Molecular-genetic mechanisms regulating tissue-specific expression of the drosophilaestS gene

A study was made of theDrosophila melanogaster est6 andD. virilis estS genes for tissue-specific esterase, and their expression at various stages of development was characterized. The former has one promoter and is expressed in the seminal ducts, whereas the latter has two promoters and is expressed in the seminal bulbs. In transgenicD. melanogaster, estS was expressed in the seminal bulbs, as observed in the donor. A region adjacent to the structural gene proved responsible for its expression in the seminal bulbs. TransgenicD. melanogaster lines were also obtained with constructs containing various fragments of theestS regulatory region and thelacZ reporter gene. Histochemical analysis with X-Gal staining allowed identification of a region that inhibitsestS expression in all organs other than seminal bulbs. An esterase S homolog was found in a marine mollusk.     

Molecular-genetic mechanisms of plant resistance to viruses

This paper gives a brief overview of the recent ideas about molecular and genetic mechanisms of plant resistance to viruses. Two plant antiviral strategies (R-gene-mediated mechanism and RNA-silencing) are considered. Examples of engineered virus resistance are presented.     

Molecular-genetic mechanisms of antigenic variability of pathogenic bacteria

The literature on the molecular genetic mechanisms for antigenic variability of pathogenic bacteria is reviewed. Ability to antigenic variability in any case discussed is considered to be a pathogenicity factor permitting efficient struggle against the immune system of the host-organism. The molecular basis for such variability is instability of the genome structure, coding for highly immunogenic bacterial proteins.     

Genes and mechanisms involved in early embryonic development in Xenopus laevis

Our laboratory is studying genes involved in the regulation of the balance between cell growth and differentiation during embryonic development in Xenopus. We have analyzed the developmental expression of the proto-oncogenes c-myc, and KiRas 2B, the proliferating cell nuclear antigen (PCNA), and the tumor suppressor gene p53. These genes, usually expressed during cell proliferation, are expressed in the oocyte in large quantities, but the majority of their maternal RNAs are degraded by the gastrula stage. The expression of c-myc and the localization of the protein indicate that c-myc has the characteristics expected for a gene involved in the regulation of the mid-blastula transition, when zygotic expression is turned on in the embryo. Its expression during late development or during regeneration indicates that it enables the cells to remain competent for cycling during organogenesis. In vitro systems that reproduce the principal cellular functions during early development are used as model systems to understand the mechanisms involved in early embryogenesis.     

Molecular-genetic mechanisms of the effect of developmental hormones in insects

A review of the available data on molecular mechanisms underlying the regulation of gene expression by the developmental hormone ecdysone and juvenile hormone. Heterodimer ESP/USP is the main ecdysone receptor in D. melanogaster. Structures similar to ESP/USP were found in other insects. The information about molecular-genetic mechanisms of the effect of juvenoids is less definite. It has been proposed that the juvenile hormone in insects is a modulator of the ecdysone effect.     

Molecular-genetic mechanisms of the effect of developmental hormones in insects

A review of the available data on molecular mechanisms underlying the regulation of gene expression by the developmental hormone ecdysone and juvenile hormone. Heterodimer ESP/USP is the main ecdysone receptor in D. melanogaster. Structures similar to ESP/USP were found in other insects. The information about molecular-genetic mechanisms of the effect of juvenoids is less definite. It has been proposed that the juvenile hormone in insects is a modulator of the ecdysone effect.     

Matrices containing glycosaminoglycans in the developing anterior chambers of chick and Xenopus embryonic eyes.

The fibrous matrix present in the anterior chamber of the chick eye on the 4th day of development has been shown by autoradiography and histochemistry to contain chondroitin sulfate, protein, neutral polysaccharides, and possibly hyaluronic acid (HA). Its synthesis, probably by the mesenchyme of the angle of the eye, is completed by around 10 days of development. In the scanning electron microscope (SEM) it can be seen that, although the matrix thins as the eye grows, it does not disappear until the 15th day. The development of the Xenopus cornea is described; this animal has a matrix in its anterior chamber from soon after the formation of the inner cornea (stage 41) until metamorphosis 7 weeks later. In the SEM, this material appears as a dense, featureless aggregate rather than as a matrix of thick fibres; in the transmission electron microscope, it is seen to be a network of fine filaments containing small dark-staining granules. Histochemistry shows that it contains HA, protein, and neutral polysaccharides. The morphological evidence is compatible with the matrix being made by the inner cornea. The probable major role of the matrix is to separate lens from cornea in establishing the anterior chamber. In the chick embryo, at least, the matrix is also likely to help stabilise the endothelium during its formation.     

