Facioscapulohumeral muscular dystrophy (FSHD), the third most common myopathy, is an autosomal dominant disease with an insidious onset and progression. Almost all FSHD patients carry deletions of an ...integral number of tandem 3.3 kb repeats, termed D4Z4, located on chromosome 4q35. In FSHD patients a deletion of the integral number of D4Z4 repeats generates a fragment that is usually smaller than 35 kb (fewer than 11 repeats), whereas in normal controls the size usually ranges from 50 to 300 kb (between 11 and 150 units). D4Z4 is a repetitive element with heterochromatic features. Recently, 4q35 genes located upstream of D4Z4 have been found to be inappropriately overexpressed specifically in FSHD muscle. An element within D4Z4 has been shown to behave as a silencer that provides a binding site for a transcriptional repressing complex. These results suggest a model in which deletion of D4Z4 leads to the inappropriate transcriptional derepression of 4q35 genes, resulting in disease.
Hox proteins are transcription factors involved in controlling axial patterning, leukaemias and hereditary malformations. Here, we show that HOXC10 oscillates in abundance during the cell cycle, ...being targeted for degradation early in mitosis by the ubiquitin‐dependent proteasome pathway. Among abdominal‐B subfamily members, the mitotic proteolysis of HOXC10 appears unique, since the levels of the paralogous HOXD10 and the related homeoprotein HOXC13 are constant throughout the cell cycle. When two destruction box motifs (D‐box) are mutated, HOXC10 is stabilized and cells accumulate in metaphase. HOXC10 appears to be a new prometaphase target of the anaphase‐promoting complex (APC), since its degradation coincides with cyclin A destruction and is suppressed by expression of a dominant‐negative form of UbcH10, an APC‐associated ubiquitin‐conjugating enzyme. Moreover, HOXC10 co‐immunoprecipitates the APC subunit CDC27, and its in vitro degradation is reduced in APC‐depleted extracts or by competition with the APC substrate cyclin A. These data imply that HOXC10 is a homeoprotein with the potential to influence mitotic progression, and might provide a link between developmental regulation and cell cycle control.
Blazars are active galactic nuclei (AGN) with relativistic jets whose non-thermal radiation is extremely variable on various timescales
. This variability seems mostly random, although some ...quasi-periodic oscillations (QPOs), implying systematic processes, have been reported in blazars and other AGN. QPOs with timescales of days or hours are especially rare
in AGN and their nature is highly debated, explained by emitting plasma moving helically inside the jet
, plasma instabilities
or orbital motion in an accretion disc
. Here we report results of intense optical and γ-ray flux monitoring of BL Lacertae (BL Lac) during a dramatic outburst in 2020 (ref.
). BL Lac, the prototype of a subclass of blazars
, is powered by a 1.7 × 10
M
(ref.
) black hole in an elliptical galaxy (distance = 313 megaparsecs (ref.
)). Our observations show QPOs of optical flux and linear polarization, and γ-ray flux, with cycles as short as approximately 13 h during the highest state of the outburst. The QPO properties match the expectations of current-driven kink instabilities
near a recollimation shock about 5 parsecs (pc) from the black hole in the wake of an apparent superluminal feature moving down the jet. Such a kink is apparent in a microwave Very Long Baseline Array (VLBA) image.
Facioscapulohumeral muscular dystrophy (FSHD), a common myopathy, is an autosomal dominant disease of unknown molecular mechanism. Almost all FSHD patients carry deletions of an integral number of ...tandem 3.3 kilobase repeats, termed D4Z4, located on chromosome 4q35. Here, we find that in FSHD muscle, 4q35 genes located upstream of D4Z4 are inappropriately overexpressed. We show that an element within D4Z4 specifically binds a multiprotein complex consisting of YY1, a known transcriptional repressor, HMGB2, an architectural protein, and nucleolin. We demonstrate that this multiprotein complex binds D4Z4 in vitro and in vivo and mediates transcriptional repression of 4q35 genes. Based upon these results, we propose that deletion of D4Z4 leads to the inappropriate transcriptional derepression of 4q35 genes resulting in disease.
ABSTRACT
In 2021 BL Lacertae underwent an extraordinary activity phase, which was intensively followed by the Whole Earth Blazar Telescope (WEBT) Collaboration. We present the WEBT optical data in ...the BVRI bands acquired at 36 observatories around the world. In mid-2021 the source showed its historical maximum, with R = 11.14. The light curves display many episodes of intraday variability, whose amplitude increases with source brightness, in agreement with a geometrical interpretation of the long-term flux behaviour. This is also supported by the long-term spectral variability, with an almost achromatic trend with brightness. In contrast, short-term variations are found to be strongly chromatic and are ascribed to energetic processes in the jet. We also analyse the optical polarimetric behaviour, finding evidence of a strong correlation between the intrinsic fast variations in flux density and those in polarization degree, with a time delay of about 13 h. This suggests a common physical origin. The overall behaviour of the source can be interpreted as the result of two mechanisms: variability on time-scales greater than several days is likely produced by orientation effects, while either shock waves propagating in the jet, or magnetic reconnection, possibly induced by kink instabilities in the jet, can explain variability on shorter time-scales. The latter scenario could also account for the appearance of quasi-periodic oscillations, with periods from a few days to a few hours, during outbursts, when the jet is more closely aligned with our line of sight and the time-scales are shortened by relativistic effects.
Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant neuromuscular disorder that is not due to a classical mutation within a protein-coding gene. Instead, almost all FSHD patients ...carry deletions of an integral number of tandem 3.3-kilobase repeat units, termed D4Z4, located on chromosome 4q35 (ref. 3). D4Z4 contains a transcriptional silencer whose deletion leads to inappropriate overexpression in FSHD skeletal muscle of 4q35 genes located upstream of D4Z4 (ref. 4). To identify the gene responsible for FSHD pathogenesis, we generated transgenic mice selectively overexpressing in skeletal muscle the 4q35 genes FRG1, FRG2 or ANT1. We find that FRG1 transgenic mice develop a muscular dystrophy with features characteristic of the human disease; by contrast, FRG2 and ANT1 transgenic mice seem normal. FRG1 is a nuclear protein and several lines of evidence suggest it is involved in pre-messenger RNA splicing. We find that in muscle of FRG1 transgenic mice and FSHD patients, specific pre-mRNAs undergo aberrant alternative splicing. Collectively, our results suggest that FSHD results from inappropriate overexpression of FRG1 in skeletal muscle, which leads to abnormal alternative splicing of specific pre-mRNAs.
Background:
B cell acute lymphoblastic leukemia (B‐ALL) is the most common pediatric cancer and the major cause of cancer‐related death before the age of 20. In up to 7% of cases, the disease is ...caused by rearrangements of the Double Homeobox 4 (DUX4) transcription factor to the immunoglobulin heavy chain (IGH) locus, giving rise to the oncogenic fusion protein DUX4‐IGH. While ectopic expression of wild type DUX4 induces apoptosis, DUX4‐IGH has transforming ability in cellular and animal models. These opposite biological activities are mirrored by the ability of DUX4 and DUX4‐IGH to drive the transcription of non‐overlapping sets of target genes, despite the two proteins share the same DNA binding domain (dbd).
Aims:
Through proteomics, we identified a specific DUX4‐IGH inhibitor. Preliminary data indicate that the inhibitor directly binds to DUX4‐IGH dbd blocking the activation of target genes. Based on this evidence, I aim to test the antileukemic activity of the inhibitor.
Methods:
Human cell lines and primary murine bone barrow progenitor cells will be lentivirally transduced to induce the expression of DUX4‐IGH alone or in combination with its inhibitor, and the effects on proliferation, transformation, clonogenic potential and self‐renewal ability in B‐cell differentiation conditions will be evaluated.
To test the efficacy of DUX4‐IGH inhibition in leukemia development, I will employ murine bone marrow transplantation assays and patient derived xenografts of DUX4‐IGH B‐ALL and assess disease latency in the presence or absence of the DUX4‐IGH inhibitor.
Results:
Preliminary data indicate that the activity of DUX4‐IGH is restricted to B‐cells, supporting the need of a B‐cell specific co‐factor. Importantly, lentiviral expression of the DUX4‐IGH inhibitor in NALM6 cells that carry a DUX4‐IGH translocation reduce the endogenous levels of DUX4‐IGH targets.
I expect to see a significant inhibition of DUX4‐IGH driven transformation in the presence of its inhibitor, associated with reduced proliferation, clonogenic and self‐renewal potential in cell culture systems. I predict that the inhibitor will rescue differentiation potential and block or significantly delay leukemia development in mice injected with DUX4‐IGH expressing pro‐B cells.
Summary/Conclusion:
Pre‐clinical validation of the DUX4‐IGH inhibitor will help defining effective therapeutic strategies for DUX4‐IGH B‐ALL patients, improving clinical outcome and lowering treatment toxicity.
G. Zerbini, R. Mangili, D. Gabellini and G. Pozza
Division of Medicine, Scientific Institute San Raffaele, University of Milan, Italy.
An elevated activity of erythrocyte Na+/Li+ countertransport ...(SLC) is an
intermediate phenotype of human essential hypertension, but cells other
than erythrocytes have not been studied. Therefore, we have examined
several transport modes of Na+/Li+ exchange in human skin fibroblasts.
External Na+-stimulated Li+ efflux was 152 +/- 31 (SE) nmol x mg
protein(-1) x min(-1) (n = 8). At intracellular pH 7.3, intracellular
Na+-stimulated Li+ influx, intracellular Li+-stimulated Na+ influx, and
external Li+-stimulated Na+ efflux were very similar, indicating the
presence of a tightly coupled 1:1 SLC. This pathway was not affected by
5-(N,N-dimethyl)-amiloride and changes in the membrane potential, but
phloretin and intracellular acidification (intracellular pH 6.8) were
markedly inhibitory. Kinetic analyses of the external Na+ site also
compared with SLC, although the internal site appeared to show a low
affinity for Li+. We conclude that an SLC pathway similar to that in human
erythrocytes is expressed in human skin fibroblasts.
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