Enzymatic deacetylation of galactoglucomannans

Several hemicellulolytic microorganisms were screened for their capability of liberating acetyl side groups from native softwood galactoglucomannan. All the microorganisms tested were found to produce an extracellular acetyl glucomannan esterase(s). The highest activity was detected in Schizophyllum commune culture filtrate. However, the enzyme produced by Aspergillus oryzae was most efficient in long-term hydrolysis. Acting alone, the purified esterase of A. oryzae was able to liberate most of the acetic acid from galactoglucomannan. The addition of other galactoglucomannan-degrading enzymes did not affect the action of esterase. On the other hand, the addition of esterase clearly enhanced the action of mannanase and -galactosidase. The purified acetyl esterase of Trichoderma reesei was able to liberate acetic acid from short oligomers of glucomannan, whereas the acetyl xylan esterase of T. reesei was unable to act on glucomannan oligomers of any size. Correspondence to: M. Tenkanen     

Nutrient fluxes and microbial activity in sediment enriched with settled seston

The chemical and microbiological responses of profundal surface sediment were monitored in sediment enriched with natural settled material collected in May, July or August, and with diatom or cyanobacteria cultures. The activation of the sediment microbial community was clearest after the addition of settled seston collected in May which was richer in organic matter than those collected later in the summer. N was released when the sediment was enriched with settled seston which had been collected in July and August and had C:N ratios lower than 10:1. The diatom-rich May-material enhanced the release of P to the interstitial water, obviously because of chemical competition between P and diatom-derived Si at the sediment surface. The July- and August-materials did not release P, nor did the diatom and cyanobacteria cultures. The results thus indicate that the seasonal variations in the quality and quantity of the settling phytoplankton affect the P dynamics at the sediment surface, both chemically and biologically.     

Lignin release and photomixotrophism in suspension cultures of Picea abies

The effect of different concentrations of sucrose (0-4%) and of two growth regulators (0–50 μ M 2,4-D and 0–25 μ M kinetin) was tested on growth and chlorophyll content of suspension cultures of Picea abies (L.) Karst. originating from chlorophyllous embryo callus in an elevated CO₂ (2%) atmosphere. A continuous chlorophyllous suspension culture was achieved on a medium containing 2% sucrose and a low level of organic nitrogen (0.25 m M arginine and 0.5 m M glutamine) supplemented with 2,4-D (0.5 μ M ) and kinetin (2.5 μ M ). The same medium with 4% sucrose gave the best growth response, but a negative correlation between chlorophyll level and growth was observed. The chlorophyllous cultures grew slowly in a medium with low (0.5%) sucrose or without any carbohydrate source, suggesting photomixotrophism. A high concentration of kinetin inhibited both growth and chlorophyll synthesis. Release of lignin into the nutrient medium was observed in several experiments, especially in slow-growing cultures supplemented with sucrose. Only a few successive passages of suspensions that produced lignin could be cultured before cell death. The cultures releasing lignin may be unique for studies on synthesis and biodegradation of this very complex compound.     

Rat tracheal epithelial cell differentiation in vitro

Summary In vitro culture conditions enabling rat tracheal epithelial (RTE) cells to differentiate to mucociliary, mucous, or squamous phenotypes are described. Medium composition for rapid cell growth to confluence in membrane insert cultures was determined, and the effects of major modifiers of differentiation were tested. Retinoic acid (RA), collagen gel substratum, and an air-liquid interface at the level of the cell layer were required for expression of a mucociliary phenotype which most closely approximated the morphology of the tracheal epithelium in vivo. Large quantities of high molecular weight, hyaluronidase-resistant glycoconjugates, most likely mucin glycoproteins, were produced in the presence of RA when the cells were grown with or without a collagen gel and in submerged as well as in interface cultures. However, extensive ciliagenesis was dependent on the simultaneous presence of RA, collagen gel, and an air-liquid interface. When RA was omitted from the media, the cells became stratified squamous and developed a cornified apical layer in air-liquid interface cultures. This phenotype was accompanied by loss of transglutaminase (TGase) type II and keratin 18 and expression of the squamous markers TGase type I and keratin 13. The ability to modulate RTE cell phenotypes in culture will facilitate future studies investigating molecular regulation of tracheal cell proliferation, differentiation, and function.     

