134,736 research outputs found
Second messenger mediated spatiotemporal control of cell cycle and development
No full textDuring the biphasic life cycle of Caulobacter crescentus motile, free-living swarmer
cells differentiate into sessile, surface attached stalked cells. The swarmer cell is
replication inert and is unable to divide. During the swarmer-to-stalked cell
differentiation, degradation of CtrA, a master regulator that blocks replication initiation,
leads the onset of chromosome replication. After this obligate cell differentiation step,
which is mainly regulated by the degradation of the master cell cycle regulator CtrA,
stalked cells immediately initiate their chromosome replication. Recently, dynamic colocalization
of CtrA and its protease ClpXP to cell pole was proposed as a timing
mechanism for cell cycle-dependent CtrA degradation.
We have identified the response regulator PopA as an essential regulator for CtrA
sequestration to the incipient stalked cell pole and for subsequent CtrA degradation by
the nearby ClpXP protease complex. Time laps fluorescence microscopy of PopA-GFP
showed that PopA itself dynamically sequesters to the cell poles during the C.
crescentus cell cycle. While PopA sequestration to the flagellated pole depends on
PodJ, a swarmer pole specificity factor, localization to the incipient stalked pole
depends on the C-terminal GGDEF output domain of PopA. We demonstrate that in
contrast to most GGDEF domain proteins, PopA lacks diguanylate cyclase activity.
Instead, PopA functions as cyclic di-GMP effector protein, which specifically binds the
bacterial second messenger at a conserved binding site (I-site) within the GGDEF
domain. An intact PopA I-site is required for PopA sequestration to the incipient stalked
pole as well as for CtrA degradation during the cell cycle. PopA directs CtrA to the
ClpXP occupied cell pole via a direct interaction with an adaptor protein, RcdA. Based
on this we postulate that c-di-GMP bound PopA facilitates the dynamic distribution of
CtrA to the cell pole where it s degraded by ClpXP. This is the first report that links cdi-
GMP to protein dynamics and cell cycle control in bacteria.
In addition to its prominent role in cell cycle control, PopA was identified as novel
component of the complex regulatory network that orchestrates polar development in
C. crescentus. PopA, together with PleD and DgcB, two active diguanylate cyclases,
controls cell motility, holdfast formation and surface attachment. Our data suggest that
PopA interferes with PleD and DgcB to coordinate cell motility, stalk biogenesis,
holdfast formation and finally surface attachment. Based on this, we propose that PopA is a bifunctional protein, involved in control and coordination of C. crescentus cell
cycle and development
Montesauria caerulea Constantinescu & Popa & Popa & Cobzaru & Mukhim & Adam 2018, sp. n.
No full text<i>Montesauria caerulea</i> Constantinescu sp. n. (Figs. 5–8) <p>Zoobank: 26BD4193-539F-4C7E-A27B-A7972AB8AD43</p> <p> <b>Type material</b> — Holotype male and 22 paratypes (11 males and 11 females), from <i>Myophonus caeruleus</i> (Scopoli, 1786) (Passeriformes: Turdidae), India, Meghalaya, Jaintia Hills, Shnongrim village, 25°21’12.36”N, 92°31’3.06”E, 22 Jan. 2014, 1151 m, subtropical forest, collector D. K. B. Mukhim.</p> <p> <b>Type deposition</b> — Holotype male (ANA 1395), 11 males (ANA1388–1394, ANA1396–</p> <p>1397, ANA1436 B1, ANA1438 B3) and 11 females (ANA1398–1407, ANA1441 B5) paratypes in MGAB collection.</p> <p> <b>Etymology</b> — The species epithet is taken from the species name of the type host and is an adjective.</p>Published as part of <i>Constantinescu, Ioana Cristina, Popa, Oana Paula, Popa, Luis Ovidiu, Cobzaru, Ioana, Mukhim, D. Khlur B. & Adam, Costică, 2018, Two new feather mite species of the genus Montesauria Oudemans (Analgoidea: Proctophyllodidae) from thrushes (Passeriformes: Turdidae) in the Indian Subcontinent, pp. 881-896 in Acarologia 58 (4)</i> on page 888, DOI: 10.24349/acarologia/20184294, <a href="http://zenodo.org/record/5393412">http://zenodo.org/record/5393412</a>
Club La Popa
No full textClub La Popa, situado diagonal a la Ermita del Pie de la Popa, fue fundado en 1911 por D. Vicente Martínez Recuero, y su esposa doña Tulia Martelo le puso el nombre.Publicado en: El lente de la nostalgia: Cartagena 1890-1955. Cartagena de Indias: Fototeca de Cartagena, 199
Insights into the activation mechanism of PopA, a cyclic di-GMP effector protein involved in cell cycle and development of "Caulobacter Crescentus"
No full textIn Caulobacter crescentus, a complex network integrating cyclic di-GMP and Phosphorylation-dependent signals controls the proteolysis of key regulatory proteins to drive cell cycle and polar morphogenesis. The c-di-GMP input is processed by the effector protein PopA. Upon binding of c-di-GMP, PopA is sequestered to the old cell pole where it recruits the replication and cell division inhibitors CtrA and KidO and mediates their destruction by the polar ClpXP protease prior to entry into S-phase. In addition to its role at the stalked cell pole, PopA localizes to the opposite cell pole in dependence of the general topology factor PodJ where it exerts a yet unknown function.
