In the tadpole of Pelobates fuscus the process of tongue formation starts at the 32nd developmental stage. In more advanced stages (older than 38th) fast anterior and faucial growth of the tongue fold has been observed. This process is accompanied by the development of the gustatory organs. The dorsal surface of the tongue fold, smooth at the beginning, in older tadpoles (developmental stages 36-39th) forms protrusions in which gustatory organs of the taste disk type (TDs) develop. In the 41st tadpole developmental stage anlages of TDs are formed by elongated cells, located more or less perpendicularly to the surface of the tongue. The diameter of the sensory area of a TD at the 45th developmental stage amounts to 94 ?m, while in metamorphosed individuals it reaches 130-140 ?m. At the base of a TD the presence of basal cell morphologically similar to that of Merkel cell was observed at the 42nd developmental stage of a tadpole. Fully developed afferent synaptic connections in the sensory epithelium of a TDwere found starting from the 44th developmental stage. Single synaptic vesicles with an electron-dense core were observed in gustatory cells as early as at the 41st developmental stage of the tadpole. From the observations reported here it can be inferred that in Pelobates fuscus development of both the tongue and TDs is similar to that already described in the representatives of the Rana genus.
The analysis of the experiments on somatic cloning of mammals reveals that possibly there is a group of cells whose nuclei have greater developmental potential than those of other cells. The group comprises cells of a particular developmental lineage, namely those originating from embryonic mesenchyme and mesoderm. The group remains to be elucidated if somatic cells effectively used for cloning are terminally differentiated, not yet fully differentiated or if they are stem cells. Developmental potential of somatic cell nuclei is best revealed when they are quiescent (i.e. in G0 phase of the cell cycle) upon being introduced into enucleated oocytes. The main obstacle in revealing the potencies of nuclei are the difficulties in their reprogramming before starting embryonic transcription, probably consisting in improper and not fast enough erasing of epigentic modifications of the genome. Developmental plasticity of whole cells as opposed to their nuclei has been experimentally presented in a particular class of somatic cells, namely in stem cells. Stem cells renewing a tissue of their origin can undergo transdifferentiation, that is, in atypical conditions they can differentiate into cells of other tissue and in chimaeras with early embryos - even into many diferent types of cells.
The differentiation of B cells along the pathway of B cell development has been well characterized. In the bone marrow, the differentiation from pro-B cells to immature B cells can be defined by several surface antigens, such as a surrogate light chain. Immature B cells become mature B cells and then circulate in the peripheral blood as naive B cells. In the peripheral lymphoid tissues, naive B cells differentiate into memory B cells, which express the CD27 molecule, or plasma cells. Primary immunodeficiencies with hypogammaglobulinemia are caused by defects of the specific molecules which are needed for the B cell differentiation. Recent studies of the genes responsible for such immunodeficiencies have clarified B cell development as well as their pathogenesis. We discuss here the molecules affecting the B cell development and primary immunodeficiencies with hypogammaglobulinemia.
Phytoplankton of Sulejow Reservoir was investigated in 1979-1993. Over that period, blue-green algae were usually a constant component of phytoplankton. Their percentage in the total phytoplankton biomass widely varied both from season to season and from year to year. Maximum values were noted in summer, although sometimes a shift of peak development toward spring or even winter was observed. The development was not uniform in the whole area of the reservoir; blue-green algae dominated in the middle and downstream, that is in the deepest parts of the reservoir. The main components of phytoplankton included Microcystis aeruginosa K?tz. and Aphanizomenon flos-aquae (L.) Ralfs.
