FRESH Bioprinting of Dynamic Hydrazone-Cross-Linked Synthetic Hydrogels.

Dynamic covalent chemistry is an attractive cross-linking strategy for hydrogel bioinks due to its ability to mimic the dynamic interactions that are natively present in the extracellular matrix. However, the inherent challenges in mixing the reactive precursor polymers during printing and the tendency of the soft printed hydrogels to collapse during free-form printing have limited the use of such chemistry in 3D bioprinting cell scaffolds. Herein, we demonstrate 3D printing of hydrazone-cross-linked poly(oligoethylene glycol methacrylate) (POEGMA) hydrogels using the freeform reversible embedding of suspended hydrogels (FRESH) technique coupled with a customized low-cost extrusion bioprinter. The dynamic nature and reversibility of hydrazone cross-links enables reconfiguration of the initially more heterogeneous gel structure to form a more homogeneous internal gel structure, even for more highly cross-linked hydrogels, over a relatively short time (<3 days) while preserving the degradability of the scaffold over longer time frames. POEGMA hydrogels can successfully print NIH/3T3 fibroblasts and human umbilical vein endothelial cells while maintaining high cell viability (>80%) and supporting F-actin-mediated adhesion to the scaffold over a 14-day in vitro incubation period, demonstrating their potential use in practical tissue engineering applications.

Hydrogels for Tissue Engineering: Addressing Key Design Needs Toward Clinical Translation.

While the soft mechanics and tunable cell interactions facilitated by hydrogels have attracted significant interest in the development of functional hydrogel-based tissue engineering scaffolds, translating the many positive results observed in the lab into the clinic remains a slow process. In this review, we address the key design criteria in terms of the materials, crosslinkers, and fabrication techniques useful for fabricating translationally-relevant tissue engineering hydrogels, with particular attention to three emerging fabrication techniques that enable simultaneous scaffold fabrication and cell loading: 3D printing, in situ tissue engineering, and cell electrospinning. In particular, we emphasize strategies for manufacturing tissue engineering hydrogels in which both macroporous scaffold fabrication and cell loading can be conducted in a single manufacturing step - electrospinning, 3D printing, and in situ tissue engineering. We suggest that combining such integrated fabrication approaches with the lessons learned from previously successful translational experiences with other hydrogels represents a promising strategy to accelerate the implementation of hydrogels for tissue engineering in the clinic.

Click Chemistry Hydrogels for Extrusion Bioprinting: Progress, Challenges, and Opportunities.

The emergence of 3D bioprinting has allowed a variety of hydrogel-based "bioinks" to be printed in the presence of cells to create precisely defined cell-loaded 3D scaffolds in a single step for advancing tissue engineering and/or regenerative medicine. While existing bioinks based primarily on ionic cross-linking, photo-cross-linking, or thermogelation have significantly advanced the field, they offer technical limitations in terms of the mechanics, degradation rates, and the cell viabilities achievable with the printed scaffolds, particularly in terms of aiming to match the wide range of mechanics and cellular microenvironments. Click chemistry offers an appealing solution to this challenge given that proper selection of the chemistry can enable precise tuning of both the gelation rate and the degradation rate, both key to successful tissue regeneration; simultaneously, the often bio-orthogonal nature of click chemistry is beneficial to maintain high cell viabilities within the scaffolds. However, to date, relatively few examples of 3D-printed click chemistry hydrogels have been reported, mostly due to the technical challenges of controlling mixing during the printing process to generate high-fidelity prints without clogging the printer. This review aims to showcase existing cross-linking modalities, characterize the advantages and disadvantages of different click chemistries reported, highlight current examples of click chemistry hydrogel bioinks, and discuss the design of mixing strategies to enable effective 3D extrusion bioprinting of click hydrogels.

