Critical-point symmetries in boson-fermion systems: the case of shape transitions in odd nuclei in a multiorbit model.

We investigate phase transitions in boson-fermion systems. We propose an analytically solvable model [E(5/12)] to describe odd nuclei at the critical point in the transition from the spherical to gamma-unstable behavior. In the model, a boson core described within the Bohr Hamiltonian interacts with an unpaired particle assumed to be moving in the three single-particle orbitals j=1/2, 3/2, 5/2. Energy spectra and electromagnetic transitions at the critical point compare well with the results obtained within the interacting boson-fermion model, with a boson-fermion Hamiltonian that describes the same physical situation.

Expression of dorsal-ventral genes during early development of Rhynchosciara americana embryos.

The establishment of dorsal-ventral polarity in Drosophila is a complex process which involves the action of maternal and zygotically expressed genes. Interspecific differences in the expression pattern of some of these genes have been described in other species. Here we present the expression of dorsal-ventral genes during early embryogenesis in the lower dipteran Rhynchosciara americana. The expression of four genes, the ventralizing genes snail (sna) and twist (twi) and the dorsalizing genes decapentaplegic (dpp) and zerknullt (zen), was investigated by whole-mount in situ hybridization. Sense and antisense mRNA were transcribed in vitro using UTP-digoxigenin and hybridized at 55 degrees C with dechorionated fixed embryos. Staining was obtained with anti-digoxigenin alkaline phosphatase-conjugated antibody revealed with NBT-BCIP solution. The results showed that, in general, the spatial-temporal expression of R. americana dorsal-ventral genes is similar to that observed in Drosophila, where twi and sna are restricted to the ventral region, while dpp and zen are expressed in the dorsal side. The differences encountered were subtle and probably represent a particular aspect of dorsal-ventral axis determination in R. americana. In this lower dipteran sna is expressed slightly later than twi and dpp expression is expanded over the lateral ectoderm during cellular blastoderm stage. These data suggest that the establishment of dorsal-ventral polarity in R. americana embryos follows a program similar to that observed in Drosophila melanogaster.

Expression of dorsal-ventral genes during early development of Rhynchosciara americana embryos

The establishment of dorsal-ventral polarity in Drosophila is a complex process which involves the action of maternal and zygotically expressed genes. Interspecific differences in the expression pattern of some of these genes have been described in other species. Here we present the expression of dorsal-ventral genes during early embryogenesis in the lower dipteran Rhynchosciara americana. The expression of four genes, the ventralizing genes snail (sna) and twist (twi) and the dorsalizing genes decapentaplegic (dpp) and zerknüllt (zen), was investigated by whole-mount in situ hybridization. Sense and antisense mRNA were transcribed in vitro using UTP-digoxigenin and hybridized at 55°C with dechorionated fixed embryos. Staining was obtained with anti-digoxigenin alkaline phosphatase-conjugated antibody revealed with NBT-BCIP solution. The results showed that, in general, the spatial-temporal expression of R. americana dorsal-ventral genes is similar to that observed in Drosophila, where twi and sna are restricted to the ventral region, while dpp and zen are expressed in the dorsal side. The differences encountered were subtle and probably represent a particular aspect of dorsal-ventral axis determination in R. americana. In this lower dipteran sna is expressed slightly later than twi and dpp expression is expanded over the lateral ectoderm during cellular blastoderm stage. These data suggest that the establishment of dorsal-ventral polarity in R. americana embryos follows a program similar to that observed in Drosophila melanogaster.

Stripe forming architecture of the gap gene system.

In this report, we show that gap genes encode exactly one set of pair-rule stripes, which occur in the native even-skipped position. The core of this work is a detailed analysis that shows how this conclusion follows from the arrangement of gap domains in the embryo. This analysis shows that: (1) pattern forming information is transmitted from gap to pair-rule genes by means of a nonredundant set of morphogenetic gradients, and (2) the stripe forming capability of the gap genes is constrained by the arrangement of these gradients and by the fact that each gap domain consists of a pair of correlated gradients. We also show that in the blastoderm, the regulatory sign of a transcriptional regulator is unlikely to change in a concentration dependent manner. The principal analytic tool used to establish these results is the gene circuit method. Here, this method is applied to examine hybrid data sets consisting of real gene expression data for four gap genes and hypothetical pair-rule expression data generated by translating native even-skipped data along the anterior-posterior axis. In this way, we are able to investigate the stripe forming capabilities of the gap gene system in the complete absence of pair-rule cross regulation. We close with an inference about evolutionary development. It is argued that the constraints on gap gene architecture identified here are a consequence of selective pressures that minimize the number of gap genes required to determine segments in long-germ band insects.

Genomic distribution of P elements in Drosophila willistoni and a search for their relationship with chromosomal inversions.

