Title

The generation of a haploid genome from somatic cells and growing oocytes

Date of Completion

January 2005

Keywords

Biology, Genetics|Biology, Cell

Degree

Ph.D.

Abstract

Initially, the idea of the generation of a haploid genome was attempting to produce artificial gametes through nuclear transfer. Mammalian oocytes are ideally suited for use as ploidy reduction machinery because they are easily obtained and manipulation techniques are well established. As the oocyte is important for generating the haploid genome, it is necessary to understand the underlying biological mechanisms: the accurate segregation of chromosomes, and maintenance of delicate epigenetic modifications. First of all, this study has demonstrated that a large percentage of oocytes containing somatic chromosomes progressed through "the first meiotic division" and were arrested at an MII-like stage. However, in all of the reconstructed oocytes the somatic chromosomes were misaligned in the newly assembled meiotic spindle. It suggested that the incompatibility between somatic chromosomes and oocyte meiotic spindles needs to be further studied and understood before achieving normal chromosome segregation. On the other hand, this incompatibility could serve as a valuable model to address the fundamental question: Does a spindle checkpoint exist in the mammalian oocyte? Specifically, the progression of the cell cycle of meiosis was not blocked or delayed by the incompatibility, and a meiotic spindle assembly checkpoint did not fully function when the somatic chromosomes were present, either before or after assembly of the spindle. Finally, these results also provide the evidence showing the reprogramming competence of an oocyte is acquired during its growth, and these reprogramming factors accumulated in the nuclei at diplotene stage. Upon resumption of meiosis, the reprogramming factors are released into the cytoplasm of the oocyte. The observations herein may provide key insights into defining epigenetic reprogramming in the mammalian oocyte. As the idea of generating an artificial gamete is emerging, comprehending the molecular mechanisms of the oocyte is just a beginning; the complexity of the process and the challenges involved in chromosome segregation, oocyte spindle checkpoint, and epigenetic reprogramming need to be addressed. The effort is highly worthwhile as the promise is identifying completely new avenues to overcome the challenges of producing artificial gametes. ^