A Hybrid Soluble gp130/Spike-Nanobody Fusion Protein Simultaneously Blocks Interleukin-6 trans-Signaling and Cellular Infection with SARS-CoV-2.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can induce mild to life-threatening symptoms. Especially individuals over 60 years of age or with underlying comorbidities, including heart or lung disease and diabetes, or immunocompromised patients are at a higher risk. Fatal multiorgan damage in coronavirus disease 2019 (COVID-19) patients can be attributed to an interleukin-6 (IL-6)-dominated cytokine storm. Consequently, IL-6 receptor (IL-6R) monoclonal antibody treatment for severe COVID-19 cases has been approved for therapy. High concentrations of soluble IL-6R (sIL-6R) were found in COVID-19 intensive care unit patients, suggesting the involvement of IL-6 trans-signaling in disease pathology. Here, in analogy to bispecific antibodies (bsAbs), we developed the first bispecific IL-6 trans-signaling inhibitor, c19s130Fc, which blocks viral infection and IL-6 trans-signaling. c19s130Fc is a designer protein of the IL-6 trans-signaling inhibitor cs130 fused to a single-domain nanobody directed against the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. c19s130Fc binds with high affinity to IL-6:sIL-6R complexes as well as the spike protein of SARS-CoV-2, as shown by surface plasmon resonance. Using cell-based assays, we demonstrate that c19s130Fc blocks IL-6 trans-signaling-induced proliferation and STAT3 phosphorylation in Ba/F3-gp130 cells as well as SARS-CoV-2 infection and STAT3 phosphorylation in Vero cells. Taken together, c19s130Fc represents a new class of bispecific inhibitors consisting of a soluble cytokine receptor fused to antiviral nanobodies and principally demonstrates the multifunctionalization of trans-signaling inhibitors. IMPORTANCE The availability of effective SARS-CoV-2 vaccines is a large step forward in managing the pandemic situation. In addition, therapeutic options, e.g., monoclonal antibodies to prevent viral cell entry and anti-inflammatory therapies, including glucocorticoid treatment, are currently developed or in clinical use to treat already infected patients. Here, we report a novel dual-specificity inhibitor to simultaneously target SARS-CoV-2 infection and virus-induced hyperinflammation. This was achieved by fusing an inhibitor of viral cell entry with a molecule blocking IL-6, a key mediator of SARS-CoV-2-induced hyperinflammation. Through this dual action, this molecule may have the potential to efficiently ameliorate symptoms of COVID-19 in infected individuals.

Fabricating Degradable Thermoresponsive Hydrogels on Multiple Length Scales via Reactive Extrusion, Microfluidics, Self-assembly, and Electrospinning.

While various smart materials have been explored for a variety of biomedical applications (e.g., drug delivery, tissue engineering, bioimaging, etc.), their ultimate clinical use has been hampered by the lack of biologically-relevant degradation observed for most smart materials. This is particularly true for temperature-responsive hydrogels, which are almost uniformly based on polymers that are functionally non-degradable (e.g., poly(N-isopropylacrylamide) (PNIPAM) or poly(oligoethylene glycol methacrylate) (POEGMA)). As such, to effectively translate the potential of thermoresponsive hydrogels to the challenges of remote-controlled or metabolism-regulated drug delivery, cell scaffolds with tunable cell-material interactions, theranostic materials with the potential for both imaging and drug delivery, and other such applications, a method is required to render the hydrogels (if not fully degradable) at least capable of renal clearance following the required lifetime of the material. To that end, this protocol describes the preparation of hydrolytically-degradable hydrazone-crosslinked hydrogels on multiple length scales based on the reaction between hydrazide and aldehyde-functionalized PNIPAM or POEGMA oligomers with molecular weights below the renal filtration limit. Specifically, methods to fabricate degradable thermoresponsive bulk hydrogels (using a double barrel syringe technique), hydrogel particles (on both the microscale through the use of a microfluidics platform facilitating simultaneous mixing and emulsification of the precursor polymers and the nanoscale through the use of a thermally-driven self-assembly and cross-linking method), and hydrogel nanofibers (using a reactive electrospinning strategy) are described. In each case, hydrogels with temperature-responsive properties similar to those achieved via conventional free radical cross-linking processes can be achieved, but the hydrazone cross-linked network can be degraded over time to re-form the oligomeric precursor polymers and enable clearance. As such, we anticipate these methods (which may be generically applied to any synthetic water-soluble polymer, not just smart materials) will enable easier translation of synthetic smart materials to clinical applications.

Dynamically Cross-Linked Self-Assembled Thermoresponsive Microgels with Homogeneous Internal Structures.

The internal morphology of temperature-responsive degradable poly(N-isopropylacrylamide) (PNIPAM) microgels formed via an aqueous self-assembly process based on hydrazide and aldehyde-functionalized PNIPAM oligomers is investigated. A combination of surface force measurements, small angle neutron scattering (SANS), and ultrasmall angle neutron scattering (USANS) was used to demonstrate that the self-assembled microgels have a homogeneously cross-linked internal structure. This result is surprising given the sequential addition process used to fabricate the microgels, which was expected to result in a densely cross-linked shell-diffuse core structure. The homogeneous internal structure identified is also significantly different than conventional microgels prepared via precipitation polymerization, which typically exhibit a diffuse shell-dense core structure. The homogeneous structure is hypothesized to result from the dynamic nature of the hydrazone cross-linking chemistry used to couple with the assembly conditions chosen that promote polymer interdiffusion. The lack of an internal cross-linking gradient within these degradable and monodisperse microgels is expected to facilitate more consistent drug release over time, improved optical properties, and other potential application benefits.

