Hormonal signals involved in the regulation of cambial activity, xylogenesis and vessel patterning in trees

The radial growth of plant stem is based on the development of cribro-vascular cambium tissues. It affects the transport efficiency of water, mineral nutrients and photoassimilates and, ultimately, also plant height. The rate of cambial cell divisions for the assembly of new xylem and phloem tissue primordia and the rate of differentiation of the primordia into mature tissues determine the amount of biomass produced and, in the case of woody species, the wood quality. These complex physiological processes proceed at a rate which depends on several factors, acting at various levels: growth regulators, resource availability and environmental factors. Several hormonal signals and, more recently, further regulatory molecules, have been shown to be involved in the induction and maintenance of cambium and the formation of secondary vascular tissues. The control of xylem cell patterning is of particular interest, because it determines the diameter of xylem vessels, which is central to the efficiency of water and nutrient transport from roots to leaves through the stem and may strongly influence the growth in height of the tree. Increasing scientific evidence have proved the role of other hormones in cambial cell activities and the study of the hormonal signals and their crosstalking in cambial cells may foster our understanding of the dynamics of xylogenesis and of the mechanism of vessel size control along the stem. In this article, the role of the hormonal signals involved in the control of cambium and xylem development in trees and their crosstalking are reviewed.     

Growth factors in invertebrate in vitro culture

Summary An increasing number of polypeptide growth factors have been identified that have proven essential in the development of defined cell culture media for mammalian cell culture. The development of defined mammalian cell culture media, in turn, has provided an environment for studying cell lines in an experimentally manageable unit for studying the action of cellular regulators and genes that determine the properties of cells. Evidence that vertebrate growth factors may be present in insects is based on DNA sequences that encode epidermal growth factor and transforming growth factor-β. However, research on the influence of commercially available vertebrate growth factors is very limited. Although the majority of insect growth-promoting substances studied were isolated directly from insect hemolymph, few of these have been purified to the extent that they could be tested in insect cell, tissue, and endoparasite cultures. Research is needed in both of these areas to aid in developing defined insect culture systems, and to understand better the regulation of postembryonic growth and development in insects.     

Physiology of Hormone Autonomous Tissue Lines Derived From Radiation-Induced Tumors of Arabidopsis thaliana

γ-Radiation-induced tumors of Arabidopsis thaliana L. have been produced as a novel approach to isolation of genes that regulate plant development. Tumors excised from irradiated plants are hormone autonomous in culture and have been maintained on hormone-free medium for up to 4 years. Five tumor tissue lines having different morphologies and growth rates were analyzed for auxin, cytokinin, and 1-aminocyclopropane-1-carboxylic acid (ACC) content, ethylene production, and response to exogenous growth regulators. Normal tissues and two crown gall tissue lines were analyzed for comparison. Rosettes and whole seedlings each contained approximately 30 nanograms· (gram fresh weight)⁻¹ free indoleacetic acid (IAA), 150 nanograms· (gram fresh weight)⁻¹ ester-conjugated IAA, and 10 to 20 micrograms· (gram fresh weight)⁻¹ amide-conjugated IAA. The crown gall lines contained similar amounts of free and ester-conjugated IAA but less amide conjugates. Whereas three of the radiation-induced tumor lines had IAA profiles similar to normal tissues, one line had 10- to 100-fold more free IAA and three- to 10-fold less amide-conjugated IAA. The fifth line had normal free IAA levels but more conjugated IAA than control tissues. Whole seedlings contained approximately 2 nanograms· (gram fresh weight)⁻¹ of both zeatin riboside and isopentenyladenosine. The crown gall lines had 100- to 1000-fold higher levels of each cytokinin. In contrast, the three radiation-induced tumor lines analyzed contained cytokinin levels similar to the control tissue. The radiation-induced tumor tissues produced very little ethylene, although each contained relatively high levels of ACC. Normal callus contained similar amounts of ACC but produced several times more ethylene than the radiation-induced tumor lines. Each of the radiation-induced tumor tissues displayed a unique set of responses to exogenously supplied growth regulators. Only one tumor line showed the same response as normal callus to both auxin and cytokinin feeding. In some cases, one or more tumor lines showed increased sensitivity to certain growth substances. In other cases, growth regulator feeding had no significant effect on tumor tissue growth. Morphology of the radiation-induced tumor tissues generally did not correlate with auxin to cytokinin ratio in the expected manner. The results suggest that a different primary genetic event led to the formation of each tumor and that growth and differentiation in the tumor tissue lines are uncoupled from the normal hormonal controls.     

