Pattern formation during vulval development in C. elegans

Previous studies have shown that the development of the vulva of the C. elegans hermaphrodite involves six multipotential hypodermal cells as well as the gonadal anchor cell, which induces vulval formation. Our further examination of the interactions among these seven cells has led to the following model. Each hypodermal precursor cell becomes determined to adopt one of its three potential fates; each of these fates is to generate a particular cell lineage. In the absence of cellular interactions each precursor cell will generate the nonvulval cell lineage; an inductive signal from the anchor cell is required for a precursor cell to generate either of the two types of vulval cell lineages. The inductive signal is spatially graded, and the potency of the signal specifies which lineage is expressed by each of the tripotential precursor cells.     

Care Seeking for Neonatal Illness in Low- and Middle-Income Countries: A Systematic Review

Background

Despite recent achievements to reduce child mortality, neonatal deaths continue to remain high, accounting for 41% of all deaths in children under five years of age worldwide, of which over 90% occur in low- and middle-income countries (LMICs). Infections are a leading cause of death and limitations in care seeking for ill neonates contribute to high mortality rates. As estimates for care-seeking behaviors in LMICs have not been studied, this review describes care seeking for neonatal illnesses in LMICs, with particular attention to type of care sought.

Methods and Findings

We conducted a systematic literature review of studies that reported the proportion of caregivers that sought care for ill or suspected ill neonates in LMICs. The initial search yielded 784 studies, of which 22 studies described relevant data from community household surveys, facility-based surveys, and intervention trials. The majority of studies were from South Asia (n = 17/22), set in rural areas (n = 17/22), and published within the last 4 years (n = 18/22). Of the 9,098 neonates who were ill or suspected to be ill, 4,320 caregivers sought some type of care, including care from a health facility (n = 370) or provider (n = 1,813). Care seeking ranged between 10% and 100% among caregivers with a median of 59%. Care seeking from a health care provider yielded a similar range and median, while care seeking at a health care facility ranged between 1% and 100%, with a median of 20%. Care-seeking estimates were limited by the few studies conducted in urban settings and regions other than South Asia. There was a lack of consistency regarding illness, care-seeking, and care provider definitions.

Conclusions

There is a paucity of data regarding newborn care-seeking behaviors; in South Asia, care seeking is low for newborn illness, especially in terms of care sought from health care facilities and medically trained providers. There is a need for representative data to describe care-seeking patterns in different geographic regions and better understand mechanisms to enhance care seeking during this vulnerable time period. Please see later in the article for the Editors'' Summary     

Heparin and its derivatives bind to HIV-1 recombinant envelope glycoproteins, rather than to recombinant HIV-1 receptor, CD4

We have employed a direct radiolabel binding assay to investigate the interaction between3H-heparin and recombinant envelope glycoproteins, rgp120s, derived from several different isolates of HIV-1. Comparable dose-dependent binding is exhibited by rgp120s from isolates IIIB, GB8, MN and SF-2. Under identical experimental conditions the binding of3H- heparin to a recombinant soluble form of the cellular receptor for gp120, CD4, is negligible. The binding of3H-heparin to rgp120 is competed for by excess unlabeled heparin and certain other, but not all, glycosaminoglycan and chemically modified heparins. Of a range of such polysaccharides tested, ability to compete with3H-heparin for binding was strictly correlated with inhibition of HIV-1 replication in vitro. Those possessing potent anti-HIV-1 activity were effective competitors, whereas those having no or little anti-HIV-1 activity were poor competitors. Scatchard analysis indicates that the K d of the interaction between heparin and rgp120 is 10 nM. Binding studies conducted in increasing salt concentrations confirm that the interaction is ionic in nature. Synthetic 33-35 amino acid peptides based on the sequence of the V3 loop of gp120 also bind to heparin with high affinity. V3 loop peptides that are cyclized due to terminal cysteine residues show more selective binding than their uncyclized counterparts. Overall, these data demonstrate further that heparin exerts its anti-HIV-1 activity by binding to the envelope glycoprotein of HIV-1, rather than its cellular receptor, CD4. This study confirms that the V3 loop of gp120 is the site at which heparin exerts its anti- HIV-1 activity. Moreover, it reveals that high affinity binding to heparin is shared by all four rgp120s examined, despite amino acid substitutions within the V3 loop.      