Microfluidic production of degradable thermoresponsive poly(N-isopropylacrylamide)-based microgels.

Highly monodisperse and hydrolytically degradable thermoresponsive microgels on the tens-to-hundreds of micron size scale have been fabricated based on simultaneous on-chip mixing and emulsification of aldehyde and hydrazide-functionalized poly(N-isopropylacrylamide) precursor polymers. The microfluidic chip can run for extended periods without upstream gelation and can produce monodisperse (<10% particle size variability) microgels on the size range of ∼30-90 µm, with size tunable according to the flow rate of the oil continuous phase. Fluorescence analysis indicates a uniform distribution of each reactive pre-polymer inside the microgels while micromechanical testing suggests that smaller microfluidic-produced microgels exhibit significantly higher compressive moduli compared to bulk hydrogels of the same composition, an effect we attribute to improved mixing (and thus crosslinking) of the precursor polymer solutions within the microfluidic device. The microgels retain the reversible volume phase transition behavior of conventional microgels but can be hydrolytically degraded back into their oligomeric precursor polymer fragments, offering potential for microgel clearance following use in vivo.

A transdisciplinary account of water research.

Water research is introduced from the combined perspectives of natural and social science and cases of citizen and stakeholder coproduction of knowledge. Using the overarching notion of transdisciplinarity, we examine how interdisciplinary and participatory water research has taken place and could be developed further. It becomes apparent that water knowledge is produced widely within society, across certified disciplinary experts and noncertified expert stakeholders and citizens. However, understanding and management interventions may remain partial, or even conflicting, as much research across and between traditional disciplines has failed to integrate disciplinary paradigms due to philosophical, methodological, and communication barriers. We argue for more agonistic relationships that challenge both certified and noncertified knowledge productively. These should include examination of how water research itself embeds and is embedded in social context and performs political work. While case studies of the cultural and political economy of water knowledge exist, we need more empirical evidence on how exactly culture, politics, and economics have shaped this knowledge and how and at what junctures this could have turned out differently. We may thus channel the coproductionist critique productively to bring perspectives, alternative knowledges, and implications into water politics where they were not previously considered; in an attempt to counter potential lock-in to particular water policies and technologies that may be inequitable, unsustainable, or unacceptable. While engaging explicitly with politics, transdisciplinary water research should remain attentive to closing down moments in the research process, such as framings, path-dependencies, vested interests, researchers' positionalities, power, and scale. WIREs Water 2016, 3:369-389. doi: 10.1002/wat2.1132 For further resources related to this article, please visit the WIREs website.

Applicability of salt reduction strategies in pizza crust.

In an effort to reduce population-wide sodium intake from processed foods, due to major health concerns, several different strategies for sodium reduction in pizza crust without any topping were evaluated by sensory analyses. It was possible to reduce sodium by 10% in one single step or to replace 30% of NaCl by KCl without a noticeable loss of salty taste. The late addition of coarse-grained NaCl (crystal size: 0.4-1.4 mm) to pizza dough led to an enhancement of saltiness through taste contrast and an accelerated sodium delivery measured in the mouth and in a model mastication simulator. Likewise, the application of an aqueous salt solution to one side of the pizza crust led to an enhancement of saltiness perception through faster sodium availability, leading to a greater contrast in sodium concentration. Each of these two strategies allowed a sodium reduction of up to 25% while maintaining taste quality.

Temperature-Induced Assembly of Monodisperse, Covalently Cross-Linked, and Degradable Poly(N-isopropylacrylamide) Microgels Based on Oligomeric Precursors.

