Larval habitat duration and size at metamorphosis in frogs

The relationship between size at metamorphosis and adult size was studied in 12 closely-related species of frog from Malawi (Central Africa). These species of frogs breed in water of different durations, and occupy different habitats as adults. We could demonstrate no correlation between size at metamorphosis and size of adults when frogs were divided into groups on the basis of occupying similar habitats as adults, but when frogs were divided into groups on the basis of similar duration of larval habitat we demonstrated a strong correlation between size at metamorphosis and adult size. Thus we suggest that duration of the larval habitat is a major determinant of size at metamorphosis, with species which breed in the more temporary habitats metamorphosing at smaller size than species which breed in more permanent habitats, but which are of similar size as adults. Such manipulation of the life cycle appears to be adaptive since it results in individuals becoming independent of water earlier when the likelyhood of early loss of larval habitat is high.     

XX sex reversal in the American cocker spaniel dog: phenotypic expression and inheritance

Summary This study was conducted to define the range of phenotypic expression and mode of inheritance of XX sex reversal in the cocker spaniel dog. Breeding experiments produced F1, F1BC, and F2 generations in which 29 XX true hermaphrodites and 3 XX males were defined by chromosome constitution, serial histologic sections of the gonads, and examination of the internal and external genitalia. In XX true hermaphrodites, the most common combination of gonads was bilateral ovotestes, followed by ovotestis and ovary, then ovotestis and testis. The amount of testicular tissue in the two gonads was closely correlated within each true hermaphrodite. The distribution of testicular tissue within ovotestes of true hermaphrodites was consistent with the hypothesis that testicular differentiation is initiated in the center of the gonad and spreads outward. XX males had bilateral aspermatogenic testes and the internal ducts and external genitalia were more masculinized than in true hermaphrodites. Results of breeding experiments are consistent with autosomal recessive inheritance, the affected phenotype being expressed only in dogs with an XX chromosome constitution. The phenotypic expression and mode of inheritance of this disorder is compared to XX sex reversal in humans and other animals.     

Homology in classical and molecular biology

Hypotheses of homology are the basis of comparative morphology and comparative molecular biology. The kinds of homologous and nonhomologous relations in classical and molecular biology are explored through the three tests that may be applied to a hypothesis of homology: congruence, conjunction, and similarity. The same three tests apply in molecular comparisons and in morphology, and in each field they differentiate eight kinds of relation. These various relations are discussed and compared. The unit or standard of comparison differs in morphology and in molecular biology; in morphology it is the adult or life cycle, but with molecules it is the haploid genome. In morphology the congruence test is decisive in separating homology and nonhomology, whereas with molecular sequence data similarity is the decisive test. Consequences of this difference are that the boundary between homology and nonhomology is not the same in molecular biology as in morphology, that homology and synapomorphy can be equated in morphology but not in all molecular comparisons, and that there is no detected molecular equivalent of convergence. Since molecular homology may reflect either species phylogeny or gene phylogeny, there are more kinds of homologous relation between molecular sequences than in morphology. The terms paraxenology and plerology are proposed for two of these kinds--respectively, the consequence of multiple xenology and of gene conversion.     

Neural function: metabolism and actions of inositol metabolites in mammalian brain

In the nervous system, a variety of cell types respond to external stimuli through the inositol lipid signalling pathways. The stimulus-coupled sequence of intracellular events has been investigated in a homogeneous model system, the cloned mammalian neural cell line NG115-401L. The neural peptide bradykinin stimulates a rapid production of identified inositol phosphate isomers and an intracellular Ca2+ discharge followed by a persistent plasma membrane influx. The temporal sequence suggests that Ins(1,4,5)P3 or Ins(1,3,4,5)P4 or both may coordinate these events in a neuronal cell, as has been suggested in other cell types. Thapsigargin, an irritant and tumour-promoting plant product, produces calcium transients in the absence of inositol phosphate production, and may provide a new tool for investigating the interactions between inositol phosphates and changes in cellular calcium homeostasis. In the 401L line, high levels of radiolabelled InsP5 and InsP6 have been detected, which has led to the evaluation of their possible occurrence and actions in normal brain. Both InsP5 and InsP6 are produced from a radiolabelled myo-inositol precursor in intact mature brain in a region-specific manner. This suggests that both inositol polyphosphates may be end products of regionally regulated biosynthetic pathways. When microinjected into a nucleus of the brainstem, or iontophoretically applied to the dorsal horn of the spinal cord, both InsP5 and InsP6, but not Ins(1,3,4,5)P4 isomers, appear to be potent neural stimulants. These results suggest that the inositol lipid signalling pathways may generate both intracellular and extracellular signals in brain.     

