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In patients with rheumatoid arthritis (RA) in sustained remission, tapering of biological disease-modifying anti-rheumatic drugs can be considered. Tapering has already been investigated, but its feasibility remains to be determined. Therefore, we explored the feasibility of tapering etanercept in RA in a setting close to practice. Patients with RA in 28-joint Disease Activity Score (DAS28) remission (≥ 6 months) and treated with etanercept 50 mg weekly (≥ 1 year) were included in the pragmatic 1 year open-label multicentre randomized controlled TapERA (Tapering Etanercept in Rheumatoid Arthritis) trial. Patients were assigned to continue etanercept weekly or to taper to every other week (EOW). Patients who lost remission [DAS28–C-reactive protein (CRP) ≥ 2.6] were re-escalated to etanercept weekly. The primary outcome was the proportion of patients maintaining DAS28-CRP remission for 6 months. Sixty-six patients were randomized to etanercept weekly (n = 34) or EOW (n = 32). After 6 months, 26/34 patients (76%) in the weekly and 19/32 (59%) in the EOW group maintained disease control (p = 0.136). In the EOW group, 20/32 patients (63%) remained on their tapered treatment during the trial. Two patients reintroduced weekly etanercept themselves. Ten patients were re-escalated to etanercept weekly by the rheumatologist, after a median (interquartile range) interval of 3.0 (2.0–6.0) months. Among these patients, 7/10 regained remission after re-escalation, four of them at the next study visit. Although non-inferiority could not be demonstrated, tapering of etanercept to EOW appeared feasible in patients in sustained remission. [ABSTRACT FROM AUTHOR]

The objectives were to assess bone mineral density (BMD) at different body sites in rheumatoid arthritis (RA) patients related to disease severity parameters, disease duration and corticosteroid intake, and to look for body composition measurements as lean body mass (LBM) and per cent fat as possible prognostic factors in RA. Body composition values were measured cross-sectionally in 89 RA patients and compared with 157 controls. Patients were divided into males and postmenopausal females, ever steroid treated and never steroid treated. BMD values of all body sites were significantly lower compared to normals in all subgroups, except for the lumbar spine (L2 L4) in all postmenopausal women and males never treated with steroids. There was also no clear BMD decrease in the arms of male RA patients. LBM was significantly lower in all body parts compared to controls, whereas the fat distribution ratio (FDR) showed a clear shift to abdominal in all patients. These are parameters of chronic illness and a predictor of cardiovascular disease, respectively. BMD data confirm our previous data in different patient groups (low at appendicular sites, normal lumbar BMD), but no clear influence of disease severity and steroid intake could be found. Body composition data, as LBM and FDR, are also altered in RA patients: decreased LMB and more central FDR. Their usefulness as prognostic markers in early RA patients needs to be clarified prospectively in these patient groups. [ABSTRACT FROM PUBLISHER]