Here we address the activation and polar sequestration mechanism of PopA guided by an existing activation model for the highly homologous c-di-GMP signaling protein PleD. PopA and PleD do not only share an identical domain organization (Rec1-Rec2-GGDEF), but also show similar spatio-temporal behavior during the cell cycle. While PleD is activated and targeted to the old cell pole via phosphorylation-induced dimerization, we show that PopA stalked pole function is phosphorylation-independent and requires c-di-GMP binding as a primary input signal for activation and polar localization. c-di-GMP binds to conserved primary and secondary I-sites within the PopA GGDEF domain and we show that intact binding sites are required for PopA positioning and function. This suggests that c-di-GMP-dependent crosslinking of adjacent GGDEF domains contributes to the localization of an active PopA dimer to the cell pole. Consistent with this, we demonstrate that the GGDEF domain encodes the polar localization signal(s), while the N-terminal receiver domains serve as interaction platform for downstream components that are actively recruited by PopA.
Among these downstream factors is RcdA, a small mediator protein that interacts with the first PopA receiver domain and helps to recruit and degrade CtrA and KidO. In a screen for additional components of the PopA pathway we identify two novel proteins that directly interact with PopA, CC1462 and CC2616. CC1462 is a ClpXP substrate that requires PopA for polar positioning and subsequent degradation during swarmer-to-stalked cell transition. Although located in a flagellar gene cluster, deletion of CC1462 did not affect flagellar assembly and function. Its cellular role as well as the significance of its cell cycle-dependent degradation requires further studies. CC2616, the second PopA interaction partner, is not proteolytically processed and thus belongs to another class of PopA-dependent substrates. CC2616 is annotated as guanine deaminase, which is predicted to catalyze the conversion from guanine to xanthine thereby irreversibly removing guanine based nucleotides from a cellular pool. A CC2616 deletion leads to increased attachment and decreased motility, a phenocopy of strains with elevated c-di-GMP levels. It is not clear whether CC2616 indeed has deaminase activity or whether it has adopted a novel function.
