H19 controls reactivation of the imprinted gene network during muscle regeneration.

The H19 locus controls fetal growth by regulating expression of several genes from the imprinted gene network (IGN). H19 is fully repressed after birth, except in skeletal muscle. Using loss-of-function H19(Δ3) mice, we investigated the function of H19 in adult muscle. Mutant muscles display hypertrophy and hyperplasia, with increased Igf2 and decreased myostatin (Mstn) expression. Many imprinted genes are expressed in muscle stem cells or satellite cells. Unexpectedly, the number of satellite cells was reduced by 50% in H19(Δ3) muscle fibers. This reduction occurred after postnatal day 21, suggesting a link with their entry into quiescence. We investigated the biological function of these mutant satellite cells in vivo using a regeneration assay induced by multiple injections of cardiotoxin. Surprisingly, despite their reduced number, the self-renewal capacity of these cells is fully retained in the absence of H19. In addition, we observed a better regeneration potential of the mutant muscles, with enhanced expression of several IGN genes and genes from the IGF pathway.

Myod and H19-Igf2 locus interactions are required for diaphragm formation in the mouse.

The myogenic regulatory factor Myod and insulin-like growth factor 2 (Igf2) have been shown to interact in vitro during myogenic differentiation. In order to understand how they interact in vivo, we produced double-mutant mice lacking both the Myod and Igf2 genes. Surprisingly, these mice display neonatal lethality due to severe diaphragm atrophy. Alteration of diaphragm muscle development occurs as early as 15.5 days post-coitum in the double-mutant embryos and leads to a defect in the terminal differentiation of muscle progenitor cells. A negative-feedback loop was detected between Myod and Igf2 in embryonic muscles. Igf2 belongs to the imprinted H19-Igf2 locus. Molecular analyses show binding of Myod on a mesodermal enhancer (CS9) of the H19 gene. Chromatin conformation capture experiments reveal direct interaction of CS9 with the H19 promoter, leading to increased H19 expression in the presence of Myod. In turn, the non-coding H19 RNA represses Igf2 expression in trans. In addition, Igf2 also negatively regulates Myod expression, possibly by reducing the expression of the Srf transcription factor, a known Myod activator. In conclusion, Igf2 and Myod are tightly co-regulated in skeletal muscles and act in parallel pathways in the diaphragm, where they affect the progression of myogenic differentiation. Igf2 is therefore an essential player in the formation of a functional diaphragm in the absence of Myod.

High Q factor InP photonic crystal nanobeam cavities on silicon wire waveguides.

High-quality (Q) factor indium phosphide (InP)-based 1D photonic crystal nanobeam cavities are fabricated on silicon on insulator waveguides. Through the optimization of the fabrication process, the intrinsic Q factor of these fully encapsulated nanocavities is demonstrated to attain values higher than 100,000. Experimental and numerical investigations are carried out on the impact, on the Q factor, of the strength of the evanescent wave coupling between the cavity and the waveguide. We reveal that this coupling can result in a modification of the electromagnetic field distribution in the resonant mode, which gives rise up to a factor 4 reduction in the intrinsic Q factor for the structures under study.

H19 lncRNA controls gene expression of the Imprinted Gene Network by recruiting MBD1.

The H19 gene controls the expression of several genes within the Imprinted Gene Network (IGN), involved in growth control of the embryo. However, the underlying mechanisms of this control remain elusive. Here, we identified the methyl-CpG-binding domain protein 1 MBD1 as a physical and functional partner of the H19 long noncoding RNA (lncRNA). The H19 lncRNA-MBD1 complex is required for the control of five genes of the IGN. For three of these genes--Igf2 (insulin-like growth factor 2), Slc38a4 (solute carrier family 38 member 4), and Peg1 (paternally expressed gene 1)--both MBD1 and H3K9me3 binding were detected on their differentially methylated regions. The H19 lncRNA-MBD1 complex, through its interaction with histone lysine methyltransferases, therefore acts by bringing repressive histone marks on the differentially methylated regions of these three direct targets of the H19 gene. Our data suggest that, besides the differential DNA methylation found on the differentially methylated regions of imprinted genes, an additional fine tuning of the expressed allele is achieved by a modulation of the H3K9me3 marks, mediated by the association of the H19 lncRNA with chromatin-modifying complexes, such as MBD1. This results in a precise control of the level of expression of growth factors in the embryo.

Subduing surface recombination for continuous-wave operation of photonic crystal nanolasers integrated on Silicon waveguides.

Detrimental surface recombination of carriers in InP-based photonic crystal nanobeams containing quantum wells is reduced by employing chemical treatment followed by silica encapsulation. Carrier lifetime is shown to recover to 2.63ns close to the bulk value. This enables us to obtain optically pumped room-temperature continuous-wave nanolasers at 1.55µm integrated onto Silicon on insulator waveguide platform with a threshold of 8µW.