The mechanisms that maintain a pool of B cells that is adequately diverse yet devoid of pathogenic autoreactivity remain poorly understood. B cells complete maturation after migrating to the periphery, where they transit several intermediate developmental stages prior to recruitment into the long-lived primary pool. Since B lineage commitment is not coupled to peripheral B cell numbers and most mature peripheral B cells are quiescent, the sizes of mature peripheral compartments are primarily determined by the proportion of immature B cells that survive transit through later developmental stages, coupled with the longevity of mature B cells themselves. Compelling evidence indicates that the B cell antigen receptor (BcR) plays an essential role in all of these processes, but further findings indicate a similar role for the recently described tumor necrosis factor family member, B lymphocyte stimulator (BLyS). Signaling through the BLyS receptor, Bcmd/BR3, controls B cell numbers in two ways: by varying the proportion of cells that complete transitional B cell development, and by serving as the primary determinant of mature B cell longevity. The striking congruence of BcR- and BLyS-mediated effects on B cell selection and survival suggests these pathways may be related. The recent discovery that BcR signaling is selectively coupled to Bcmd/BR3 expression links BcR- and BLyS-mediated activities in transitional and mature B cells, suggesting specificity-based selection and survival may be mechanistically similar processes.
The Notch family are proteins which function both as cell surface receptors and regulators of gene transcription. Notch proteins influence cell-fate decisions during lymphopoesis, neurogenesis and myogenesis. During lymphopoesis Notch1 is implicated in differentiation of lymphoid precursor CLP towards T-cells but not B-cells lineage. In spite of earlier results suggesting involvement of Notch1 in commitment towards alpha beta and gamm a delta or CD4 and CD8 T cell lineage, later experiments didn?t confirm this possibility.
In this study, active chloride cell density in some tissues (gill arch epithelium, skin, and yolk-sac membrane) of rainbow trout (Oncorhynchus mykiss Walbaum, 1792) larvae during the early development stage was investigated using a vital fluorescence staining technique. It was found that the numbers of active chloride cells were very variable, depending on the tissue and age of the larvae. Active chloride cells were most abundant in the skin and yolk-sac membrane, but less so in the gill arch epithelium of newly hatched larvae. With larval age, the density of active chloride cells in the gill epithelium increased, while that in the skin and yolk-sac membrane decreased.
Accurate codon recognition by tRNAs is necessary for correct translation of mRNA nucleotide sequence into the protein sequence. Here, different factors contributing to the correct codon reading by tRNAs are reviewed. In particular, the monitoring of codon-anticodon helix geometry by 16S rRNA bases, and the role of tRNA sequence elements and posttranscriptional modifications for modulating codon-anticodon interactions are discussed.
We investigated the rate of cell proliferation and death in the retina of the Monodelphis opossum during its postnatal development and the influence of early monocular enucleation on these processes. Our results show that in the opossum, as in other marsupials, the peak of the retinal cells divisions occurs postnatally and that generation of retinal cells continues till the time of eye opening (P34), except of the marginal rim, where it continued till P60. Ganglion and amacrine cells are generated between postnatal days (P) P4 and P9, while bipolar cells and photoreceptors are generated simultaneously between P14 and P25. The peak of ganglion cell death as detected by the TUNEL method occurs around P14?19 in the center of retina. The second peak of apoptosis appears in the inner nuclear layer (INL) at P19?25. Gliogenesis takes place between P25 and P34. We also found that monocular enucleation performed during the early period of retinal development (P0?P7) did not influence proliferation, developmental apoptosis or other developmental processes in the retina of the remaining eye.
The key of the immune system is to protect the host from foreign threat posed by pathogens and from the internal threat posed by self-attacking lymphocytes. The ability to discriminate self versus non-self ensures that only 'non-self' pathogens, but not the self antigens, are attacked. Such tolerance to 'self' arises from the central tolerance mechanisms that include the deletion of thymocytes with high reactivity to self antigens and also the induction of unresponsiveness of autoreactive T cells in the periphery. Natural regulatory T cells (nTregs) directly inhibit effector T cells, and keep their proliferation in control. Apart from preventing autoimmune reactions, Tregs also contribute to peripheral immune homeostasis as evidenced by the excessive lymphocyte accumulation in peripheral lymphoid organs and intestinal inflammation in the absence of nTregs. Here we discuss the molecular aspects of the development and suppressive function of naturally occurring Tregs. Accumulating evidence shows the importance of these Tregs in autoimmunity, tumor immunity, organ transplantation, allergy, and microbial immunity.