Taken together, this work provides insight into the activation mechanism of a c-di-GMP effector protein. We propose that PopA has evolved through gene duplication from its ancestor, the catalytic PleD response regulator but has lost catalytic activity of the diguanylate cyclase domain. Moreover, PopA has adopted an inverse intra-molecular information transfer originating through c-di-GMP binding at the C-terminal GGDEF domain, which in turn activates the N-terminal receiver stem to serve as platform for downstream partner recruitment
ARISTOTLE ON MATERIAL DISPOSITIONS IN METEOROLOGY IV
No full textARISTOTLE ON MATERIAL DISPOSITIONS IN METEOROLOGY IVTiberiu M. Popa, PhDUniversity of Pittsburgh, 2005 The purpose of this dissertation is twofold: to elucidate crucial aspects of an important but somewhat understudied Aristotelian text, the fourth book of his Meteorology, and, implicitly, to contribute to a deeper understanding of Aristotle's treatment of dispositions. Meteorology IV is concerned to a great extent with the properties of organic and inorganic homogeneous materials. The first chapter of my dissertation is meant to clarify the structure of this text, to demonstrate - by appealing to a few new arguments - that Meteorology IV is to be attributed to Aristotle and to point out that, contrary to most scholarship on this topic, not all homogeneous materials (homoiomerç) are mixtures. I subsequently build on these preliminaries and address three major questions in the next chapters: What are material dispositions, according to Meteorology IV? How does Aristotle account for the emergence of dispositional properties in uniform materials? What role do dispositions play in the context of Aristotle's scientific method? I answer the first question chiefly by distinguishing in the Aristotelian text between what one might call today dispositional differentiae (e.g. solubility) and categorical properties corresponding to them (a particular composition or microstructure) and conclude that dispositions are not reducible to categorical features in Aristotle's 'chemistry', but are properties, perceived as being part of a homogeneous material's nature (in a non-teleological context). The emergence of dispositions in the homoiomerç receives a more articulate treatment in Meteorology IV than in any other Aristotelian work, but its limitations point to Aristotle's preference not to engage in pure speculation, when he cannot rely on an acceptable degree of probability or plausibility; his treatment of the emergence of dispositions points (in virtue of an understood conditional necessity) to the link between his 'chemistry' and his biological corpus. Finally, I give prominence to the central role of dispositions in Aristotle's method of division and in his effort to gain insight into the composition and microstructure of homogeneous bodies. These aspects of the scientific method deployed in Meteorology IV also emphasize the dominant functions of this treatise and its place within the Aristotelian oeuvre
Activation and polar sequestration of PopA, a c-di-GMP effector protein involved in Caulobacter crescentus cell cycle control
No full textWhen Caulobacter crescentus enters S-phase the replication initiation inhibitor CtrA dynamically positions to the old cell pole to be degraded by the polar ClpXP protease. Polar delivery of CtrA requires PopA and the diguanylate cyclase PleD that positions to the same pole. Here we present evidence that PopA originated through gene duplication from its paralogue response regulator PleD and subsequent co-option as c-di-GMP effector protein. While the C-terminal catalytic domain (GGDEF) of PleD is activated by phosphorylation of the N-terminal receiver domain, functional adaptation has reversed signal transduction in PopA with the GGDEF domain adopting input function and the receiver domain serving as regulatory output. We show that the N-terminal receiver domain of PopA specifically interacts with RcdA, a component required for CtrA degradation. In contrast, the GGDEF domain serves to target PopA to the cell pole in response to c-di-GMP binding. In agreement with the divergent activation and targeting mechanisms, distinct markers sequester PleD and PopA to the old cell pole upon S-phase entry. Together these data indicate that PopA adopted a novel role as topology specificity factor to help recruit components of the CtrA degradation pathway to the protease specific old cell pole of C. crescentus
Pique de proa i Pique de popa
No full textIl·lustració parts interior d' un vaixell antic, pic de proa i pic de popa Dibuix realitzat per il·lustrar els apunts de l’assignatura de “Introducción a las Ciencias Náuticas” que es va crear amb el canvi de Pla d’estudis l’any 1977 (BOE núm. 254, de 24 d’Octubre de 1977), fins el canvi del Pla d’estudis de 1995 (BOE núm. 239, de 6 d’Octubre de 1995)
Two new feather mite species of the genus Montesauria Oudemans (Analgoidea: Proctophyllodidae) from thrushes (Passeriformes: Turdidae) in the Indian Subcontinent
No full textConstantinescu, Ioana Cristina, Popa, Oana Paula, Popa, Luis Ovidiu, Cobzaru, Ioana, Mukhim, D. Khlur B., Adam, Costică (2018): Two new feather mite species of the genus Montesauria Oudemans (Analgoidea: Proctophyllodidae) from thrushes (Passeriformes: Turdidae) in the Indian Subcontinent. Acarologia 58 (4): 881-896, DOI: 10.24349/acarologia/20184294, URL: http://dx.doi.org/10.24349/acarologia/2018429
Pique de proa i Pique de popa
No full textIl·lustració parts interior d' un vaixell antic, pic de proa i pic de popa Dibuix realitzat per il·lustrar els apunts de l’assignatura de “Introducción a las Ciencias Náuticas” que es va crear amb el canvi de Pla d’estudis l’any 1977 (BOE núm. 254, de 24 d’Octubre de 1977), fins el canvi del Pla d’estudis de 1995 (BOE núm. 239, de 6 d’Octubre de 1995)
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