Germ‐line specific variants of components of the mitochondrial outer membrane import machinery in Drosophila

Abstract

A search of the Drosophila genome for genes encoding components of the mitochondrial translocase of outer membrane (TOM) complex revealed duplication of genes encoding homologues of Tom20 and Tom40. Tom20 and Tom40 were represented by two differentially expressed homologues in the Drosophila genome. While dtom20 and dtom40 appeared to be expressed ubiquitously, the second variants, called tomboy20 and tomboy40, were expressed only in the male germ-line. Transcripts for tomboy20 and tomboy40 were detected in primary spermatocytes as well as post-meiotic stages. Transcription of tomboy20 and tomboy40 in spermatocytes was not dependent on the transcription factor Cannonball, which is responsible for controlling expression of gene products exclusively required for post-meiotic germ cell differentiation. Epitope-tagging and transient expression of dTom20 and Tomboy40 in mammalian cell culture showed proper targeting to mitochondria.

Patterns that Define the Four Domains Conserved in Known and Novel Isoforms of the Protein Import Receptor Tom20

“…Data from D. melanogaster, including a very recent report confirms that the variant Tom20 is testisspecific, with in situ analysis revealing the transcript is restricted to primary spermatocytes and bundles of early spermatids. 50 Only recently have we started to understand how control over gene expression might be exerted during spermatogenesis. 51,52 It is known that regulation of gene expression, and the actual general transcription machinery, differ substantially between somatic and male germ cells.…”

The C-terminal Region of TIM17 Links the Outer and Inner Mitochondrial Membranes in Arabidopsis and Is Essential for Protein Import

“…terization of these components needs to be undertaken in each organism (39,46,47). This is especially true when orthologous components have additional protein extensions or domains not present in yeast, such as in TIM17 in Arabidopsis.…”

Duplicated proteasome subunit genes in Drosophila and their roles in spermatogenesis

“…The generation of testis-specific genes by such a mechanism might indicate that some features of spermatogenesis require an increased amount of some particular gene product, or that there is a need for a version of the protein with an altered activity better adapted to its specific role in spermatogenic cells. The occurrence of testis-specific isoforms of various proteins generated by gene duplication events is not uncommon in Drosophila (for example, casein kinase 2 , mitochondrial translocase of the outer membrane (Hwa et al, 2004), TAFs , OXPHOS genes (Tripoli et al, 2005), myosin VI light chain (Frank et al, 2006), glycogen synthase kinase-3 (Kalamegham et al, 2007), eIF4G (Baker and Fuller, 2007;Franklin-Dumont et al, 2007), see also Mikhaylova et al, 2008)), and is also documented for some mammalian genes (for example, phosphoglycerate kinase (McCarrey and Thomas, 1987), cytochrome c (Hake et al, 1994), ornithine decarboxylase antizyme (Ivanov et al, 2000), TAF(II)250 (Wang and Page, 2002)). However, the degree to which the proteasome subunit genes have undergone such rapid proliferation in the Drosophila genome to produce testis-specific genes is remarkable.…”