Molecular cloning and functional characterization of an oocyte specific homeobox gene - Ohx
Date Issued
2005
Date
2005
Author(s)
Yeh, Yu-Jung
DOI
zh-TW
Abstract
Life begins when sperm fertilizes an egg to form a zygote. In the mouse ovaries, growing oocytes produce a group of maternal regulatory molecules sufficient to support completion of meiosis, fertilization, and development to the 8-cell stage. Formation of a 2-cell mouse embryo marks the transition from maternal gene to zygotic gene dependence. Such regulation is achieved by coordinated functional expression of a large repertoire of transcription factors to control these processes. A number of these factors have been characterized, and thereby found to possess specific modular structural motifs, such as homeodomains. Ohx (oocyte-specific homeobox gene) was one of the genes identified by in silico cloning involved in early embryo development. There were evidences showed that Ohx was preferentially expressed in one- and two-cell embryons, as well as in the oocytes of mature ovaries. Since the development of a single follicle is under the control of hormones to stimulate follicular maturation, ovulation and luteogenesis, we treated immature females with PMSG and hCG to study the hormones effects on the expression of Ohx gene. Weak signals of Ohx mRNA were detected in the follicles of the untreated ovaries of 4-week-old mice. The Ohx mRNA was clearly detected in the oocytes 9 h post-hCG. These results indicate that Ohx is predominantly expressed in oocytes of the mature ovary and may be under the regulation of an LH surge.
To determine its biological function, we generated Ohx-null mouse lines by gene targeting approch. There was no remarkable difference between Ohx heterozygous and wild-type mice. However, prenatal lethality was found for Ohx homozygous mutants. In order to detect when the mutants died, the embryos were collected and studied at different embryonic stages. The preliminary data showed that the Ohx-null embryos probably died before blastocyst stage.
A shRNA construct was also used to generate transgenic mice. The H1-Ohxi transgenic founders appeared normally, except that two of the five transgenic female did not produce any progeny after repeated mating at the age of 6 month. These two infertile founders were sacrificed at the age of 8 month and many luteal cells were found in their ovaries. To further investigate the roles of Ohx during oogenesis, we generated transgenic mice with Ohx gene over-expressed. Four male transgenic founders were produced, and appeared fertile. The transgene was later proven to be germline transmitted. We found many antrum follicles in the ovaries of the offspring (F2) produced by F1 intercrossed. The results of RT-PCR also demonstrated a remarkable increasing expression of antrum follicle-specific gene, P450 aromatase (Cyp19), in the ovaries of those F2 mice. In conclusion, Ohx plays several significant roles during oogenesis and early embryonic development in mice.
Subjects
同源箱基因
胚
埋植前
卵母細胞
oocyte
preimplantation
embryo
homeobox gene
Type
thesis
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