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S A Endow

Publications and source records attributed to S A Endow.

62 records · Page 4Linked to original sources
PubMed1982

Polytenization of the ribosomal genes on the X and Y chromosomes of Drosophila melanogaster.

It has previously been shown (Endow and Glover 1979), that polytenization of the ribosomal genes in D. melanogaster Ore-R X/Y cells and in hybrid X/X cells (Endow 1980) involves replication of genes predominantly from one of the cell's two nucleolus organizers. This analysis takes advantage of strain-specific differences in X and Y chromosome rDNA hybridization patterns detected using the Southern blotting technique. In this report, I extend the previous observations by examining polytene rDNA patterns in wild-type and hybrid X/Y cells. A dominance hierarchy for the X and Y chromosomes from three strains of D. melanogaster is presented and possible mechanisms of replicative dominance are discussed.

Animals↗
PubMed1982

Molecular characterization of ribosomal genes on the Ybb- chromosome of Drosophila melanogaster.

The question of whether the Ybb- chromosome contains ribosomal genes has been examined by using Southern blot analysis and comparing rDNA hybridization patterns for X/X and X/Ybb- DNA. The results demonstrate that the Ybb- chromosome contains sequences that hybridize to an rDNA probe under stringent conditions. Differential hybridization of some of these sequences with DNAs corresponding to different regions of a complete ribosomal gene repeat provides evidence that some of the genes on the Ybb- chromosome are type 2 repeats. Because data obtained by other workers suggest that type 2 repeats are transcribed only to low levels, these repeats may be classed as "nonfunctional". A further finding is that the ribosomal genes on the Ybb- chromosome do not undergo multiple rounds of DNA replication during polytenization of X/Ybb- cells.

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PubMed1980

On ribosomal gene compensation in Drosophila.

Recent studies indicate that genes from only one nucleolus organizer undergo replication during polytenization of salivary gland cells of X/Y flies. This report presents evidence that this is also true X/X polytene cells. Interstrain hybrids were constructed which contain X chromosomes with different rDNA hybridization patterns following digestion with Eco RI, and DNA from diploid or polytene tissue was analyzed using Southern transfers. DNA from diploid tissue of X/X hybrids shows rDNA patterns from both X chromosomes, while DNA from polytene tissue of hybrids shows a pattern characteristic of only one of the X chromosomes. The polytene pattern of the hybrid is independent of whether the dominant X chromosome was derived from the female or male parent. These results suggest that genes from only one nucleolus organizer undergo multiple rounds of replication in X/X polytene cells, and account for the finding that X/O and X/X polytene cells contain similar levels of rDNA without postulating compensation as a ribosomal gene rectification mechanism.

Animals↗
PubMed1979

Differential replication of ribosomal gene repeats in polytene nuclei of Drosophila.

The genes coding for the 18S and 28S rRNAs in D. melanogaster were examined using Southern transfers of DNA from diploid or polytene tissue. A ribosomal gene repeat 12 kb in length is present in DNA from diploid tissue of males and is the major repeat on the Y chromosome. This repeat is present in low amounts on the X chromosome, which contains major repeats of 17 and 11.5 kb. In polytene nuclei of males, the 12 kb band is disproportionately replicated, and only a very low amount of the 11.5 kb repeat and no 17 kb repeat are detected. Polytene nuclei of females contain reduced amounts of the 17 kb repeat relative to the 11.5 kb repeat. This disproportionate replication of specific ribosomal gene repeats suggests that polytenization of the rDNA may involve an extrachromosomal mechanism. Evidence that genes from only one nucleolus organizer are replicated during polytenization in X/Y and X/X flies is discussed. A method for analyzing DNA from tissue of individual larvae was developed to test for population heterogeneity in ribosomal gene structure. Heterogeneity was observed in the ribosomal genes of three Ore R lines, four other D. melanogaster strains and between males and females of the same strain.

Animals↗
PubMed1975

Differential replication of satellite DNA in polyploid tissues of Drosophila virilis.

Satellite DNA amounts were examined in adult tissues of Drosophila virilis, a species whose DNA contains three prominent satellites. Satellite amounts in DNA from six of the seven tissues were lower than in DNA from diploid (adult brain) tissue. Satellite amounts in adult ovary DNA, however, were equivalent to or greater than diploid levels. When DNA from pupal ovaries was examined, a 30% increase in satellite amounts over diploid levels was found. An RNA-DNA hybridization experiment showed that the ribosomal RNA genes in pupal ovary DNA were under-replicated relative to diploid DNA levels.

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