Development of a highly sensitive platform for protein-protein interaction detection and regulation of T cell function.

We developed a highly sensitive assay for detecting protein-protein interaction using chimeric receptors comprising two molecules of interest in the extracellular domain and interferon alpha and beta receptor subunit 1 or 2 (IFNAR1/2) in the intracellular domain. This intracellular IFNAR1/2 reconstitution system (IFNARRS) proved markedly more sensitive than the NanoBiT system, currently considered one of the best detection systems for protein interaction. Employing chimeric receptors with extracellular domains from the IFNγ or IL-2 receptor and the intracellular domains of IFNAR1/2, the IFNARRS system effectively identifies low IFNγ or IL-2 levels. Cells stably expressing these chimeric receptors responded to IFNγ secreted by activated T cells following various stimuli, including a specific peptide-antigen. The activation signals were further enhanced by the expression of relevant genes, such as costimulators, via IFN-stimulated response elements in the promoters. Besides IFNγ or IL-2, the IFNARRS system demonstrated the capability to detect other cytokines by using the corresponding extracellular domains from these target cytokine receptors.

Inhibition of PLK4 remodels histone methylation and activates the immune response via the cGAS-STING pathway in TP53-mutated AML.

Acute myeloid leukemia (AML) with TP53 mutation is one of the most lethal cancers and portends an extremely poor prognosis. Based on in silico analyses of druggable genes and differential gene expression in TP53-mutated AML, we identified pololike kinase 4 (PLK4) as a novel therapeutic target and examined its expression, regulation, pathogenetic mechanisms, and therapeutic potential in TP53-mutated AML. PLK4 expression was suppressed by activated p53 signaling in TP53 wild-type AML and was increased in TP53-mutated AML cell lines and primary samples. Short-term PLK4 inhibition induced DNA damage and apoptosis in TP53 wild-type AML. Prolonged PLK4 inhibition suppressed the growth of TP53-mutated AML and was associated with DNA damage, apoptosis, senescence, polyploidy, and defective cytokinesis. A hitherto undescribed PLK4/PRMT5/EZH2/H3K27me3 axis was demonstrated in both TP53 wild-type and mutated AML, resulting in histone modification through PLK4-induced PRMT5 phosphorylation. In TP53-mutated AML, combined effects of histone modification and polyploidy activated the cGAS-STING pathway, leading to secretion of cytokines and chemokines and activation of macrophages and T cells upon coculture with AML cells. In vivo, PLK4 inhibition also induced cytokine and chemokine expression in mouse recipients, and its combination with anti-CD47 antibody, which inhibited the "don't-eat-me" signal in macrophages, synergistically reduced leukemic burden and prolonged animal survival. The study shed important light on the pathogenetic role of PLK4 and might lead to novel therapeutic strategies in TP53-mutated AML.

CFI-402257, a TTK inhibitor, effectively suppresses hepatocellular carcinoma.

Deregulation of cell cycle is a typical feature of cancer cells. Normal cells rely on the strictly coordinated spindle assembly checkpoint (SAC) to maintain the genome integrity and survive. However, cancer cells could bypass this checkpoint mechanism. In this study, we showed the clinical relevance of threonine tyrosine kinase (TTK) protein kinase, a central regulator of the SAC, in hepatocellular carcinoma (HCC) and its potential as therapeutic target. Here, we reported that a newly developed, orally active small molecule inhibitor targeting TTK (CFI-402257) effectively suppressed HCC growth and induced highly aneuploid HCC cells, DNA damage, and micronuclei formation. We identified that CFI-402257 also induced cytosolic DNA, senescence-like response, and activated DDX41-STING cytosolic DNA sensing pathway to produce senescence-associated secretory phenotypes (SASPs) in HCC cells. These SASPs subsequently led to recruitment of different subsets of immune cells (natural killer cells, CD4+ T cells, and CD8+ T cells) for tumor clearance. Our mass cytometry data illustrated the dynamic changes in the tumor-infiltrating immune populations after treatment with CFI-402257. Further, CFI-402257 improved survival in HCC-bearing mice treated with anti-PD-1, suggesting the possibility of combination treatment with immune checkpoint inhibitors in HCC patients. In summary, our study characterized CFI-402257 as a potential therapeutic for HCC, both used as a single agent and in combination therapy.

Polo-like kinase 4 inhibitor CFI-400945 suppresses liver cancer through cell cycle perturbation and eliciting antitumor immunity.

