雌核发育银鲫的受精生物学研究——天然雌核发育银鲫繁殖方式的讨论

本文研究了同源雌核发育银鲫精子在4种类型的雌核发育银鲫卵中的发育特征。初步揭示了天然雌核发育银鲫根据精子的来源不同而分别具有二种不同的繁殖方式,对其在维持雌核发育银鲫种群生存,促使克隆分化等方面的独特的生物学意义进行了讨论。     

An additional editing site is present in apolipoprotein B mRNA.

Human intestinal apolipoprotein (apo) B mRNA undergoes a C to U RNA editing at nucleotide 6666 to generate a translation stop at codon 2153, which defines the carboxy-terminal of apo B48. Here we show that two of eleven human intestinal cDNAs spanning residue 6666 were edited from a genomically-encoded C to a T at residue 6802 as well as at residue 6666. This additional editing converts Thr (ACA) codon 2198 to Ile (AUA). Synthetic RNA including the nucleotide 6802 was edited in vitro by intestinal extracts at 10-15% of the editing efficiency of nucleotide 6666. A sequence is identified as important for recognition by the editing activity. No secondary structural homology was identified between the two edited sites. No other sequence in the region between 6411 and 6893 nucleotides of apo B mRNA was found to be edited in vivo or in vitro. Apo B RNA editing extracts from intestine did not edit maize cytochrome oxidase II mRNA.     

Identification of a Putative Structural Gene for Cathepsin D in Caenorhabditis Elegans

Mutants of Caenorhabditis elegans having about 10% of wild-type activity of the aspartyl protease cathepsin D have been isolated by screening. Mutant homozygotes have normal growth rates and no obvious morphological or developmental abnormalities. The mutant gene (cad-1) has been mapped to the right extremity of linkage group II. Heterozygous animals (cad-1/+) show intermediate enzyme levels and animals heterozygous for chromosomal deficiencies of the right extremity of linkage group II have 50% of wild-type activity. Cathepsin D purified from a mutant strain has a lower activity per unit mass of pure enzyme. These data suggest that cad-1 is a structural gene for cathepsin D.     

The Molecular through Ecological Genetics of Abnormal Abdomen in DROSOPHILA MERCATORUM. I. Basic Genetics

The abnormal abdomen syndrome (aa) in Drosophila mercatorum is characterized by the persistence of juvenilized cuticle on the adult abdomen. The aa phenotype is shown to depend on at least two X-linked genetic elements that are about one map unit apart near the centromeric end of the X chromosome. These two genetic elements are necessary for aa expression; one behaves as a dominant element and the other as a recessive. Overlaying these genetic studies upon molecular work reported elsewhere, it is argued that the dominant element is the presence of a 5 kb insertion in a majority of the X-linked repeats coding for the 28S ribosomal RNA. The recessive element appears to be a locus controlling differential replication of noninserted over inserted 28S genes during polytenization. The aa syndrome requires both the presence of the inserted repeats and the failure to preferentially amplify noninserted repeats. Given the necessary X-linked elements for aa, a variety of modifiers are revealed. First, aa expression in males is Y-linked, apparently corresponding to a deletion of the 18S/28S rDNA gene cluster normally found on the Y. Moreover, all major autosomes can modify the penetrance of aa.     

Mol- mutants of Klebsiella pneumoniae requiring high levels of molybdate for nitrogenase activity.

Mol- mutants of Klebsiella pneumoniae requiring high levels of molybdate for nitrogenase and nitrate reductase activity were characterized. The effects of mol mutations on nitrogenase activity were very similar to those caused by nifQ mutations. Mol- mutants of K. pneumoniae appear to be equivalent to ChlD- mutants of Escherichia coli.     

Subcellular Distribution and Developmental Expression of Cholesterol Ester Hydrolases in Fetal Rat Brain Cultures

Abstract: Cholesterol ester hydrolase activities previously have been identified in brain and linked to the production of myelin, which has very low levels of esterified cholesterol. We have studied two cholesterol ester hydrolase activities (termed the pH 6.0 and pH 7.2 activities) in cultures derived from 19- to 21-day-old dissociated fetal rat brains and in developing rat brain. In vivo the levels of both the pH 6.0 and pH 7.2 activities began to increase by about 10 postnatal days, reached maximal levels at 20 days (20 and 1.5 nmol/h/mg protein, respectively), and thereafter remained nearly constant (pH 6.0) or decreased somewhat before becoming constant (pH 7.2). In contrast, in the cultures the pH 6.0 cholesterol ester hydrolase activity was low until 21 days in culture (DIC; 20 nmol/h/mg protein), increased to a peak activity at 31 DIC (60 nmol/h/mg protein), remained high for 24 days, and finally decreased (18 nmol/h/mg protein at 63 DIC); the pH 7.2 cholesterol ester hydrolase activity was very low until 20 DIC, increased to a peak activity at 31 days (3 nmol/h/mg protein), and thereafter decreased to a lower level (2 nmol/h/mg protein) that was maintained for about 24 days before decreasing (0.7 nmol/h/mg protein at 63 DIC). Therefore, (a) the time courses of appearance of both cholesterol ester hydrolase activities were delayed by 10–14 days relative to that seen in vivo, and (b) the specific activities observed in the cultures were transiently two- to three-fold higher than in rat brain, but then declined to levels characteristic of whole brain homogenates. Subcellular fractionation of the cultures demonstrated that the pH 7.2 cholesterol ester hydrolase activity, along with myelin basic protein and 2′,3′-cyclic nucleotide-3′-phosphohydrolase activity, was enriched in a membrane fraction collected at an interface between 0.32 M and 0.9 M sucrose; the pH 6.0 cholesterol ester hydrolase activity, in contrast, was enriched in the microsomal fraction.     

In vitro development of the hamster and chick secondary palate

A series of experiments were undertaken to compare the in vitro behaviour of the medial edge epithelium (MEE) of hamster, in which palatal shelves normally fuse, and chick, in which they do not fuse. Homotypic pairs of hamster and chick embryo palatal processes, single palatal processes, and heterotypic palatal shelves of both animals were grown in vitro. The results indicated that contact between palatal shelves may not be crucial for MEE differentiation in mammals. The ability to acquire pre-fusion characteristics may be present in mammalian palatal tissue from their early development and may be expressed by cessation of DNA synthesis in the MEE, elevation of cAMP, and MEE cell death. Isolated chick palatal shelf cultured under identical conditions did not express these mammalian pre-fusion characteristics. When MEE of hamster and chick palatal shelves were placed in contact with one another, the intervening epithelia underwent cytolysis. This could be due to either the destruction of chick MEE by lysosomal enzymes liberated from adjacent degenerating hamster MEE cells, or by induction of cell death in chick MEE by hamster mesenchyme. Heterotypic palatal tissue combinations also suggest that release of lysosomal enzymes in the hamster MEE, which leads to its dissolution, may be the terminal event in epithelial differentiation prior to the establishment of mesenchymal continuity. It is suggested that an inverse relationship exists between DNA synthesis and cAMP levels during palatogenesis: when palate closes (as in mammals) the MEE is eliminated by increasing cAMP levels, whereas when palate remains open (as in birds) low level of cAMP preserve the integrity of MEE by supporting DNA synthesis.