Most species of freshwater cyclopoid copepods follow a conventional course of DNA replication during gametogenesis, but certain species regularly undergo chromatin diminution during early embryogenesis, a process that is accompanied by the exclusion of large amounts of heterochromatic DNA from progenitor somatic cells and selective retention of this DNA by primordial germ cells after their segregation from the soma. We have used scanning microdensitometry and image analysis cytometry of individual Feulgen-stained nuclei to determine the DNA levels of individual somatic cell nuclei, oocytes, spermatocytes, and sperm for seven species, including Acanthocyclops brevispinosus, Acanthocyclops vernalis, Ectocyclops phaleratus, Eucyclops agilis, Eucyclops ensifer, Macrocyclops albidus, and Thermocyclops decipiens. The oocyte nuclei of these species have twice the DNA content of their diploid somatic cell nuclei. In specimens of Cyclops strenuus, Mesocyclops edax, Mesocyclops longisetus, Mesocyclops longisetus curvatus, and Metacyclops mendocinus, marked increases in DNA levels were noted in both female and male germ cells before meiosis. The appearance of enlarged nuclei with densely stained chromocenters is a distinguishing feature of oocytes and spermatocytes of cyclopoid species that exhibit excessive accumulations of DNA during gametogenesis and subsequently undergo chromatin diminution. The net increase in DNA content of the prediminution nuclei is 6-10 times the DNA level of their somatic cell nuclei and is largely attributable to increases in the amount of DNA associated with their heterochromatic chromocenters. The identification of a morphologically distinctive type of germ cell and its dramatic accumulation of large amounts of DNA before meiosis are discussed in terms of the selective elimination of heterochromatin during early cleavage stages in these cyclopoid species.

No description available.

Study 1 was conducted to determine if partial restriction of testicular thermoregulation affects spermatogenesis when compared to full restriction by mild scrotal insulation for 48 h. Study 2 and Study 3 were conducted to investigate the efficiencies of selected semen separation techniques on the removal of abnormal spermatozoa. in Study 1, semen from control and partial scrotal insulation (Pl) bulls did not differ between the pre-insult and post-insult period for any variable measured. Full scrotal insulation (Fl) bulls differed for several variables measured, but at different intervals and for different durations post-insulation. Spermatozoal motility and acrosomal integrity were reduced during Period 3 only of semen collection with no effect on sperm output. Full insulation caused abnormalities to be ejaculated from d 10 to 33 post-insulation. Specific morphologically abnormal cells occurred in a chronological order. The order of occurrence was: tailless heads, diadem defect, nuclear vacuole defect, pyriform shaped heads, protoplasmic droplets, severely misshapened heads, acrosomal abnormalities, and the dag defect. In Study 2, a pooled sample of frozen-thawed semen from FI bulls in Study 1 was separated using swim-up separation, glass wool filtration, Percoll® density gradients (45/90% two-layer and 50/70/90% three-layer), and Sephadex® filtration. Glass wool filtration was basically without effect and will be excluded from further discussion. All other separation techniques improved motility from the initial sample at the expense of spermatozoal harvest. The subtle head abnormalities were unaffected by separation for all techniques and spermatozoa with nuclear vacuoles on normal shaped heads were enriched; however, head abnormalities were removed with increasing frequency as the severity of the head distortion increased. In Study 3, frozen-thawed ejaculates with a high concentration of spermatozoa with nuclear vacuoles (>20%) were separated using 45/90% Percoll® and 45/100% Percoll® density techniques. The greater the number of nuclear vacuoles per sperm head, the more efficient the removal of such sperm. The separation of spermatozoa with subtie head distortion as well as spermatozoa with nuclear vacuoles on normal shaped heads by density separation, would allow further assessment of the importance of these abnormal sperm to decreased fertility and increased embryonic mortality. / Ph. D.

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Zoology / Master / Master of Philosophy

published_or_final_version / Obstetrics and Gynaecology / Master / Master of Philosophy

Meiotic sex chromosome inactivation (MSCI) is an essential epigenetic process, which transcriptionally silences X and Y chromosomes during spermatogenesis. It is accompanied by substantial chromatin remodeling resulting in a formation of so called sex or XY body, which is a characteristic of male pachytene spermatocytes. In spite of MSCI indispensability for male fertility, its biological role and molecular nature still remain rather unclear. However, the described link between chromosomal asynapsis and transcriptional silencing demonstrated that MSCI is tightly associated with the asynapsis of largely non-homologous sex chromosomes and is a specific form of more general mechanism called meiotic silencing of unsynapsed chromatin (MSUC). The essential role of MSCI was demonstrated using mouse models, such as carriers of X- autosome translocations, where anomalous synapsis of sex chromosomes leads to impairment of MSCI and male sterility. Intriguingly, the exclusive spermatogenic arrest is a hallmark of not only X-autosome translocations but even various autosomal rearrangements, including autosomal translocations, inversions, or other structural mutations. Because the rearranged autosomes often intimately associate with the sex body, it...

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 71-83).

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 128-151). Also available in print.