Single cell studies of the cell cycle and some models

Analysis of growth and division often involves measurements made on cell populations, which tend to average data. The value of single cell analysis needs to be appreciated, and models based on findings from single cells should be taken into greater consideration in our understanding of the way in which cell size and division are co-ordinated. Examples are given of some single cell analyses in mammalian cells, yeast and other microorganisms. There is also a short discussion on how far the results are in accord with simple models.     

Echocardiographic assessment and percutaneous closure of multiple atrial septal defects

Percutaneous coronary intervention can be associated with distal embolization of thrombotic material causing myocardial necrosis and infarction. We discuss the role of intravascular imaging to guide the use of a distal protection device by describing the outcome of a young woman presenting with non-ST elevation myocardial infarction. Coronary angiography demonstrated an isolated minor stenosis in the proximal left anterior descending coronary artery with slight haziness beyond the lesion. Intravascular ultrasound confirmed an extensive thrombus overlying a bulky atherosclerotic plaque. A distal filter wire was therefore successfully used to reduce the risk of distal embolization. The use of intravascular ultrasound in patients presenting with acute coronary syndrome may reveal large thrombi that are difficult to image using conventional angiographic techniques. Intravascular ultrasound can therefore be used as a tool to select lesions requiring distal protection.     

The evolutionary analysis of the Tnt1 retrotransposon in Nicotiana species reveals the high variability of its regulatory sequences

We studied the evolution of the tobacco Tnt1 retrotransposon by analyzing Tnt1 partial sequences containing both coding domains and U3 regulatory sequences obtained from a number of Nicotiana species. We detected three different subfamilies of Tnt1 elements, Tnt1A, Tnt1B, and Tnt1C, that differ completely in their U3 regions but share conserved flanking coding and LTR regions. U3 divergence between the three subfamilies is found in the region that contains the regulatory sequences that control the expression of the well-characterized Tnt1-94 element. This suggests that expression of the three Tnt1 subfamilies might be differently regulated. The three Tnt1 subfamilies were present in the Nicotiana genome at the time of species divergence, but have evolved independently since then in the different genomes. Each Tnt1 subfamily seems to have conserved its ability to transpose in a limited and different number of Nicotiana species. Our results illustrate the high variability of Tnt1 regulatory sequences. We propose that this high sequence variability could allow these elements to evolve regulatory mechanisms in order to optimize their coexistence with their host genome.      

A novel liver specific isoform of the rat LAR transcript is expressed as a truncated isoform encoded from a 5'UTR located within intron 11

Background  

The leukocyte common antigen related receptor (LAR) protein has been shown to modulate the signal transduction of a number of different growth factors, including insulin and insulin-like growth factor 1. Splice variants exhibit differing roles and are expressed according to tissue type and developmental stage.     

Evidence for two interacting ligand binding sites in human multidrug resistance protein 2 (ATP binding cassette C2)

Multidrug resistance protein 2 (MRP2) belongs to the ATP binding cassette family of transporters. Its substrates include organic anions and anticancer drugs. We have used transport assays with vesicles derived from Sf9 insect cells overproducing MRP2 to study the interactions of drugs, organic anions, and bile acids with three MRP2 substrates: estradiol-17-beta-d-glucuronide (E217betaG), methotrexate, and glutathione-S-dinitrophenol. Complex inhibition and stimulation patterns were obtained, different from those observed with the related transporters MRP1 and MRP3. In contrast to a previous report, we found that the rate of E217betaG transport by MRP2 increases sigmoidally with substrate concentration indicative of homotropic cooperativity. Half-maximal transport was obtained at 120 microm E217betaG, in contrast to values < 20 microm for MRP1 and 3. MRP2 stimulators, such as indomethacin and sulfanitran, strongly increased the affinity of MRP2 for E217betaG (half-maximal transport rates at 65 and 16 microm E217betaG, respectively) and shifted the sigmoidal dependence of transport rate on substrate concentration to a more hyperbolic one, without substantially affecting the maximal transport rate. Sulfanitran also stimulated MRP2 activity in cells, i.e. the transport of saquinavir through monolayers of Madin-Darby canine kidney II cells. Some compounds that stimulate E217betaG transport, such as penicillin G or pantoprazole, are not detectably transported by MRP2, suggesting that they allosterically stimulate transport without being cotransported with E217betaG. We propose that MRP2 contains two similar but nonidentical ligand binding sites: one site from which substrate is transported and a second site that regulates the affinity of the transport site for the substrate.     

A systematic screen for genes expressed in definitive endoderm by Serial Analysis of Gene Expression (SAGE)

Background  

The embryonic definitive endoderm (DE) gives rise to organs of the gastrointestinal and respiratory tract including the liver, pancreas and epithelia of the lung and colon. Understanding how DE progenitor cells generate these tissues is critical to understanding the cause of visceral organ disorders and cancers, and will ultimately lead to novel therapies including tissue and organ regeneration. However, investigation into the molecular mechanisms of DE differentiation has been hindered by the lack of early DE-specific markers.