Objectives: To investigate if patients with early rheumatoid arthritis responding insufficiently to initial methotrexate (MTX) and bridging glucocorticoids (GCs) could benefit from early but temporary etanercept introduction as a second remission-induction attempt., Methods: CareRA2020 (NCT03649061) was a 2-year, open-label, multicentre, pragmatic randomised controlled trial. Treatment-naïve patients started MTX and GC bridging (COBRA-Slim: CS). Within a time window from week (W) 8 until W32, early insufficient responders (28-joint Disease Activity Score - C-reactive Protein (DAS28-CRP) >3.2 between W8 and W32 or ≥2.6 at W32) were randomised to a Standard-CS strategy (adding leflunomide first) or Bio-induction-CS strategy (adding etanercept for 24 weeks). Additional treatment adaptations followed the treat-to-target principle. Longitudinal disease activity (DAS28-CRP) over 104 weeks (primary outcome), achievement of DAS28-CRP <2.6 28 weeks after randomisation, and biologic or targeted synthetic disease-modifying antirheumatic drug (b/tsDMARD) use at W104 were compared between randomisation groups., Results: Following CS treatment, 142 patients were early responders; 55 early insufficient responders received Standard-CS and 55 Bio-induction-CS. Superiority of Bio-induction-CS over Standard-CS could not be demonstrated (ß=-0.204, (95% CI -0.486 to 0.078), p=0.157) for the primary outcome. More patients on Bio-induction-CS achieved DAS28-CRP <2.6 at 28 weeks after randomisation (59% (95% CI 44% to 72%) vs 44% (95% CI 31% to 59%) in Standard-CS) and they were treated less frequently with b/tsDMARDs at W104 (19/55, 35%) compared with Standard-CS (29/55, 53%)., Conclusion: Half of the patients responded well to initial COBRA-Slim induction therapy. In early insufficient responders, adding etanercept for 6 months did not improve disease control over 104 weeks versus adding leflunomide first. However, temporary introduction of etanercept resulted in improved disease control early after randomisation and less patients on b/tsDMARDs at W104., Trial Registration Number: NCT03649061., Ctr Pilot Approval Belgium: S59474, EudraCT number: 2017-004054-41., Competing Interests: Competing interests: RJ received consulting fees from Novartis, Pfizer, Amgen, AbbVie; speakers fee from Novartis; support for meeting/travel from Fresenius Kabi; and participation on advisory board from AbbVie, Amgen, Novartis and Fresenius Kabi. KT received consulting fees and payment/honoraria for speakers/manuscript writing/education from Eli Lilly, AbbVie, Amgen, Novartis, Pfizer, Celgene, Otsuka, Celltrion, Galapagos, Viatris, UCB and Sandoz. JV received support for meeting/travel from UCB and Novartis. SA received support for meeting/travel from Eli Lilly, payment/honoraria for speakers/manuscript writing/education from Eli Lilly, and was member of Research Foundation – Flanders (FWO) expert panel. AD received consulting fees from Amgen, support for meeting/travel from Galapagos, Eli Lilly, Sanofi and UCB; participation on data safety monitoring board/advisory board from Agmen. MD reported a grant from Research Foundation – Flanders (FWO), and support for meeting/travel from AbbVie, Novartis, Galapagos and UCB. EDM reported a grant from Research Foundation – Flanders (FWO). RW received consulting fees from Galapagos, and payment/honoraria for speakers/manuscript writing/education from Galapagos and Celltrion. PV received institution grants from Pfizer, Galapagos; consulting fees from Galapagos, Sidekick Health, Pfizer and Boehringer Ingelheim; payment/honoraria for speakers/manuscript writing/education from Eli Lilly, Galapagos and Roularta; support for meeting/travel from AbbVie; participation on data safety monitoring board/advisory board from Eli Lilly, Galapagos, Pfizer, AbbVie, Celltrion and vice president of the Royal Belgian Society for Rheumatology. The remaining authors declared no disclosures., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Background & Aims: Malnutrition and cystic fibrosis related diabetes (CFRD) are common comorbidities in cystic fibrosis (CF). Cystic fibrosis transmembrane regulator (CFTR) modulators have shown beneficial effects on respiratory status. This study aims to determine the effect of elexacaftor-tezacaftor-ivacaftor (ETI) on body mass index (BMI) and glycemic control., Methods: A retrospective, observational study of a cohort of 17 adult CF patients was conducted at the CF reference center of Ghent University Hospital. BMI evolution was analyzed 18 months before and 0, 3, 6, 12 and 18 months after the start of ETI. The evolution of insulin dependence and the 2 h oral glucose tolerance test (OGTT) results were described until 36 months after start of ETI, in a small subgroup of ten patients with CFRD or impaired glucose tolerance (IGT)., Results: A significant increase in mean BMI of 1.2 kg/m 2 (±1.3 SD) was observed. Most weight gain was observed in the first 3 months after starting treatment. This effect was sustained during the observed period of 18 months. Six patients had insulin dependent CFRD, of which three were able to stop insulin after starting ETI. Two patients with CFRD treated with dietary measures showed an initial normalization of the 2 h OGTT, but deterioration at 36 month follow-up., Conclusions: After initiation of ETI an increase in BMI was observed in adults with CF. ETI can have a beneficial impact on glucose metabolism in patients with CFRD, leading to a possible need for reduction or cessation of insulin therapy., Competing Interests: Declarations of competing interest EVB is principal investigator in multiple clinical trials with CFTR modulators from Abbvie and Vertex, for which her institution received fees., (Copyright © 2023. Published by Elsevier Ltd.)

