Bgs1p is responsible for primary septum formation

[EN]Cytokinesis is a crucial event in the cell cycle of all living cells. In fungal cells, it requires coordinated contraction of an actomyosin ring and synthesis of both plasmatic membrane and a septum structure that will constitute the new cell wall end. Schizosaccharomyces pombe contains four essential putative (1,3)β-D-glucan synthase catalytic subunits, Bgs1p to Bgs4p. Here we examined the function of Bgs1p in septation by studying the lethal phenotypes of bgs1 + shut-off and bgs1 Δ cells and demonstrated that Bgs1p is responsible and essential for linear (1,3)β-D-glucan and primary septum formation. bgs1 + shut-off generates a more than 300-fold Bgs1p reduction, but the septa still present large amounts of disorganized linear (1,3)β-D-glucan and partial primary septa. Conversely, both structures are absent in bgs1 Δ cells, where there is no Bgs1p. The septum analysis of bgs1+-repressed cells indicates that linear (1,3)β-D-glucan is necessary but not sufficient for primary septum formation. Linear (1,3)β-D-glucan is the polysaccharide that specifically interacts with the fluorochrome Calcofluor white in fission yeast. We also show that in the absence of Bgs1p abnormal septa are formed, but the cells cannot separate and eventually die

Estudio del mecanismo de supervivencia en ausencia de la actividad esencial ß-(1-3) glucán sintasa

Trabajo presentado en el XV Congreso Nacional de Micología, celebrado en Valencia (España), del 7 al 9 de septiembre de 202

In Vitro Activity of Tebipenem, a New Oral Carbapenem Antibiotic, against Penicillin-Nonsusceptible Streptococcus pneumoniae

The in vitro activity of tebipenem (TBM), a new oral carbapenem antibiotic, against Streptococcus pneumoniae clinical isolates (n = 202) was compared with those of 15 reference agents. The isolates were classified into five genotypic classes after PCR identification of abnormal pbp1a, pbp2x, and pbp2b genes: (i) penicillin-susceptible S. pneumoniae (PSSP) isolates with no abnormal pbp genes (n = 34; 16.8%), (ii) genotypic penicillin-intermediate S. pneumoniae (gPISP) isolates with only an abnormal pbp2x gene [gPISP (2x)] (n = 48; 23.8%), (iii) gPISP isolates with abnormal pbp1a and pbp2x genes (n = 32; 15.8%), (iv) gPISP isolates with abnormal pbp2x and pbp2b genes (n = 16; 7.9%), and (v) genotypic penicillin-resistant S. pneumoniae (gPRSP) isolates with three abnormal pbp genes (n = 72; 35.6%). The majority of the strains tested had mefA (n = 59; 29.2%) or ermB (n = 91; 45%) gene-mediating macrolide resistance. For these isolates the MIC at which 90% of isolates are inhibited was significantly lower for TBM than for the reference oral antibiotics, as follows: 0.002 μg/ml for PSSP, 0.004 μg/ml for gPISP (2x), 0.016 μg/ml for gPISP (isolates with abnormal pbp1a and pbp2x genes and isolates with abnormal pbp2x and pbp2b genes), and 0.063 μg/ml for gPRSP. In addition, TBM showed excellent bactericidal activity against gPRSP isolates, which exhibited a 3-log(10) decrease within 2 h when they were incubated with a concentration greater than or equal to the MIC. Inhibition of cell wall synthesis toward the long axis and subsequent cell lysis were observed by scanning electron microscopy after a short-term exposure to TBM, unlike the effects seen with cephalosporins. These data suggest that TBM has potent activity against multidrug-resistant S. pneumoniae, the causative pathogen of community-acquired respiratory tract infections

The Arabidopsis D-Type Cyclin CYCD4 Controls Cell Division in the Stomatal Lineage of the Hypocotyl Epidermis[W]

Cyclin D (CYCD) plays an important role in cell cycle progression and reentry in response to external signals. Here, we demonstrate that Arabidopsis thaliana CYCD4 is associated with specific cell divisions in the hypocotyl. We observed that cycd4 T-DNA insertion mutants had a reduced number of nonprotruding cells and stomata in the hypocotyl epidermis. Conversely, CYCD4 overexpression enhanced cell division in nonprotruding cell files in the upper region of the hypocotyls, where stomata are usually formed in wild-type plants. The overproliferative cells were of stomatal lineage, which is marked by the expression of the TOO MANY MOUTHS gene, but unlike the meristemoids, most of them were not triangular. Although the phytohormone gibberellin promoted stomatal differentiation in the hypocotyl, inhibition of gibberellin biosynthesis did not prevent CYCD4 from inducing cell division. These results suggested that CYCD4 has a specialized function in the proliferation of stomatal lineage progenitors rather than in stomatal differentiation. We propose that CYCD4 controls cell division in the initial step of stomata formation in the hypocotyl

Role of Septins and the Exocyst Complex in the Function of Hydrolytic Enzymes Responsible for Fission Yeast Cell Separation

Cell separation in Schizosaccharomyces pombe is achieved by the concerted action of the Eng1 endo-β-1,3-glucanase and the Agn1 endo-α-1,3-glucanase, which are transported to the septum and localize to a ringlike structure that surrounds the septum. The requirements for the correct localization of both hydrolases as a ring were analyzed using green fluorescent protein fusion proteins. Targeting to the septum required a functional exocyst, because both proteins failed to localize correctly in sec8-1 or exo70Δ mutants, suggesting that Agn1 and Eng1 might be two of the cargo proteins present in the vesicles that accumulate in exocyst mutants. Septins and Mid2 were also required for correct formation of a ring. In their absence, Eng1 and Agn1 were found in a disklike structure that spanned the septum, rather than in a ring. Even though septin and mid2Δ mutants have a cell separation defect, the septum and the distribution of linear β-1,3-glucans were normal in these cells, suggesting that mislocalization of Eng1 and Agn1 might be the reason underlying the failure to separate efficiently. Thus, one of the functions of the septin ring would be to act as a positional marker for the localization of hydrolytic proteins to the medial region