Abnormalities of the ear associated with exencephaly in mouse fetuses induced by maternal exposure to cadmium

Exencephaly was induced in mouse fetuses by maternal injection of cadmium chloride (CdCl2) on day 7 of gestation. The heads of exencephalic, nonexencephalic experimental, and control fetuses were embedded in paraffin and sections were stained with hematoxylin and eosin. Compared to those of controls, the ears of the exencephalic fetuses were smaller (microtia) and low set. The meatal plug representing the external auditory canal was thick, variously branched, and often directed inferiorly. Usually, there were just two ossicles. The stapedial artery, facial nerve, and stapedius muscle were hypoplastic; the tensor tympani was small or absent. There were 1.0 to 2.0 turns of the cochlea in contrast to 2.5 turns in the controls. The organ of Corti was underdifferentiated; the spiral ganglion had fewer cells. In the control, the long axes of the anterior and posterior semicircular ducts were at right angles to each other and in vertical planes, but in the exencephalics, they tended more laterally towards the horizontal plane. The differentiation of the cristae ampullares and maculae was also severely affected. In several specimens, the entire membranous labyrinth had been distended; these labyrinths also had unusual epithelial infoldings. In cadmium-treated nonexencephalic fetuses, the external ears were normal and appropriate to the body size; five of them were examined histologically; in all, the five middle ear contents were hypoplastic; in three, the cochlea had a maximum of two turns and the organ of Corti, crista ampullaris, and macula were hypoplastic. By an analogy to abnormalities of mutants with neural tube defects, it is suggested that the exencephaly induced by cadmium might affect the differentiation of the ear. Partial involvement of the ear in nonexencephalic experimental embryos may be the result of direct action of cadmium during critical stages of development.     

Pathogenesis of exencephaly and cranioschisis induced in the rat after neural tube closure: role of the mesenchyme

Exencephaly was induced after neural tube closure by administration of a single dose of 15 mg/kg cyclophosphamide (CPA) to pregnant Wistar rats. Embryos were collected at 6, 8, and 10 hr and then at 24-hr intervals until day 17 of gestation and processed for electronmicroscopy. Sections cut at the level of foramen of Monro and at the otic vesicle level were examined and compared with similarly processed and age-matched control embryonic tissues. The earliest changes in the CPA-treated embryonic mesenchyme (ME) included a relative reduction in polyribosomes and an accumulation of cellular debris in apparently normal cells and in the extracellular space (ECS). While dead cells were disintegrating in the ECS, numerous cells were engaged in phagocytosis and digestion of fragments of dead cells. Continued cell loss and inhibition of cell proliferation lead to a marked increase in ECS and loss of intercellular contacts. At 10 hr postinjection, these changes were accentuated. By day 13, the capillaries in the ME were found to have their endothelium attenuated; they also had no pericyte association. Unlike in controls, the CPA embryos never developed a proper primordium of the skull vault. Differentiation of the poorly organised ME cells was slow, and glycogen appeared in them late and persisted until day 17. The endoplasmic reticulum was dilated; lipid and lysosomes accumulated, and matrix secretion was inhibited. Macrophages were numerous. The capillaries proliferated and possessed intraluminal cytoplasmic flaps resembling capillaries in the controls at earlier stages of development. The ECS in the ME became edematous while blebs developed subcutaneously. The weak neuroepithelium had several cavities that communicated internally with the ventricle and externally with the blebs. Cell death, inhibition of cell proliferation, and failure of the appearance of skull vault primordium resulted in poor support to the NE. The mounting intraventricular pressure possibly lead to a breakdown of the unsupported NE, resulting in reopening of the neural tube.     

The structure and evolution of the spider monkey delta-globin gene

We have isolated the delta-globin gene of the New-World spider monkey, Ateles geoffroyi, and compared its nucleotide sequence with those of other primate delta- and beta-globin genes. Among primate delta-globin genes, the rate of nonsynonymous substitutions is much less than the rate of synonymous substitutions. This suggests that primate delta- globin genes may remain under evolutionary conservation, perhaps because hemoglobin A2 has an as yet unknown physiological importance.      

Biochemical pathways in prokaryotes can be traced backward through evolutionary time

For the first time, a credible prokaryotic phylogenetic tree is being assembled by Woese and others using quantitative sequence analysis of oligonucleotides in the highly conservative rRNA. This provides an evolutionary scale against which the evolutionary steps that led to the arrangement and regulation of contemporary biochemical pathways can be measured. This paper presents an emerging evolutionary picture of aromatic amino acid biosynthesis within a large superfamily assemblage of prokaryotes that is sufficiently developed to illustrate a new perspective that will be applicable to many other biochemical pathways.      

Guanine deaminase inhibitor from rat liver. Isolation and characterization

1. An inhibitor of cytoplasmic guanine deaminase of rat liver was isolated from liver ;heavy mitochondrial' fraction after freezing and thawing and treatment with Triton X-100. 2. Submitochondrial fractionation revealed that the inhibitor was localized in the outer-membrane fraction. 3. The method of purification of inhibitor, involving precipitation with (NH(4))(2)SO(4) and chromatography on DEAE-cellulose, its precipitability by trichloroacetic acid and the pattern of absorption in the u.v. indicated that the inhibitor was a protein. In confirmation, tryptic digestion of the isolated material resulted in destruction of the inhibitor activity. The inhibitor was stable to acid, but labile to heat. 4. The isolated inhibitor required phosphatidylcholine (lecithin) for activity. Phosphatidylcholine also partially protected the inhibitor against heat inactivation. 5. When detergent treatment was omitted, the inhibitor activity of frozen mitochondria was precipitated by (NH(4))(2)SO(4) in a fully active form without supplementation with phosphatidylcholine, indicating that Triton X-100 ruptured the linkage between inhibitor and lipid. 6. A reconstituted sample of inhibitor-phosphatidylcholine complex was precipitated in a fully active form by dialysis against 2-mercaptoethanol, but treatment of the precipitate with NaCl yielded an extract which was inactive unless supplemented with fresh phosphatidylcholine. 7. We interpret the results as evidence that the inhibitor was present in vivo as a lipoprotein and that once the complex was dissociated by the action of detergent and the protein precipitated, there was an absolute need for exogenous phosphatidylcholine for its activity. The manner in which inhibitor associated with the outer membrane of rat liver mitochondria might regulate the activity of the enzyme in the supernatant has been suggested.     