USP26: a genetic risk factor for sperm X‐Y aneuploidy

Segregation of the largely non‐homologous X and Y sex chromosomes during male meiosis is not a trivial task, because their pairing, synapsis, and crossover formation are restricted to a tiny region of homology, the pseudoautosomal region. In humans, meiotic X‐Y missegregation can lead to 47, XXY offspring, also known as Klinefelter syndrome, but to what extent genetic factors predispose to paternal sex chromosome aneuploidy has remained elusive. In this issue, Liu et al (2021) provide evidence that deleterious mutations in the USP26 gene constitute one such factor.Subject Categories: Cell Cycle, Development & Differentiation, Molecular Biology of Disease

Analyses of Klinefelter syndrome patients and Usp26‐deficient mice have revealed a genetic influence on age‐dependent sex chromosome missegregation during male meiosis.

Multilayered mechanisms have evolved to ensure successful X‐Y recombination, as a prerequisite for subsequent normal chromosome segregation. These include a distinct chromatin structure as well as specialized proteins on the pseudoautosomal region (Kauppi et al, 2011; Acquaviva et al, 2020). Even so, X‐Y recombination fails fairly often, especially in the face of even modest meiotic perturbations. It is perhaps not surprising then that X‐Y aneuploidy—but not autosomal aneuploidy—in sperm increases with age (Lowe et al, 2001; Arnedo et al, 2006), as does the risk of fathering sons with Klinefelter syndrome (De Souza & Morris, 2010).Klinefelter syndrome is one of the most common aneuploidies in liveborn individuals (Thomas & Hassold, 2003). While most human trisomies result from errors in maternal chromosome segregation, this is not the case for Klinefelter syndrome, where the extra X chromosome is equally likely to be of maternal or paternal origin (Thomas & Hassold, 2003; Arnedo et al, 2006). Little is known about genetic factors in humans that predispose to paternal XY aneuploidy, i.e., that increase the risk of fathering Klinefelter syndrome offspring. The general notion has been that paternally derived Klinefelter syndrome arises stochastically. However, fathers of Klinefelter syndrome patients have elevated rates of XY aneuploid sperm (Lowe et al, 2001; Arnedo et al, 2006), implying a persistent defect in spermatogenesis in these individuals rather than a one‐off meiotic error.To identify possible genetic factors contributing to Klinefelter syndrome risk, Liu et al (2021) performed whole‐exome sequencing in a discovery cohort of > 100 Klinefelter syndrome patients, followed by targeted sequencing in a much larger cohort of patients and controls, as well as Klinefelter syndrome family trios. The authors homed in on a mutational cluster (“mutated haplotype”) in ubiquitin‐specific protease 26 (USP26), a testis‐expressed gene located on the X chromosome. Effects of this gene’s loss of function (Usp26‐deficient mice) on spermatogenesis have recently been independently reported by several laboratories and ranged from no detectable fertility phenotype (Felipe‐Medina et al, 2019) to subfertility/sterility associated with both meiotic and spermiogenic defects (Sakai et al, 2019; Tian et al, 2019). With their Klinefelter syndrome cohort findings, Liu et al (2021) also turned to Usp26 null mice, paying particular attention to X‐Y chromosome behavior and—unlike earlier mouse studies—including older mice in their analyses. They found that Usp26‐deficient animals often failed to achieve stable pairing and synapsis of X‐Y chromosomes in spermatocytes, produced XY aneuploid sperm at an abnormally high frequency, and sometimes also sired XXY offspring. Importantly, these phenotypes only occurred at an advanced age: XY aneuploidy was seen in six‐month‐old, but not two‐month‐old Usp26‐deficient males. Moreover, levels of spindle assembly checkpoint (SAC) proteins also reduced in six‐month‐old males. Thus, in older Usp26 null mice, the combination of less efficient X‐Y pairing and less stringent SAC‐mediated surveillance of faithful chromosome segregation allows for sperm aneuploidy, providing another example of SAC leakiness in males (see Lane & Kauppi, 2019 for discussion).Liu et al’s analyses shed some light on what molecular mechanisms may be responsible for the reduced efficiency of X‐Y pairing and synapsis in Usp26‐deficient spermatocytes. USP26 codes for a deubiquitinating enzyme that has several substrates in the testis. Because USP26 prevents degradation of these substrates, their