Transgenic Expression of the piRNA-Resistant Masculinizer Gene Induces Female-Specific Lethality and Partial Female-to-Male Sex Reversal in the Silkworm, Bombyx mori.

Hiroki Sakai,Kensuke Yahata,Megumi Sumitani,Takashi Kiuchi,Hideki Sezutsu,Keiro Uchino,Yasuhiko Chikami,Susumu Katsuma,Fugaku Aoki,Masataka G Suzuki,Artyom Kopp

doi:10.1371/journal.pgen.1006203

Hiroki Sakai, Kensuke Yahata + Show 9 more

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https://doi.org/10.1371/journal.pgen.1006203

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Abstract

In Bombyx mori (B. mori), Fem piRNA originates from the W chromosome and is responsible for femaleness. The Fem piRNA-PIWI complex targets and cleaves mRNAs transcribed from the Masc gene. Masc encodes a novel CCCH type zinc-finger protein and is required for male-specific splicing of B. mori doublesex (Bmdsx) transcripts. In the present study, several silkworm strains carrying a transgene, which encodes a Fem piRNA-resistant Masc mRNA (Masc-R), were generated. Forced expression of the Masc-R transgene caused female-specific lethality during the larval stages. One of the Masc-R strains weakly expressed Masc-R in various tissues. Females heterozygous for the transgene expressed male-specific isoform of the Bombyx homolog of insulin-like growth factor II mRNA-binding protein (ImpM) and Bmdsx. All examined females showed a lower inducibility of vitellogenin synthesis and exhibited abnormalities in the ovaries. Testis-like tissues were observed in abnormal ovaries and, notably, the tissues contained considerable numbers of sperm bundles. Homozygous expression of the transgene resulted in formation of the male-specific abdominal segment in adult females and caused partial male differentiation in female genitalia. These results strongly suggest that Masc is an important regulatory gene of maleness in B. mori.

Highlights

Most animal species have two sexes and display various sexual dimorphisms
Fem transcript yields a PIWI-interacting RNAs (piRNAs) (Fem piRNA) and Fem- piRNA-PIWI complex targets and cleaves mRNAs transcribed from the Masculinizer (Masc)
Masc is required for male-specific expression of B. mori doublesex (Bmdsx), which is an important regulatory gene for sexual differentiation, and Masc is considered to be essential for maleness

Summary

Introduction

Most animal species have two sexes and display various sexual dimorphisms. Mechanisms of sex determination are highly different among phyla [1,2,3]. The temperature at which eggs are incubated determines their sex [4]. In Daphnia magna, a shortening of the photoperiod, lack of food, and increase in population density leads to the production of males that are genetically identical to females [5]. Mammals show genotypic sex determination, with sex determined by the expression of a Y-linked gene, Sry [6]. In the African clawed frog, Xenopus laevis, DM-W located on the W chromosome induces female development [7]

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