According to the recent-invasion hypothesis, Drosophila melanogaster may have acquired its P elements in a fairly recent process of horizontal transmission between species. Drosophila willistoni has been identified as the potential donor species in that transfer process. A most remarkable feature of D. willistoni is its extensive chromosomal polymorphism due to inversions-the adaptiveness of which has been the subject of many classical studies on evolutionary genetics. In this article, we further extend the study of P elements in D. willistoni, focusing on the possible role they may play in the generation of chromosomal inversions. Our results may be summarized as follows. P-homologous sequences were detected in South American populations of D. willistoni. In two of them, a recently collected wild population and an old laboratory stock, the P insertion sites were located in the polytene chromosomes. Several hybridization sites were mapped in all major chromosome arms of the natural population, which was also chromosomally polymorphic; in the laboratory population, nearly devoid of inversions, hybridization sites were found to be confined to the chromocenter. In the wild population, 10 of the 24 P hybridized sites coincided with several inversions break points and another five sites located themselves very close to those points. The results are discussed within the context of evolutionary hypotheses.

Embryonic expression of the engrailed homologue of Rhynchosciara americana.

The segment polarity gene engrailed is involved in the determination of segment posterior identity in Drosophila. engrailed has been largely used for comparative developmental studies due to its evolutionary conservation from nematodes to humans. By in situ hybridization of an engrailed cDNA probe from Drosophila to polytene chromosomes of fourth instar larvae of Rhynchosciara americana we have shown that engrailed-like sequences must be localized in band 6 of chromosome A in this species. The pattern of engrailed protein expression during R. americana embryo development is diffuse at first evolving into a nuclear striped pattern after quite a length of time. In addition, our results suggest a possible developmentally regulated molecular modification of engrailed protein in R. americana embryos.

Targeted ribozymes reveal a conserved function of the Drosophila paired gene in sensory organ development.

The Drosophila paired (prd) gene, the founding member of the PAX gene family, is required for normal embryonic segmentation and is re-expressed later in development in the head and developing CNS. As for most embryonically active genes, global defects resulting from loss of early prd function obscure an analysis of the role of later expression phases. We used inducible targeted ribozymes to functionally 'knock-out' prd at late stages. When prd protein levels in the head are reduced in this fashion, the maxillary chemosensory ventral organs fail to develop and dorsal-lateral cirri rows are disrupted. These studies reveal a role for prd in sensory organ development that appears to be conserved in PAX genes throughout the animal kingdom.

Highly polymorphic repetitive sequences in Rhynchosciara americana genome.

Rhynchosciara americana genomic DNA when digested with EcoR1 or BamH1 presents visible fragments suggestive of repetitive sequences after fractionation on EtBr stained agarose gels. The cloning and molecular analysis of some of these fragments showed a highly polymorphic family of repetitive sequences. These were mapped by in situ hybridization to telomeres and some heterochromatic regions on polytene chromosomes.

Inhibitory effect of sodium ursodeoxycholate on basal and stimulated short-circuit current across the isolated toad skin.

The effect of sodium ursodeoxycholate (U) on short-circuit current (SCC), an index of basal and stimulated net ion transport across isolated skins of Bufo arenarum toads, was tested. U inhibited basal SCC when added to the epidermal side of the skins. The inhibitory effect was reversible after rinsing the preparation during 60 min. U also inhibited the natriferic response to oxytocin, db-cAMP and theophylline by 82%, 49% and 47%, respectively. Inhibition of SCC by exposure to U was reversed by the polyene antibiotic nystatin. In turn, SCC induced by nystatin in the amiloride-treated skin was insensitive to U and blocked by ouabain, a Na+, K(+)-ATPase inhibitor. These results strongly suggest that the effect of U is exerted at the apical membrane of sodium transporting cells, and rule out the existence of an additional site of inhibitory action of U.

Multiple regulatory elements direct the complex expression pattern of the Drosophila segmentation gene paired.

The paired (prd) gene of Drosophila belongs to the pair-rule class of segmentation genes involved in establishing the metameric organization of the Drosophila body plan. The complex expression pattern of prd has previously been shown to depend upon a number of segmentation genes, including gap and pair-rule genes. In an attempt to characterize and analyze the regulatory regions necessary and sufficient for prd expression, we have identified an 18-kb genomic fragment, consisting of the transcribed portion of prd and 10 kb of 5'- and 5 kb of 3'-flanking region, that is able to rescue prd mutant embryos to full viability. Analysis of a series of prd-lacZ fusion constructs containing progressively reduced lengths of prd 5'-flanking sequences delimits different cis-regulatory regions. The entire 5'-flanking region directs fusion gene expression in a pattern similar, but not identical, to the endogenous prd protein pattern. This 10-kb fragment contains both activator and repressor regions that mediate the establishment of the seven-stripe prd pattern, as well as the splitting into anterior and posterior stripes for the 14-stripe expression phase. The prd intron in combination with a minimal upstream region (0.15 kb) is able to direct low levels of prd-lacZ fusion gene expression in stripes. Information for expression of the anterior dorsal spot and of the early seven-stripe pattern is located downstream of the prd coding region. We propose that regulation of prd by pair-rule and gap gene products is mediated by upstream and downstream cis-regulatory elements. Regulation during separate but overlapping phases of expression by separable regulatory regions might be a general characteristic of segmentation genes.