The morphometrical and volumetrical changes of the middle cerebral artery (MCA) during the fetal period of development were analyzed by digital-image analysis system (DIAS). Examinations were performed on 304 MCAs from 152 brains of human fetuses ranging from the 12th to 40th weeks of gestation. MCAs were analyzed with respect to its branching from the internal carotid artery and its division into the main cortical branches. No statistically significant differences were found between the mean values of the diameter, length and volume of the left and right M1 segments of the MCAs in all studied age groups.
Embryonic stem (ES) cells derived from preimplantation mouse embryo provide a powerful tool for genome manipulation in mammals. The two principal genetic approaches are used to modify genomes of embryonic stem cells, which may be introduced into blastocyst to produce chimeras, and these animals transmit the genetic alteration into the next generation. One approach, targeted mutagenesis, is designed to disrupt the function of specific murine genes that are known by their homology to genes of other organisms. The other approach, gene trapping by randomly insertional mutagenesis, is designed to identify novel, developmentally regulated genes in mouse embryos. In vivo screens allow for the identification and studying of genes that are expressed either within specific tissue or in spatiotemporal patterns. As an alternative to in vivo gene study, gene expression within specific cell types may be monitored in different ES cell cultures.
A factorial experiment was performed in the fodder broad bean to analyse effects of soil drought on the development and yield components of two varieties of different morphotype: ?Nadwislanski? (traditional) and ?Tim? (determinate growth habit). Plants were grown in Mitscherlich?s pots under three different soil moistures: 70%, 50% and 30% of field water capacity. The soil water shortage contributed to a considerable depression in the developmental characteristics and yield traits of both varieties. Under all conditions, the variety ?Nadwislanski? yielded more seeds than did ?Tim?. The traditional variety was more resistant to drought than the new ?Tim?.
Caspases are crucial mediators of apoptosis, a form of physiological cell death. Their activation is carefully controlled by a philogenetically conserved death program, which is indispensable for the homeostasis and development of higher organisms. Dysregulation of apoptosis contributes to the pathogenesis of many human diseases. As effectors of the apoptotic machinery, caspases are considered potential therapeutic targets. In vitro studies have demonstrated the requirement of caspases activity for both the triggering phase as well as the execution of apoptosis, thus providing a molecular base for the fine-tuning of this process by pharmacological agents. The precise roles of the individual caspases in vivo and their functional relation to each other have been best demonstrated in genetically modified animals. The generation of single caspase-deficient mice have confirmed most of the data obtained in vitro and exposed some new aspects previously undetected in the cell culture system. Interestingly, inactivation of many caspases revealed not only their expected participation in apoptotic events as well as in the maturation of cytokine, but also provided hints about the role of at least some caspases in cell differentation and stimulatory repsonses. In this review we will discuss what these studies have unveiled about the role of individual caspases in development, apoptosis, and inflammation, with particular focus on their role beyond the apoptotic process.
Jasmonic acid (JA), methyl jasmonate (JA-Me) and their related compounds which are designated as jasmonates, are widely distributed in the plant kingdom and show various important biological activities in the regulation of plant growth and development, resulting in a consideration that they are putative new plant hormones. Endogenous levels of jasmonates, mainly JA, increase rapidly and transiently in plants or their organs under both abiotic and biotic stress conditions. Jasmonates consist of an integral part of the signal transduction chain between stress signal(s) and stress response(s). In this article, we focused on and reviewed the role of jasmonates in control of differentiation processes in tissue cultures, regeneration and micropropagation, somatic embryo formation, tuber initiation and formation. The involvement of jasmonates in tuberization, tuberous root formation and bulb formation was inferred from their ability to induce the processes in vitro, and from changes in the levels of endogenous jasmonates during the growth of the plants which can account for the initiation of tuberization. The tuberization and the expansion of cells induced by jasmonates always involve the reorientation of cortical microtubules. Differential effect of jasmonic acid on cell cycle progression is also presented. It is still an open question about interactions between jasmonates and other hormones (auxin, ethylene, cytokinins, abscisic acid) in the regulation of meristem activities, cell cycle and other physiological processes.
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