Establishment and regulation of polar growth in Streptomyces

A fundamental question in developmental biology is how cells establish polarity, and most strikingly how cells grow polarly. From neuronal dendrites and root hairs to bud emergence and elongation of yeast, broadly conserved pathways control cell polarity in eukaryotes. In contrast, virtually nothing is known about the regulatory mechanisms controlling polar cell growth in prokaryotes. In evolutionary terms, the most ancient form of polar growth is found in the branching hyphae of the filamentous bacteria Streptomyces, and it is clear that the essential coiled-coil protein DivIVA, which forms part of a tip-organising, multiprotein polarisome complex, plays a key role in the control of cell polarity, apical growth and hyphal branching in Streptomyces coelicolor. I identified and characterised two regulatory mechanisms, both reminiscent of aspects of cell polarity control in eukaryotes. First, I show that the mechanistic basis of branch-site selection during hyphal growth in Streptomyces is a novel polarisome splitting mechanism, in which the apical tip polarisome splits to leave behind a small daughter polarisome on the lateral membrane as the tip grows away. This daughter polarisome gradually grows in size, and ultimately initiates the outgrowth of a new branch. Second, I show that the Ser/Thr protein kinase AfsK is part of an apparatus that controls the polarisome complex at the hyphal tip. Activated AfsK directly phosphorylates DivIVA and profoundly alters the subcellular localisation of DivIVA to establish multiple new sites of polar growth. Thereby, AfsK modulates apical growth and lateral branching during normal growth and cell wall stress. I suggest that this is part of a stress response that provides Streptomyces with a mechanism to dismantle the apical growth apparatus at established hyphal tips that encounter problems with cell wall synthesis (for example through exposure to an antibiotic or by hitting a physical obstacle in the soil) and instead direct emergence of new branches elsewhere along the hyphae

Altersspezifische Prognosefaktoren für das Überleben bei älteren Patientinnen (>70 Jahre) mit fortgeschrittenem Ovarialkarzinom unter Platin-Taxanhaltiger Chemotherapie: eine kombinierte explorative Analyse von drei multizentrischen prospektiv randomisierten Phase III Studien der AGO-OVAR

Alter per se ist einer wichtigsten Prognosefaktoren beim Ovarialkarzinom und angesichts der demografischen Entwicklung sind die sogenannten "Elderly patients" die derzeit am stärksten wachsende Patientinnengruppe. Der therapeutische Fortschritt der letzten Jahre scheint allerdings gerade am Kollektiv der älteren Patientinnen vorbeigegangen zu sein. Dies scheint unter anderem durch eine therapeutische Zurückhaltung gerade beim älteren Patientinnenkollektiv begründet zu sein. Ziel war daher die Evaluation der Therapieführung bei älteren (>70jährigen) Patientinnen sowie die Identifizierung von altersspezifischen Prognosefaktoren anhand eines Metadatensatzes dreier Phase III Studien zur Therapie des fortgeschrittenen Ovarialkarzinoms mittels platin-taxanhaltiger Chemotherapie. Alter konnte als unabhängiger Prognosefaktor für das altersspezifische Überleben hinsichtlich des Progressionsfreien Überleben und des Gesamtüberleben bestätigt werden. In einer Subgruppenanalyse der sogenannten Optimaltherapierten (TUR=0, >5 Zyklen Chemotherapie)zeigte sich eine nahezu verdoppelte Überlebensprognose der optimaltherapierten älteren Patientinnen gegenüber den nicht optimaltherapierten älteren Patientinnen. Therapiequalität im operativen und medikamentösen Bereich scheint demnach auch bei den Älteren einen erheblichen Einfluss auf deren Überlebensprognose zu haben. Und da ältere Patientinnen eine signikant höhere Therapieabbruchrate aufweisen und die Anzahl der durchgeführten Therapiezyklen nicht aber Zyklusverlängerungen und Dosisreduktionen einen unabhängigen prognostischen Einfluss zeigten, scheinen altersangepasste Therapiemodifikationen im Rahmen von Studienprotokollen möglich und könnten die Durchführung der medikamentösen Therapie und damit schlussendlich das Outcome der älteren Patientinnen verbessern