levels should be downregulated in Usp26 null testes. Liu et al (2021) show that USP26 interacts with TEX11, a protein required for stable pairing and normal segregation of the X and Y chromosomes in mouse meiosis (Adelman & Petrini, 2008). USP26 can de‐ubiquitinate TEX11 in vitro, and in Usp26 null testes, TEX11 was almost undetectable. It is worth noting that USP26 has several other known substrates, including the androgen receptor (AR), and therefore, USP26 disruption likely contributes to compromised spermatogenesis via multiple mechanisms. For example, AR signaling‐dependent hormone levels are misregulated in Usp26 null mice (Tian et al, 2019).The sex chromosome phenotypes observed in Usp26 null mice predict that men with USP26 mutations may be fertile, but producing XY aneuploid sperm at an abnormally high frequency, and that spermatogenic defects should increase with age (Fig 1). These predictions were testable, because the mutated USP26 haplotype, present in 13% of Klinefelter syndrome patients, was reasonably common also in fertile men (7–10%). Indeed, sperm XY aneuploidy was substantially higher in fertile men with the mutated USP26 haplotype than in those without USP26 mutations. Some mutation carriers produced > 4% aneuploid sperm. Moreover, age‐dependent oligospermia was also found associated with the mutated USP26 haplotype.Open in a separate windowFigure 1Mutated USP26 as genetic risk factor for age‐dependent X‐Y defects in spermatogenesisMouse genetics demonstrate that deleterious USP26 mutations lead to less‐efficient X‐Y pairing and recombination with advancing age. Concomitant decrease of spindle assembly checkpoint (SAC) protein levels leads to less‐efficient elimination of metaphase I spermatocytes that contain misaligned X and Y chromosomes. This allows for the formation of XY aneuploid sperm in older individuals and subsequently increased age‐dependent risk for fathering Klinefelter syndrome (KS) offspring, two correlates also observed in human USP26 mutation carriers. At the same time, oligospermia/subfertility also increases with advanced age in both Usp26‐deficient mice and USP26 mutation‐carrying men, tempering Klinefelter syndrome offspring risk but also decreasing fecundity.As indicated by its prevalence in the normal control population, the USP26 mutated haplotype is not selected against in the human population. With > 95% of sperm in USP26 mutation carriers having normal haploid chromosomal composition, the risk of producing (infertile) Klinefelter syndrome offspring remains modest, likely explaining why USP26 mutant alleles are not eliminated. Given that full Usp26 disruption barely affects fertility of male mice during their prime reproductive age (Felipe‐Medina et al, 2019; Tian et al, 2019; Liu et al, 2021), there is little reason to assume strong negative selection against USP26 variants in humans. USP26 as the first‐ever genetic risk factor predisposing to sperm X‐Y aneuploidy and paternal origin Klinefelter syndrome offspring in humans, as uncovered by Liu et al, may be just one of many. 90% of Liu et al’s Klinefelter syndrome cases were not associated with USP26 mutations. But even in the age of genomics, discovery of Klinefelter syndrome risk factors is not straightforward, since most sperm of risk mutation carriers will not be XY aneuploid and thus not give rise to Klinefelter syndrome offspring. In addition, as Usp26 null mice demonstrate, both genetic and non‐genetic modifiers impact on penetrance of the XY aneuploidy phenotype: Spermatogenesis in the absence of Usp26 was impaired in the DBA/2 but not the C57BL/6 mouse strain background (Sakai et al, 2019), and in older mice, there was substantial inter‐individual variation in the severity of the X‐Y defect (Liu et al, 2021). In human cohorts, genetic and non‐genetic modifiers are expected to blur the picture even more.Future identification of sex chromosome aneuploidy risk factors has human health implications beyond Klinefelter syndrome. Firstly, XXY incidence is not only relevant for Klinefelter syndrome livebirths—it also contributes to stillbirths and spontaneous abortions, at a 4‐fold higher rate than to livebirths (Thomas & Hassold, 2003). Secondly, persistent meiotic X‐Y defects can, over time, result in oligospermia and even infertility. Since the mean age of first‐time fathers is steadily rising and currently well over 30 years in many Western countries, age‐dependent spermatogenic defects will be of ever‐increasing clinical relevance.     