Synthetic lethal mutations suggest interactions between U5 small nuclear RNA and four proteins required for the second step of splicing.

To investigate the function of the U5 small nuclear ribonucleoprotein (snRNP) in pre-mRNA splicing, we have screened for factors that genetically interact with Saccharomyces cerevisiae U5 snRNA. We isolated trans-acting mutations that exacerbate the phenotypes of conditional alleles of the U5 snRNA and named these genes SLU, for synergistically lethal with U5 snRNA. SLU1 and SLU2 are essential for the first catalytic step of splicing, while SLU7 and SLU4 (an allele of PRP17 [U. Vijayraghavan, M. Company, and J. Abelson, Genes Dev. 3:1206-1216, 1989]) are required only for the second step of splicing. Furthermore, slu4-1 and slu7-1 are lethal in combination with mutations in PRP16 and PRP18, which also function in the second step, but not with mutations in factors required for the first catalytic step, such as PRP8 and PRP4. We infer from these data that SLU4, SLU7, PRP18, PRP16, and the U5 snRNA interact functionally and that a major role of the U5 snRNP is to coordinate a set of factors that are required for the completion of the second catalytic step of splicing.     

Dbp73D, a Drosophila gene expressed in ovary, encodes a novel D-E-A-D box protein.

Proteins of the D-E-A-D family of putative ATP-dependent RNA helicases have been implicated in translation initiation and RNA splicing in a variety of organisms from E. coli to man. The Drosophila vasa protein, a member of this family, is required in the female germ line for fertility and for specification of germ line and posterior positional information in progeny embryos. We report the isolation of another D-E-A-D gene from Drosophila, which, like vasa, is expressed in germ line tissue. The predicted amino acid sequence of this new gene, Dbp73D, contains all of the highly conserved helicase motifs, but is otherwise the farthest-diverged member of the family so far identified.     

Neurotrophin expression in rat hippocampal slices: a stimulus paradigm inducing LTP in CA1 evokes increases in BDNF and NT-3 mRNAs.

We report that stimulation inducing long-term potentiation (LTP) in the CA1 pyramidal cell layer of the hippocampus evokes significant increases in both BDNF and NT-3 mRNAs in CA1 neurons. No changes in BDNF or NT-3 mRNA levels were seen in the nonstimulated regions of the pyramidal cell layer or the dentate. No change was seen in the levels of NGF mRNA at the time point examined. These results suggest that relatively normal levels of activity may regulate region-specific neurotrophin levels in the hippocampus. Given that known effects of NGF (and presumably of BDNF and NT-3) include elevation of neurotransmitter levels, elevation of sodium channels, and promotion of axonal terminal sprouting, activity-associated changes in neurotrophin levels may play a role in regulating neural connections in the adult as well as the developing nervous system.     

Sensitivity of some common grain fungi to irradiation on grain and in phosphate-buffered saline

The sensitivity of nine cereal fungi to irradiation on grain and in phosphate-buffered saline (PBS) was investigated. Species of Fusarium and Alternaria were more resistant to irradiation (higher D ₁₀ value) than Aspergillus spp. and Penicillium spp. Generally D ₁₀ values determined on grain were lower than the corresponding values measured in PBS. The plating medium did not significantly affect the D ₁₀ values.