ABSTRACT
In zebrafish, ovulated oocytes contain both maternal cortisol and the mRNA for the glucocorticoid receptor (gr), which is spread as granular structures throughout the ooplasm. At 0.2 hpf, this transcript is relocated in the blastodisc area and partitioned among blastomeres. At 6-8 hpf, it is replaced by zygotic transcript. We used morpholinos to block translation of both maternal and zygotic gr transcripts, and a missplicing morpholino to block post-transcriptionally the zygotic transcript alone. Only knockdown of translation produced an increase of apoptosis and subsequent craniofacial and caudal deformities with severe malformations of neural, vascular, and visceral organs in embryos and 5-dpf larvae. Such defects were rescued with trout gr2 mRNA. Microarray analysis revealed that 114 and 37 highly expressed transcripts were up- and down-regulated, respectively, by maternal Gr protein deficiency in 5-hpf embryos. These results indicate that the maternal gr transcript and protein participate in the maternal programming of zebrafish development.
Subject(s)
Embryonic Development/genetics , RNA, Messenger, Stored/genetics , Receptors, Glucocorticoid/genetics , Zebrafish/embryology , Zebrafish/genetics , Animals , Animals, Genetically Modified , Apoptosis/genetics , Apoptosis/physiology , Base Sequence , Embryo, Nonmammalian , Female , Gene Expression Regulation, Developmental , Gene Knockdown Techniques , Larva/genetics , Larva/growth & development , Larva/metabolism , Molecular Sequence Data , RNA, Messenger/genetics , RNA, Messenger/metabolism , RNA, Messenger, Stored/metabolism , Receptors, Glucocorticoid/metabolism , Zebrafish/metabolismABSTRACT
We have analyzed by qRT-PCR and/or RT-PCR the abundance and degradation rate of maternal mRNAs for nine steroid hormone receptors and their possible replacement by corresponding embryonic transcripts in both ovulated oocytes and embryos of zebrafish collected at 0, 1, 2, 4, 8, 12, 24 and 48 h post-fertilization (hpf). The mRNAs encoded the nuclear receptors for progesterone (pr), androgen (ar), estrogen (er alpha, er beta 1 and er beta 2), glucocorticoids (gr), mineralocorticoids (mr) and the membrane progestin receptor-alpha and beta (mpr alpha and beta). gr mRNA was the most abundant maternal transcript in oocytes and early embryos followed by er beta 2 and ar mRNAs. They declined during the first 8 hpf, being replaced, thereafter, by the embryonic messengers. er beta 1 and mr transcript levels were low until 8 hpf, but increased steadily during embryonic transcription from 24 to 48 hpf. pr transcripts were detectable only in ovulated oocytes and at 24 and 48 hpf. At these stages, there was a slight increase of er alpha mRNA that initially was very low. mPr alpha and beta mRNAs were expressed in ovulated oocytes and faintly persisted during the first 4 hpf. There was no subsequent embryonic expression of these transcripts. The possible involvement of maternal mRNAs for glucocorticoid and sex hormone receptors in the programming of early zebrafish development is intriguing, since they mainly occur at stages in which gene replication predominates over transcription.