Involvement of Plant Hormones and Plant Growth Regulators on in vitro Somatic Embryogenesis

In spite of the importance attained by somatic embryogenesis and of the many studies that have been conducted on this developmental process, there are still many aspects that are not fully understood. Among those features, the involvement of plant hormones and plant growth regulators on deTermining the conversion of somatic onto embryogenic tissues, and on allowing progression and maturation of somatic embryos, are far away from being completely comprehended. Part of these difficulties relies on the frequent appearance of contradictory results when studying the effect of a particular stimulus over a specific stage in somatic embryogenesis. Recent progress achieved on understanding the interaction between exogenously added plant growth regulators over the concentration of endogenous hormones, together with the involvement of sensitivity of the tissues to particular hormone groups, might help clarifying the occurrence of divergent patterns in somatic embryogenesis, and in tissue culture in general. The aspects described above, emphasizing on the effect of the concentration of plant hormones and of the addition of plant growth regulators during the different phases of somatic embryogenesis, will be reviewed in this paper. Citations will be limited to review articles as much as possible and to individual articles only in those cases in which very specific or recent information is presented.     

Hormone dependence in breast and prostate tumor cell lines

Knowledge about the role of sex hormones in the control of cell proliferation and cell-type specific protein synthesis is mainly collected by using cell culture techniques. The adoption of cell culture models addressed at defining these issues is due to the uncomplicated assessment of reliable proliferation-related parameters. Established cell lines derived from estrogen and androgen sensitive tissues, have been used in proliferation studies for more than thirty years. The data gathered so far can be summarized in three following working hypotheses: the direct and indirect-positive hypotheses and the indirect-negative hypothesis. Further characterization and assessment of the hormone dependence of growth factors and growth inhibitors will allow for the mechanistic understanding of the regulation of cell proliferation by sex hormones.     

Hormonal Regulation of Tomato Fruit Development: A Molecular Perspective

Fruit development is a complex yet tightly regulated process. The developing fruit undergoes phases of cell division and expansion followed by numerous metabolic changes leading to ripening. Plant hormones are known to affect many aspects of fruit growth and development. In addition to the five classic hormones (auxins, gibberellins, cytokinins, abscisic acid and ethylene) a few other growth regulators that play roles in fruit development are now gaining recognition. Exogenous application of various hormones to different stages of developing fruits and endogenous quantifications have highlighted their importance during fruit development. Information acquired through biochemical, genetic and molecular studies is now beginning to reveal the possible mode of hormonal regulation of fruit development at molecular levels. In the present article, we have reviewed studies revealing hormonal control of fruit development using tomato as a model system with emphasis on molecular genetics.     

Intestinal tissue and cell cultures

The culture of animal cells and tissues is a widely used technique in the field of cellular and molecular biology; one of the most interesting aspect being linked to the study of the mechanisms of cell differentiation. In the specific case of intestinal epithelial cells, various tissue culture technologies have proved to be important tools for the study of precise facets related to intestinal function, pathology and differentiation. Concerning this latter aspect, organ culture experiments have brought about interesting data on the hormonal or nutritional control of intestinal maturation. Nevertheless, the study of the precise mechanisms underlying epithelial proliferation and/or differentiation at the cellular level needs more adequate cell culture model systems. One of them has been described for two cell lines derived from human colonic adenocarcinomas, in which the cells can be induced to achieve enterocytic-like differentiation. Up to date, none of the continuous cell lines starting from normal undifferentiated cells have allowed generation of morphological or functional enterocytic polarity. In contrast, primary cell cultures which allow maintenance of a more physiological environment for the epithelial cells like contacts with their in vivo counterparts, mesenchymal cells or extracellular matrix molecules, have proved to be promising approaches.     