In vitro neuronal changes induced by beta-aminopropionitrile.

beta-Aminopropionitrile (beta APN), a peptide found in leguminous plants, is a multifunctional aminonitrile because it has some action on collagen, elastin, and nervous cells. Due to its action on the nervous system, it is very interesting to show its inhibitory effect on cultures of neurons. In the present study, we have demonstrated that beta APN can produce progressive degeneration of neurons and that this effect is dose-dependant. Neuronal cultures were prepared from 14-day-old rat embryos with a cell density of 10(4) cells/cm2 in the control plates. Progressive concentrations of beta APN (from 10(-7) M to 10(-3) M) were added and a 50 Inhibitory Dose (ID50) of 10(-5) M was found. At concentrations of 10(-5) M of beta APN, the neurons showed a loss of synapsis and thinning of neuronal prolongations. Based on the morphological changes observed, we think that beta APN may be used as a neurodegeneration model similar to that obtained with acrylamide, carbon disulfide, beta-beta'-iminodipropionitrile, or aluminum salts.

"In vitro" effects of methyl-mercury on the nervous system: a neurotoxicologic study.

Many of the currently prevailing toxicologic problems are due to the use of organic mercurial compounds in pesticides and fungicides. During recent years, environmental pollution has originated from the incorrect use of these organometals. Methyl-mercury (Me-Hg) is absorbed quickly from the gastrointestinal tract and is distributed to most tissues. The most important effect of Me-Hg is on the nervous tissue and is more relevant in the fetal brain. We were interested in assessing the neurotoxic effects of Me-Hg on the central and peripheral nervous system. Neuronal cells cultures from 14-day-old fetal Wistar rats and ciliary ganglion cells cultures from 8-day-old chick embryos were used. Various Me-Hg concentrations (10(-3) M to 10(-8) M) were added to these cultures after 36 hr to study the morphologic changes. At 10(-3) M and 10(-4) M concentrations, cellular degeneration and death in the central nervous system (CNS) were noted. At 10(-5) M concentrations, axonal and nerve fibers degeneration, loss of synapsis, and inhibition in the cellular development in CNS were seen; regroupment and destruction in the peripheral nervous system (PNS) was noted. Finally, at 10(-6) M and 10(-7) M concentrations, there were hardly any modifications in the CNS, whereas only the nervous processes were affected in the PNS.

Transcription in Rhynchosciara americana embryos' early development.

Embryonic transcription starts about 6 hr postfertilization and increases during the first 72 hr of development. During this stage rRNA is the most abundant transcript, but some premessenger RNAs are also present. At 96 hr of development poly(A+) mRNA starts to be detected concordant with gastrulation movements.

Effect of rat cardionatrin I (rat ANF 99-126) on the response of toad skin to angiotensin II.

The atrial natriuretic peptide cardionatrin I (cardionatrin I is ANF 99-126) was used in studies directed to assess its effects on osmotic water permeability (Posm) and short-circuit current (SCC) in isolated toad skin. Results showed that ANF 99-126 (10(-7) M) added to the dermal side of the skin had no effect on basal Posm or SCC. However, ANF 99-126 (3.3 x 10(-8) M) was able to produce a 50% reversible inhibition of the maximal Posm response to angiotensin II (AII) (3.2 x 10(-8) M). These effects were seen when the skins were preincubated with ANF 99-126 for 10 min or less before the addition of AII. Longer preincubation appeared to inactivate ANF 99-126 through proteolysis. ANF 99-126(10(-7) M) failed to inhibit the SCC response to AII (10(-5) M) in toad skin. These results are compatible with a modulatory function for ANF on several systems including those involved in the regulation of extracellular fluid volume.

Effect of sodium taurocholate and sodium cholate on short-circuit current on amphibian membranes.

The effects of the bile salts, sodium taurocholate (NaTc) and sodium cholate (NaCh), and toad bile gallbladder (bile) on short-circuit current (SCC) across isolated skin, and sodium taurocholate (NaTc) on isolated bladder of Bufo arenarum toads were tested. Sodium taurocholate (NaTc), sodium cholate (NaCh) and toad bile gallbladder (bile) promoted an increase in SCC, when added to the external side. The stimulatory effect was reversible after rinsing the preparation for 60 min. Implications on in vivo renal function of these results are discussed.