BACKGROUND AND AIMS: Prognosis of HCC remains poor due to lack of effective therapies. Immune checkpoint inhibitors (ICIs) have delayed response and are only effective in a subset of patients. Treatments that could effectively shrink the tumors within a short period of time are idealistic to be employed together with ICIs for durable tumor suppressive effects. HCC acquires increased tolerance to aneuploidy. The rapid division of HCC cells relies on centrosome duplication. In this study, we found that polo-like kinase 4 (PLK4), a centrosome duplication regulator, represents a therapeutic vulnerability in HCC. APPROACH AND RESULTS: An orally available PLK4 inhibitor, CFI-400945, potently suppressed proliferating HCC cells by perturbing centrosome duplication. CFI-400945 induced endoreplication without stopping DNA replication, causing severe aneuploidy, DNA damage, micronuclei formation, cytosolic DNA accumulation, and senescence. The cytosolic DNA accumulation elicited the DEAD box helicase 41-stimulator of interferon genes-interferon regulatory factor 3/7-NF-κß cytosolic DNA sensing pathway, thereby driving the transcription of senescence-associated secretory phenotypes, which recruit immune cells. CFI-400945 was evaluated in liver-specific p53/phosphatase and tensin homolog knockout mouse HCC models established by hydrodynamic tail vein injection. Tumor-infiltrated immune cells were analyzed. CFI-400945 significantly impeded HCC growth and increased infiltration of cluster of differentiation 4-positive (CD4 + ), CD8 + T cells, macrophages, and natural killer cells. Combination therapy of CFI-400945 with anti-programmed death-1 showed a tendency to improve HCC survival. CONCLUSIONS: We show that by targeting a centrosome regulator, PLK4, to activate the cytosolic DNA sensing-mediated immune response, CFI-400945 effectively restrained tumor progression through cell cycle inhibition and inducing antitumor immunity to achieve a durable suppressive effect even in late-stage mouse HCC.

Passenger Mutations Identified in the Blink of an Eye.

Passenger mutations specific to particular mouse strains can distort experimental outcomes. In this issue of Immunity, Vanden Berghe et al. (2015) demonstrate that passenger mutations are frequent in most genetically engineered congenic mice and persist even after extensive backcrossing.

Nucleolar stress: Molecular mechanisms and related human diseases.

Ribosome biogenesis in the nucleolus is an important process that consumes 80% of a cell's intracellular energy supply. Disruption of this process results in nucleolar stress, triggering the activation of molecular systems that respond to this stress to maintain homeostasis. Although nucleolar stress was originally thought to be caused solely by abnormalities of ribosomal RNA (rRNA) and ribosomal proteins (RPs), an accumulating body of more current evidence suggests that many other factors, including the DNA damage response and oncogenic stress, are also involved in nucleolar stress response signaling. Cells reacting to nucleolar stress undergo cell cycle arrest or programmed death, mainly driven by activation of the tumor suppressor p53. This observation has nominated nucleolar stress as a promising target for cancer therapy. However, paradoxically, some RP mutations have also been implicated in cancer initiation and progression, necessitating caution. In this article, we summarize recent findings on the molecular mechanisms of nucleolar stress and the human ribosomal diseases and cancers that arise in its wake.

N-(3,4-dimethoxyphenethyl)-6-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-amine inhibits bladder cancer progression by suppressing YAP1/TAZ.

Bladder cancer (BlC) is the fourth most common cancer in males worldwide, but few systemic chemotherapy options for its effective treatment exist. The development of new molecularly-targeted agents against BlC is therefore an urgent issue. The Hippo signaling pathway, with its upstream LATS kinases and downstream transcriptional co-activators YAP1 and TAZ, plays a pivotal role in diverse cell functions, including cell proliferation. Recent studies have shown that overexpression of YAP1 occurs in advanced BlCs and is associated with poor patient prognosis. Accessing data from our previous screening of a chemical library of compounds targeting the Hippo pathway, we identified DMPCA (N-(3,4-dimethoxyphenethyl)-6-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-amine) as an agent able to induce the phosphorylation of LATS1 and YAP1/TAZ in BlC cells, thereby suppressing their viability both in vitro and in mouse xenografts. Our data indicate that DMPCA has a potent anti-tumor effect, and raise the possibility that this agent may represent a new and effective therapeutic option for BlC.

