Title

Spermatogenesis and meiotic chromosome biology in the North American gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae)

Date of Completion

January 2001

Keywords

Biology, Genetics|Biology, Cell

Degree

Ph.D.

Abstract

Spermatogenesis in the gypsy moth, Lymantria dispar (L.), involves the differentiation of two sperm types, apyrene and eupyrene. The apyrene sperm are anucleate and while they do not participate directly in fertilization, they are required for successful fertilization of eggs by the nucleate, eupyrene sperm. Using electron microscopy, light microscopy and immunocytochemistry, I examined apyrene and eupyrene spermatogenesis in an attempt to explain the events, which lead to the missegregation of meiotic chromosomes in apyrene spermatocytes. Briefly, by the end of meiotic prophase I, bivalents were not present in apyrene spermatocytes. Additionally, pairing, synapsis and recombination were either defective or not present in apyrene spermatocytes. In 1997, Friedlander suggested that an event, occurring early in prophase I is sensitive to the onset of pupation and triggers apyrene spermatogenesis (Friedlander, 1997). I support this hypothesis and suggest that failure to form a chromosomal bouquet during leptotene/zygotene prevents the differentiation of functional meiosis I bivalents, leading to chromosome missegregation and subsequent aneuploidy in apyrene cells. ^ Similar to the majority of moths and butterflies, this moth has a haploid number of 31 and the female is the heterogametic (ZW) sex (Krider and Shields 1997). Here, attempts to induce reproducible banding patterns on mitotic chromosomes failed. This failure is attributable the holocentric organization of gypsy moth chromosomes. Reproducible banding patterns were observed along meiotic (pachytene) chromosomes. I conclude that these DAPI positive bands correspond to chromomeres and can be used for mapping. Finally, I examined a nucleosomal modification associated with open chromatin structure and transcriptional activation and found that it is not excluded from these chromomeres. ^ To further understand germ line development and to advance the development germ line transformation technology in the gypsy moth, I attempted to identify a DNA sequence, which could be used as a primordial germ cell marker. Such a marker would allow for the examination of the origin and morphogenesis of primordial germ cells in the gypsy moth. Using degenerate PCR, DNA sequences possibly related to two primoridial germ cell markers of Drosophila melanogaster, primordial germ cell component (pgc) and vasa were cloned and analyzed. ^