Understanding human disease on a molecular level, and translating this understanding into targeted diagnostics and therapies are central tenets of molecular medicine 1 . Realizing this doctrine requires an efficient adaptation of molecular discoveries into the clinic. We present an approach to facilitate this process by describing the Imageable Genome, the part of the human genome whose expression can be assessed via molecular imaging. Using a deep learning-based hybrid human-AI pipeline, we bridge individual genes and their relevance in human diseases with specific molecular imaging methods. Cross-referencing the Imageable Genome with RNA-seq data from over 60,000 individuals reveals diagnostic, prognostic and predictive imageable genes for a wide variety of major human diseases. Having both the critical size and focus to be altered in its expression during the development and progression of any human disease, the Imageable Genome will generate new imaging tools that improve the understanding, diagnosis and management of human diseases., (© 2023. The Author(s).)

Background: Rheumatoid arthritis (RA) is a chronic auto-immune disease, typically affecting the joints, which can also present with lung involvement (pleuritis, interstitial lung disease, pulmonary nodules, etc.). Lung ultrasound (LUS) is an upcoming tool in the detection of these pulmonary manifestations., Methods: We performed a 72-window LUS in 75 patients presenting to the outpatient rheumatology clinic and describe the abnormalities (presence of B-lines (vertical comet-tail artefacts), pleural abnormalities, pleural effusions, and subpleural nodules) on lung ultrasound. We created a topological mapping of the number of B-lines per intercostal zone., Results: We observed pleural effusions, pleural abnormalities, and pleural nodules in, respectively, 1.3%, 45.3%, and 14% of patients. There were 35 (46.7%) patients who had less than 5 B-lines, 15 (20%) patients who had between 5 and 10 B-lines, 11 (14.6%) between 10 and 20, 10 (13.3%) between 20 and 50, 1 (1.3%) between 50 and 100, and 3 (4%) of patients who had more than 100 B-lines., Conclusions: LUS in patients with RA shows an array of abnormalities ranging from interstitial syndromes to pleural abnormalities, subpleural nodules, and pleural effusions. Hotspots for the presence of B-lines are situated bilaterally in the posterior subscapular regions, as well as the anterior right mid-clavicular region.

Objectives: To present a case of metastatic struma ovarii, to review the literature on malignant struma ovarii and to discuss the management in locoregional and metastatic disease., Methods: We present a case of an 82-year-old patient with a malignant struma ovarii and liver metastasis. The patient was treated with pelvic surgery, total thyroidectomy, radioactive iodine therapy and TSH suppression therapy with levothyroxine. We performed a PubMed search for case reports of metastatic struma ovarii., Results: 43 cases of metastatic struma ovarii were identified. 53.5% of patients presented with metastatic disease at diagnosis. Mean time to development of metastasis was 6.9 years in the group with initial locoregional disease. First-line treatment was pelvic surgery in all patients. Thyroidectomy was performed in 83.7% of patients, subsequent radioactive iodine therapy in 79.1%, followed by TSH suppression therapy in 46.5% of patients. Mean time of follow-up after diagnosis of metastases was 3.6 years, ranging from 0.5 to 24 years. At the end of the follow-up, 51.1% of patients were free of disease, 34.9% were alive with disease, 7.0% died of disease and 7.0% were lost to follow-up., Conclusion: The majority of patients with metastatic struma ovarii were treated with pelvic surgery, total thyroidectomy and radioactive iodine therapy. Suppression of TSH with levothyroxine was given in less than half of the patients. In non-metastatic setting, the same approach could be considered depending on the patient profile.