TAZ inhibits acinar cell differentiation but promotes immature ductal cell proliferation in adult mouse salivary glands.

There are currently no treatments for salivary gland diseases, making it vital to understand signaling mechanisms operating in acinar and ductal cells so as to develop regenerative therapies. To date, little work has focused on elucidating the signaling cascades controlling the differentiation of these cell types in adult mammals. To analyze the function of the Hippo-TAZ/YAP1 pathway in adult mouse salivary glands, we generated adMOB1DKO mice in which both MOB1A and MOB1B were TAM-inducibly deleted when the animals were adults. Three weeks after TAM treatment, adMOB1DKO mice exhibited smaller submandibular glands (SMGs) than controls with a decreased number of acinar cells and an increased number of immature dysplastic ductal cells. The mutants suffered from reduced saliva production accompanied by mild inflammatory cell infiltration and fibrosis in SMGs, similar to the Sjogren's syndrome. MOB1-deficient acinar cells showed normal proliferation and apoptosis but decreased differentiation, leading to an increase in acinar/ductal bilineage progenitor cells. These changes were TAZ-dependent but YAP1-independent. Biochemically, MOB1-deficient salivary epithelial cells showed activation of the TAZ/YAP1 and ß-catenin in ductal cells, but reduced SOX2 and SOX10 expression in acinar cells. Thus, Hippo-TAZ signaling is critical for proper ductal and acinar cell differentiation and function in adult mice.

The role of Hippo-YAP signaling in squamous cell carcinomas.

The Hippo-YAP pathway regulates organ size, tissue homeostasis, and tumorigenesis in mammals. In response to cell density, external mechanical pressure, and/or other stimuli, the Hippo core complex controls the translocation of YAP1/TAZ proteins to the nucleus and thereby regulates cell growth. Abnormal upregulation or nuclear localization of YAP1/TAZ occurs in many human malignancies and promotes their formation, progression, and metastasis. A key example is squamous cell carcinoma (SCC) genesis. Many risk factors and crucial signals associated with SCC development in various tissues accelerate YAP1/TAZ accumulation, and mice possessing constitutively activated YAP1/TAZ show immediate carcinoma in situ (CIS) formation in these tissues. Because CIS onset is so rapid in these mutants, we propose that many SCCs initiate and progress when YAP1 activity is sustained and exceeds a certain oncogenic threshold. In this review, we summarize the latest findings on the roles of YAP1/TAZ in several types of SCCs. We also discuss whether targeting aberrant YAP1/TAZ activation might be a promising strategy for SCC treatment.

Alantolactone is a natural product that potently inhibits YAP1/TAZ through promotion of reactive oxygen species accumulation.

Yes-associated protein 1 (YAP1) and its paralogue PDZ-binding motif (TAZ) play pivotal roles in cell proliferation, migration, and invasion, and abnormal activation of these TEAD transcriptional coactivators is found in diverse cancers in humans and mice. Targeting YAP1/TAZ signaling is thus a promising therapeutic avenue but, to date, few selective YAP1/TAZ inhibitors have been effective against cancer cells either in vitro or in vivo. We screened chemical libraries for potent YAP1/TAZ inhibitors using a highly sensitive luciferase reporter system to monitor YAP1/TAZ-TEAD transcriptional activity in cells. Among 29 049 low-molecular-weight compounds screened, we obtained nine hits, and the four of these that were the most effective shared a core structure with the natural product alantolactone (ALT). We also tested 16 other structural derivatives of ALT and found that natural ALT was the most efficient at increasing ROS-induced LATS kinase activities and thus YAP1/TAZ phosphorylation. Phosphorylated YAP1/TAZ proteins were subject to nuclear exclusion and proteosomic degradation such that the growth of ALT-treated tumor cells was inhibited both in vitro and in vivo. Our data show for the first time that ALT can be used to target the ROS-YAP pathway driving tumor cell growth and so could be a potent anticancer drug.

Loss of Mob1a/b in mice results in chondrodysplasia due to YAP1/TAZ-TEAD-dependent repression of SOX9.

