles. Approximately half the pups suckling Btn1a1(-/-) animals died within the first 20 days, and weaning weights for the surviving pups were 60-80% of those suckling wild-type mice. Thus, expression of Btn1a1 is essential for the regulated secretion of milk-lipid droplets. We speculate that Btn1a1 functions either as a structural protein or as a signaling receptor by binding to xanthine dehydrogenase/oxidase.

Human ERMAP: an erythroid adhesion/receptor transmembrane protein

A human cDNA and gene encoding for human ERMAP, a putative erythroid transmembrane adhesion/receptor protein, is reported. The predicted protein is made up of 475 amino acids and shares high homology with the murine ERMAP (73% identity and 14% conservative changes). Human Ermap is highly expressed in erythroid tissues and the protein localizes to the plasma membrane, particularly in sites of cell contact, and "cytoplasmic bodies." The extracellular segment contains one IgV fold that shares high homology with the butyrophilin family of milk proteins, autoantigens, and avian blood group antigens. In the intracellular region, there is a conserved B30.2 domain that is encoded by a single exon and is highly homologous with a similar domain in a diverse group of proteins, including butyrophilin, pyrin, and MID 1. The human Ermap gene is composed of 11 exons spanning 19 kb on chromosome 1p34.

The familial Mediterranean fever protein, pyrin, associates with microtubules and colocalizes with actin filaments

Familial Mediterranean fever (FMF) is a recessive disorder characterized by episodes of fever and intense inflammation. FMF attacks are unique in their sensitivity to the microtubule inhibitor colchicine, contrasted with their refractoriness to the anti-inflammatory effects of glucocorticoids. The FMF gene, MEFV, was recently identified by positional cloning; it is expressed at high levels in granulocytes and monocytes. The present study investigated the subcellular localization of the normal gene product, pyrin. These experiments did not support previously proposed nuclear or Golgi localizations. Instead fluorescence microscopy demonstrated colocalization of full-length GFP- and epitope-tagged pyrin with microtubules; this was markedly accentuated in paclitaxel-treated cells. Moreover, immunoblot analysis of precipitates of stabilized microtubules with recombinant pyrin demonstrated a direct interaction in vitro. Pyrin expression did not affect the stability of microtubules. Deletion constructs showed that the unique N-terminal domain of pyrin is necessary and sufficient for colocalization, whereas disease-associated mutations in the C-terminal B30.2 (rfp) domain did not disrupt this interaction. By phalloidin staining, a colocalization of pyrin with actin was also observed in perinuclear filaments and in peripheral lamellar ruffles. The proposal is made that pyrin regulates inflammatory responses at the level of leukocyte cytoskeletal organization and that the unique therapeutic effect of colchicine in FMF may be dependent on this interaction. (Blood. 2001;98:851-859)

Cloning and characterization of human erythroid membrane-associated protein, human ERMAP

We describe here the cloning and characterization of the human gene ERMAP, identified by subtractive hybridization using early and late gestation human fetal liver. By in situ hybridization, we found human ERMAP to be expressed not only in erythoid cells in fetal liver and adult bone marrow, but also in reticulocytes and circulating erythroblasts in 8-12-week fetal cord blood. The human ERMAP protein is predicted to contain a transmembrane segment and one extracellular immunoglobulin fold (IgV). The cytoplasmic region contains a highly conserved B30.2 motif, multiple consensus sequences for kinases, and post-Golgi sorting signals. The protein was localized to the cell surface as shown by an antibody specific for a peptide predicted from the IgV fold. The amino acid sequence of human ERMAP is highly homologous with that of mouse ERMAP, but differs in the number of extracellular immunoglobulin folds. Human ERMAP represents a new unique member of the rapidly growing B30.2 domain proteins.

Enterophilins, a new family of leucine zipper proteins bearing a b30.2 domain and associated with enterocyte differentiation

Enterocyte terminal differentiation occurs at the crypt-villus junction through the transcriptional activation of cell-specific genes, many of which code for proteins of the brush border membrane such as intestinal alkaline phosphatase, sucrase-isomaltase, or the microvillar structural protein villin. Several studies have shown that this sharp increase in specific mRNA levels is intimately associated with arrest of cell proliferation. We isolated several clones from a guinea pig intestine cDNA library. They encode new proteins characterized by an original structure associating a carboxyl-terminal B30.2/RFP-like domain and a long leucine zipper at the amino terminus. The first member of this novel gene family codes for a 65-kDa protein termed enterophilin-1, which is specifically expressed in enterocytes before their final differentiation. Enterophilin-1 is the most abundant in the small intestine but is still present in significant amounts in colonic enterocytes. In Caco-2 cells, a similar 65-kDa protein was recognized by a specific anti-enterophilin-1 antibody, and its expression was positively correlated with cell differentiation status. In addition, transfection of HT-29 cells with enterophilin-1 full-length cDNA slightly inhibited cell growth and promoted an increase in alkaline phosphatase activity. Taken together, these data identify enterophilins as a new family of proteins associated with enterocyte differentiation.

The cluster of BTN genes in the extended major histocompatibility complex

We sequenced the 170-kb cluster of BTN genes in the extended major histocompatibility complex region, 4 Mb telomeric of human leukocyte antigen class I genes, at 6p22.1. The cluster consists of seven genes belonging to the expanding B7/butyrophilin-like group, a subset of the immunoglobulin gene superfamily. The main complex is composed of six genes, from two subfamilies, BTN2 and BTN3, arranged in pairs. This alternating pattern must have evolved by duplications of an original block of two genes, one from each subfamily. The sequences from the two subfamilies share approximately 50% amino acid identity. By analysis of repeat elements within each block, these duplications may be dated to approximately 100 million years ago, at about the time of the branching of the Rodentia and Primate lineages. The single BTN1A1 (butyrophilin) gene was positioned approximately 25 kb centromeric to the cluster. Each gene covers approximately 12 kb and consists of seven (BTN2 subfamily) or nine (BTN3 subfamily) coding exons. The predicted leader sequence, immunoglobulin-like IgV (variable)/IgC (constant) ectodomains, and the predicted transmembrane domain are encoded on separate exons and are separated from a B30.2 domain by a variable number of very short exons, 21 and 27 nucleotides in length. BTN transcripts were detected in all tissues examined. Alternative splicing, involving particularly the carboxyl-terminal B30.2 domain, was a notable feature. Most transcripts of BTN2 subfamily genes contained this domain, whereas BTN3 genes did not. Using immunofluorescence, we showed surface expression of BTN-green fluorescent protein fusions in mammalian cell transfectants.