Drosophila intersex orthologue in the silkworm, Bombyx mori and related species

Abstract

Intersex (ix), a gene required for female sexual development in Drosophila, acts in concert with doublesex (dsx) at the end of the sex determination pathway. In the present study a homologue of ix was identified in Bombyx mori. Expression analysis of this gene by RT-PCR and RNase protection assay revealed a diagnostic alternative splice form present only in testis, whereas the most common splice form was found to express in all other tissues from early embryonic developmental stages. The present study provides evidence for the presence of an alternative splice form of ix in three species of silkmoths examined. Taken together with the results of an earlier study on ix in piralid moth, Maruca vitrata (Cavaliere et al. 2009), the present study suggests that the testis-specific splice form may be a characteristic feature of lepidopterans. Though ix lacks a conserved splicing pattern it appears to have retained its functional conservation in terminal sexual differentiation. We speculate that the presence of an additional splice form, perhaps encoding non-functional protein only in testis, may prevent the feminizing effects exerted by the functional IX protein.

Double nexus--Doublesex is the connecting element in sex determination

“…In transgenic D. melanogaster , expression of an ix ortholog of Megaselia scalaris or Bombyx mori completely or partially rescues the sexual development of mutant ix females [ 52 ]. However, apart from a study in B. mori [ 53 ], no follow-up research has been done on the presence and function of ix homologs in insects, and the requirement of IX for DSX F function outside Drosophila is unknown.…”

Characteristic and Functional Study of Intersex, a Gene Related to Female Fertility in Bemisia tabaci

“…However, in M. vitrata and B. mori, the ix orthologs present, respectively, five and six exons (Cavaliere et al, 2009). A female-specific and pupae-stage specific ix transcript is found in M. vitrata, and a testis-specific splice form of ix is found in B. mori (Cavaliere et al, 2009;Arunkumar and Nagaraju, 2011). In B. tabaci, the Btix gene contains four exons; a female-specific isoform (Btix F ) and a male-specific isoform (Btix M ) were found in B. tabaci adults (Figure 2).…”

“…In D. melanogaster, ix is intronless and produce only one mRNA in all tissues of both males and females (Garrett-Engele et al, 2002). However, in Maruca vitrata and B. mori, ix is a multiexon gene with alternative splicing (AS) (Cavaliere et al, 2009;Arunkumar and Nagaraju, 2011). Dmix Bmix and Mvix mRNAs encode highly related and similarly sized proteins.…”

Lepidopteran Sex Determination: A Cascade of Surprises

“…Though IX is expressed in both sexes, it is known to function only with DSX F to regulate female differentiation [Garrett-Engele et al, 2002]. Among lepidopterans, ix homologs have been reported to be present in domesticated and wild silkmoths, including B. mori , A. assama , A. mylitta , and Samia cynthia ricini [Siegal and Baker, 2005;Arunkumar and Nagaraju, 2011]. Besides silkmoths, ix has also been characterized in Maruca vitrata , a Piralidae moth [Cavaliere et al, 2009].…”

“…Besides silkmoths, ix has also been characterized in Maruca vitrata , a Piralidae moth [Cavaliere et al, 2009]. Unlike Drosophila , ix in B. mori , A. assama , and M. vitrata produces sex-specific alternatively spliced isoforms [Cavaliere et al, 2009;Arunkumar and Nagaraju, 2011]. Functional significance of the different IX isoforms in lepidopteran sex determination has yet to be investigated.…”