Replacement of vertebrate serum with lipids and other factors in the culture of invertebrate cells,tissues, parasites,and pathogens

Summary Culture medium supplementation with vertebrate serum results in the selection of fibroblastoid insect cell lines and a general decline during continuous subculturing of both morphologic and functional differentiation of the surviving cells. Essential lipid mixtures can substitute for vertebrate serum in the culture of insect and some vertebrate cells, tissues, parasites, and pathogens. The provision of sterols and essential (with nonessential) polyunsaturated fatty acids as phospholipids in oxidation-protected peptoliposomes or proteoliposomes allows cells in culture to duplicate in vivo specific membranes more accurately. Such lipid-corrected membranes allow cultured cells to communicate with neighboring cells through the extracellular matrix, effectively transmit hormonal signals directly and via receptor control, and respond with various tissue-specific functions and differentiation states as directed.     

Development and characterization of insect cell lines

Conclusions With the wide availability of insect cell culture media, it can generally be considered a routine process to develop new cell lines. Exceptions to this statement do exist, of course. Difficulties may arise when attempting to culture a specific cell type. For example, while there are a few cell lines from insect fat body and at least one from the midgut, it may not be possible to obtain cell lines from these tissues from all insect species due to terminal differentiation and other factors. Also, researchers have desired cell lines from certain species, such as the honey bee, for which no success has been obtained. As in the early days of tissue culture, it is difficult to discern why negative results occur. However, as more is learned about the physiology and nutrition of various insects and tissues, we may get clues which will help solve these questions.The remaining chapters in this book will provide the reader with exciting uses for insect cell culture. As I mentioned earlier, the baculovirus expression vector system has provided a stimulus to the field of insect cell culture not seen previously.Abbreviations ICD Isocitrate dehydrogenase - ME malic enzyme - PGI phosphoglucose isomerase - PGM phosphoglucose mutase     

Mechanisms of formation and biological role of protein carbamates

Experimental data are presented evidencing for the fact that tissue proteins under conditions in vivo are subjected to enzymic carboxylation with formation of carbaminic groups. In this case a charge variation in definite sites of protein molecule is observed, which specifies variation of the protein conformation and biological properties. Basic regularities of protein carbamate formation reactions are revealed with factors affecting their intensity enumerated. The reactions are shown to be of great biological significance for the respiration processes, realization of hormonal effects of peptide and protein hormones as well as for regulation of tissue homeostasis under conditions of acidic-alkaline state variation in the organism.     

Insect cell culture and applications to research and pest management

Building on earlier research, insect cell culture began with the successful establishment of one cell line from pupal ovarian tissue. The field has grown to the extent that now over 500 insect cell lines have been established from many insect species representing numerous insect orders and from several different tissue sources. These cell lines are used as research tools in virology, in studies of signaling mechanisms to study insect immunity, hemocyte migration, and to test hypotheses about gene expression, and in screening programs designed to discover new insecticide chemistries. Virology research is revealing fundamentally new information on virus/host cell interactions. Studies in gene expression are uncovering signal transduction pathways that are new to insect science. Research is leading to the development of high-speed screening technologies that are essential in the search for new insect pest management tools. A few insect cell lines are, in routine industrial processes, designed to produce proteins of biomedical significance. Both primary cell cultures and established lines are used in basic biological studies to reveal how insect cells work. This review is designed to briefly cover the history of insect cell culture, recount some recent advances in the field, and offer a vision of the future of insect cell culture.     

Auxin and ethylene: collaborators or competitors?

The individual roles of auxin and ethylene in controlling the growth and development of young seedlings have been well studied. In recent years, these two hormones have been shown to act synergistically to control specific growth and developmental processes, such as root elongation and root hair formation, as well as antagonistically in other processes, such as lateral root formation and hypocotyl elongation. This review examines the growth and developmental processes that are regulated by crosstalk between these two hormones and explores the mechanistic basis for the regulation of these processes. The emerging trend from these experiments is that ethylene modulates auxin synthesis, transport, and signaling with unique targets and responses in a range of tissues to fine-tune seedling growth and development.     

