Expression and intracytoplasmic distribution of staufen and calreticulin in maturing human oocytes

Abstract

Purpose 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. Methods 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. Results 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. Conclusions 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.

Shared Cell Biological Functions May Underlie Pleiotropy of Molecular Interactions in the Germ Lines and Nervous Systems of Animals

“…In mice, stau mRNA is expressed in oocytes and during meiosis in males (Saunders et al, 2000). In human oocytes, immunofluorescence studies show that STAU protein is present throughout all stages of oocyte maturation, and that its subcellular localization changes throughout oogenesis, initially dispersed throughout the cytoplasm and later localized into large discrete granules at the cortex (De Santis et al, 2015). As in D. melanogaster oocytes (St Johnston et al, 1991;van Eeden et al, 2001), Stau localization to a specific region of the Xenopus laevis oocyte cytoplasm is required to specify PGCs (Yoon and Mowry, 2004).…”

Complex chromosomal aberrations in a fetus originating from oocytes with smooth endoplasmic reticulum (SER) aggregates

“…Under normal conditions SER vesicles are present in oocytes and act as Ca 2+ stores (Sa et al 2011;Sathananthan et al, 1997). SER regulates and releases calcium ions which play a crucial role in fertilization and early embryo development, in the stress response in the oocyte or embryo (Latham 2015), as well as in the regulation of the meiotic spindle (De Santis et al 2015). However, under unknown conditions the presence of SERa disturbs these Ca 2+ stores and oscillations that could in turn affect fertilization and embryonic development.…”

Policy of IVF centres towards oocytes affected by Smooth Endoplasmic Reticulum aggregates: a multicentre survey study

“…However, they have also been observed in unfertilized oocytes, aging oocytes and embryos [3,11,18]. New evidence demonstrates that the Endoplasmic Reticulum (smooth or rough) plays additional crucial roles in stress responses in the oocyte or embryo [19] as well as in the regulation of the meiotic spindle [20]. Different malformations and pathologies have been described after transfer of an embryo originating from a SERa+ oocyte [21,22] but equally when a non affected embryo from the same oocyte cohort is transferred [9,12].…”