Abstract
Yun7Ge is a giant egg mutant found in the silkworm variety Yun7. In comparison with the giant mutant Ge, the eggs of Yun7Ge are larger. The number of laid eggs and hatching rate of Yun7Ge are reduced, which is not conducive to reproduction. In this work, the target gene controlling giant egg trait is located on the Z chromosome and was determined through genetic analysis. Transcriptome results showed that phytanoyl-CoA dioxygenase domain-containing protein 1 (PHYHD1) on the Z chromosome was silenced, and the 25 chorion genes on chromosome 2 were remarkably downregulated. Sequence analysis showed that the 73.5 kb sequence including the PHYHD1 was replaced by a ~3.0 kb sequence. After knocking out the PHYHD1 by using CRISPR/Cas9, the chorion genes were significantly downregulated. Hence, the silencing of PHYHD1 leads to the downregulation of many chorion protein genes, thus directly causing giant eggs.
Highlights
The eggshell of Bombyx mori plays a significant role in protecting the developing embryo from external environmental hazards after oviposition
The eggshell is mainly comprised of chorion proteins, which are synthesized and secreted only by follicular cells located in a series of eight pupal ovarioles in B. mori [1]
The gene that controls the giant egg trait of Ge is located on the Z chromosome [7]
Summary
The eggshell of Bombyx mori plays a significant role in protecting the developing embryo from external environmental hazards after oviposition. All the chorion genes of B. mori are located on chromosome 2 [1], but not every mutant is caused by mutations of chorion genes. The gene responsible for the formation of elp eggs is located on chromosome 18 [3], and the BmEP80 gene responsible for the change of eggshell structure of l-em mutant is located on chromosome 10 [6]. These non-chorion genes may indirectly affect the eggshell structure during egg formation
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