A simple, rapid, solvent-free, and scalable thermally driven self-assembly approach is described to produce monodisperse, covalently cross-linked, and degradable poly(N-isopropylacrylamide) (PNIPAM) microgels based on mixing hydrazide (PNIPAM-Hzd) and aldehyde (PNIPAM-Ald) functionalized PNIPAM precursors. Preheating of a seed PNIPAM-Hzd solution above its phase transition temperature produces nanoaggregates that are subsequently stabilized and cross-linked by the addition of PNIPAM-Ald. The ratio of PNIPAM-Hzd:PNIPAM-Ald used to prepare the microgels, the time between PNIPAM-Ald addition and cooling, the temperature to which the PNIPAM-Hzd polymer solution is preheated, and the concentration of PNIPAM-Hzd in the initial seed solution can all be used to control the size of the resulting microgels. The microgels exhibit similar thermal phase transition behavior to conventional precipitation-based microgels but are fully degradable into oligomeric precursor polymers. The microgels can also be lyophilized and redispersed without any change in colloidal stability or particle size and exhibit no significant cytotoxicity in vitro. We anticipate that microgels fabricated using this approach may facilitate translation of the attractive properties of such microgels in vivo without the concerns regarding microgel clearance that exist with other PNIPAM-based microgels.

Dopaminergic foundations of schizotypy as measured by the German version of the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE)-a suitable endophenotype of schizophrenia.

The concept of schizotypy or "psychosis proneness" captures individual differences in perceptual, cognitive, and affective experiences that may relate to a range of psychotic disorders. The concept is an important way to assess the contribution of pre-existing psychological and genetically based biological features to the development of illnesses such as schizophrenia (so called endophenotypes). The Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE) is a widely used multi-dimensional measure of the construct and consists of four scales which mirror several groups of psychotic symptoms: Unusual Experiences (UnEx; positive symptoms), Cognitive Disorganization (CogDis; cognitive symptoms), Introvertive Anhedonia (IntAn; negative symptoms), and Impulsive Nonconformity (ImpNon; impulsive and antisocial symptoms). For the purpose of evaluating the suitability of schizotypy as an endophenotype of schizophrenia the current version of the O-LIFE was translated into German: its psychometric properties (including re-test reliability and construct validity) were examined in a large sample (n > 1200) and compared to those of the English original. The German version was both highly reliable and consistent with the original. The study aimed to show that schizotypy as measured by the O-LIFE can indeed be regarded as an endophenotype of schizophrenia in terms of genetic associations regarding relevant dopamine-related candidate polymorphisms of schizotypy [i.e., Val(158)Met-polymorphism of the COMT gene, uVNTR of the MAOA gene, Taq1A-polymorphism of the DRD2 gene, VNTR of the SLC6A3 (DAT) gene]. We also wanted to compare the genetic associations of the O-LIFE to those published using other operationalizations of schizotypy. Our results show a large number of significant associations and borderline-significant trends between the O-LIFE sub-scales and a range of genes, thereby supporting using the O-LIFE in the search for endophenotypic markers.

Genetic variants within the dopaminergic system interact to modulate endocrine stress reactivity and recovery.

Catecholamines modulate endocrine stress reactivity by affecting regulatory influences of extra-hypothalamic brain structures on hypothalamus-pituitary-adrenal (HPA)-axis. Therefore, we aimed to investigate combined effects of functional allelic variations that affect dopamine availability in both cortical (COMT Val¹58Met polymorphism) and subcortical (DAT1 VNTR) brain regions on HPA-axis reactivity to psychosocial stress. By using a standardized laboratory stress task (public speaking) we obtained saliva cortisol samples during stress exposure and an extended recovery period in 100 healthy male adults. We report for the first time significant epistasis between COMT Val¹58Met and DAT1 VNTR on cortisol response patterns. Subjects homozygous for both the Met¹58 and the 10-repeat allele of DAT1 VNTR were characterized by markedly elevated cortisol reactivity and impaired stress recovery compared to all other groups. Our results indicate a crucial role of functional genetic variants within the dopaminergic system in the modulation of HPA-axis response patterns and highlight the need to investigate combined effects of specific candidate genes on stress-related endophenotypes.

The BDNF Val66Met polymorphism affects HPA-axis reactivity to acute stress.

