Symmetrical division of mouse oocytes during meiotic maturation can lead to the development of twin embryos that amalgamate to form a chimeric hermaphrodite

Authors: Otsuki, Junko; Nagai, Yasushi; Lopata, Alexander; Chiba, Kazuyoshi; Yasmin, Lubna; Sankai, Tadashi

Source: Human Reproduction, Volume 27, Number 2, 5 February 2012 , pp. 380-387(8)

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Abstract:

BACKGROUND

Gentle compression of mouse oocytes during meiosis-1 prevented the usual extrusion of a small polar body and resulted in the symmetrical division of the ooplasm into two cells of similar size within the zona pellucida. The purpose of our study was to determine whether such cells, equivalent to two small oocytes, were capable of embryonic development and would result in birth following transfer to the uterus.

METHODS

IVF of the 2-celled oocytes was performed and the twin intra-zonal embryos were observed. In each case, the two embryos that originated from fertilized cells with two pronuclei were observed to amalgamate and form a single morula and subsequent blastocyst that was transferred to the uterus of a recipient of a different mouse strain. FISH analysis was performed on sectioned paraffin-embedded tissue of the offspring.

RESULTS

In symmetrically divided oocytes each cell contained a metaphase II spindle. Both cells were fertilizable and cleaved to form twin embryos within the same zona pellucida. Most twin embryos amalgamated to form a single compacted morula, which progressed to hatched blastocysts that contained a single inner cell mass. In total, 104 of these blastocysts were transferred to 19 mice, two of which became pregnant, resulting in the birth of three offspring. FISH analysis showed that one newborn contained both XX and XY cells.

CONCLUSIONS

We found that two small oocytes fertilized within the same zona pellucida to form twin embryos that amalgamate to establish a single chimeric embryo. This may be one mechanism that leads to the formation of a chimeric hermaphrodite when an embryo containing XX cells mixes with its intra-zonal twin containing XY cells.

Keywords: 2-celled oocytes; meiotic spindle; embryo amalgamation; chimera; hermaphrodite origin

Document Type: Research article

DOI: http://dx.doi.org/10.1093/humrep/der408

Publication date: 2012-02-05

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Human Reproduction features full-length, peer-reviewed papers reporting original research, clinical case histories, as well as opinions and debates on topical issues. Papers published cover the scientific and medical aspects of reproductive physiology and pathology, endocrinology, andrology, gonad function, gametogenesis, fertilization, embryo development, implantation, pregnancy, genetics, genetic diagnosis, oncology, infectious disease, surgery, contraception, infertility treatment, psychology, ethics and social issues. The highest scientific and editorial standard is maintained throughout the journal along with a rapid rate of publication.

Symmetrical division of mouse oocytes during meiotic maturation can lead to the development of twin embryos that amalgamate to form a chimeric hermaphrodite

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