Hippo signaling is modulated in response to cell density, external mechanical forces, and rigidity of the extracellular matrix (ECM). The Mps one binder kinase activator (MOB) adaptor proteins are core components of Hippo signaling and influence Yes-associated protein 1 (YAP1) and transcriptional co-activator with PDZ-binding motif (TAZ), which are potent transcriptional regulators. YAP1/TAZ are key contributors to cartilage and bone development but the molecular mechanisms by which the Hippo pathway controls chondrogenesis are largely unknown. Cartilage is rich in ECM and also subject to strong external forces - two upstream factors regulating Hippo signaling. Chondrogenesis and endochondral ossification are tightly controlled by growth factors, morphogens, hormones, and transcriptional factors that engage in crosstalk with Hippo-YAP1/TAZ signaling. Here, we generated tamoxifen-inducible, chondrocyte-specific Mob1a/b-deficient mice and show that hyperactivation of endogenous YAP1/TAZ impairs chondrocyte proliferation and differentiation/maturation, leading to chondrodysplasia. These defects were linked to suppression of SOX9, a master regulator of chondrogenesis, the expression of which is mediated by TEAD transcription factors. Our data indicate that a MOB1-dependent YAP1/TAZ-TEAD complex functions as a transcriptional repressor of SOX9 and thereby negatively regulates chondrogenesis.

MOB1 regulates thymocyte egress and T-cell survival in mice in a YAP1-independent manner.

Mammalian STE20-like protein kinase 1/2 (MST1/2) and nuclear Dbf2-related kinase 1/2 (NDR1/2) are core components of Hippo signaling that are also known to be important regulators of lymphocyte trafficking. However, little is understood about the roles of other Hippo pathway molecules in these cells. Here, we present the first analysis of the function of Mps one binder kinase activator-1 (MOB1) in T lymphocytes in vivo. T-cell-specific double knockout (DKO) of MOB1A/B in mice [tMob1 DKO mice] reduces the number of naïve T cells in both the circulation and secondary lymphoid organs, but leads to an accumulation of CD4+ CD8- and CD4- CD8+ single-positive (SP) cells in the thymus. In vitro, naïve MOB1A/B-deficient T cells show increased apoptosis and display impaired trafficking capacity in response to the chemokine CCL19. These defects are linked to suppression of the activation of MST and NDR kinases, but are independent of the downstream transcriptional co-activator Yes-associated protein 1 (YAP1). Thus, MOB1 proteins play an important role in thymic egress and T-cell survival that is mediated by a pathway other than conventional Hippo-YAP1 signaling.

Hippo pathway controls cell adhesion and context-dependent cell competition to influence skin engraftment efficiency.

Cell competition is involved in mammalian embryogenesis and tumor elimination and progression. It was previously shown that, whereas NIH3T3 mouse fibroblasts expressing high levels of the yes-associated protein 1(YAP1) target TEA domain family (TEAD) transcription factors become "winners" in cell competitions, Madin-Darby canine kidney cells expressing activated YAP1 become "losers" and are eliminated from culture monolayers. Thus, YAP1's role in cell competitions is clearly context dependent. Here, we show that keratinocytes overexpressing a constitutively activated YAP1 mutant lose in in vitro competitions with control cells conducted in standard tissue culture dishes and undergo apical extrusion. Similarly, cells in which endogenous YAP1 is activated by NF2 knockdown become losers. The YAP1-overexpressing cells exhibit a decrease in cell-matrix adhesion because of defective expression of adhesion molecules such as fibronectin-1. Cell adhesion-mediated proliferation is also impaired. However, because of intrinsic factors, YAP1-expressing cells proliferate faster than control cells when cocultured in dishes impeding cell adhesion. In vivo, Mob1a/b-deficient (YAP1-activated) epidermis, which shows decreased expression of type XVII collagen, cannot be engrafted successfully onto donor mice. YAP1-activated skin grafts shrink away from surrounding control skin, and the epidermis peels off the basement membrane. Our data show that YAP1 activation controls cell competition in part by decreasing cell adhesion.-Nishio, M., Miyachi, Y., Otani, J., Tane, S., Omori, H., Ueda, F., Togashi, H., Sasaki, T., Mak, T. W., Nakao, K., Fujita, Y., Nishina, H., Maehama, T., Suzuki, A. Hippo pathway controls cell adhesion and context-dependent cell competition to influence skin engraftment efficiency.

TAp73 depletion accelerates aging through metabolic dysregulation.