Molecular-genetic mechanisms for the functionally determined isogene selections in muscle

In embryonic development, differentiation consists in the modification of a fraction of the genes into a form irreversibly blocked from expression. In fetal development, there are further differentiation phenomena, often representing the selective expression of isogenes or members of a gene family. These subdifferentiations are reversibly determined by functional influences exerted by the nervous system and by hormones. The myosin heavy-chain (MHC) isogene family is a favorable case for such studies. In skeletal muscle, the MHC type is regulated by the innervation determining the myonal types slow (S) and fast (F). In the heart, the isoforms MHC and are regulated by thyroid hormone (TH). The details depend on the species. While TH always promotes , the euthyroid state can be either or , the latter being the rule. In skeletal S and F types, the reversibility of regulation is demonstrated by the nerve-crossing experiment, which causes a reciprocal SF and FS reprogramming; this requires months, even years to be completed. Such reprogrammings are pleiotropic, affecting a number of type characteristics, which eventually reach a new functional harmony. Ongoing work is described on the question of whether the nerve communicates its influence by impulse patterns or by determinant substances.     

Kinetic behavior of 30S rRNA intermediate labeled in developing embryonic cells of Xenopus laevis

In Xenopus neurula cells, "30S" RNA was found to be labeled with 3H-uridine after a relatively short labeling period. Results obtained from cumulative labeling and pulse-labeling and chase experiments with cells from late gastrulae, yolk plug-stage embryos, and neurulae showed that the 30S RNA is an intermediate in rRNA processing and is derived from 40S pre-rRNA and processed to 28S rRNA. The half-life of the 30S rRNA intermediate was about 7.5 min or less at the three stages examined.     

Fatty acids of glycerophosphatides in developing chick embryonic brain and liver

Fatty acid compositions of glycerophosphatides of developing chick embryonic brain and liver were compared. In brain, ethanolamine and serine glycerophosphatides contained 30-40% polyunsaturated fatty acids, lecithin almost none (except for arachidonic). In the liver, these acids were equally distributed in the phospholipid fractions. The principal polyunsaturated fatty acids of the ethanolamine and serine glycerophosphatides in brain, liver, and yolk were 22:6, 20:4, and 18:2, respectively. During embryonic development of brain from the 8th day of incubation to hatching, the fatty acid composition of individual glycerophosphatide fractions remained constant. Because of the relative increase of ethanolamine glycerophosphatides and decrease of lecithin, total glycerophosphatides showed a decrease in 16:0 and an increase in 18:0. Substantial amounts of palmitaldehyde and stearaldehyde were present on the 8th day of incubation in the brain ethanolamine glycerophosphatide fraction. During the 3rd week of incubation, the liver showed a two-fold increase in the relative amount of 18:2 in all glycerophosphatide fractions. A decrease of 16:0 in the lecithin fraction and consequently in total glycerophosphatides was also observed during this period. No significant changes in glycerophosphatide fatty acids were observed in the yolk throughout incubation.     

Two novel Xenopus frizzled genes expressed in developing heart and brain.

A family of genes related to the Drosophila wingless receptor frizzled have been found in vertebrates. We have cloned full length cDNAs of two novel frizzled genes from embryonic Xenopus tissue. We are calling them Xfz7 and Xfz9 (for Xenopus frizzled) because their deduced peptide sequences show extensive similarity to other vertebrate frizzled molecules. Xfz7 is closely related to human, chick and mouse frz-7 and Xfz9 is most related to human FZD9 and mouse fzd9. Xfz7 is expressed in a broad, complex and dynamic pattern beginning at gastrulation. At later stages Xfz7 expression is found in neural crest, neural tube, eye, pronephric duct and the heart. Xfz9 expression in contrast is more restricted to the neuroectoderm and, at later stages of development, to the dorsal regions of the mid- and hindbrain.     