Anaplastic thyroid carcinoma (ATC) is refractory to radioiodine therapy in part because of impaired iodine metabolism. We targeted the mitogen-activated protein kinase and phosphatidylinositol 3-kinase (PI3'K) pathways with the intent to induce radioiodine uptake for radioiodine treatment of ATC. Methods: Human ATC cells were used to evaluate the ability of pharmacologic inhibition of the mitogen-activated protein kinase and PI3'K pathways to induce radioiodine uptake. Thyrocyte-specific double-mutant BRAF V600E PIK3CA H1047R mice were treated with a MEK inhibitor followed by radioiodine treatment, and tumor burden was monitored by ultrasound imaging. Results: ATC cell lines showed an increase in sodium-iodine symporter transcription when treated with a MEK or BRAF V600E inhibitor alone and in combination with PI3'K inhibitor. This translated into a dose-dependent elevation of iodine uptake after treatment with a MEK inhibitor alone and in combination with a PI3'K inhibitor. In vivo, MEK inhibition but not BRAF or PI3'K inhibition upregulated sodium-iodine symporter transcription. This translated into a stable reduction of tumor burden when mice were treated with a MEK inhibitor before radioiodine administration. Conclusion: This study confirms the ability of MEK inhibition to induce iodine uptake in in vitro and in vivo models of ATC. The approach of using a MEK inhibitor before radioiodine treatment could readily be translated into clinical practice and provide a much-needed therapeutic option for patients with ATC., (© 2019 by the Society of Nuclear Medicine and Molecular Imaging.)

Objective: Discrepancies in illness representations between patients and physicians result in treatment difficulties, decreased well-being of patients and misunderstandings and disrupted communication. Hence, the objective of this study was to compare illness perceptions of individual patients with systemic lupus erythematosus (SLE) and systemic sclerosis (SSc), their rheumatologists and their general practitioners (GPs) and explore potential differences., Methods: This study has a cross-sectional design. Patients with SLE and SSc, who were followed at the rheumatology department of the University Hospitals Leuven (Belgium), completed the revised Illness Perception Questionnaire which measures patients' perceptions of their condition and captures nine dimensions. Physicians completed the Revised Illness Perception Questionnaire for Healthcare Professionals which consists of seven dimensions and measures perceptions of the healthcare professional regarding the disease of their patients. Intraclass correlation was performed to examine relationships between pairs of respondents; Cohen's d was used for estimating the magnitude of the difference., Results: Questionnaires were sent to 284 patients of whom 241 (113 SSc and 128 SLE patients) were included. Five rheumatologists and 160 GPs participated. For both diseases, positive correlations were found for 'consequences', 'illness coherence' and 'emotional representations' among patients, rheumatologists and GPs. GPs scored higher on the 'consequences' of these diseases for the patient (d=0.71 for SLE; d=0.80 for SSc). Differences between rheumatologists and GPs were small for SSc and moderate to large for 'consequences' (d=0.56) and 'timeline acute/chronic' (d=0.95) in SLE with higher scores for GPs., Conclusions: For both diseases and among the three groups, significant correlations are detected for the dimensions 'consequences', 'illness coherence' and 'emotional representations'. Differences between rheumatologists and GPs were mainly detected in the case of SLE patients. This can have implications for the collaboration between these two groups of physicians in daily clinical practice., Clinical Trial Registration: NCT02655640; Pre-results., Competing Interests: Competing interests: None declared.