Role of fibroblast growth factor 8 in growth and progression of hormonal cancer

Hormonal cancers such as breast and prostate cancer arise from steroid hormone-regulated tissues. In addition to breast and prostate cancer hormonal regulation has also a role in endometrial, ovarian, testis and thyroid carcinomas. The effects of estrogens, androgens and progestagens on tumor growth are largely mediated by paracrine and autocrine target molecules which include growth factors and growth factor receptors. During cancer progression the hormonal growth regulation is often lost or overcome by an inappropriate activation of growth factor signaling cascades. One of the growth factors which have been associated with the regulation of growth and progression of hormonal cancer is fibroblast growth factor 8 (FGF8) which has also been recognized as an oncogene. FGF8 is widely expressed during embryonic development. It has been shown to mediate embryonic epithelial-mesenchymal transition and to have a crucial role in gastrulation and early organization and differentiation of midbrain/hindbrain, pharyngeal, cardiac, urogenital and limb structures. During adulthood FGF8 expression is much more restricted but in hormonal cancers it becomes frequently activated. High level of FGF8 expression in tumors is associated with a poor prognosis at least in prostate cancer. In experimental models FGF8 induces and facilitates prostate tumorigenesis and increases growth and angiogenesis of tumors. Several lines of evidence for autocrine and paracrine loops in the growth regulation of breast, prostate and ovarian cancer by FGF8 have been suggested.     

Historical perspectives in fat cell biology: the fat cell as a model for the investigation of hormonal and metabolic pathways

For many years, there was little interest in the biochemistry or physiology of adipose tissue. It is now well recognized that adipocytes play an important dynamic role in metabolic regulation. They are able to sense metabolic states via their ability to perceive a large number of nervous and hormonal signals. They are also able to produce hormones, called adipokines, that affect nutrient intake, metabolism and energy expenditure. The report by Rodbell in 1964 that intact fat cells can be obtained by collagenase digestion of adipose tissue revolutionized studies on the hormonal regulation and metabolism of the fat cell. In the context of the advent of systems biology in the field of cell biology, the present seems an appropriate time to look back at the global contribution of the fat cell to cell biology knowledge. This review focuses on the very early approaches that used the fat cell as a tool to discover and understand various cellular mechanisms. Attention essentially focuses on the early investigations revealing the major contribution of mature fat cells and also fat cells originating from adipose cell lines to the discovery of major events related to hormone action (hormone receptors and transduction pathways involved in hormonal signaling) and mechanisms involved in metabolite processing (hexose uptake and uptake, storage, and efflux of fatty acids). Dormant preadipocytes exist in the stroma-vascular fraction of the adipose tissue of rodents and humans; cell culture systems have proven to be valuable models for the study of the processes involved in the formation of new fat cells. Finally, more recent insights into adipocyte secretion, a completely new role with major metabolic impact, are also briefly summarized.     

Angiogenesis in the female reproductive system.

In adult tissues, capillary growth (angiogenesis) occurs normally during tissue repair, such as in healing of wounds and fractures. Rampant capillary growth is associated with various pathological conditions, including tumor growth, retinopathies, hemangiomas, fibroses and rheumatoid arthritis. The female reproductive organs (i.e., ovary, uterus, and placenta) exhibit dynamic, periodic growth and regression accompanied by equally dramatic changes in rates of blood flow. It is not surprising, therefore, that they are some of the few adult tissues in which angiogenesis occurs as a normal process. Thus, the female reproductive system provides a unique model for studying regulation of angiogenesis during growth and differentiation of normal adult tissues. Ovarian, uterine, and placental tissues recently have been shown to contain and produce angiogenic and anti-angiogenic factors. This review discusses the current state of knowledge regarding angiogenic processes and their regulation in female reproductive tissues. In addition, implications of this research for regulation of fertility as well as for control of angiogenesis in other normal and pathological processes are discussed.     

Regulation of growth and differentiation of a rat hepatoma cell line by the synergistic interactions of hormones and collagenous substrata

