Otefin, a Nuclear Membrane Protein, Determines the Fate of Germline Stem Cells in Drosophila via Interaction with Smad Complexes

Abstract

Nuclear envelope proteins play important roles in chromatin organization, gene regulation, and signal transduction; however, the physiological role of these proteins remains elusive. We found that otefin (ote), which encodes a nuclear lamin-binding protein [corrected], is essential for germline stem cell (GSC) maintenance. We show that Ote, as an intrinsic factor, is both necessary and sufficient to regulate GSC fate. Furthermore, we demonstrate that ote is required for the Dpp/BMP signaling pathway to silence bam transcription. By structure-function analysis, we demonstrate that the nuclear membrane localization of Ote is essential for its role in GSC maintenance. Finally, we show that Ote physically interacts with Medea/Smad4 at the bam silencer element to regulate GSC fate. Thus, we demonstrate that specific nuclear membrane components mediate signal-dependent transcriptional effects to control stem cell behavior.

Tissue-Specific Defects Are Caused by Loss of the Drosophila MAN1 LEM Domain Protein

“…LEM-D proteins interact with transcriptional repressors, such as germ cell-less and Bcl-2-associated transcription factor (Haraguchi et al 2004;Mansharamani and Wilson 2005). In addition, interactions with the downstream transcriptional effectors of multiple signal transduction pathways have been observed, such as Smads [receptor-regulated (R)-Smads], retinoblastoma protein, and b-catenin (Markiewicz et al 2002(Markiewicz et al , 2006Osada et al 2003;Raju et al 2003;Lin et al 2005;Pan et al 2005;Jiang et al 2008). These latter observations suggest that LEM-D proteins have a role in the regulation of gene expression.…”

“…Genetic analyses of a second Drosophila LEM domain gene, otefin, have been recently reported ( Jiang et al 2008). These studies showed that otefin is a nonessential gene, with flies showing developmental defects that are limited to the female germ line.…”

“…Genetic studies have shown that dBAF is essential for viability, with null mutants displaying a typical mitotic phenotype (Furukawa et al 2003). That the loss of neither dMAN1 nor Otefin ( Jiang et al 2008) is lethal suggests one of two possibilities. Either Drosophila LEM-D proteins share roles in regulating BAF nuclear envelope interactions or dBAF has LEM-independent functions that are essential for survival.…”

“…These proteins are produced through all stages of Drosophila development, with the levels of dMAN1 and Otefin most abundant in the embryo (Wagner et al 2006). Immunolocalization studies demonstrate that dMAN1, Bocksbeutel, and Otefin are enriched at the nuclear envelope (Padan et al 1990;Ashery-Padan et al 1997a,b;Wagner et al 2004aWagner et al , 2006Jiang et al 2008). Drosophila provides an excellent model for studies of the developmental roles of the nuclear lamina proteins, as homologs of many vertebrate lamina proteins have been identified, including A-and B-type lamins (lamin C and lamin Dm 0 , respectively) (Fisher et al 1982;Lenz-Bohme et al 1997;Osouda et al 2005;Schulze et al 2005), Drosophila (d)BAF (Furukawa et al 2003), the lamin B receptor (Wagner et al 2004b), and proteins in the linker of nucleoskeleton and cytoskeleton (LINC) complex (Starr and Fischer 2005;Stewart et al 2007).…”

Somatic gonadal cells: The supporting cast for the germline

“…Mechanistically, LIS-1 binds and stabilizes MAD to promote its phosphorylation, thereby inhibiting bam transcription and maintaining GSCs . OTE associates with MED to silence bam transcription and maintain GSCs (Jiang et al, 2008). Finally, systemic factors expressed outside of the gonad also regulate BMP signaling.…”