Objectives: Combining disease-modifying antirheumatic drugs (DMARDs) with glucocorticoids (GCs) is an effective treatment strategy for early rheumatoid arthritis (ERA), yet the ideal schedule and feasibility in daily practice are debated. We evaluated different DMARD combinations and GC remission induction schemes in poor prognosis patients; and methotrexate (MTX) with or without GC remission induction in good prognosis patients, during the first treatment year., Methods: The Care in ERA (CareRA) trial is a 2-year investigator-initiated randomised pragmatic open-label superiority trial comparing remission induction regimens in a treat-to-target approach. DMARD-inexperienced patients with ERA were stratified into a high-risk or low-risk group based upon presence of erosions, disease activity, rheumatoid factor and anticitrullinated protein antibodies. High-risk patients were randomised to a COBRA Classic (MTX + sulfasalazine + prednisone step-down from 60 mg), COBRA Slim (MTX + prednisone step-down from 30 mg) or COBRA Avant Garde (MTX + leflunomide + prednisone step-down from 30 mg) scheme. Low-risk patients were randomised to MTX tight step-up (MTX-TSU) or COBRA Slim. Primary outcome was the proportion of patients in 28 joint disease activity score calculated with C-reactive protein remission at week 52 in an intention-to-treat analysis. Secondary outcomes were safety and effectiveness (ClinicalTrial.gov identifier NCT01172639)., Results: 98 COBRA Classic, 98 COBRA Slim (high risk), 93 COBRA Avant Garde, 47 MTX-TSU and 43 COBRA Slim (low risk) patients were evaluated. Remission was achieved in 64.3% (63/98) COBRA Classic, 60.2% (59/98) COBRA Slim (high risk) and 62.4% (58/93) COBRA Avant Garde patients at W52 (p=0.840); and in 57.4% (27/47) MTX-TSU and 67.4% (29/43) COBRA Slim (low risk) patients (p=0.329). Less adverse events occurred per patient with COBRA Slim (high risk) compared with COBRA Classic or COBRA Avant Garde (p=0.038). Adverse events were similar in MTX-TSU and COBRA Slim (low risk) patients (p=0.871). At W52, 76.0% patients were on DMARD monotherapy, 5.2% used GCs and 7.5% biologicals., Conclusions: MTX with a moderate-dose GC remission induction scheme (COBRA Slim) seems an effective, safe, low-cost and feasible initial treatment strategy for patients with ERA regardless of their prognostic profile, provided a treat-to-target approach is followed., Trial Registration Numbers: EudraCT-number 2008-007225-39 and NCT01172639; Results., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.)

Objectives: To compare the efficacy and safety of intensive combination strategies with glucocorticoids (GCs) in the first 16 weeks (W) of early rheumatoid arthritis (eRA) treatment, focusing on high-risk patients, in the Care in early RA trial., Methods: 400 disease-modifying antirheumatic drugs (DMARD)-naive patients with eRA were recruited and stratified into high risk or low risk according to classical prognostic markers. High-risk patients (n=290) were randomised to 1/3 treatment strategies: combination therapy for early rheumatoid arthritis (COBRA) Classic (methotrexate (MTX)+ sulfasalazine+60 mg prednisone tapered to 7.5 mg daily from W7), COBRA Slim (MTX+30 mg prednisone tapered to 5 mg from W6) and COBRA Avant-Garde (MTX+leflunomide+30 mg prednisone tapered to 5 mg from W6). Treatment modifications to target low-disease activity were mandatory from W8, if desirable and feasible according to the rheumatologist. The primary outcome was remission (28 joint disease activity score calculated with C-reactive protein <2.6) at W16 (intention-to-treat analysis). Secondary endpoints were good European League Against Rheumatism response, clinically meaningful health assessment questionnaire (HAQ) response and HAQ equal to zero. Adverse events (AEs) were registered., Results: Data from 98 Classic, 98 Slim and 94 Avant-Garde patients were analysed. At W16, remission was reached in 70.4% Classic, 73.6% Slim and 68.1% Avant-Garde patients (p=0.713). Likewise, no significant differences were shown in other secondary endpoints. However, therapy-related AEs were reported in 61.2% of Classic, in 46.9% of Slim and in 69.1% of Avant-Garde patients (p=0.006)., Conclusions: For high-risk eRA, MTX associated with a moderate step-down dose of GCs was as effective in inducing remission at W16 as DMARD combination therapies with moderate or high step-down GC doses and it showed a more favourable short-term safety profile., Eudract Number: 2008-007225-39., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

