The creation of a living heart valve is a much-wanted alternative for current valve prostheses that suffer from limited durability and thromboembolic complications. Current strategies to create such valves, however, require the use of cells for in vitro culture, or decellularized human- or animal-derived donor tissue for in situ engineering. Here, we propose and demonstrate proof-of-concept of in situ heart valve tissue engineering using a synthetic approach, in which a cell-free, slow degrading elastomeric valvular implant is populated by endogenous cells to form new valvular tissue inside the heart. We designed a fibrous valvular scaffold, fabricated from a novel supramolecular elastomer, that enables endogenous cells to enter and produce matrix. Orthotopic implantations as pulmonary valve in sheep demonstrated sustained functionality up to 12 months, while the implant was gradually replaced by a layered collagen and elastic matrix in pace with cell-driven polymer resorption. Our results offer new perspectives for endogenous heart valve replacement starting from a readily-available synthetic graft that is compatible with surgical and transcatheter implantation procedures.

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We have generated transgenic mice containing hybrid llama͞ human antibody loci that contain two llama variable regions and the human D, J, and C and͞or C␥ constant regions. Such loci rearrange productively and rescue B cell development efficiently without LC rearrangement. Heavy-chain-only antibodies (HCAb) are expressed at high levels, provided that the CH1 domain is deleted from the constant regions. HCAb production does not require an IgM stage for effective pre-B cell signaling. Antigenspecific heavy-chain-only IgM or IgGs are produced upon immunization. The IgG is dimeric, whereas IgM is multimeric. The chimeric HCAb loci are subject to allelic exclusion, but several copies of the transgenic locus can be rearranged and expressed successfully on the same allele in the same cell. Such cells are not subject to negative selection. The mice produce a full antibody repertoire and provide a previously undescribed avenue to produce specific human HCAb in the future.immunoglobulin rearrangement ͉ transgenic C onventional antibodies contain two heavy and light chains (LC) coded for by heavy and LC loci. B cell development and antibody production starts in the bone marrow (BM) by heavy chain (HC) VDJ recombination and expression of IgM associated with a surrogate LC on the cell surface. In a second round of recombination, one of the LC rearranges in pre-B cells. If successful, the B cells undergo selection, affinity maturation, and switching to different HC constant regions to result in B cells, which express tetrameric antibodies of different isotypes (IgA, IgG, and IgE). Normally absence of HC or LC expression leads to arrest of B cell development. However, some species produce HC-only antibodies (HCAb) as part of their normal B cell development and repertoire. The best-known HCAb (i.e., no LC) are IgG2 and IgG3 in camelids (1). They undergo antigen-mediated selection and affinity maturation, and their variable domains are subject to somatic hypermutation (2, 3). HCAb are thought to recognize unusual epitopes, such as clefts on the antigen surface (4). The first domain of the constant region, CH1, is spliced out because of the loss of a consensus splice signal (5, 6). CH1 exon loss also has been described in other mammals, albeit associated with disease, e.g., in mouse myelomas (7) and human HC disease (HCD) (8-10).Camelid HCAbs contain a complete VDJ region. Its size, stability, specificity, and solubility have generated considerable biotechnological interest. The antigen-binding site, a single-variable domain (VHH), resembles VH of conventional Abs. However, differences in FR2 and CDR3 prevent VHH to pair with a variable LC, whereas hydrophilic amino acids provide solubility (11). HCAb of the IgM class have not been found in camelids, suggesting that the IgM ϩ stage of HCAb formation is very transient and͞or circumvented.Murine NSO myeloma cells can express a rearranged camelid VHH-␥2a gene (12) and, recently, the same gene was expressed in transgenic mice (13). Here, we describe transgenic mice containing various...

Gluconobacter oxydans contains pyrroloquinoline quinone-dependent glucose dehydrogenase (GDH). Two isogenic G. oxydans strains, P1 and P2, which differ in their substrate specificity with respect to oxidation of sugars have been analysed. P1 can oxidize only D-glucose, whereas P2 is also capable of the oxidation of the disaccharide maltose. To investigate the nature of this maltose-oxidizing property we cloned the gene encoding GDH from P2. Expression of P2 gdh in P1 enables the latter strain to oxidize maltose, indicating that a mutation in the P2 gdh gene is responsible for the change in substrate specificity. This mutation could be ascribed to a 1 bp substitution resulting in the replacement of His 787 by Asn.