Aging is associated with impaired scavenging of reactive oxygen species (ROS). Here, we show that TAp73, a p53 family member, protects against aging by regulating mitochondrial activity and preventing ROS accumulation. TAp73-null mice show more pronounced aging with increased oxidative damage and senescence. TAp73 deletion reduces cellular ATP levels, oxygen consumption, and mitochondrial complex IV activity, with increased ROS production and oxidative stress sensitivity. We show that the mitochondrial complex IV subunit cytochrome C oxidase subunit 4 (Cox4i1) is a direct TAp73 target and that Cox4i1 knockdown phenocopies the cellular senescence of TAp73-null cells. Results indicate that TAp73 affects mitochondrial respiration and ROS homeostasis, thus regulating aging.

D-2-hydroxyglutarate produced by mutant IDH1 perturbs collagen maturation and basement membrane function.

Isocitrate dehydrogenase-1 (IDH1) R132 mutations occur in glioma, but their physiological significance is unknown. Here we describe the generation and characterization of brain-specific Idh1 R132H conditional knock-in (KI) mice. Idh1 mutation results in hemorrhage and perinatal lethality. Surprisingly, intracellular reactive oxygen species (ROS) are attenuated in Idh1-KI brain cells despite an apparent increase in the NADP(+)/NADPH ratio. Idh1-KI cells also show high levels of D-2-hydroxyglutarate (D2HG) that are associated with inhibited prolyl-hydroxylation of hypoxia-inducible transcription factor-1α (Hif1α) and up-regulated Hif1α target gene transcription. Intriguingly, D2HG also blocks prolyl-hydroxylation of collagen, causing a defect in collagen protein maturation. An endoplasmic reticulum (ER) stress response induced by the accumulation of immature collagens may account for the embryonic lethality of these mutants. Importantly, D2HG-mediated impairment of collagen maturation also led to basement membrane (BM) aberrations that could play a part in glioma progression. Our study presents strong in vivo evidence that the D2HG produced by the mutant Idh1 enzyme is responsible for the above effects.

Triggering receptor expressed on myeloid cells-1 (TREM-1) deficiency augments BAFF production to promote lupus progression.

Sensing of nucleic acids by pattern recognition receptors is the key for the initiation and development of systemic lupus erythematosus (SLE). Triggering receptor expressed on myeloid cells-1 (TREM-1) is a novel innate immune receptor, which can amplify Toll-like receptor (TLR)-induced inflammatory responses. Although patients with lupus exhibit increased serum levels of soluble TREM-1 (sTREM-1), the role of TREM-1 in SLE remains unknown. In current study, we found serum sTREM-1 levels were significantly increased in lupus patients and positively correlated with disease activity. Additionally, diseased B6.lpr mice had elevated TREM-1 in the serum, spleen, and lymph nodes. To investigate the role of TREM-1 in lupus, we established Trem-1-/-.lpr mice. Trem-1-/-.lpr mice exhibited lower survival rates and more severe lupus symptoms, including elevated proteinuria, serum anti-dsDNA antibody levels, renal immune complex depositions and lymphocyte subpopulation expansions in both the spleen and lymph nodes. Besides, Trem-1-/-.lpr mice expressed higher serum B cell-activating factor (BAFF) levels and lymph node dendritic cells (DCs) were the major source of increased BAFF. Activation of membrane-bound TREM-1 could suppress TLR9-induced BAFF expression in bone marrow-derived DCs of B6.lpr mice. Moreover, levels of sTREM-1, which could act as an antagonist of membrane-bound TREM-1, were positively correlated with levels of BAFF in the sera of lupus patients. Our findings suggest a novel modulatory role of TREM-1 in the pathogenesis of SLE. sTREM-1 production is a useful diagnostic marker and a molecular target for combination therapy of lupus.

Absence of intestinal PPARγ aggravates acute infectious colitis in mice through a lipocalin-2-dependent pathway.

To be able to colonize its host, invading Salmonella enterica serovar Typhimurium must disrupt and severely affect host-microbiome homeostasis. Here we report that S. Typhimurium induces acute infectious colitis by inhibiting peroxisome proliferator-activated receptor gamma (PPARγ) expression in intestinal epithelial cells. Interestingly, this PPARγ down-regulation by S. Typhimurium is independent of TLR-4 signaling but triggers a marked elevation of host innate immune response genes, including that encoding the antimicrobial peptide lipocalin-2 (Lcn2). Accumulation of Lcn2 stabilizes the metalloproteinase MMP-9 via extracellular binding, which further aggravates the colitis. Remarkably, when exposed to S. Typhimurium, Lcn2-null mice exhibited a drastic reduction of the colitis and remained protected even at later stages of infection. Our data suggest a mechanism in which S. Typhimurium hijacks the control of host immune response genes such as those encoding PPARγ and Lcn2 to acquire residence in a host, which by evolution has established a symbiotic relation with its microbiome community to prevent pathogen invasion.

