Formation Mechanisms of the Ellipsoid Egg in Silkworm (Bombyx mori): Insights from Transcriptomic Profiling

The elongated egg is a morphological mutant of silkworm (Bombyx mori) eggs, yet the biochemical processes and molecular mechanisms underlying this trait remain unclear.

In this study, we performed transcriptome sequencing on the ovaries of female pupae from the Nistari silkworm strain (comparing normal and elongated eggs) during the first three days post-pupation using high-throughput sequencing.

A total of 153.56 Gb of filtered data was obtained, identifying 23,366 genes and 35,798 mRNAs. Comparative analysis across three control groups revealed 374 differentially expressed genes (DEGs), with 131 upregulated and 243 downregulated genes in the elongated egg group. Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that these DEGs were primarily associated with protein hydrolysis, DNA metabolic processes, and euchromatin/heterochromatin organization. Trend expression analysis revealed that transcriptional activity in elongated eggs was significantly higher than in normal eggs, particularly on day 3 of the pupal stage.

Weighted gene co-expression network analysis (WGCNA) classified gene expression patterns into twelve modules, with two modules showing specificity. Thirteen hub genes were identified, which are functionally linked to translation initiation, protein density regulation, post-translational modification, and protein turnover. These findings provide foundational insights into the molecular mechanisms driving the formation of the elongated egg in silkworms.