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Biomedical subjects

D Hirsh

Publications and source records attributed to D Hirsh.

At least 73 records · Page 4Linked to original sources
PubMed1983

Segregation of germline granules in early embryos of Caenorhabditis elegans: an electron microscopic analysis.

Using an improved fixation method for electron microscopy, we have found germline granules in Caenorhabditis elegans embryos shortly after fertilization and prior to the first cleavage. They are localized in the egg cytoplasm which becomes segregated into the posterior blastomere at the first cleavage. In the following divisions, the granules continue this pattern of asymmetric segregation and are ultimately segregated into the germline precursor cell. The granules are then symmetrically segregated into the germline cells.

Animals↗
PubMed1982

Comparisons of the complete sequences of two collagen genes from Caenorhabditis elegans.

Several collagen genes have been isolated from the nematode Caenorhabditis elegans. The complete nucleotide sequences of two of these genes, col-1 and col-2, have been determined. These collagen genes differ from vertebrate collagen genes in that they contain only one or two introns, their triplehelical regions are interrupted by nonhelical amino acid sequences and they are smaller. A high degree of nucleotide and amino acid homology exists between col-1 and col-2. In particular, the regions around cysteines and lysines are most highly conserved. The C. elegans genome contains 50 or more collagen genes, the majority of which probably encode cuticle collagens; col-1 and col-2 apparently are members of this large family of cuticle collagen genes.

Amino Acid Sequence↗
PubMed1979

Analysis of the constancy of DNA sequences during development and evolution of the nematode Caenorhabditis elegans.

In order to test for the occurrence of rearrangements in DNA during development and to assess the rate of DNA divergence during evolution, we have compared restriction fragments derived from DNA from four sources: sperm cells and somatic tissues of one strain of the nematode Caenorhabditis elegans, somatic tissues of a second strain of the same species, and whole animals of a closely related species. Restriction fragments were detected by hybridizing radioactive cloned fragments to restriction digests that had been fractionated by size on agarose gels and transferred to nitrocellulose sheets. In this way, approximately 50 BamHI restriction fragments were visualized and compared. Fragments from sperm and somatic DNAs were found to be identical; 15% differed in size between the two strains. Little cross homology was found between the two species. We conclude that, if rearrangements occur in C. elegans DNA during development, they must affect fewer than a few percent of the restriction fragments or restriction sites. The difference found between the two strains and the two species is surprisingly great.

Animals↗
PubMed1977

Roller mutants of the nematode Caenorhabditis elegans.

The wild type nematode, Caenorhabditis elegans, moves in a sinusoidal wave pattern and leaves sinusoidal paths behind it on a bacterial lawn. The nematode crawls on its side on a special cuticular tread that extends straight down the length of its body. Wild type worms also have rows of musculature and a ventral nerve cord that extend straight down the body. Roller mutants rotate around their long axis as they crawl and move in circular paths. Three roller mutants have been studied. Two mutants are left rollers and one is a right roller. The left rollers have left-handed helical treads, body musculatures, and ventral nerve cords whereas these structures are right-handed helices in the right roller. Double mutants constructed from roller mutants and long mutants indicate that long rollers have helices of the same pitch as normal length rollers. Double mutants constructed from rollers and dumpy mutants that are short and fat indicate dumpy phenotype is epistatic to roller. Double mutants constructed from rollers and blister mutants that have cuticular swelling indicate roller phenotype is epistatic to blister. The results suggest that the roller phenotypes are due to cuticular lesions. Rollers can chemotaxe up a gradient of an attractant by turning off their body muscle movement and continuing their head movements.

Animals↗