Interphase chromosome movement during the midblastula transition in Drosophila melanogaster
AdvisorRykowski, Mary C.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractEukaryotic chromatin is functionally active only in the interphase nucleus. Indirectly we know that global chromatin changes occur, such that gene expression and replication proceed. I undertook to directly observe the structural changes of interphase chromatin, at a time in Drosophila embryogenesis when many nuclear processes were just beginning to be established. I reasoned that cycle 14 was the ideal time in which to observe chromatin changes as a result of functional processes. During this embryonic stage cellular processes shifts from maternal to zygotic control. Chromosomes also undergo significant changes. To infer the native structure of chromatin, I developed an ultra-sensitive two colour in situ hybridization (FISH) technique and established its limits of resolution. Combining ultrasensitive FISH, with high resolution three-dimensional imaging techniques, I can visualize directly the compaction, position and orientation of genes within the interphase nucleus. I first characterized to a greater extent the chromatin changes in the Notch gene during the mid-blastula transition. I observe that the Notch gene decondense as the embryo ages in cycle 14. I further localized both individually and simultaneously, a variety of genes on the three large chromosomes of Drosophila. I observe that during a single interphase, portions of chromosomes move in a cell cycle specific and directed fashion; both independently and over long distances. From these results I conclude that global chromatin changes occur during interphase. I suggest that chromatin is organized beyond the Rab1 orientation such that the position of the gene on the chromosome allows loci to move independently within the active interphase nucleus. I propose a model for chromatin organization within the Drosophila interphase nucleus. Within the Rab1 order, higher-order chromatin is organized into loop domains, ranging in size from 5--100s of kb. I postulate that loop domains that are centromere proximal are small in size, 5-50 kb, while those centromere distal are larger, often greater than 100 kbs, consistent with the observation that the centromere proximal histone gene cluster is arranged in a 5 kb loop (Mirkovitch et al., 1984), while the Notch gene which is near the telomere, is part of a larger loop (Gunawardena et al., 1999a). The loops are attached to each other by a chromosomal backbone structure. My observations demonstrate that interphase nuclear function is superimposed and permitted on this loop-backbone chromatin organization, such that gene movement occurs (Gunawardena et al., 1999b).
Degree ProgramGraduate College