Abstract
Maternal genes play an important role in the early embryonic development of the silkworm. Early embryonic development without new transcription depends on maternal components stored in the egg during oocyte maturation. The maternal-to-zygotic transition (MZT) is a tightly regulated process that includes maternal mRNAs elimination and zygotic transcription initiation. This process has been extensively studied within model species. Each model organism has a unique pattern of maternal transcriptional clearance classes in MZT. In this study, we identified 66 maternal genes through bioinformatics analysis and expression analysis in the eggs of silkworm virgin moths (Bombyx mori). All 66 maternal genes were expressed in vitellogenesis in day eight female pupae. During MZT, the degradation of maternal gene mRNAs could be divided into three clusters. We found that eight maternal genes of cluster 1 remained stable from 0 to 3.0 h, 17 maternal genes of cluster 2 were significantly decayed from 0.5 to 1.0 h and 41 maternal genes of cluster 3 were significantly decayed after 1.5 h. Therefore, the initial time-point of degradation of cluster 2 was earlier than that of cluster 3. The maternal gene mRNAs decay of clusters 2 and 3 is first initiated by maternal degradation activity. Our study expands upon the identification of silkworm maternal genes and provides a perspective for further research of the embryo development in Bombyx mori.
Highlights
The transition from the oocyte depending on maternally supplied RNA and protein complements the commencement of zygotic transcription is a key process in the earliest stages of early embryonic development [1,2,3]
68 preliminary potential maternal genes were identified in the B. mori genome
The mRNAs of maternal genes are produced by the females and stored in embryos [2,6]
Summary
The transition from the oocyte depending on maternally supplied RNA and protein complements the commencement of zygotic transcription is a key process in the earliest stages of early embryonic development [1,2,3]. Maternal mRNAs and proteins stored in oocytes are activated to initiate and regulate embryonic development. Following the period of maternal transcriptional silence, the embryonic zygote’s own genome starts transcription and plays a role in the development of embryos [4]. The transition from the maternal to the zygotic genome is a key process in the final transformation of the zygotic regulation of individual development [2]. Following the maternal-to-zygotic transition (MZT) period, the maternal control of development begins to decline and maternal mRNAs begin to degrade [5,6]. Later developmental control is exhibited via a combination of the maternal RNAs and proteins being eliminated and the zygotic genome becoming transcriptionally active [7]
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