A novel TLR2-triggered signalling crosstalk synergistically intensifies TNF-mediated IL-6 induction.

Toll-like receptors (TLR) recognize pathogens and trigger the production of vigorous pro-inflammatory cytokines [such as tumour necrosis factor (TNF)] that induce systemic damages associated with sepsis and chronic inflammation. Cooperation between signals of TLR and TNF receptor has been demonstrated through the participation of TNF receptor 1 (TNFR) adaptors in endotoxin tolerance. Here, we identify a TLR2-mediated synergy, through a MyD88-independent crosstalk, which enhances subsequent TNF-mediated nuclear factor-kappa B activation and interleukin-6 induction. Membrane-associated adaptor MAL conduces the link between TNF receptor-associated factor 6 (TRAF6) and TNFR-associated death domain, leading to a distinctive K63-ubiquitinylated TRAF6 recruitment into TNFR complex. In summary, our results reveal a novel route of TLR signal that synergistically amplifies TNF-mediated responses, indicating an innovative target for inflammation manipulation.

PTEN-inducible kinase 1 (PINK1)/Park6 is indispensable for normal heart function.

Oxidative stress is caused by an imbalance between reactive oxygen species (ROS) production and the ability of an organism to eliminate these toxic intermediates. Mutations in PTEN-inducible kinase 1 (PINK1) link mitochondrial dysfunction, increased sensitivity to ROS, and apoptosis in Parkinson's disease. Whereas PINK1 has been linked to the regulation of oxidative stress, the exact mechanism by which this occurs has remained elusive. Oxidative stress with associated mitochondrial dysfunction leads to cardiac dysfunction and heart failure (HF). We hypothesized that loss of PINK1 in the heart would have deleterious consequences on mitochondrial function. Here, we observed that PINK1 protein levels are markedly reduced in end-stage human HF. We also report that PINK1 localizes exclusively to the mitochondria. PINK1(-/-) mice develop left ventricular dysfunction and evidence of pathological cardiac hypertrophy as early as 2 mo of age. Of note, PINK1(-/-) mice have greater levels of oxidative stress and impaired mitochondrial function. There were also higher degrees of fibrosis, cardiomyocyte apoptosis, and a reciprocal reduction in capillary density associated with this baseline cardiac phenotype. Collectively, our in vivo data demonstrate that PINK1 activity is crucial for postnatal myocardial development, through its role in maintaining mitochondrial function, and redox homeostasis in cardiomyocytes. In conclusion, PINK1 possesses a distinct, nonredundant function in the surveillance and maintenance of cardiac tissue homeostasis.

Acidic nuclear phosphoprotein 32kDa (ANP32)B-deficient mouse reveals a hierarchy of ANP32 importance in mammalian development.

The highly conserved ANP32 proteins are proposed to function in a broad array of physiological activities through molecular mechanisms as diverse as phosphatase inhibition, chromatin regulation, caspase activation, and intracellular transport. On the basis of previous analyses of mice bearing targeted mutations of Anp32a or Anp32e, there has been speculation that all ANP32 proteins play redundant roles and are dispensable for normal development. However, more recent work has suggested that ANP32B may in fact have functions that are not shared by other ANP32 family members. Here we report that ANP32B expression is associated with a poor prognosis in human breast cancer, consistent with the increased levels of Anp32b mRNA present in proliferating wild-type (WT) murine embryonic fibroblasts and stimulated WT B and T lymphocytes. Moreover, we show that, contrary to previous assumptions, Anp32b is very important for murine embryogenesis. In a mixed genetic background, ANP32B-deficient mice displayed a partially penetrant perinatal lethality that became fully penetrant in a pure C57BL/6 background. Surviving ANP32B-deficient mice showed reduced viability due to variable defects in various organ systems. Study of compound mutants lacking ANP32A, ANP32B, and/or ANP32E revealed previously hidden roles for ANP32A in mouse development that became apparent only in the complete absence of ANP32B. Our data demonstrate a hierarchy of importance for the mammalian Anp32 genes, with Anp32b being the most critical for normal development.