Abstract
Maternal genes are important in directing early development and determining egg quality in fish. We here report the de novo transcriptome from four tissue libraries of the cyprinid loach, Misgurnus anguillicaudatus, and for the first time identified maternal gene transcripts in unfertilized eggs and suggest their immune system involvement. Expression profiles and functional enrichment revealed a total 24,116 transcripts were expressed as maternal transcripts in unfertilized eggs, which were involved in a wide range of biological functions and pathways. Comparison expression profiles and analysis of tissue specificity revealed that the large numbers of maternal transcripts were stored in unfertilized eggs near the late phase of ovarian maturation and before ovulation. Functional classification showed a total of 279 maternal immune-related transcripts classified with immune system process GO term and immune system KEGG pathway. qPCR analysis showed that transcript levels of identified maternal immune-related candidate genes were dynamically modulated during development and early ontogeny of M. anguillicaudatus. Taken together, this study could not only provide knowledge on the protective roles of maternal immune-related genes during early life stage of M. anguillicaudatus but could also be a valuable transcriptomic/genomic resource for further analysis of maternally provisioned genes in M. anguillicaudatus and other related teleost fishes.
Highlights
Before embryos begin to utilize newly synthesized products derived from the zygotic genome, maternally inherited components such as RNA transcripts and proteins direct virtually all aspects of early development in animal embryos [1,2,3,4]
(377 Kyoto Encyclopedia of Genes and Genomes (KEGG) orthology (KO)), global and overview maps (236 KOs), endocrine system (187 KOs), and immune system (171 KOs) were the most enriched KEGG pathways (Figure 3). These results indicate that various transcripts involved in a wide range of biological functions and pathways were stored during oogenesis, and these transcripts will be contributed in early embryonic developmental competence until the onset of zygotic transcription [46]
To further investigate maternal transcripts associated with immune function during early embryo development in M. anguillicaudatus, which may have a pleiotropic function as mentioned above or share the function to the developmental mechanism in early embryonic development, we identified candidate transcripts related to immune functions
Summary
Before embryos begin to utilize newly synthesized products derived from the zygotic genome, maternally inherited components such as RNA transcripts and proteins direct virtually all aspects of early development in animal embryos [1,2,3,4]. The immune system in vertebrates including teleost fishes utilizes complex and highly organized gene sets of molecular signaling pathways that protect against environmental invasions and regulate dynamic changes in an organism [13,14]. This complex and organized immune system would make to intertwine and share certain common features in developmental mechanisms and operational modes. Maternal immunity is believed to be the principal means of fish embryo and larval protection until they have developed a complete immune system [5] It is of interest, to identify maternal immune-related genes/transcripts to extend insights into dynamic changes during the early embryonic development process. As the analysis of massive quantities of genes has allowed gene discovery and expression profiling, recent transcriptome data for several fishes have provided notable insights into the distinctive features in oocyte development and early embryonic development [19,22,23,24,25]
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