Serum-free, hormonally defined media have been developed for optimal growth of a rat hepatoma cell line. The cells' hormonal requirements for growth are dramatically altered both qualitatively and quantitatively by whether they were plated onto tissue culture plastic or collagenous substrata. On collagenous substrata, the cells required insulin, glucagon, growth hormone, prolactin, and linoleic acid (bound to BSA), and zinc, copper, and selenium. For growth on tissue culture plastic, the cells required the above factors at higher concentrations plus several additional factors: transferrin, hydrocortisone, and triiodothyronine. To ascertain the relative influence of hormones versus substratum on the growth and differentiation of rat hepatoma cells, various parameters of growth and of liver-specific and housekeeping functions were compared in cells grown in serum-free, hormonally supplemented, or serum-supplemented medium and on either tissue culture plastic or type I collagen gels. The substratum was found to be the primary determinant of attachment and survival of the cells. Even in serum-free media, the cells showed attachment and survival efficiencies of 40-50% at low seeding densities and even higher efficiencies at high seeding densities when the cells were plated onto collagenous substrata. However, optimal attachment and survival efficiencies of the cells on collagenous substrata still required either serum or hormonal supplements. On tissue culture plastic, there was no survival of the cells at any seeding density without either serum or hormonal supplements added to the medium. A defined medium designed for cells plated on tissue culture plastic, containing increased levels of hormones plus additional factors over those in the defined medium designed for cells on collagenous substrata, was found to permit attachment and survival of the cells plated into serum-free medium and onto tissue culture plastic. Growth of the cells was influenced by both substrata and hormones. When plated onto collagen gel substrata as compared with tissue culture plastic, the cells required fewer hormones and growth factors in the serum-free, hormone-supplemented media to achieve optimal growth rates. Growth rates of the cells at low and high seeding densities were equivalent in the hormonally and serum-supplemented media as long as comparisons were made on the same substratum and the hormonally supplemented medium used was the one designed for that substratum. For a given medium, either serum or hormonally supplemented, the saturation densities were highest for tissue culture plastic as compared with collagen gels.(ABSTRACT TRUNCATED AT 400 WORDS)     

Hormone/growth factor interactions mediating epithelial/stromal communication in mammary gland development and carcinogenesis

Epithelial/mesenchymal interactions begin during embryonic development of the mammary gland and continue throughout mammary gland development into adult life. Stromal and epithelial growth factors that may mediate interactions between these compartments of the mammary gland are reviewed. Since mammogenic hormones are the primary regulators of mammary gland development, special consideration is given to hormonal regulation of growth factors in order to explore the integration of hormones and growth factors in the regulation of mammary gland growth and neoplasia. Examination of hormonal regulation of the fibroblast growth factor (FGF)-7/FGFR2-IIIb receptor system in the mammary gland reveals that mammogenic hormones differentially regulate the synthesis of stromal growth factors and their epithelial receptors. These effects serve to optimize the action of estrogen and progesterone on mammary gland development and illustrate that the ratio of these two hormones is critical in regulating this growth factor axis. The role of stromal/epithelial mitogenic microenvironments in modulating the genotype and phenotype of preneoplastic and neoplastic lesions by chemical carcinogens is discussed. Finally, changes in growth factor expression during mammary tumor progression are described to illustrate the relative roles that stromally-derived and epithelial-derived growth factors may play during progression to hormone independent tumor growth.     

Locust flight activity as a model for hormonal regulation of lipid mobilization and transport

Flight activity of insects provides a fascinating yet relatively simple model system for studying the regulation of processes involved in energy metabolism. This is particularly highlighted during long-distance flight, for which the locust constitutes a long-standing favored model insect, which as one of the most infamous agricultural pests additionally has considerable economical importance. Remarkably many aspects and processes pivotal to our understanding of (neuro)hormonal regulation of lipid mobilization and transport during insect flight activity have been discovered in the locust; among which are the peptide adipokinetic hormones (AKHs), synthesized and stored by the neurosecretory cells of the corpus cardiacum, that regulate and integrate lipid (diacylglycerol) mobilization and transport, the functioning of the reversible conversions of lipoproteins (lipophorins) in the hemolymph during flight activity, revealing novel concepts for the transport of lipids in the circulatory system, and the structure and functioning of the exchangeable apolipopotein, apolipophorin III, which exhibits a dual capacity to exist in both lipid-bound and lipid-free states that is essential to these lipophorin conversions. Besides, the lipophorin receptor (LpR) was identified and characterized in the locust.In an integrative approach, this short review aims at highlighting the locust as an unrivalled model for studying (neuro)hormonal regulation of lipid mobilization and transport during insect flight activity, that additionally has offered a broad and profound research model for integrative physiology and biochemistry, and particularly focuses on recent developments in the concept of AKH-induced changes in the lipophorin system during locust flight, that deviates fundamentally from the lipoprotein-based transport of lipids in the circulation of mammals. Current studies in this field employing the locust as a model continue to attribute to its role as a favored model organism, but also reveal some disadvantages compared to model insects with a completely sequenced genome.