Effect of antikeratin microinjection on the embryonic development of Xenopus laevis

Anti-keratin monoclonal antibody AF5 was introduced into fertilized eggs of Xenopus laevis.,and its effects on embryonic development were studied.Survival rate of the antikeratin-injected embryos was much lower(only 35.67% at gastrula)than that of the control(74.85% at gastrula),in which embryos were injected with mouse IgG.Most of survivors in the experimental series showed aberrant external appearance.On the other hand,in cleavage stage,ie 2-7h after fertilization,immunohistochemical staining of embryos showed that the expermental embryos were mostly keratin negative,while embryos of the control ones were keratin positive.When introducing this antikeratin into one cell of a 2-cell embryo,only the uninjected half of the embryo continued its development while the other half could not develop at all.These results suggested that intact keratin cytoskeleton in early embryos is indispensable to the embryonic development of Xenopus laevis.     

Xfin: an embryonic gene encoding a multifingered protein in Xenopus.

The Xenopus laevis genome was screened for putative DNA-binding gene products by using the 'finger' region of the Drosophila gene Krüppel as a probe. The one gene detected, named Xfin, codes for a protein with 37 finger domains that comprise nearly 90% of the protein. In the light of studies by Rhodes and Klug (Cell, 46, 123-132, 1986), these data suggest that the Xfin protein has the capacity to bind an unusually large stretch (185 bases) of DNA. The Xfin gene is expressed as a maternal and zygotic mRNA that undergoes extensive polyadenylation changes during early development. The Xfin mRNA expression pattern and the potential DNA binding activity of the protein point to the possibility that the Xfin gene may have a role in controlling gene activity during early embryonic development.     

An approach for developing an experimentally based model for simulating flight-phase dynamics

 This paper presents an approach for developing an experimentally validated dynamic multisegment model to simulate human flight-phase dynamics and multijoint control. Modeling and experimental techniques were integrated to systematically examine the contribution of multiple error sources to the accuracy of the model and to determine the complexity of a model that adequately emulates the dynamic behavior at the total-body and multijoint levels during flight. The accuracy of the model and of the experimental data was assessed using an inverse dynamics simulation of flight-phase motion for two representative cases: (i) a physical model released from a bar and (ii) a gymnast performing a layout dismount from a bar. Multijoint models with varying numbers of segments were assessed in order to determine the complexity of the model that adequately simulates the flight-phase task. A five-segment model was found to adequately simulate the layout dismount performed by the gymnast. The error introduced during modeling and digitizing contributed to an apparent violation of the conservation law manifested as large external forces acting on the nonactuated joints. These results demonstrate the need to reduce sources of error prior to testing hypotheses regarding feedforward and feedback components of the multijoint control system. The proposed approach for quantifying sources of error provides a crucial step that is required in the development of experimentally based dynamic models designed to examine and test hypotheses regarding multijoint control logic. Received: 5 April 2001 / Accepted in revised form: 25 April 2002 Acknowledgements. This work was funded by Intel, a dissertation awarded from the International Society of Biomechanics, the Internationale Federation de Gymnastique, the International Olympic Committee, and Pfizer. We express our special thanks to Kathleen Costa and Witaya Mathiyakom for their assistance in data collection. Correspondence to: P. S. Requejo (e-mail: requejo@rcf.usc.edu)     

Characterization of an RNA granule from developing brain

In brain, mRNAs are transported from the cell body to the processes, allowing for local protein translation at sites distant from the nucleus. Using subcellular fractionation, we isolated a fraction from rat embryonic day 18 brains enriched for structures that resemble amorphous collections of ribosomes. This fraction was enriched for the mRNA encoding beta-actin, an mRNA that is transported in dendrites and axons of developing neurons. Abundant protein components of this fraction, determined by tandem mass spectrometry, include ribosomal proteins, RNA-binding proteins, microtubule-associated proteins (including the motor protein dynein), and several proteins described only as potential open reading frames. The conjunction of RNA-binding proteins, transported mRNA, ribosomal machinery, and transporting motor proteins defines these structures as RNA granules. Expression of a subset of the identified proteins in cultured hippocampal neurons confirmed that proteins identified in the proteomics were present in neurites associated with ribosomes and mRNAs. Moreover many of the expressed proteins co-localized together. Time lapse video microscopy indicated that complexes containing one of these proteins, the DEAD box 3 helicase, migrated in dendrites of hippocampal neurons at the same speed as that reported for RNA granules. Although the speed of the granules was unchanged by activity or the neurotrophin brain-derived neurotrophic factor, brain-derived neurotrophic factor, but not activity, increased the proportion of moving granules. These studies define the isolation and composition of RNA granules expressed in developing brain.