Parasexuality in Race 65 Colletotrichum lindemuthianum Isolates

ABSTRACT. Heterokaryosis is the initial step of the parasexual cycle, a process that provides genetic variability in filamentous fungi through the production of heterozygous diploid nuclei. To characterize the parasexual cycle in Colletotrichum lindemuthianum, we evaluated the presence of heterokaryosis, vegetative compatibility reactions, and diploid formation among isolates of Race 65 collected from different Brazilian states. Vegetative compatibility groups were identified among the isolates according to their ability to form heterokaryons. Two heterozygous diploids were selected from compatible heterokaryons, which were characterized by the segregation of the parental auxotrophic markers and by RAPD profiles.     

GSK-3β as a driving force in ovarian cancer

Ovarian cancer is one of the most lethal malignancies in women. Identification of new therapeutic targets would provide opportunities for developing potentially more effective treatment regimes. In the July issue of Cell Research, Cao et al. reports that glycogen synthase kinase-3β （GSK-3β） plays an important role in positively regulating the proliferation of human ovarian cancer cells, and thus it may represent such a target [ 1 ]. GSK-3β is a serine/threonine kinase that is known to be involved in regulation of β-catenin signaling, where it participates in the formation of a multi-component destruction complex that promotes the phosphorylation and subsequent degradation of β-catenin. Given that overactive β-catenin signaling is involved in many forms of human cancer, this classic mode of GSK-3β action should qualify it as a ＂tumor suppressor＂. Intriguingly, however, two recent studies have implicated that GSK-3β may actually play a pro-tumor role in pancreatic and colorectal cancers [2, 3]. Since ovarian tumors often exhibit increased expression of GSK-3β, these recent findings prompted Cao et al. to examine the potential role of GSK-3β in ovarian cancer cells.     

Selective degradation of the IκB kinase （IKK） by autophagy

Proteasome-mediated degradation and autophagy are the two major pathways mediating the turnover of cellular proteins. The proteasomal pathway is known to be a highly specific and regulated process mediating the degradation of short-lived proteins such as many important factors involved in cellular signaling. In contrast, it is generally thought that autophagy is rather nonselective as it is responsible for the bulk degradation of long-lived proteins and organelles. Challenging this general view, in this issue of Cell Research, Qing et al. report that selective degradation of the IκB kinase （IKK） triggered by the loss of Hsp90 function is mediated by autophagy [1].     

Heparin interacting protein mediated assembly of nano-fibrous hydrogel scaffolds for guided stem cell differentiation

A new methodology is developed to conjugate hyaluronic acid (HA) hydrogel with novel nano-fibrous architectures via non-covalent assembly that specifically allows for targeted adipose-derived stem cells (ASCs) differentiation and soft tissue engineering. The assembly of non-covalently associated hydrogel network produced via the interaction of a low molecular weight heparin (LMWH) modified HA derivative and heparin interacting protein (HIP). The multifunctional star poly(ethylene glycol) (PEG) and HIP copolymer has the capability to mediate the non-covalent assembly of nano-fibrous HA hydrogel networks via affinity interactions with LMWH. The effect of the HIP mediation on in vitro gelation, rheological characteristics, degradation, equilibrium swelling, adipose-derived stem cells (ASCs) proliferation and differentiation of nano-fibrous hydrogel is examined. The results suggest the potential utility of this unique design of the bioactive nano-fibrous HA hydrogel in directing the differentiation of ASCs and adipogenesis in ECM-mimetic scaffolds in vitro. These studies demonstrate that this nano-fibrous HA hydrogel can render the formulation of a therapeutically effective platform for in vitro adipogenesis applications.     

L-citrulline supplementation reverses the impaired airway relaxation in neonatal rats exposed to hyperoxia

Background

Hyperoxia is shown to impair airway relaxation via limiting L-arginine bioavailability to nitric oxide synthase (NOS) and reducing NO production as a consequence. L-arginine can also be synthesized by L-citrulline recycling. The role of L-citrulline supplementation was investigated in the reversing of hyperoxia-induced impaired relaxation of rat tracheal smooth muscle (TSM).

Methods

Electrical field stimulation (EFS, 2–20 V)-induced relaxation was measured under in vitro conditions in preconstricted tracheal preparations obtained from 12 day old rat pups exposed to room air or hyperoxia (>95% oxygen) for 7 days supplemented with L-citrulline or saline (in vitro or in vivo). The role of the L-citrulline/L-arginine cycle under basal conditions was studied by incubation of preparations in the presence of argininosuccinate synthase (ASS) inhibitor [α-methyl-D, L-aspartate, 1 mM] or argininosuccinate lyase inhibitor (ASL) succinate (1 mM) and/or NOS inhibitor [N^ω-nitro-L-arginine methyl ester; 100 μM] with respect to the presence or absence of L-citrulline (2 mM).

Results

Hyperoxia impaired the EFS-induced relaxation of TSM as compared to room air control (p < 0.001; 0.5 ± 0.1% at 2 V to 50.6 ± 5.7% at 20 V in hyperoxic group: 0.7 ± 0.2 at 2 V to 80.0 ± 5.6% at 20 V in room air group). Inhibition of ASS or ASL, and L-citrulline supplementation did not affect relaxation responses under basal conditions. However, inhibition of NOS significantly reduced relaxation responses (p < 0.001), which were restored to control level by L-citrulline. L-citrulline supplementation in vivo and in vitro also reversed the hyperoxia-impaired relaxation. The differences were significant (p <0.001; 0.8 ± 0.3% at 2 V to 47.1 ± 4.1% at 20 V without L-citrulline; 0.9 ± 0.3% at 2 V to 68.2 ± 4.8% at 20 V with L-citrulline). Inhibition of ASS or ASL prevented this effect of L-citrulline.

Conclusion

The results indicate the presence of an L-citrulline/L-arginine cycle in the airways of rat pups. L-citrulline recycling does not play a major role under basal conditions in airways, but it has an important role under conditions of substrate limitations to NOS as a source of L-arginine, and L-citrulline supplementation reverses the impaired relaxation of airways under hyperoxic conditions.