Molecular evolution of mammalian lactate dehydrogenase-A genes and pseudogenes: association of a mouse processed pseudogene with a B1 repetitive sequence

A mouse genomic clone containing a lactate dehydrogenase-A (LDH-A) processed pseudogene and a B1 repetitive element was isolated, and a nucleotide sequence of approximately 3 kb was determined. The pseudogene and B1 element are flanked by perfect 13-bp repeats, and the B1 sequence starts at 14 nucleotides 3' to the presumptive polyadenylation signal of the pseudogene. The nucleotide sequences of the LDH-A genes and processed pseudogenes from mouse, rat, and human were compared, and a phylogenetic tree was constructed. The rate and pattern of nucleotide substitutions in the LDH-A pseudogenes are similar to previously reported results (Li et al. 1984). The average rate of nucleotide substitutions in the LDH-A pseudogenes is 4.3 X 10(- 9)/site/year. The substitutions of C----T and G----A are most frequent, and A----G substitutions are relatively high. The rate of synonymous substitutions in the LDH-A genes is 5.3 X 10(-9), which is not significantly higher than the average rate of 4.7 X 10(-9) for 35 mammalian genes. The rate of nonsynonymous substitutions in the LDH-A genes is 0.20 X 10(-9), which is considerably lower than the average rate of 0.88 X 10(-9) for 35 mammalian genes. Thus, the mammalian LDH-A gene appears to be highly conserved in evolution.      

CED-2/CrkII and CED-10/Rac control phagocytosis and cell migration in Caenorhabditis elegans

Engulfment of apoptotic cells in Caenorhabditis elegans is controlled by two partially redundant pathways. Mutations in genes in one of these pathways, defined by the genes ced-2, ced-5 and ced-10, result in defects both in the engulfment of dying cells and in the migrations of the two distal tip cells of the developing gonad. Here we find that ced-2 and ced-10 encode proteins similar to the human adaptor protein CrkII and the human GTPase Rac, respectively. Together with the previous observation that ced-5 encodes a protein similar to human DOCK180, our findings define a signalling pathway that controls phagocytosis and cell migration. We provide evidence that CED-2 and CED-10 function in engulfing rather than dying cells to control the phagocytosis of cell corpses, that CED-2 and CED-5 physically interact, and that ced-10 probably functions downstream of ced-2 and ced-5. We propose that CED-2/CrkII and CED-5/DOCK180 function to activate CED-10/Rac in a GTPase signalling pathway that controls the polarized extension of cell surfaces.     

Mechanisms of the antinociceptive action of (?) Epicatechin obtained from the hydroalcoholic fraction of Combretum leprosum Mart & Eic in rodents

ABSTRACT: BACKGROUND: The mechanisms of the antinociceptive activity of () epicatechin (EPI), a compound isolated from the hydroalcoholic fraction of Combreum leprosum Mart & Eicher. METHODS: were assessed in the model of chemical nociception induced by glutamate (20 mumol/paw). To evaluate the mechanisms involved, the animals , male Swiss mice (25-30 g), received EPI (50 mg/kg p.o.) after pretreatment with naloxone (2 mg/kg s.c. opioid antagonist), glibenclamide (2 mg/kg s.c. antagonist K + channels sensitive to ATP), ketanserin (0.3 mg/kg s.c. antagonist of receptor 5-HT2A), yoimbine (0.15 mg/kg s.c. alpha2 adrenergic receptor antagonist), pindolol (1 mg/kg s.c. 5-HT1a/1b receptor antagonist), atropine (0.1 mg/kg s.c. muscarinic antagonist) and caffeine (3 mg/kg s.c. adenosine receptor antagonist), ondansetron (0.5 mg/kg s.c. for 5-HT3 receptor) and L-arginine (600 mg/kg i.p.). RESULTS: The antinociceptive effect of EPI was reversed by pretreatment with naloxone and glibenclamide, ketanserin, yoimbine, atropine and pindolol, which demonstrates the involvement of opioid receptors and potassium channels sensitive to ATP, the serotoninergic (receptor 5HT1A and 5HT2A), adrenergic (receptor alpha 2) and cholinergic (muscarinic receptor) systems in the activities that were observed. The effects of EPI, however, were not reversed by pretreatment with caffeine, L-arginine or ondansetron, which shows that there is no involvement of 5HT3 receptors or the purinergic and nitrergic systems in the antinociceptive effect of EPI. In the Open Field and Rotarod test, EPI had no significant effect, which shows that there was no central nervous system depressant or muscle relaxant effect on the results. CONCLUSIONS: This study demonstrates that the antinociceptive activity of EPI in the glutamate model involves the participation of the opioid system, serotonin, adrenergic and cholinergic.     