Mitotic cell division ensures that two daughter somatic cells inherit identical genetic material. Previous work has shown that signaling by the Smad1 transcription factor is terminated by polyubiquitinylation and proteasomal degradation after essential phosphorylations by MAPK and glycogen synthase kinase 3 (GSK3). Here, we show that, unexpectedly, proteins specifically targeted for proteasomal degradation are inherited preferentially by one mitotic daughter during somatic cell division. Experiments with dividing human embryonic stem cells and other mammalian cultured cell lines demonstrated that in many supposedly equal mitoses the segregation of proteins destined for degradation (Smad1 phosphorylated by MAPK and GSK3, phospho-beta-catenin, and total polyubiquitinylated proteins) was asymmetric. Transport of pSmad1 targeted for degradation to the centrosome required functional microtubules. In vivo, an antibody specific for Mad phosphorylated by MAPK showed that this antigen was associated preferentially with one of the two centrosomes in Drosophila embryos at cellular blastoderm stage. We propose that this remarkable cellular property may be explained by the asymmetric inheritance of peripheral centrosomal proteins when centrioles separate and migrate to opposite poles of the cell, so that one mitotic daughter remains pristine. We conclude that many mitotic divisions are unequal, unlike what was previously thought.

Wnt signaling pathways are essential for embryonic patterning, and they are disturbed in a wide spectrum of diseases, including cancer. An unresolved question is how the different Wnt pathways are supported and regulated. We previously established that the postsynaptic density 95/disc-large/zona occludens (PDZ) protein syntenin binds to syndecans, Wnt coreceptors, and known stimulators of protein kinase C (PKC)alpha and CDC42 activity. Here, we show that syntenin also interacts with the C-terminal PDZ binding motif of several Frizzled Wnt receptors, without compromising the recruitment of Dishevelled, a key downstream Wnt-signaling component. Syntenin is coexpressed with cognate Frizzled during early development in Xenopus. Overexpression and down-regulation of syntenin disrupt convergent extension movements, supporting a role for syntenin in noncanonical Wnt signaling. Syntenin stimulates c-jun phosphorylation and modulates Frizzled 7 signaling, in particular the PKCalpha/CDC42 noncanonical Wnt signaling cascade. The syntenin-Frizzled 7 binding mode indicates syntenin can accommodate Frizzled 7-syndecan complexes. We propose that syntenin is a novel component of the Wnt signal transduction cascade and that it might function as a direct intracellular link between Frizzled and syndecans.

We report two rheumatoid arthritis patients developing sarcoidosis possibly induced by etanercept. Both women, aged 46 and 53, had erosive, rheumatoid-factor-positive rheumatoid arthritis (RA) for 7 and 6 years, respectively. The eldest had received infliximab for over a year with good response, which was stopped because of a perfusion reaction. She developed a cough and dyspnea after 6 months of etanercept treatment. The other developed erythema nodosum and a plaque lesion on the right arm after 1 year of etanercept. Imaging showed, in both cases, mediastinal adenopathies. Biopsies were compatible with sarcoidosis. Etanercept withdrawal led to a complete remission. Recently, there have been reports of noninfectious granulomatous syndromes in patients receiving etanercept for a variety of diseases. In our cases, the temporal association with etanercept therapy and the complete remission after suspension of etanercept suggest a triggering role of this agent. Possible mechanisms of action and supporting evidence are discussed.

The DNA-binding transcription factor Smad-interacting protein-1 (Sip1) (also named Zfhx1b/ZEB2) plays essential roles in vertebrate embryogenesis. In Xenopus, XSip1 is essential at the gastrula stage for neural tissue formation, but the precise molecular mechanisms that underlie this process have not been fully identified yet. Here we show that XSip1 functions as a transcriptional repressor during neural induction. We observed that constitutive activation of BMP signaling prevents neural induction by XSip1 but not the inhibition of several epidermal genes. We provide evidence that XSip1 binds directly to the BMP4 proximal promoter and modulates its activity. Finally, by deletion and mutational analysis, we show that XSip1 possesses multiple repression domains and that CtBPs contribute to its repression activity. Consistent with this, interference with XCtBP function reduced XSip1 neuralizing activity. These results suggest that Sip1 acts in neural tissue formation through direct repression of BMP4 but that BMP-independent mechanisms are involved as well. Our data also provide the first demonstration of the importance of CtBP binding in Sip1 transcriptional activity in vivo.

