Factors controlling somatic embryogenesis

Histological and ultrastructural, molecular and elemental distribution changes were investigated during the induction of direct somatic embryogenesis using theCamellia japonica leaf culture system. In this culture system, direct somatic embryogenesis is induced in a controlled way in a specific leaf region (leaf blade) within a leaf. Embryogenic and non-embryogenic leaf regions have characteristic energy-dispersive X-ray spectra already before induction. According to these results electron probe X-ray microanalysis (EPMA) can be a tool for early diagnosis of embryogenic competence. Histological studies showed that severe fluctuations in the number of calcium oxalate crystals and in starch accumulation occur after induction but only in induced tissues. Changes in the cell wall composition of competent cells occur shortly after the induction treatment. The induction of morphogenesis is linked to the appearance of callose covering the surface cells of induced leaves and calluses. A 2^nd deposition of material (cutin) is necessary for normal somatic embryogenesis to occur. The involvement of lipid transfer proteins in the appearance of cutin in the embryogenic regions of the explant is suggested.     

Cytokines: signalling molecules controlling ovarian functions

The present short review demonstrates an important role of different cytokines (colony stimulating factors, tumor necrosis factors, interleukins, anti-Mullerian hormone, inhibin, activin, follistatin, bone morphogenetic proteins, growth and differentiation factors) in the control of different ovarian functions - ovarian cell proliferation, apoptosis, folliculogenesis, luteogenesis, oogenesis, release of hormones, response to upstream hormonal regulators, fertility and, in some cases, in development of ovarian disorders. The possibility of practical application of these molecules for characterization, prediction and regulation of the ovarian state including treatment of ovarian disorders is demonstrated.     

Protein kinases: Signaling molecules controlling ovarian functions

The present focus survey represents a review of current knowledge concerning involvement of protein kinases in control of basic ovarian functions in mammals. Ovarian cells produce a number of protein kinases, whose expression depends on type of cells, their state and action of hormones and other protein kinases. A number of protein kinases are involved in control of ovarian cell proliferation, apoptosis, oocyte maturation, hormone release, reception and response to hormones, as well as in mediating action of hormones on these ovarian functions. Protein kinases and their regulators could be used for characterization, prediction and control of ovarian folliculogenesis and atresia, corpus luteum functions, oocyte maturation, fertility, release of hormones, response of ovarian structures to hormonal regulators, as well as for treatment of some reproductive disorders.     

Factors controlling pancreatic islet neogenesis.

We have established a model in which cellophane wrapping induces reiteration of the normal ontogeny of beta-cell differentiation from ductal tissue. The secretion of insulin is physiologic and coordinated to the needs of the animal. Streptozotocin-induced diabetes in hamsters can be "cured" at least half the time. There appears to be activation of growth factor(s) within the pancreas, acting in an autocrine, paracrine, or juxtacrine manner to induce ductal cell proliferation and differentiation into functioning beta cells. Given the results of our studies to date, it does not seem premature to envisage new approaches to the treatment of diabetes mellitus. Identification of the factor(s) regulating islet-cell proliferation and differentiation in our model may permit islets to be grown in culture. This concept could be extended to induce endocrine cell differentiation in vitro as well. Furthermore, islet-cell growth factors could be used to provide "trophic support" to islet transplants as a means of maintaining graft viability. There may also be greater scope for gene therapy when the growth factor(s) have been isolated, purified, sequenced, and cloned.     

Factors controlling resource allocation in mountain birch

We present a comprehensive analysis of factors affecting resource allocation and crown formation in a subarctic birch tree, Betula pubescens ssp. czerepanovii (Orlova) Hämet-Ahti. Using biomass measurements and digitized data on tree architecture, we investigated several hypotheses on various factors that may modify plant growth. We also analyzed the extent to which different mechanisms operate at different scales, ranging from individual shoots to the whole branches or trees. Different factors affected allocation at different levels of organization. Stem age had a minor effect, suggesting that similar control mechanisms operate at all stages of development. Fates of individual shoots were affected by their local growing conditions as indicated, for example, by the dependence of long shoot production on light. Buds formed in the current long shoots were likely to become new long shoots. In the innermost crown parts, radial growth had priority compared to long shoot production. Elongation of individual long shoots was controlled by two conflicting factors. Long distance from the roots suppressed growth, probably indicating costs associated with resource transportation, whereas a high level of light augmented growth. In contrast, growth of entire branches was not so clearly related to the availability of resources, but showed limitation due to allometric scaling. This set a relationship between the maximum long shoot number and the overall branch size, and may indicate allometric constraints to the way a tree is constructed. Strict allometric relationships existed also between other structural traits of mountain birch, most of them similar at all levels of branching hierarchy. However, despite the upper level restrictions set by allometry, source-sink interactions and localized responses of individual shoots operated as local processes that directed allocation towards the most favourable positions. This may be a mechanism for achieving efficient tree architecture in terms of resource intake and costs of transportation.     

Factors controlling cardiac neural crest cell migration

Cardiac neural crest cells originate as part of the postotic caudal rhombencephalic neural crest stream. Ectomesenchymal cells in this stream migrate to the circumpharyngeal ridge and then into the caudal pharyngeal arches where they condense to form first a sheath and then the smooth muscle tunics of the persisting pharyngeal arch arteries. A subset of the cells continue migrating into the cardiac outflow tract where they will condense to form the aorticopulmonary septum. Cell signaling, extracellular matrix and cell-cell contacts are all critical for the initial migration, pauses, continued migration, and condensation of these cells. This review elucidates what is currently known about these factors.     