BACKGROUND: Growing evidence suggests that individual differences in HPA-axis reactivity to psychosocial stress are partly due to heritable influences. However, knowledge about the role of specific genetic variants remains very limited to date. Since brain-derived neurotrophic factor (BDNF) not only exhibits neurotrophic actions but is also involved in the regulation of hypothalamic neuropeptides, we investigated the role of a common functional polymorphism within the BDNF gene (BDNF Val66Met) in the context of endocrine and cardiovascular stress reactivity. METHODS: Healthy male adults (N=100) were genotyped and exposed to a standardized laboratory stress task (Public Speaking). Saliva cortisol and self-reported mood levels were obtained at 6 time points prior to the stressor and during an extended recovery period. Furthermore, heart rate reactivity as an indicator of sympathetic activation was monitored continuously during the experimental procedure. RESULTS: We report a small, but significant effect of the BDNF Val66Met polymorphism on stress reactivity. More precisely, carriers of the met-allele showed a significantly attenuated HPA-axis and cardiovascular reactivity to the psychosocial stressor compared to subjects with the val/val genotype. Furthermore, the diminished physiological response in met-allele carriers was also attended by significantly lower self-reported ratings of perceived stress and nervousness. CONCLUSION: Our findings of a diminished endocrine and cardiovascular stress response in healthy male adults is consistent with a previously published study and adds further evidence for a crucial role of the BDNF Val66Met polymorphism in the modulation of stress reactivity.

Aggression--interactions of serotonin and testosterone in healthy men and women.

Serotonin (5-HT) and testosterone (T) have both been implicated in the regulation of aggression. Findings in humans however are very inconclusive, with respect to main effects of either system. Animal models implicate T to modulate 5-HT system activity, and furthermore have shown behaviorally relevant interactions of T and 5-HT with respect to aggression. We tested for associations between habitual T-level and 5-HT system activity, as well as behaviorally relevant interactions of T and 5-HT with respect to trait aggression in 48 healthy male and female subjects. 5-HT activity was measured by means of neuroendocrine challenge paradigm with S-citalopram. T-levels were measured in saliva samples. Trait aggression was assessed by self-report measures. T-levels were not associated with indices of central 5-HT activity. Results showed significant interaction effects between 5-HT and T for trait aggression in men only (p<0.05). Trait aggression was significantly higher in the combinations "high T+high cortisol responses" (indicating decreased 5-HT availability), and "low T+low cortisol responses" (indicating increased 5-HT availability), after S-citalopram. Results support the notion of behaviorally relevant interactions between T and 5-HT, with respect to aggression in humans, but also indicate the need for further studies.

Novel roles of hakai in cell proliferation and oncogenesis.

During tumor development, cells acquire multiple phenotypic changes upon misregulation of oncoproteins and tumor suppressor proteins. Hakai was originally identified as an E3 ubiquitin-ligase for the E-cadherin complex that regulates cell-cell contacts. Here, we present evidence that Hakai plays a crucial role in various cellular processes and tumorigenesis. Overexpression of Hakai affects not only cell-cell contacts but also proliferation in both epithelial and fibroblast cells. Furthermore, the knockdown of Hakai significantly suppresses proliferation of transformed epithelial cells. Expression of Hakai is correlated to the proliferation rate in human tissues and is highly up-regulated in human colon and gastric adenocarcinomas. Moreover, we identify PTB-associated splicing factor (PSF), an RNA-binding protein, as a novel Hakai-interacting protein. By using cDNA arrays, we have determined various specific PSF-associated mRNAs encoding proteins that are involved in several cancer-related processes. Hakai affects the ability of PSF to bind these mRNAs, and expression of PSF short hairpin RNA or a dominant-negative PSF mutant significantly suppresses proliferation of Hakai-overexpressing cells. Collectively, these results suggest that Hakai is an important regulator of cell proliferation and that Hakai may be an oncoprotein and a potential molecular target for cancer treatment.

Signal responsiveness of IkappaB kinases is determined by Cdc37-assisted transient interaction with Hsp90.

The IkappaB kinase (IKK) holocomplex, containing the kinases IKKalpha, IKKbeta, and the scaffold NEMO (NF-kappaB essential modifier), mediates activation of NF-kappaB by numerous physiological stimuli. Heat shock protein 90 (Hsp90) and the co-chaperone Cdc37 have been indicated as additional subunits, but their specific functions in signal transduction are indistinct. Using an RNA interference approach, we demonstrate that Cdc37 recruits Hsp90 to the IKK complex in a transitory manner, preferentially via IKKalpha. Binding is conferred by N-terminal as well as C-terminal residues of Cdc37. Cdc37 is essential for the maturation of de novo synthesized IKKs into enzymatically competent kinases but not for assembly of an IKK holocomplex. Mature IKKs, T-loop-phosphorylated after stimulation either by receptor-mediated signaling or upon DNA damage, further require Hsp90-Cdc37 to generate an activated state. Thus, the present data denote Hsp90-Cdc37 as a transiently acting essential regulatory component of IKK signaling.

