Abstract
Factor in the germline alpha (FIGLA) is an oocyte-specific basic helix-loop-helix transcription factor essential for primordial follicle formation and expression of many genes required for folliculogenesis, fertilization and early embryonic survival. Here we report the characterization of bovine FIGLA gene and its regulation during early embryogenesis. Bovine FIGLA mRNA expression is restricted to gonads and is detected in fetal ovaries harvested as early as 90 days of gestation. FIGLA mRNA and protein are abundant in germinal vesicle and metaphase II stage oocytes, as well as in embryos from pronuclear to eight-cell stage but barely detectable at morula and blastocyst stages, suggesting that FIGLA might be a maternal effect gene. Recent studies in zebrafish and mice have highlighted the importance of non-coding small RNAs (microRNAs) as key regulatory molecules targeting maternal mRNAs for degradation during embryonic development. We hypothesized that FIGLA, as a maternal transcript, is regulated by microRNAs during early embryogenesis. Computational predictions identified a potential microRNA recognition element (MRE) for miR-212 in the 3’ UTR of the bovine FIGLA mRNA. Bovine miR-212 is expressed in oocytes and tends to increase in four-cell and eight-cell stage embryos followed by a decline at morula and blastocyst stages. Transient transfection and reporter assays revealed that miR-212 represses the expression of FIGLA in a MRE dependent manner. In addition, ectopic expression of miR-212 mimic in bovine early embryos dramatically reduced the expression of FIGLA protein. Collectively, our results demonstrate that FIGLA is temporally regulated during bovine early embryogenesis and miR-212 is an important negative regulator of FIGLA during the maternal to zygotic transition in bovine embryos.
Highlights
During oocyte growth and follicular development, oocytes accumulate maternal effect factors necessary for oocyte maturation, fertilization and early embryogenesis [1]
Since we have shown that miR-212 is capable of regulating Factor in the germline alpha (FIGLA) expression through direct binding to the 3’ UTR of its mRNA and that miR-212 is differentially expressed during early embryogenesis, we investigated whether miR-212 regulates FIGLA expression in early embryos
Our results provide novel information regarding the temporal expression of FIGLA during bovine oocyte maturation and early embryonic development
Summary
During oocyte growth and follicular development, oocytes accumulate maternal effect factors necessary for oocyte maturation, fertilization and early embryogenesis [1]. Figla transcript is expressed in mouse embryonic gonad as early as E15.5, and undergoes a dramatic increase at the end of embryonic development to peak by postnatal day 2 - a time when the oocyte has become enclosed in primordial follicles and persists throughout folliculogenesis [5]. Recently it was shown that physiological expression of FIGLA plays a critical dual role in activation of oocyte-associated genes and repression of sperm-associated genes during normal postnatal oogenesis [12]. These observations indicate that FIGLA plays a key regulatory role in female germline follicle development, fertilization and early embryogenesis. Despite its established role in control of oocyte gene expression, the temporal expression and regulation of FIGLA during early embryogenesis have not been investigated
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