Factors controlling micropropagation of mature Fagus sylvatica

The influence of several endogenous factors on micropropagation of mature elite trees of beech (Fagus sylvatica L.) has been investigated. February was the most beneficial month for explantation of dormant buds, since infection with endogenous bacteria was still low and in vitro growth of the plant material was the highest. The genotypes tested gave different results concerning their growth on various tissue culture media. Out of 51 mature grafted genotypes only seven could be established in vitro. Grafting of branches of mature stock plants on juvenile rootstocks resulted in a high increase of multiplication rate compared with corresponding mature material, which could not be subcultured in vitro. Apical buds, larger than 20 mm, from 1-year-old shoots proved to be the most suitable explant source. Plant material could be subcultured for several years and rooted successfully.Abbreviations BA benzyladenine - BTM Broad-leaved Tree Medium - GD Gresshoff Doy Medium - IBA indole-3-butyric acid - MS Murashige Skoog Medium - PVP polyvinylpyrrolidone - SH Schenk Hildebrandt Medium - WPM Woody Plant Medium     

Factors controlling the K+ conductance inChara

Summary Previous current/voltage (I/V) investigations of theChara K⁺ state have been extended by increasing the voltage range (up to +200 mV) through blocking the action potential with La³⁺. A region of negative slope was found in theI/V characteristics at positive PD's, similar to that already observed at PD's more negative than the resting level. These decreases in membrane currents at PD's more negative than –150 mV and at PD's close to 0 or positive are thought to arise from the K⁺ channel closure. Both the negative slope regions could be reversibly abolished by 0.1mm K⁺, 20mm Na⁺, more than 10mm Ca²⁺ or 5mm tetraethylammonium (TEA). The K⁺ channels are therefore blocked by TEA, closed by low [K⁺] _o or high [Ca²⁺] _o and are highly selective to K⁺ over Na⁺. With the K⁺ channels closed, the remainingI/V profile was approximately linear over the interval of 400 mV (suggesting a leakage current), but large rectifying currents were observed at PD's more positive than +50 mV. These currents showed a substantial decrease in high [Ca²⁺] _o , sometimes displayed a slight shift to more positive PD's with increasing [K⁺] _o and were unaffected by TEA or changes in [Na⁺] _o . The slope of the linear part of theI/V profile was steeper in low [K⁺] _o than in TEA or high [Na⁺] _o (indicating participation of K⁺, but not Na⁺, in the leak current). Diethylstilbestrol (DES) was employed to inhibit the proton pump, but it was found that the leakage current and later the K⁺ channels were also strongly affected.     

Factors controlling cardiac neural crest cell migration

Cardiac neural crest cells originate as part of the postotic caudal rhombencephalic neural crest stream. Ectomesenchymal cells in this stream migrate to the circumpharyngeal ridge and then into the caudal pharyngeal arches where they condense to form first a sheath and then the smooth muscle tunics of the persisting pharyngeal arch arteries. A subset of the cells continues migrating into the cardiac outflow tract where they will condense to form the aorticopulmonary septum. Cell signaling, extracellular matrix and cell-cell contacts are all critical for the initial migration, pauses, continued migration and condensation of these cells. This Review elucidates what is currently known about these factors.Key words: cardiac neural crest, migration, signaling, matrix, pharyngeal arches, rhombencephalic streams     

Factors controlling community structure in heterogeneous metacommunities

1.  Modern theories of species coexistence recognize the importance of environmental heterogeneity.
2.  Despite the existence of many observational studies, few experimental studies have evaluated the extent to which, and mechanisms by which, fixed spatial heterogeneity increases community diversity and alters community structure.
3  In experimental protist communities, we found that non-spatial mechanisms unrelated to heterogeneity were responsible for a large component of baseline diversity. Above this baseline, fixed spatial heterogeneity produced small but predictable increases in metacommunity diversity through species sorting, while heterogeneity and dispersal together altered local community structure (composition and relative abundance) through mass effects.
4.  Our study illustrates that heterogeneity is not always the strongest driver of diversity, while experimentally demonstrating mechanisms by which heterogeneity alters community structure.     

Green tea extract affects porcine ovarian cell apoptosis

Green tea is a commonly used beverage and green tea extract is a common dietary herbal supplement manufactured into different over-the-counter products. The aim of this in vitro study was to examine the steroid hormone secretion (progesterone and 17-β estradiol), proliferation and apoptosis of porcine ovarian granulosa cells after addition of green tea extract. Granulosa cells were incubated with green tea extract at five doses (0.1, 1, 10, 100 and 200?μg/ml) and the release of hormones by granulosa cells was assessed by EIA after 24?h exposure. The presence of proliferation and apoptotic markers was assessed by immunocytochemistry. Secretion of steroid hormones was not affected by green tea extract at all the doses in comparison to control. Also, markers of proliferation (PCNA and cyclin B1) were not affected by green tea extract. However, the highest dose (200?μg/ml) of green tea extract used in this study increased the accumulation of apoptotic markers caspase-3 and p53 in granulosa cells. In conclusion, our results indicate the impact of green tea extract at the highest dose used in this study on ovarian apoptosis through pathway that includes activation of caspase-3 and p53. Potential stimulation of these intracellular regulators could induce the process of apoptosis in ovarian cells.     

The regulation of apoptosis in preantral ovarian follicles

Less than 1% of ovarian follicles ever mature to ovulation. The remainder undergo atretic degeneration via apoptosis during development. Though the regulation of antral and preovulatory survival has been studied for many years, very little is known about the regulation of survival and development of preantral follicles. This review discusses recent findings regarding preantral follicle development with emphasis on the regulation of preantral follicle apoptosis.