Limiting transport steps and novel interactions of Connexin-43 along the secretory pathway.

Connexins are four-transmembrane-domain proteins expressed in all vertebrates which form permeable gap junction channels that connect cells. Here, we analysed Connexin-43 (Cx43) transport to the plasma membrane and studied the effects of small GTPases acting along the secretory pathway. We show that both GTP- and GDP-restricted Sar1 prevents exit of Cx43 from the endoplasmic reticulum (ER), but only GTP-restricted Sar1 arrests Cx43 in COP II-coated ER exit sites and accumulates 14-3-3 proteins in the ER fraction. FRET-FLIM data confirm that already in ER exit sites Cx43 exists in oligomeric form, suggesting an in vivo role for 14-3-3 in Cx43 oligomerization. Exit of Cx43 from the ER can be blocked by other factors—such as expression of the β subunit of the COP I coat or p50/dynamitin that acts on the microtubule-based dynein motor complex. GTP-restricted Arf1 blocks Cx43 in the Golgi. Lastly, we show that GTP-restricted Arf6 removes Cx43 gap junction plaques from the cell–cell interface and targets them to degradation. These data provide a molecular explanation of how small GTPases act to regulate Cx43 transport through the secretory pathway, facilitating or abolishing cell–cell communication through gap junctions

FTIP1 Is an Essential Regulator Required for Florigen Transport

FT-INTERACTING PROTEIN 1 is a novel protein that is involved in transporting florigen, a long-known mobile signal that induces flowering in plants in response to day length, from companion cells to sieve elements in the phloem of Arabidopsis

Repression of Flowering by the miR172 Target SMZ

The flowering repressors SMZ and FLM, members of the AP-2 and MADS domain transcription factor families, unexpectedly work together to regulate flowering time via their effects on expression of the FT gene

Geminivirus-Mediated Delivery of Florigen Promotes Determinate Growth in Aerial Organs and Uncouples Flowering from Photoperiod in Cotton

This article discusses geminivirus-mediated delivery of florigen. Florigen acts as a general growth hormone, advancing determinate growth. The findings extend our understanding of florigen as a general growth hormone and could benefit crop management techniques

Study of nuclear remodeling in reconstructed mouse embryos by optical and electron microscopy

To date, there is a large body of information on the structural composition of oocytes and embryonic cells of mammals, embryonal nucleogenesis, processes of gene expression, and specific protein synthesis during the preimplantation period. Different factors playing the key role in the transformation of the oocyte to the embryo after in the fertilization and activation of the embryonic genome [1–3] have been revealed. The number of such factors, revealed, as a rule, in the oocyte cytoplasm, constantly increases. In numerous studies on nucleus transplantation it was convincingly shown that oocytes contain specific factors causing genes highly specialized somatic cells to behave as the embryonic genome. It was established that these changes in gene expression are accompanied by considerable structural rearrangement of nuclei of these cells and their chromosome material [4–6]. As a result, the nuclei acquire the potential to direct and support embryonic development to term, though with an extremely low probability. The ability of mature oocytes to induce epigenetic reprogramming of nuclei and transform highly specialized cells ito stem cells is unique. Paradoxically, oocytes become unable to support these processes immediately after fertilization [6, 7]. Currently, the topical studies on derivation of embryonic stem cells from reconstructed embryos for therapeutic use challenge the problem of determination of the main strategy of cell reprogramming It is necessary to know in detail the spatiotemporal pattern of structural and functional rearrangements in donor nuclei and in reconstructed embryos to elucidate the mechanisms underlying these processes, and their influence on further embryo development. Among different methods of cell studies, the optical and electron microscopy are most adequate to provide a clear picture of localization of nuclei and chromatin structure and detect even very small changes in cells. Preparation of serial sections with subsequent three-dimensional reconstruction of objects on the basis of electron microscopy is a very useful approach to studying the rearrangements of nuclei in somatic cells being transferred into oocytes. No studies of this kind have been performed thus far. In this study, we obtained mouse embryos with the genome of cumulus cells and examined rearrangements in cumulus cell nuclei at early stages of their remodelling in the oocyte cytoplasm using serial ultrathin sections and three-dimensional reconstruction

AND MOLECULAR BIOLOGY Study of the Effect of Acetylcholine on Intracellular Homeostasis of True Pacemaker Cells of Rabbit Sinus Node Using Computer Simulation

Acetylcholine, a neurotransmitter secreted by postline had opposite effects on the concentrations of differganglionic parasympathetic termini, plays a key role in ent ions in the cell: Na+ concentration gradually the regulation of spontaneous activity and excitation increased, K+ concentration gradually decreased, and propagation in the sinus node of mammals in normalcy Ca2+ concentration rapidly adapted to new conditions. and pathology. In previous works, we studied the effect Apparently, Na+ and K+, in contrast to Ca2+, do not of acetylcholine on electric activity of sinus-node cells reach steady-state level within the time interval speci-[1, 2]. In this study, we investigated the effect of acetylfied.choline on intracellular ion homeostasis. We found that the characteristic time of the onset of homeostasis ( T1/2) was 34 s for sodium and potassium ions and 1 s for calcium ions. A considerable difference in values is determined by the functioning of sarcoplasmic reticulum (SR). Conditions of numerical experiments. The descriptions of the model of the electrical activity of sinus-node cell membranes, the effect of acetylcholine, and the methods of numerical integration used in this study were described in [1–4]. When simulating the slow dynamics of calcium, the Ca-ATPase current was also taken into consideration [5]. To simulate intracellular homeostasis, we took into account changes in the concentration of Na, K+, and Ca2+ in the cell. The balance of these ions was determined by the respective incoming and outgoing membrane currents (Fig. 1). To determine Ca2+ balance, the function of SR (specifically, Ca2+ uptake by SERCA2 pump, accumulation o

AND MOLECULAR BIOLOGY Study of the Preautomatic Pause under Exposure to Acetylcholine in True Pacemaker Cells of Rabbit Sinus Node Using Computer Simulation

Preautomatic pause, which is required for the resto- Fig. 1, 20 nM acetylcholine caused the development of ration of automatism in pacemakers, plays a key role in such a pause. Long-term measurements of the potential heart functioning. In this work, we studied the effect of and intracellular concentrations of Na+, K+, and Ca2+ acetylcholine and the role of intracellular ion homeo- (Fig. 2) show that the concentrations of Na+ and K+ stasis on the occurrence of preautomatic pause in true gradually increased and decreased, respectively, upon pacemaker cells of rabbit sinus node. It is demonstrated stimulation, whereas the concentration of Ca2+ was rap-that, in the absence of acetylcholine, the pause is only idly adjusted to new steady-state values and practically 0.4 s, whereas in the presence of acetylcholine it may did not change until the end of stimulation (Fig. 2, t = last for tens seconds. The occurrence of the pause and 5–65 s). After the cessation of stimulation, the direction escape from it is determined by slow changes in intrac- of changes in the concentration of Na+ and K+ altered to ellular concentrations of Na+, K+, and Ca2+. Under- the opposite, and the fluctuations in the transmembrane threshold fluctuations in membrane potential of potential and intracellular Ca2+ were not observed ( t = increasing amplitude are the sign of automatism resto- 65–132 s). Note that the steady-state transmembrane ration. potential (approximately –40 mV) is close to the inac-Conditions of numerical experiments. The electrical activity of membranes of sinus-node cells and the effect of acetylcholine were studied in the model based on rabbit SN cells [1, 2]. When simulating the intracellular ion homeostasis, we took into account the changes in the concentration of Na, K