Identification of MEDIATOR16 as the Arabidopsis COBRA suppressor MONGOOSE1.

We performed a screen for genetic suppressors of cobra, an Arabidopsis mutant with defects in cellulose formation and an increased ratio of unesterified/esterified pectin. We identified a suppressor named mongoose1 (mon1) that suppressed the growth defects of cobra, partially restored cellulose levels, and restored the esterification ratio of pectin to wild-type levels. mon1 was mapped to the MEDIATOR16 (MED16) locus, a tail mediator subunit, also known as SENSITIVE TO FREEZING6 (SFR6). When separated from the cobra mutation, mutations in MED16 caused resistance to cellulose biosynthesis inhibitors, consistent with their ability to suppress the cobra cellulose deficiency. Transcriptome analysis revealed that a number of cell wall genes are misregulated in med16 mutants. Two of these genes encode pectin methylesterase inhibitors, which, when ectopically expressed, partially suppressed the cobra phenotype. This suggests that cellulose biosynthesis can be affected by the esterification levels of pectin, possibly through modifying cell wall integrity or the interaction of pectin and cellulose.

A comparative systems analysis of polysaccharide-elicited responses in Neurospora crassa reveals carbon source-specific cellular adaptations.

Filamentous fungi are powerful producers of hydrolytic enzymes for the deconstruction of plant cell wall polysaccharides. However, the central question of how these sugars are perceived in the context of the complex cell wall matrix remains largely elusive. To address this question in a systematic fashion we performed an extensive comparative systems analysis of how the model filamentous fungus Neurospora crassa responds to the three main cell wall polysaccharides: pectin, hemicellulose and cellulose. We found the pectic response to be largely independent of the cellulolytic one with some overlap to hemicellulose, and in its extent surprisingly high, suggesting advantages for the fungus beyond being a mere carbon source. Our approach furthermore allowed us to identify carbon source-specific adaptations, such as the induction of the unfolded protein response on cellulose, and a commonly induced set of 29 genes likely involved in carbon scouting. Moreover, by hierarchical clustering we generated a coexpression matrix useful for the discovery of new components involved in polysaccharide utilization. This is exemplified by the identification of lat-1, which we demonstrate to encode for the physiologically relevant arabinose transporter in Neurospora. The analyses presented here are an important step towards understanding fungal degradation processes of complex biomass.

Targeted therapeutic approach for an anaplastic thyroid cancer in vitro and in vivo.

Anaplastic thyroid carcinoma (ATC) is among the most aggressive human malignancies, being responsible for the majority of thyroid cancer-related deaths. Despite multimodal therapy including surgery, chemotherapy, and radiotherapy, the outcome of ATC is poor. The human ATC cell line MB1, derived from tumor tissue of a 57-year-old man with thyroid cancer and pronounced neutrophilia, was established from surgically excised tumor tissue. The karyotype of the cell line shows many chromosomal abnormalities. Preclinical investigations have shown antitumor activity and effectiveness of the BRAF kinase inhibitor Sorafenib and the proteasome inhibitor Bortezomib. After establishment of the MB1 cell line these agents were applied in vitro and, showing activity in a cell culture model, were also used for in vivo treatment. Sorafenib had some clinical effect, namely normalization of leucocytosis, but had no sustained impact on subsequent tumor growth and development of distant metastasis. Molecular diagnostics of the tumor demonstrated no BRAF mutations in exons 11 and 15 concordant with a rather modest effect of Sorafenib on MB1 cell growth. Clinical benefit was seen with subsequent bortezomib therapy inducing a temporary halt to lymph node growth and a progression-free interval of 7 weeks. Our observations together with previous data from preclinical models could serve as a rationale for selecting those patients suffering from ATC most likely to benefit from targeted therapy. A prospective controlled randomized trial integrating kinase and proteasome inhibitors into a therapeutic regime for ATC is warranted.

The Arabidopsis irregular xylem8 mutant is deficient in glucuronoxylan and homogalacturonan, which are essential for secondary cell wall integrity.

The secondary cell wall in higher plants consists mainly of cellulose, lignin, and xylan and is the major component of biomass in many species. The Arabidopsis thaliana irregular xylem8 (irx8) mutant is dwarfed and has a significant reduction in secondary cell wall thickness. IRX8 belongs to a subgroup of glycosyltransferase family 8 called the GAUT1-related gene family, whose members include GAUT1, a homogalacturonan galacturonosyltransferase, and GAUT12 (IRX8). Here, we use comparative cell wall analyses to show that the irx8 mutant contains significantly reduced levels of xylan and homogalacturonan. Immunohistochemical analyses confirmed that the level of xylan was significantly reduced in the mutant. Structural fingerprinting of the cell wall polymers further revealed that irx8 is deficient in glucuronoxylan. To explore the biological function of IRX8, we crossed irx8 with irx1 (affecting cellulose synthase 8). The homozygous irx1 irx8 exhibited severely dwarfed phenotypes, suggesting that IRX8 is essential for cell wall integrity during cellulose deficiency. Taken together, the data presented show that IRX8 affects the level of glucuronoxylan and homogalacturonan in higher plants and that IRX8 provides an important link between the xylan polymer and the secondary cell wall matrix and directly affects secondary cell wall integrity.