Neurons and glial cells differentiate from common multipotent precursors in the vertebrate retina. We have identified a novel member of the hairy/Enhancer of split [E(spl)] gene family in Xenopus, XHes2, as a regulator to bias retinal precursor cells towards a glial fate. XHes2 expression is predominantly restricted to sensory organ territories, including the retina. Using in vivo lipofection in the optic vesicle, we found that XHes2 overexpression dramatically increases gliogenesis at the expense of neurogenesis. This increase in glial cells correlates with a delayed cell cycle withdrawal of some retinal progenitors. In addition, birthdating experiments suggest that XHes2 deviates some early born cell types towards a glial fate that would normally have given rise to neurons. Conversely, a significant inhibition of glial differentiation is observed upon XHes2 loss of function. The gliogenic activity of XHes2 relies on its ability to inhibit neuronal differentiation by at least two distinct mechanisms: it not only negatively regulates XNgnr1 and NeuroD transcription, but it also physically interacts with a subset of proneural bHLH proteins.

Notch signaling has been shown to play a role in cell fate decisions in the Xenopus pronephros anlagen. Here, we show that the Xenopus Hairy-related transcription factor (HRT) gene XHRT1, and the Hairy/Enhancer of split (HES) genes Xhairy1, Xhairy2b, esr9 and esr10, have distinct restricted dynamic expression patterns during pronephros development, and that their expression is regulated by Notch. XHRT1, which is the earliest and strongest gene expressed in the pronephric region, is initially transcribed predominantly in the forming glomus, where it is downregulated by antisense morpholino oligonucleotide inhibition of xWT1. Later, it is activated in the most dorsoanterior part of the pronephros anlagen that gives rise to the proximal tubules. In agreement with this dynamic expression profile, we found that early activation of Notch favors glomus, whereas only later activation promotes proximal tubule formation. We show that, among the bHLH-O factors tested, only XHRT1 efficiently inhibits distal tubule and duct formation, and that only its translational inhibition causes a reduction of the expression of proximal tubule and glomus markers. Using domain swap experiments, we found that the XHRT1 C-terminal region is crucial for its activity. Together, our results provide evidence that XHRT1 plays an important role in glomerular development and early proximodistal patterning that is distinct from those of the other pronephric bHLH repressors.

The zinc finger/homeo-domain transcription factor (zfh x 1) family in vertebrates consists of two members, deltaEF1 and SIP1. They have been proposed to display antagonistic activities in the interpretation of Smad-dependent TGFbeta signaling during mesoderm formation. We cloned Xenopus deltaEF1 cDNA, analyzed the expression profile of the gene, and compared the inducing and interacting properties of the protein to that of XSIP1. Whereas XSIP1 RNA is selectively expressed in the early developing nervous system, we show that XdeltaEF1 gene transcription is only activated during neurulation and that its expression is restricted to the paraxial mesoderm. From early tail bud stage, XdeltaEF1 and XSIP1 are coexpressed in migratory cranial neural crest, in the retina, and in the neural tube. Overproduction of XdeltaEF1 in RNA-injected embryos, like that of XSIP1, reduced the expression of BMP-dependent genes but only XSIP1 has the ability to induce neural markers. We find that XdeltaEF1 and XSIP1 can both form complexes, although with different efficiency, with Smad3, with the coactivators p300 and pCAF, and with the corepressor CtBP1. Together, these results indicate that deltaEF1 and SIP1 do not function as antagonists during Xenopus early embryogenesis but do display different repression efficiencies and interaction properties., (Developmental Dynamics 235:1491-1500, 2006. (c) 2006 Wiley-Liss, Inc.)

