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Biomedical subjects

J Heslop-Harrison

Publications and source records attributed to J Heslop-Harrison.

At least 19 recordsLinked to original sources
PubMed2000

The species and chromosomal distribution of the centromeric alpha-satellite I sequence from sheep in the tribe Caprini and other Bovidae.

The evolution of chromosomes in species in the family Bovidae includes fusion and fission of chromosome arms (giving different numbers of acrocentric and metacentric chromosomes with a relatively conserved total number of arms) and evolution in both DNA sequence and copy number of the pericentromeric alpha-satellite I repetitive DNA sequence. Here, a probe representing the sheep alpha-satellite I sequence was isolated and hybridized to genomic DNA digests and metaphase chromosomes from various Bovidae species. The probe was highly homologous to the centromeric sequence in all species in the tribe Caprini, including sheep (Ovis aries), goat (Capra hircus) and the aoudad or Barbary sheep (Amnotragus lervia), but showed no detectable hybridization to the alpha-satellite I sequence present in the tribe Bovini and at most very weak to species in the tribes Hippotragini, Alcelaphini or Aepycerotini. The sex chromosomes of sheep, goat and aoudad did not contain detectable alpha-satellite I sequence; in sheep, one of the three metacentric autosomal chromosomes does not carry the sequence, while in aoudad, it is essentially absent in three large autosomal pairs as well as the large metacentric chromosome pair. The satellite probes can be used as robust chromosome and karyotype markers of evolution among tribes and increase the resolution of the evolutionary tree at the base of the Artiodactyla.

Animals↗
PubMed1996

The Ty1-copia group retrotransposons in Vicia species: copy number, sequence heterogeneity and chromosomal localisation.

We present an in-depth study of the Ty1-copia group of retrotransposons within the plant genus Vicia, which contains species with widely differing genome sizes. We have compared the numbers and sequence heterogeneities of these genetic elements in three diploid Vicia species chosen to represent large (V. faba, 1C = 13.3 pg), medium (V. melanops, 1C = 11.5 pg) and small (V. sativa, 1C = 2.3 pg) genomes within the genus. The copy numbers of the retrotransposons are all high but vary greatly, with V. faba containing approximately 10(6) copies, V. melanops about 1000 copies and V. sativa 5000 copies. The degree of sequence heterogeneity of Ty1-copia group elements correlates with their copy number within each genome, but neither heterogeneity nor copy number are related to the genome size of the host. In situ hybridization to metaphase chromosomes shows that the retrotransposons in V.faba are distributed throughout all chromosomes but are much less abundant in certain heterochromatic regions. These results are discussed in the context of plant retrotransposon evolution.

Amino Acid Sequence↗
PubMed1985

Surfaces and secretions in the pollen-stigma interaction: a brief review.

Interactions between pollen and pistil are key events in angiosperm reproduction, and for this reason they have been the target of an increasing volume of research in recent years. The regulation of fertilization has proved to be remarkably complex, involving controls of various kinds imposed at several different levels. Pollen hydration, governance of germination and stigma penetration, guidance and nutrition of the pollen tube in the style-as well as various, still enigmatic, direct interactions between male and female gametophytes - may all be concerned, individually or in combination, in determining whether fertilization will or will not be effected. The controls differ in degree of efficiency and specificity. Depending largely on the taxonomic remoteness of the parents, interspecific incompatibility may result simply from lack of physiological co-adaptation between the partners, or from rejection mechanisms of a more specific kind. Intraspecific incompatibility, although generally having a deceptively simple genetic basis, has proved to be surprisingly diverse in its physiological manifestations. The paper will present a brief conspectus of the present status of research in the field, and review some recent interpretations of the specific recognition events that may be involved in some of the interactions.

Cell Adhesion↗
PubMed1985

Germination of stress-tolerant Eucalyptus pollen.

Earlier reports have indicated that the pollen of Eucalyptus is mechanically robust and unusually resistant to the osmotic stress imposed by immersion in water. We have investigated some of the features of the germination mechanism in the pollen of E. rhodantha with a view to clarifying the role of pollen-wall specializations in determining this resistance. Cultured in vitro, the pollen showed erratic germination, with a scatter of germination times up to 24 h. This was associated with variation between individual grains in the rate of hydration and dispersal of the pectins of the oncus, the thickened outer component of the intine present at each aperture. The oncus is itself differentiated, with a refractive outer layer lying within a sporopollenin operculum and itself overlying the protein-bearing layer of the intine. The outer layer, interpreted as a compacted pectin, undergoes only slow dissolution in aqueous media after the lifting of the operculum, and it is this that apparently protects the grain from the effects of short-term osmotic stress. The rate of dissolution varies between grains, possibly as a consequence of minor differences in developmental rate in the final stages of differentiation in the anther, and this contributes to the wider scatter of germination times. The dehydrated pollen gave one-third of the potential germination after 24 h exposure to 60 degrees C, and a small proportion survived 24 h at 70 degrees C. This degree of heat tolerance must primarily reflect properties of the protoplast of the vegetative cell, not examined in the present study; but the wall specializations may well provide a guard against extreme desiccation, and it is noteworthy that the function of the germination mechanism is not prejudiced by exposure to high temperatures.

Cell Membrane↗
PubMed1977

Ribosomes, membranes and organelles during meiosis in angiosperms.

Evidence is presented from both observational and analytical techniques indicating profound changes to take place in the ribosome population during male and female meiosis in some flowering plants. During microsporogenesis these appear to involve the elimination of the major part of the ribosome complement early in the meiotic prophase, and its subsequent restoration by the disintegration in the tetrad cytoplasm of 'nucleoloids', themselves synthesized in the nucleus during late prophase. In female tissue the process is essentially similar except for differences in the restoration of the ribosome population. Immediately before the eradication of the ribosomes in both sexes, a sizeable proportion of the meiocyte cytoplasm is encapsulated by double, or multiple unit membrane profiles. Significantly this cytoplasm remains unaffected by the agents responsible for the degredation of the ribosome population. These events are also reflected in the organelle populations where cycles of dedifferentiation and redifferentiation take place. In view of evidence from other organisms, it is considered unlikely that these cycles are in any way a prerequisite of meiosis, but more a characteristic of cells undergoing major changes of phase, where a cytoplasmic 'clean-up' is required before the next stage of growth may begin.

Acid Phosphatase↗