Structure of the hirulog 3-thrombin complex and nature of the S' subsites of substrates and inhibitors.

The X-ray crystallographic structure of the human alpha-thrombin complex with hirulog 3 (a potent, noncleavable hirudin-based peptide of the "hirulog" class containing a beta-homoarginine at the scissile bond), which is isomorphous with that of the hirugen-thrombin crystal structure, was solved at 2.3-A resolution by starting with a model for thrombin derived from the hirugen-thrombin complex and was refined by restrained least squares methods (R = 0.132). Residues of hirulog 3 were well-defined in the electron density, which included most of the pentaglycine linker and the C-terminal helical turn that was disordered in a related structure of thrombin with hirulog 1. The interactions of D-Phe1'-Pro2'-beta-homoArg3' with the active site of thrombin were essentially identical to those of related structures of PPACK- (D-Phe-Pro-Arg chloromethyl ketone) and hirulog 1-thrombin, with the guanidinium function of the arginyl P1 residue forming a hydrogen-bonding ion pair with Asp189 of the S1 site. A noticeable shift in the CA atom of beta-homoArg3' due to the methylene insertion displaces the scissile bond from attack by Ser195, thus imparting proteolytic stability to the beta-homoArg hirulog derivative. Resolution of the pentaglycine spacer, linking N- and C-terminal functional domains into a single oligopeptide bivalent inhibitor, permitted delineation of corresponding S' subsites of thrombin. The position of Gly4' (P1') is stabilized by three hydrogen bonds with His57, Lys60F, and Ser195, while the conformational angles maintained in a strained, nonallowed configuration for non-glycyl amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)     

The evolutionary history of the amylase multigene family in Drosophila pseudoobscura

In Drosophila pseudoobscura, the amylase (Amy) multigene family is contained within a series of inversions, or gene arrangements, on the third chromosome. The Standard (ST), Santa Cruz (SC), and Tree Line (TL) inversions are central to the phylogeny of arrangements, and have clusters of other arrangements derived from them. The gene arrangements belonging to each of these three clusters have a characteristic number of Amy genes, ranging from three in ST to two in SC to one in TL. This distribution pattern can reflect a history of either duplications or deletions, although the data available in the past did not permit a decision between these alternatives. We provide unambiguous evidence that three Amy genes were present before the divergence of the ST, SC, and TL arrangements. Thus, the current status of the Amy multigene family is the result of deletions in the TL and SC arrangements, which created three new pseudogenes: TL Amy2-psi, TL Amy3-psi, and SC Amy3- psi. Analysis of pseudogene sequences revealed that, in the SC and ST arrangements, pseudogene evolution has been retarded, most likely due to the homogenization effect of gene conversion. Finally, by determining the original copy number, we have reconstructed the evolutionary history of the Amy multigene family and linked it with the evolution of the central gene arrangements.      

Dry-season spawning in a cyprinid fish of southern India

Synopsis A population of the S. Indian cyprinid fishBarbus melanampyx was sampled monthly through 24 months. Seasonal cycles of the gonado-somatic index (GSI), ovarian stages, male breeding tubercles, spawning behaviour and population structure were assessed. These fish breed strictly seasonally during the main dry period: December/January through April. Comparison with other Barbus species of the same general region led to the conclusion that the patterns of reproductive investment ofB. melanampyx are similar to those of perennial species, and different from those of wet-season spawners. The reasons for this rather unexpected result were found in the more constant conditions prevailing during a dry season as compared to the monsoon. It was argued thatB. melanampyx and the species spawning perennially are in effect small-brood spawners, rather than partial spawners.     

Fish oil supplementation reduces excretion of 2,3-dinor-6-oxo-PGF1α and the 11-dehydrothromboxane B2/2,3-dinor-6-oxo-PGF1α excretion ratio in adult men

Dietary supplementation with a fish oil concentrate (FOC) reduced the endogenous synthesis of prostacyclin (PGI₂), as measured by the excretion of its major urinary catabolite, 2,3-dinor-6-oxo-PGF_1α (PGI₂-M). Thirty-four healthy men (24–57 years old) were given controlled diets and supplements that provided 40% of the energy from fat and a minimum of 22 mg/d of α-tocopherol for two consecutive experimental periods of 10 weeks each. During the experimental periods, the men received capsules containing 15 g/d of a placebo oil (PO) (period 1) or 15 g/d of the FOC (period 2). In addition to the PO or FOC, capsules contained 1 mg of α-tocopherol per g of fat as an antioxidant. The average daily excretion of PGI₂-M during the last week of FOC supplementation (period 2) was 22% less (P = 0.0001) than at the end of the first period. These results are at variance with those reported in comparable human studies conducted by other investigators during the middle and late 1980s. A 20% reduction (P = 0.003) in the 11-dehydrothromboxane B₂ to 2,3-dinor-6-oxo-PGF_1α excretion ratio at the end of period 2 in this study demonstrates that a shift of the n-6 to n-3 polyunsaturated fatty acid ratio from 12.5 to 2.3 brings about a substantial modulation of the eicosanoid system.