Archive for the ‘Chimeric Mouse’ Category

Live-Borns from XX but Not XY Oocytes: DISCUSSION(4)

The defect in the XY oocyte remains to be clarified. Hunt and LeMaire have reported a high frequency of precocious dissociation between the X and Y chromosomes in oocytes isolated from the B6.Ypos female mouse at the diakinesis/metaphase I stage. Accordingly, it is conceivable that the B6YTIR female may lose its embryos because of aneuploidy. However, the XO female mouse is invariably fertile although it lacks the pairing partner for the single X chromosome and suffers from a high incidence of aneuploidy and embryo death. Furthermore, some strains of XY sex-reversed female mice demonstrate high frequencies of aneuploidy and yet produce litters, albeit in small numbers. Therefore, the rate of aneuploidy must be very high to be the sole cause of the complete absence of progeny in the Вб.У™ female. Actual aneuploidy in matured or fertilized eggs from the B6.YTIR female remains to be examined.

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Live-Borns from XX but Not XY Oocytes: DISCUSSION(3)

DISCUSSION(3)

Absence of Live-Borns from XY Oocytes

Despite the fertility of all chimeric females, no live-boms were produced from XY oocytes. This observation suggests that the presence of XX cells failed to make the XY oocyte competent for reproduction. Therefore, the developmental failure of the XY oocyte is most likely intrinsic to the oocyte itself, and not to the surrounding somatic cells in the B6.YTIR ovary. Possible competition between the germ cells of two mouse strains in the chimera has been reported previously. Accordingly, it is conceivable that XY oocytes were excluded from the chimeric ovaries in competition with XX oocytes. In the present study, however, we confirmed the presence of XY oocytes at different stages of follicular development in XX BALB/c <-> XY B6.YTIR chimeric ovaries. It remains possible that XX oocytes were favorably recruited for ovulation and, therefore, the absence of progeny derived from XY oocytes may be attributable to the paucity of XY-derived eggs ovulated rather than death of XY-derived embryos. Nonetheless, it must be emphasized that the XY genotype of the oocyte, and not of somatic cells, appears to be responsible for exclusion of XY oocytes from the reproductive process, whether at ovulation or after fertilization. buy flovent inhaler

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Live-Borns from XX but Not XY Oocytes: DISCUSSION(1)

Predominant Development of Female Chimeras

In the present study, all but one (89%) of the live-born chimeras, which were composed of B6.YTIR and XX BALB/c cells in varying proportions, developed the female phenotype. The only exception was a male with bilateral testes. This strong bias towards the female sex was unexpected. When chimeric mice are composed of XX and XY cells, the XY cells usually exert a dominating effect on sexual differentiation. Singh et al. have reported that as little as 10% contribution of XY cells is sufficient to induce testis formation. ventolin inhaler

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Live-Borns from XX but Not XY Oocytes: DISCUSSION(2)

Live-Borns from XX Oocytes

After mating with normal males, all XX XY chimeric females produced progeny exclusively derived from XX oocytes irrespective of the degree of XY contribution in body formation. Therefore, the fertility of XX oocytes was not abolished by the presence of XY somatic cells. We have previously reported several abnormal aspects of the B6.YTIR ovary during development, for example, transcription of the Sry gene in the ovarian primordium, postnatal development of abnormal endocrine features, and absence of regular estrous cyclicity at puberty. Since all XX XY chimeric females turned out to be fertile, the abnormalities that we have observed in the somatic components of the B6.YTIR female appear to be either not critical for fertility, caused only locally by the XY oocyte, or overcome by the presence of a small number of XX cells. birth control pills

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Live-Borns from XX but Not XY Oocytes: RESULTS(5)

RESULTS(5)

Y-Labeling was also found in oocytes of XX BALB/c о XY B6.Y™ chimeric ovaries. In the ovary (#15) with the highest contribution of XY cells, all three preantral follicles identified contained oocytes with hybridization signals. In the ovaries (#14 and #2) with a high contribution of XY cells, hybridization signals were seen in the majority of oocytes encompassed by follicles from primary to antral stages (Fig. 5b). In other chimeric ovaries with a lower contribution of XY cells, detection of Dig labeling in oocytes was less frequent than expected from the contribution of XY somatic cells. In the ovaries of XY BALB/c <-» XX B6* chimera, Y labeling was found in various ovarian somatic cell types in agreement with the proportion (12%) of XY cells in nongonadal tissues, except that the surface epithelium appeared to be more populated with XY cells (not shown). No oocyte was found labeled. No hybridization signal was found in negative control, XX BALB/c <-» XX B6* chimeric ovaries (Fig. 5d). ventolin inhalers

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Live-Borns from XX but Not XY Oocytes: RESULTS(4)

The ovaries from three XX BALB/c XX B6* chimeric females (#3, #13, #20) at 87, 157, and 88 dpp, respectively, were compared (Table 4, Fig. 4, d and e). They contained comparable numbers of follicles at various stages irrespective of age, although the number was slightly lower than in the majority of XX BALB/c XY B6.Y™ ovaries. The number of corpora lutea varied with a range similar to that in XX BALB/c XY B6.YTIR ovaries. Similar numbers of follicular structures were also observed in the ovaries of an XX B6* female mouse. buy levaquin online

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Live-Borns from XX but Not XY Oocytes: RESULTS(3)

RESULTS(3)

In XX <н> XX chimeric females, the contribution of B6* and BALB/c cells was deduced only from coat-color chi-merism (Table 3). All seven females had a dominant area or equal area of black coat color. Two females (#20 and #25) became pregnant after the first mating, and the rest did so at the second trial. All produced live-boms, with an average litter size of 6.8, which was comparable with the litter size of XX BALB/c о XY B6.YTIR chimeric females and the known litter sizes of the BALB/c and B6 strains. Five females (#1, #3, #13, #20, #21) that were dominated by black coat color produced exclusively or predominantly agouti progeny. A female (#24) that had equal distribution of the two coat colors produced only agouti progeny at the first delivery, but a balanced number of progeny with either skin color at the second delivery. A female (#25) that had balanced distribution of the two coat colors produced equal numbers of albino and agouti progeny. buy ampicillin

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