The presence of porcine endogenous retroviruses presents a potential risk of transmission of infectious diseases (xenozoonosis) if tissues and organs from genetically modified pigs are to be used in xenotransplantation. Here, we report that intracellular expression of a llama single-domain antibody against p15, the matrix domain protein of the porcine endogenous retrovirus Gag polyprotein, blocks retrovirus production, providing the possibility of eliminating the risk of infection in xenotransplantation

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The creation of living heart valve replacements via tissue engineering is actively being pursued by many research groups. Numerous strategies have been described, aimed either at culturing autologous living valves in a bioreactor (in vitro) or inducing endogenous regeneration by the host via resorbable scaffolds (in situ). Whereas a lot of effort is being invested in the optimization of heart valve scaffold parameters and culturing conditions, the pathophysiological in vivo remodeling processes to which tissue-engineered heart valves are subjected upon implantation have been largely under-investigated. This is partly due to the unavailability of suitable immunohistochemical tools specific to sheep, which serves as the gold standard animal model in translational research on heart valve replacements. Therefore, the goal of this study was to comprise and validate a comprehensive sheep-specific panel of antibodies for the immunohistochemical analysis of tissue-engineered heart valve explants. For the selection of our panel we took inspiration from previous histopathological studies describing the morphology, extracellular matrix composition and cellular composition of native human heart valves throughout development and adult stages. Moreover, we included a range of immunological markers, which are particularly relevant to assess the host inflammatory response evoked by the implanted heart valve. The markers specifically identifying extracellular matrix components and cell phenotypes were tested on formalin-fixed paraffin-embedded sections of native sheep aortic valves. Markers for inflammation and apoptosis were tested on ovine spleen and kidney tissues. Taken together, this panel of antibodies could serve as a tool to study the spatiotemporal expression of proteins in remodeling tissue-engineered heart valves after implantation in a sheep model, thereby contributing to our understanding of the in vivo processes which ultimately determine long-term success or failure of tissue-engineered heart valves.

The online version of this article has a Supplementary Appendix. BackgroundIn erythroblasts, the CoREST repressor complex is recruited to target promoters by the transcription factor Gfi1b, leading to repression of genes mainly involved in erythroid differentiation. Hmg20b is a subunit of CoREST, but its role in erythropoiesis has not yet been established. Design and MethodsTo study the role of Hmg20b in erythropoiesis, we performed knockdown experiments in a differentiation-competent mouse fetal liver cell line, and in primary mouse fetal liver cells. The effects on globin gene expression were determined. We used microarrays to investigate global gene expression changes induced by Hmg20b knockdown. Functional analysis was carried out on Hrasls3, an Hmg20b target gene. ResultsWe show that Hmg20b depletion induces spontaneous differentiation. To identify the target genes of Hmg20b, microarray analysis was performed on Hmg20b knockdown cells and controls. In line with its association to the CoREST complex, we found that 85% (527 out of 620) of the deregulated genes are up-regulated when Hmg20b levels are reduced. Among the few down-regulated genes was Gfi1b, a known repressor of erythroid differentiation. Among the consistently up-regulated targets were embryonic β-like globins and the phospholipase HRASlike suppressor 3 (Hrasls3). We show that Hrasls3 expression is induced during erythroid differentiation and that knockdown of Hrasls3 inhibits terminal differentiation of proerythroblasts. ConclusionsWe conclude that Hmg20b acts as an inhibitor of erythroid differentiation, through the downregulation of genes involved in differentiation such as Hrasls3, and activation of repressors of differentiation such as Gfi1b. In addition, Hmg20b suppresses embryonic β-like globins.Key words: Hmg20b, CoREST, erythropoiesis, Gfi1b, Hrasls3, embryonic β-like globins.Citation: Esteghamat F, van Dijk TB, Braun H, Dekker S, van der Linden R, Hou J, Fanis P, Demmers J, van IJcken W, Özgür Z, Horos R, Pourfarzad F, von Lindern M, and