XHRT1 is a member of the HRT/Hey protein subfamily that are known as Notch effectors. XHRT1 is expressed in the developing floor plate and encodes a basic helix-loop-helix (bHLH) transcription repressor. Here, we show that XHRT1 misexpression in the neural plate inhibits differentiation of neural precursor cells and thus may be important for floor plate cells to prevent them from adopting a neuronal fate. Deletion analysis indicated that inhibition of differentiation by XHRT1 requires the DNA-binding bHLH motif and either the Orange domain or the C-terminal region. XHRT1 could efficiently homodimerize and heterodimerize with hairy proteins. Among those hairy genes, Xhairy2b shows extensive overlap of expression with XHRT1 in floor plate precursors and may be a biologically relevant XHRT1 partner. Dimerization is mediated through both the bHLH and downstream sequences, the Orange domain being particularly important for the efficiency of the interaction. Using chimeric constructs between XHRT1 and the ESR9 bHLH-O protein that does not interact with Xhairy1 and Xhairy2b, we found that both the bHLH domain and downstream sequences of XHRT1 were required for heterodimerization with Xhairy2b, while only the XHRT1 sequences downstream of the Orange domain are required for the interaction with Xhairy1. Together, these results suggest that XHRT1 plays a role in floor plate cell development and highlight the importance of the Orange and downstream sequences in dimerization and in the selection of the bHLH partners.

Hairy-related transcription factors (HRTs) constitute a recently identified subfamily of basic-helix-loop-helix transcription factors containing an Orange domain (bHLH-O factors). As compared to the related HES proteins, HRTs exhibit distinct DNA-binding activities in vitro and the molecular mechanisms underlying their transcriptional activity remain poorly understood. We have identified here the sequence "ggCACGTGcc" as predominant binding site for Xenopus HRT1 (XHRT1). In transiently transfected 3T3 cells, XHRT1 represses the expression of a luciferase reporter gene under the control of multimerized XHRT1 binding sites. Deletion analysis indicated that repression by XHRT1 requires the presence of the DNA-binding bHLH motif and the Orange domain. However, the presence of the sequence motif YRPWGTEIGAF located at the very C-terminus of XHRT1 is dispensable. Accordingly, the groucho co-repressor, which is known to mediate transcriptional repression by HES factors through binding their C-terminal WRPW sequence, does not recognize the related YRPW motif present in the C-terminal part of XHRT1 significantly in vitro. As the C-terminus of HRTs is well conserved, our observation indicates that this part of HRTs, unlike the corresponding part of HES proteins, does not recruit the groucho co-repressor efficiently.

Hairy-related transcription factor (HRT/Hey) genes encode a novel subfamily of basic helix-loop-helix (bHLH) transcription factors related to the Drosophila hairy and Enhancer-of-split (E(spl)) and the mammalian HES proteins that function as downstream mediators of Notch signaling. Using the yeast two-hybrid approach, a previously uncharacterized protein was identified in Xenopus that interacts with XHRT1 (originally referred to as bc8), one member of the HRT/Hey subclass. This protein is evolutionarily conserved in chordates. It binds to sequences adjacent to the bHLH domain of XHRT1 known as the Orange domain and has been named bc8 Orange interacting protein (BOIP). BOIP shows a rather uniform subcellular localization and is recruited to the nucleus upon binding to XHRT1. In Xenopus, XBOIP mRNA is detected by RNase protection analysis throughout embryogenesis. In the adult, the strongest expression is detected in testis. In the mouse, high levels of BOIP mRNA are also found in adult testis. No expression is detected in the embryo and in any of the other adult organs tested. In situ hybridization revealed that BOIP transcripts were detected almost exclusively in round spermatids and that this expression overlaps with that of Hey1 (HRT1), which is expressed throughout spermatogenesis. In view of the importance of the Orange domain for HRT/Hey function, the newly identified BOIP proteins may serve as regulators specifically of HRT1/Hey1 activity., (Copyright 2003 Wiley-Liss, Inc.)

We have isolated a Xenopus homologue of the mammalian hairy and Enhancer of split related gene HRT1. XHRT1 expression in late gastrula and early neurula embryos is restricted to two stripes of cells in the medial neural plate and in dorsal endodermal cells. At later stages, XHRT1 is expressed in the floor plate, in hypochord cells and in the somitogenic and anterior presomitic mesoderm. By tailbud stage, XHRT1 is also highly expressed in the dorsal hindbrain, telencephalon and eye vesicles, olfactory placodes, pronephros, branchial arches and tail fin. We also show that XHRT1 expression in medial neural cells is induced by Notch signaling and that there are differences in the way XHRT1 and other H/E(spl) genes are regulated.