Documenting Freedom From Disease and Re-Establishing a Free Status After a Breakdown Rabies

Rabies reappeared in Finland in the spring of 1988 after a 29-year absence. This time rabies occurred in sylvatic form and the major species involved was the raccoon dog. During the outbreak 1988–89 66 animals were diagnosed rabid. Vaccination of cats, cattle and horses was strongly recommended and vaccination of dogs was compulsory in the outbreak area. A field trial was started on oral immunisation of raccoon dogs and foxes against rabies using baits containing rabies vaccine strain. The outbreak area and a wide buffer zone were baited three times. Finland was declared free of rabies again in 1991. Oral vaccination campaign with vaccine baits has been organised along the southeastern border once a year since the beginning of 90s. Continuous surveillance and epidemiological screening is necessary to detect any new outbreaks of rabies at an early stage.     

Chronic nicotine modifies the effects of morphine on extracellular striatal dopamine and ventral tegmental GABA

Previously, we have shown that 7-week oral nicotine treatment enhances morphine-induced behaviors and dopaminergic activity in the mouse brain. In this study, we further characterized the nicotine-morphine interaction in the mesolimbic and nigrostriatal dopaminergic systems, as well as in the GABAergic control of these systems. In nicotine-pretreated mice, morphine-induced dopamine release in the caudate putamen and nucleus accumbens was significantly augmented, as measured by microdialysis. Chronic nicotine treatment did not change basal extracellular concentrations of dopamine and its metabolites in the caudate putamen and nucleus accumbens, nor did it affect the rate of dopamine synthesis, as assessed by 3-hydroxybenzylhydrazine dihydrochloride-induced DOPA accumulation. GABAergic control of dopaminergic activity was studied by measuring extracellular GABA in the presence of nipecotic acid, an inhibitor of GABA uptake. Acute (0.3 mg/kg or 0.5 mg/kg i.p.) and chronic nicotine, as well as morphine (15 mg/kg s.c.) in control mice decreased nipecotic acid-induced increase in extracellular GABA in the ventral tegmental area/substantia nigra (VTA/SN). In contrast, in nicotine-treated mice, morphine increased GABA levels in the presence of nipecotic acid. We did not find any alterations in GABA(B)-receptor function after chronic nicotine treatment. Thus, our data show that chronic nicotine treatment sensitizes dopaminergic systems to morphine and affects GABAergic systems in the VTA/SN.     

Hydrolysis of amorphous and crystalline cellulose by heterologously produced cellulases of Melanocarpus albomyces

Three thermostable neutral cellulases from Melanocarpus albomyces, a 20-kDa endoglucanase (Cel45A), a 50-kDa endoglucanase (Cel7A), and a 50-kDa cellobiohydrolase (Cel7B) heterologously produced in a recombinant Trichoderma reesei were purified and studied in hydrolysis (50 degrees C, pH 6.0) of crystalline and amorphous cellulose. To improve their efficiency, M. albomyces cellulases naturally harboring no cellulose-binding module (CBM) were genetically modified to carry the CBM of T. reesei CBHI/Cel7A, and were studied under similar experimental conditions. Hydrolysis performance and product profiles were used to evaluate hydrolytic features of the investigated enzymes. Each cellulase proved to be active against the tested substrates; the cellobiohydrolase Cel7B had greater activity than the endoglucanases Cel45A and Cel7A against crystalline cellulose, whereas in the case of amorphous substrate the order was reversed. Evidence of synergism was observed when mixtures of the novel enzymes were applied in a constant total protein dosage. Presence of the CBM improved the hydrolytic potential of each enzyme in all experimental configurations; it had a greater effect on the endoglucanases Cel45A and Cel7A than the cellobiohydrolase Cel7B, especially against crystalline substrate. The novel cellobiohydrolase performed comparably to the major cellobiohydrolase of T. reesei (CBHI/Cel7A) under the applied experimental conditions.