Precise Timing of Transcription by c-di-GMP Coordinates Cell Cycle and Morphogenesis in Caulobacter

Bacteria adapt their growth rate to their metabolic status and environmental conditions by modulating the length of their G1 period. Here we demonstrate that a gradual increase in the concentration of the second messenger c-di-GMP determines precise gene expression during G1/S transition in Caulobacter crescentus . We show that c-di-GMP stimulates the kinase ShkA by binding to its central pseudo-receiver domain, activates the TacA transcription factor, and initiates a G1/S-specific transcription program leading to cell morphogenesis and S-phase entry. Activation of the ShkA-dependent genetic program causes c-di-GMP to reach peak levels, which triggers S-phase entry and promotes proteolysis of ShkA and TacA. Thus, a gradual increase of c-di-GMP results in precise control of ShkA-TacA activity, enabling G1/S-specific gene expression that coordinates cell cycle and morphogenesis

Mechanistic Basis of Branch-Site Selection in Filamentous Bacteria

Many filamentous organisms, such as fungi, grow by tip-extension and by forming new branches behind the tips. A similar growth mode occurs in filamentous bacteria, including the genus Streptomyces, although here our mechanistic understanding has been very limited. The Streptomyces protein DivIVA is a critical determinant of hyphal growth and localizes in foci at hyphal tips and sites of future branch development. However, how such foci form was previously unknown. Here, we show experimentally that DivIVA focus-formation involves a novel mechanism in which new DivIVA foci break off from existing tip-foci, bypassing the need for initial nucleation or de novo branch-site selection. We develop a mathematical model for DivIVA-dependent growth and branching, involving DivIVA focus-formation by tip-focus splitting, focus growth, and the initiation of new branches at a critical focus size. We quantitatively fit our model to the experimentally-measured tip-to-branch and branch-to-branch length distributions. The model predicts a particular bimodal tip-to-branch distribution results from tip-focus splitting, a prediction we confirm experimentally. Our work provides mechanistic understanding of a novel mode of hyphal growth regulation that may be widely employed

Males and Females Contribute Unequally to Offspring Genetic Diversity in the Polygynandrous Mating System of Wild Boar

The maintenance of genetic diversity across generations depends on both the number of reproducing males and females. Variance in reproductive success, multiple paternity and litter size can all affect the relative contributions of male and female parents to genetic variation of progeny. The mating system of the wild boar (Sus scrofa) has been described as polygynous, although evidence of multiple paternity in litters has been found. Using 14 microsatellite markers, we evaluated the contribution of males and females to genetic variation in the next generation in independent wild boar populations from the Iberian Peninsula and Hungary. Genetic contributions of males and females were obtained by distinguishing the paternal and maternal genetic component inherited by the progeny. We found that the paternally inherited genetic component of progeny was more diverse than the maternally inherited component. Simulations showed that this finding might be due to a sampling bias. However, after controlling for the bias by fitting both the genetic diversity in the adult population and the number of reproductive individuals in the models, paternally inherited genotypes remained more diverse than those inherited maternally. Our results suggest new insights into how promiscuous mating systems can help maintain genetic variation

Assemblies of DivIVA mark sites for hyphal branching and can establish new zones of cell wall growth in Streptomyces coelicolor.

Time-lapse imaging of Streptomyces hyphae revealed foci of the essential protein DivIVA at sites where lateral branches will emerge. Overexpression experiments showed that DivIVA foci can trigger establishment of new zones of cell wall assembly, suggesting a key role of DivIVA in directing peptidoglycan synthesis and cell shape in Streptomyces

Regulation of apical growth and hyphal branching in Streptomyces

The filamentous bacteria Streptomyces grow by tip extension and through the initiation of new branches, and this apical growth is directed by a polarisome-like complex involving the essential polarity protein DivIVA. New branch sites must be marked de novo and, until recently, there was no understanding of how these new sites are selected. Equally, hyphal branching patterns are affected by environmental conditions, but there was no insight into how polar growth and hyphal branching might be regulated in response to external or internal cues. This review focuses on recent discoveries that reveal the principal mechanism of branch site selection in Streptomyces, and the first mechanism to be identified that regulates polarisome behaviour to modulate polar growth and hyphal branching