Three New Classes of Mutations in the Caenorhabditis Elegans Muscle Gene Sup-9

We are studying five interacting genes involved in the regulation or coordination of muscle contraction in Caenorhabditis elegans. A distinctive ``rubber-ban'''' muscle-defective phenotype was previously shown to result from rare altered-function mutations in either of two of these genes, unc-93 and sup-10. Null mutations in sup-9, sup-10, sup-18 or unc-93 act as essentially recessive suppressors of these rubber-band mutations. In this work, we identify three new classes of sup-9 alleles: altered-function rubber-band, partial loss-of-function and dominant-suppressor. The existence of rubber-band mutations in sup-9, sup-10 and unc-93 and the suppression of these mutations by null mutations in any of these three genes suggest that these proteins are required at the same step in muscle contraction. Moreover, allele-specific interactions shown by the partial loss-of-function mutations indicate that the products of these interacting genes may physically contact each other in a multiple subunit protein complex. Finally, the phenotypes of double rubber-band mutant combinations suggest that the rubber-band mutations affect a neurogenic rather than a myogenic input in excitation-contraction coupling in muscle.     

A normally attractive cell interaction is repulsive in two C. elegans mesodermal cell migration mutants.

In wild-type Caenorhabditis elegans hermaphrodites, two bilaterally symmetric sex myoblasts (SMs) migrate anteriorly to flank the precise center of the gonad, where they divide to generate the muscles required for egg laying (J. E. Sulston and H. R. Horvitz (1977) Devl Biol. 56, 110-156). Although this migration is largely independent of the gonad, a signal from the gonad attracts the SMs to their precise final positions (J. H. Thomas, M. J. Stern and H. R. Horvitz (1990) Cell 62, 1041-1052). Here we show that mutations in either of two genes, egl-15 and egl-17, cause the premature termination of the migrations of the SMs. This incomplete migration is caused by the repulsion of the SMs by the same cells in the somatic gonad that are the source of the attractive signal in wild-type animals.     

Nondisjunction Mutants of the Nematode CAENORHABDITIS ELEGANS

The frequency of males (5AA; XO) among the self progeny of wild-type Caenorhabditis elegans hermaphrodites (5AA; XX) is about one in 500. Fifteen him (for "high incidence of males") mutations have been identified that increase this frequency by a factor of ten to 150, as a result of increased X-chromosome nondisjunction. The mutations define ten complementation groups, which have been mapped: nine are autosomal, and one sex linked. Most of the mutants are superficially wild type in anatomy and behavior; however, him-4 mutants display gonadal abnormalities, and unc-86 mutants, which have a Him phenotype, exhibit a variety of anatomical and behavioral abnormalities. All the mutants segregate fertile 3X hermaphrodite progeny as well as XO male progeny. Some produce large numbers of inviable zygotes. Mutants in all ten genes produce diplo-X and nullo-X exceptional ova, and in the four strains tested, diplo-X and nullo-X exceptional sperm are produced by 2X "transformed" males. It appears likely that most of the mutants have defects in both gamete lines of the hermaphrodite. XO males of him strains other than him-4 and unc-86 are similar to wild-type males in anatomy and behavior, and all produce equal or almost equal numbers of haplo-X and nullo-X sperm, and no diplo-X sperm. Male fertility is reduced to varying extents in all him mutants. In four of the strains, nondisjunction during oogenesis has been shown to occur at a reductional division, and in three of these strains, abnormalities in recombination have been demonstrated. One mutant also exhibits autosomal nondisjunction, but many of the others probably do not. Therefore, the X chromosome of C. elegans may differ from the autosomes in the mechanisms controlling its meiotic behavior.——3X hermaphrodites are shorter and less fertile than 2X hermaphrodites, and they produce many inviable zygotes among their self progeny: these are probably 4X zygotes. Haplo-X and diplo-X ova are produced in 2:1 ratio by 3X hermaphrodites. him mutations are expressed in these animals, increasing the frequency of self-progeny males and 2X hermaphrodites.