Molecular analysis of the interaction between cardosin A and phospholipase D(alpha). Identification of RGD/KGE sequences as binding motifs for C2 domains.

Here we report the identification of phospholipase Dalpha as a cardosin A-binding protein. The interaction was confirmed by coimmunoprecipitation studies and pull-down assays. To investigate the structural and molecular determinants involved in the interaction, pull-down assays with cardosin A and various glutathione S-transferase-fused phospholipase Dalpha constructs were performed. Results revealed that the C2 domain of phospholipase Dalpha contains the cardosin A-binding activity. Further assays with mutated recombinant forms of cardosin A showed that the RGD motif as well as the unprecedented KGE motif, which is structurally and charge-wise very similar to RGD, are indispensable for the interaction. Taken together our results indicate that the C2 domain of plant phospholipase Dalpha can act as a cardosin A-binding domain and suggest that plant C2 domains may have an additional role as RGD/KGE-recognition domains.

The interaction of protein kinase C isozymes alpha, iota, and theta with the cytoplasmic domain of L-selectin is modulated by phosphorylation of the receptor.

The leukocyte adhesion molecule L-selectin has an important role in the initial steps of leukocyte extravasation during inflammation and lymphocyte homing. Its cytoplasmic domain is involved in signal transduction after L-selectin cross-linking and in the regulation of receptor binding activity in response to intracellular signals. However, the signaling events occurring at the level of the receptor are largely unknown. This study therefore addressed the question of whether protein kinases associate with the cytoplasmic domain of the receptor and mediate its phosphorylation. Using a glutathione S-transferase fusion protein of the L-selectin cytoplasmic domain, we isolated a kinase activity from cellular extracts of the human leukemic Jurkat T-cell line that phosphorylated L-selectin on serine residues. This kinase showed characteristics of the protein kinase C (PKC) family. Moreover, the Ca(2+)-independent PKC isozymes theta and iota were found associated with the cytoplasmic domain of L-selectin. Pseudosubstrate inhibitors of these isozymes abolished phosphorylation of the cytoplasmic domain, demonstrating that these kinases are responsible for the phosphorylation. Analysis of proteins specifically bound to the phosphorylated cytoplasmic tail of L-selectin revealed that PKCalpha and -theta are strongly associated with the phosphorylated cytoplasmic domain of L-selectin. Binding of these isozymes to L-selectin was also found in intact cells after phorbol ester treatment inducing serine phosphorylation of the receptor. Furthermore, stimulation of Jurkat T-cells by CD3 cross-linking induced association of PKCalpha and -theta with L-selectin, indicating a role of these kinases in the regulation of L-selectin through the T-cell receptor complex. The phosphorylation-regulated association of PKC isozymes with the cytoplasmic domain of L-selectin indicates an important role of this kinase family in L-selectin signal transduction.

Cloning, sequencing and recombinant expression of the open reading frame encoding a novel member of the Sarcocystis muris (Apicomplexa) microneme lectin family.

Micronemes are characteristic secretory organelles located within the apical cell region of apicomplexan parasites. The protein contents are exocytosed during an early phase of host cell invasion and contribute to parasite motility and the invasion of target cells. We report here on the cloning and heterologous expression of a novel member of the Sarcocystis muris microneme lectin family. The deduced amino acid sequence is in total agreement with that obtained after sequencing the native protein and is characterized by two copies of the apple domain motif. The recombinant polypeptide is expressed in a biologically active conformation as demonstrated by its galactose binding properties.

Essential role of the apolipoprotein E receptor-2 in sperm development.

The apolipoprotein (apo) E receptor-2 (apoER2) is a member of the low density lipoprotein receptor gene family and an important regulator of neuronal migration. It acts as a receptor for the signaling factor Reelin and provides positional cues to neurons that migrate to their proper position in the developing brain. Besides brain formation defects, apoER2-deficient mice also exhibit male infertility. The role of the receptor in male reproduction, however, remained unclear. Here we demonstrate that apoER2 is highly expressed in the initial segment of the epididymis, where it affects the functional expression of clusterin and phospholipid hydroperoxide glutathione peroxidase (PHGPx), two proteins required for sperm maturation. Reduced PHGPx expression in apoER2 knockout mice results in the inability of the sperm to regulate the cell volume and in abnormal sperm morphology and immotility. Because insufficient expression of PHGPx is a major cause of infertility in men, these findings not only highlight an important new function for apoER2 that is unrelated to neuronal migration, but they also suggest a possible role for apoER2 in human infertility.