No description available.

When the Y chromosome of a Mus musculus domesticus mouse is placed onto the C57BL/6J (B6) inbred genetic background, the XY (B6.Y TIR) progeny develop only ovaries or ovotestes during fetal life. At puberty, while some of the hermaphroditic males become fertile, none of the XY sex-reversed females produce litters. The objective of my study was to clarify the cause of infertility in B6.YTIR females. We have previously demonstrated that the eggs ovulated from B6.YTIR ovaries undergo fertilization efficiently, but cannot develop beyond the 2-cell stage. In the present study, we collected oocytes directly from XY ovaries, and examined their maturation, fertilization and embryonic development in vitro. The results show that the majority of fertilized eggs fail to reach the blastocyst stage. To determine whether developmental incompetence of XY oocytes can be attributed to defects in the oocytes themselves or the surrounding XY somatic cells, we constructed female mouse chimera composed of B6.YTIR and XX BALB/c cells. All chimeric females produced progeny exclusively derived from XX oocytes. For comparison, most of XX ↔ XX chimeric females produced progeny derived from oocytes of either strain. / The ability of XY oocytes to regulate granulosa cell differentiation and functions was assessed in oocyte-cumulus complexes (OCC) in vitro . Microsurgical removal of oocytes prevented cumulus cell expansion and suppressed estradiol production while it promoted progesterone production. Coculture of the oocytectomized OCC with denuded oocytes from either XX or XY ovaries resumed cumulus expansion and the normal endocrine profile. Morphometric analyses indicated that XY oocytes were significantly smaller and their zona pellucida layer thinner than XX oocytes as early as the preantral stage. Furthermore, XY oocytes were attached with fewer cumulus cells in antral follicles. To determine whether developmental incompetence of the zygotes from XY ovaries resides in the nuclear or cytoplasmic component, we exchanged the pronuclei between the zygotes derived from B6.YTIR oocytes and those from XX oocytes and examined their development in vitro. The results indicate that both compartments are defective in the B6.YTIR oocyte. / In conclusion, the XY oocyte becomes cell-autonomously defective in both nuclear and cytoplasmic components during early oogenesis.

Oocyte loss and meiotic prophase progression was studied in XY sex-reversed and XO female mice, two mouse models that lack pairing between their sex chromosomes. An arrest at the pachytene stage of meiosis was not observed, nor was a significant loss of oocytes at this stage compared to normal XX control mice. Thus, it was concluded that a pairing checkpoint either does not exist in oocytes or is not as stringent as the one observed in males. / The effect of mutating the pro-apoptotic Bax molecule was studied at three distinct ages corresponding to the time when female germ cells are premeiotic, in meiotic prophase, and arrested in dictyotene. Although it appeared that more germ cells were retained in the Bax homozygous mutant compared to the wild-type and heterozygous mice at 18.5 dpc, by 24.5 dpc all of the mice possessed similar numbers of germ cells. These results indicate a role for Bax in germ cell death but also support the idea that an alternative pathway can compensate for the elimination of this molecule.

No description available.

No description available.

Abstract not available

Recently, the timing of oocyte loss during murine development has been brought into question as authors using mouse vasa homologue (MVH) as a germ cell marker did not observe a loss of oocytes during fetal life. Instead the major loss was observed in the days following birth, after chromosome pairing has occurred. / In this study the controversy was addressed by establishing a new and reliable method to quantify murine oocytes in meiotic prophase, as well as to determine the gestation age and meiotic prophase stage of oocyte loss. Earlier limitations were overcome through the use of Germ Cell Nuclear Antigen-1 (GCNA-1) antibody as a germ cell specific marker, and the novel addition of a cytospin centrifugation step to the method. Progress through meiotic prophase was examined in chromosome spread preparations where meiotic stages were assessed using an antiserum against synaptonemal complex (SC) proteins. Quantification was accomplished by counting the number of GCNA-1 immunoreactive cells in chromosome spread preparations and estimated in histological sections using the ratio estimation model. (Abstract shortened by UMI.)

H1 histones are potentially significant to nuclear reprogramming during the oocyte-to-embryo transition. One characteristic distinguishing the H1 subtypes is that the somatic H1 histones are found primarily in dividing cells, whereas the H10 subtype is predominantly found in differentiated cells. The H1 complement in mouse oocytes and preimplantation embryos from wild-type and H10-/- animals was investigated. / Immunocytochemistry of wild-type cells demonstrated that H10 was predominant in oocytes while somatic H1 began accumulating in the 2-cell embryo. In H10-/- cells H10 was not detected, but, surprisingly, somatic H1 was detected beginning at the 1-cell stage. Radiolabeling of wild-type and H10-/- cells revealed that somatic H1 synthesis intensified after meiotic maturation, and therefore prior to its detection in embryos. The functional study found that loss of H10 impaired oogenesis but enhanced embryogenesis. The patterns of H1 immunodetection and synthesis are integrated, and the significance of H1 composition in development is discussed.

At fertilization, the remodelling of the sperm nucleus into the male pronucleus is critical for normal development. Morphological and functional changes to the nucleus are underpinned by biochemical changes in the chromatin composition, most notably the removal of sperm specific protamines and assembly of histones onto the paternal DNA. This exchange is controlled by oocyte factors, as exemplified in Xenopus by nucleoplasmin. Though mammalian factors remain unidentified, a functional assay based on antibodies recognizing core histones has been developed to test the activity in oocytes that transfers histones onto sperm DNA, named histone transfer activity (HTA). The assay was applied to growing and maturing murine oocytes to determine when during oogenesis HTA develops, and to probe potential regulatory mechanisms. Fully-grown oocytes develop HTA upon maturation, in a protein-synthesis dependent manner. Large, growing oocytes also develop HTA upon entry into M-phase. Small growing meiotically incompetent oocytes, ones that do not spontaneously enter M-phase, do not develop HTA, though this can be overcome by culture of oocytes to meiotic competence, or by treatment with strontium to induce intracellular calcium oscillations. Taken together these findings form a model of how HTA develops throughout oogenesis. Finally, an attempt is made to identify a potential mammalian HTA factor. Transcripts for two remodelling factors, mNAP and Npm3, are identified in the murine oocyte, and injection of anti-sense oligonucleotides reveals that Npm3 plays a significant role in the deposition of histories and the remodelling of sperm chromatin at fertilization. Combined with the findings of the HTA assay, the data forms a testable model of how Npm3 may be regulated throughout oogenesis.

No description available.