Thermal management in hybrid InP/silicon photonic crystal nanobeam laser.

Thermal properties of InP-based quantum well photonic crystal nanobeam lasers heterogeneously integrated on silicon on insulator waveguides are studied. We show both numerically and experimentally the reduction of the thermal resistance of the III-V cavities by adjusting the composition of the layer which bonds the III-V materials to the silicon wafer and by adding an over-cladding on top of the cavities. Using a bonding layer made of benzocyclobutene and SiO(2) and an over-cladding of MgF(2), we found a decrease by a factor higher than 35 compared to air-suspended photonic crystal nanobeam cavities. Such optimized structures are demonstrated to operate under continuous wave pumping for several 10's of minutes despite the adverse effect of non-radiative surface recombination of carriers.

Accelerated generation of gene-engineered monoclonal CHO cell lines using FluidFM nanoinjection and CRISPR/Cas9.

Chinese hamster ovary (CHO) cells are the commonly used mammalian host system to manufacture recombinant proteins including monoclonal antibodies. However unfavorable non-human glycoprofile displayed on CHO-produced monoclonal antibodies have negative impacts on product quality, pharmacokinetics, and therapeutic efficiency. Glycoengineering such as genetic elimination of genes involved in glycosylation pathway in CHO cells is a viable solution but constrained due to longer timeline and laborious workflow. Here, in this proof-of-concept (PoC) study, we present a novel approach coined CellEDIT to engineer CHO cells by intranuclear delivery of the CRISPR components to single cells using the FluidFM technology. Co-injection of CRISPR system targeting BAX, DHFR, and FUT8 directly into the nucleus of single cells, enabled us to generate triple knockout CHO-K1 cell lines within a short time frame. The proposed technique assures the origin of monoclonality without the requirement of limiting dilution, cell sorting or positive selection. Furthermore, the approach is compatible to develop both single and multiple knockout clones (FUT8, BAX, and DHFR) in CHO cells. Further analyses on single and multiple knockout clones confirmed the targeted genetic disruption and altered protein expression. The knockout CHO-K1 clones showed the persistence of gene editing during the subsequent passages, compatible with serum free chemically defined media and showed equivalent transgene expression like parental clone.

The H19 lincRNA is a developmental reservoir of miR-675 that suppresses growth and Igf1r.

The H19 large intergenic non-coding RNA (lincRNA) is one of the most highly abundant and conserved transcripts in mammalian development, being expressed in both embryonic and extra-embryonic cell lineages, yet its physiological function is unknown. Here we show that miR-675, a microRNA (miRNA) embedded in H19's first exon, is expressed exclusively in the placenta from the gestational time point when placental growth normally ceases, and placentas that lack H19 continue to grow. Overexpression of miR-675 in a range of embryonic and extra-embryonic cell lines results in their reduced proliferation; targets of the miRNA are upregulated in the H19 null placenta, including the growth-promoting insulin-like growth factor 1 receptor (Igf1r) gene. Moreover, the excision of miR-675 from H19 is dynamically regulated by the stress-response RNA-binding protein HuR. These results suggest that H19's main physiological role is in limiting growth of the placenta before birth, by regulated processing of miR-675. The controlled release of miR-675 from H19 may also allow rapid inhibition of cell proliferation in response to cellular stress or oncogenic signals.

A genome-wide approach reveals novel imprinted genes expressed in the human placenta.

Genomic imprinting characterizes genes with a monoallelic expression, which is dependent on the parental origin of each allele. Approximately 150 imprinted genes are known to date, in humans and mice but, though computational searches have tried to extract intrinsic characteristics of these genes to identify new ones, the existing list is probably far from being comprehensive. We used a high-throughput strategy by diverting the classical use of genotyping microarrays to compare the genotypes of mRNA/cDNA vs. genomic DNA to identify new genes presenting monoallelic expression, starting from human placental material. After filtering of data, we obtained a list of 1,082 putative candidate monoallelic SNPs located in more than one hundred candidate genes. Among these, we found known imprinted genes, such as IPW, GRB10, INPP5F and ZNF597, which contribute to validate the approach. We also explored some likely candidates of our list and identified seven new imprinted genes, including ZFAT, ZFAT-AS1, GLIS3, NTM, MAGI2, ZC3H12Cand LIN28B, four of which encode zinc finger transcription factors. They are, however, not imprinted in the mouse placenta, except for Magi2. We analyzed in more details the ZFAT gene, which is paternally expressed in the placenta (as ZFAT-AS1, a non-coding antisense RNA) but biallelic in other tissues. The ZFAT protein is expressed in endothelial cells, as well as in syncytiotrophoblasts. The expression of this gene is, moreover, downregulated in placentas from complicated pregnancies. With this work we increase by about 10% the number of known imprinted genes in humans.