The staufen gene product is a double-stranded RNA (dsRNA)-binding protein that contains several copies of a consensus
dsRNA-binding domain (RBD). Mouse and human STAU are 90% identical
on the amino acid level. The RBDs are well conserved between Drosophila and mammalian staufen proteins in terms of
overall structure and relative positions, and share 47 to 66% identity. However, the mammalian proteins lack the first RBD
found in Drosophila staufen and contain a putative microtubule-binding domain not found in the Drosophila protein. In vitro,
STAU bound dsRNA and tubulin, suggesting that it crosslinks cytoskeletal and RNA components. In mammalian cells
expressing epitope-tagged STAU, immunofluorescence experiments revealed that STAU is localized to the rough
endoplasmic reticulum.
NCBI Summary:
Staufen is a member of the family of double-stranded RNA (dsRNA)-binding proteins involved in the transport and/or localization of mRNAs to different subcellular compartments and/or organelles. These proteins are characterized by the presence of multiple dsRNA-binding domains which are required to bind RNAs having double-stranded secondary structures. The human homologue of staufen encoded by STAU, in addition contains a microtubule- binding domain similar to that of microtubule-associated protein 1B, and binds tubulin. The STAU gene product has been shown to be present in the cytoplasm in association with the rough endoplasmic reticulum (RER), implicating this protein in the transport of mRNA via the microtubule network to the RER, the site of translation. Four transcript variants resulting from alternative splicing of STAU gene and encoding two isoforms with different N-terminal ends, have been described. Three of these variants encode the same isoform, however, differ in their 5'UTR. The significance of the various transcripts is not known.
Oogenesis, Oocyte maturation, Early embryo development
Comment
Two distinct Staufen isoforms in Xenopus are vegetally localized during oogenesis.
Allison R, et al .
Localization of mRNA is an important way of generating early asymmetries in the developing embryo. In Drosophila, Staufen is intimately involved in the localization of maternally inherited mRNAs critical for cell fate determination in the embryo. We show that double-stranded RNA-binding Staufen proteins are present in the oocytes of a vertebrate, Xenopus, and are localized to the vegetal cytoplasm, a region where important mRNAs including VegT and Vg1 mRNA become localized. We identified two Staufen isoforms named XStau1 and XStau2, where XStau1 was found to be the principal Staufen protein in oocytes, eggs, and embryos, the levels of both proteins peaking during mid-oogenesis. In adults, Xenopus Staufens are principally expressed in ovary and testis. XStau1 was detectable throughout the oocyte cytoplasm by immunofluorescence and was concentrated in the vegetal cortical region from stage II onward. It showed partial codistribution with subcortical endoplasmic reticulum (ER), raising the possibility that Staufen may anchor mRNAs to specific ER-rich domains. We further showed that XStau proteins are transiently phosphorylated by the MAPK pathway during meiotic maturation, a period during which RNAs such as Vg1 RNA are released from their tight localization at the vegetal cortex. These findings provide evidence that Staufen proteins are involved in targeting and/or anchoring of maternal determinants to the vegetal cortex of the oocyte in Xenopus. The Xenopus oocyte should thus provide a valuable system to dissect the role of Staufen proteins in RNA localization and vertebrate development.
Expression regulated by
Comment
Ovarian localization
Oocyte
Comment
Expression and intracytoplasmic distribution of staufen and calreticulin in maturing human oocytes. De Santis L et al. (2015) In this study we hypothesized that the mRNA vector Staufen mediates RNA relocalization during meiotic maturation, and by virtue of its interactions with endoplasmic reticulum, provides a possible mechanism by which protein synthesis is regulated. We assessed the expression of staufen (STAU) and calreticulin (CALR), the latter adopted as a marker of the endoplasmic reticulum, in human oocytes at different stages of maturation: GV, metaphase MI and MII. Oocytes were subjected to polymerase chain reaction in order to investigate the expression of STAU and CALR. The corresponding protein products were identified by immunofluorescence and confocal laser scanning microscopy. STAU and CALR were constantly expressed and selectively localized during oocyte maturation. At the GV stage the both proteins displayed a dispersed distribution localization throughout the cytoplasm. Progressing to the MII stage, STAU tended to compartmentalize towards the cortical area of the oocyte clustering in granules of larger sizes. At the MII stage, CALR assumed a pattern reminiscent and possibly coincident with the position of the meiotic spindle. The changing pattern of STAU distribution during meiotic maturation of human oocytes implicates a novel mechanism for the regulation of protein synthesis based on mRNA localization. Moreover, the unique disposition of CALR at the MII spindle uncovers a physical interaction with endoplasmic reticulum that may mediate cytoskeletal remodelling during oocyte maturation.//////////////////
P.T.K. Saunders et al reported that mouse staufen genes are expressed in germ cells during
oogenesis and spermatogenesis.
They identified two
mouse cDNA expressed sequence tags (ESTs), encoding proteins with significant homology to Dm Stau and used these firstly
to screen a mouse kidney cDNA library and secondly to determine whether staufen mRNAs are expressed in the ovaries and
testes of mice and rats. Sequence analysis of the cDNAs revealed that they originated from two different genes. Using
Northern blots of RNAs from kidneys, ovaries and testes, both cDNAs hybridized to mRNA species of ~3 kb in all three
tissues. On sections of mouse ovaries, staufen mRNA was localized specifically to oocytes.
Expression of the zebrafish Staufen gene in the embryo and adult Bateman MJ, et al .
Staufen, a double stranded RNA binding protein, has been shown to be involved in creating and maintaining cellular asymmetry in the Drosophila oocyte, neuroblast, and mammalian neuron. Staufen binds to the 3' UTR of specific mRNAs and acts in their localization and anchoring to various subcellular domains. Staufen's molecular interactions during development have been limited to investigations in Drosophila melanogaster. Since a vertebrate Staufen has not been studied in a developmental system, the aim of this study was to clone and characterize a staufen orthologue gene in the vertebrate developmental model, zebrafish. The zebrafish staufen-like sequence shows a 64% homology to the human staufen with a 81.2% homology in the highly conserved double stranded RNA binding domain (dsRBDs). Staufen maps on the LN54 radiation hybrid panel to linkage group 6, 16.25 cR from Z265 between fb22h06 and fi16e01. Northern blot and in situ hybridization showed that staufen is expressed both maternally and zygotically. Zygotically expressed staufen is localized to the developing nervous system and at 24h is highly concentrated in the subventricular zone of the developing brain. Maternally expressed staufen is dispersed in the mature oocyte and early embryo. In the adult, staufen is expressed in specific brain nuclei, the testis, neurons and Leydig cells.