|
General Comment |
Gas6 is expressed as an
abundant 2.6-kb mRNA in starved cells but decreases significantly upon stimulation of cells with
serum or fibroblast growth factor. A human homolog was isolated from HeLa cells and was
predicted to encode a 678-amino acid protein with 81% identity to the mouse protein and 44%
identity to human protein S (OMIM 176880), a vitamin-K dependent negative coregulator in the blood
coagulation pathway. Regions of greatest similarity between Gas6 and protein S occur in a gamma
carboxylated glutamic acid-rich domain and in 4 EGF-like domains.
The AXL receptor tyrosine kinase (OMIM 109135 may be involved in the stimulation of cell proliferation in response to an
appropriate signal, i.e., a ligand that activates the receptor. The AXL stimulatory factor is identical to the product of the GAS6 gene.
NCBI Summary:
This gene encodes a gamma-carboxyglutamic acid (Gla)-containing protein thought to be involved in the stimulation of cell proliferation. This gene is frequently overexpressed in many cancers and has been implicated as an adverse prognostic marker. Elevated protein levels are additionally associated with a variety of disease states, including venous thromboembolic disease, systemic lupus erythematosus, chronic renal failure, and preeclampsia. [provided by RefSeq, Aug 2014]
|
|
Comment |
GAS6 ameliorates advanced age-associated meiotic defects in mouse oocytes by modulating mitochondrial function. Kim KH et al. (2021) Previously, we reported that the silencing of growth arrest-specific gene 6 (Gas6) expression in oocytes impairs cytoplasmic maturation by suppressing mitophagy and inducing mitochondrial dysfunction, resulting in fertilization failure. Here, we show that oocyte aging is accompanied by an increase in meiotic defects associated with chromosome misalignment and abnormal spindle organization. Intriguingly, decreased Gas6 mRNA and protein expression were observed in aged oocytes from older females. We further explored the effect of GAS6 on the quality and fertility of aged mouse oocytes using a GAS6 rescue analysis. After treatment with the GAS6 protein, aged oocytes matured normally to the meiosis II (MII) stage. Additionally, maternal age-related meiotic defects were reduced by GAS6 protein microinjection. Restoring GAS6 ameliorated the mitochondrial dysfunction induced by maternal aging. Ultimately, GAS6-rescued MII oocytes exhibited increased ATP levels, reduced ROS levels and elevated glutathione (GSH) levels, collectively indicating improved mitochondrial function in aged oocytes. Thus, the age-associated decrease in oocyte quality was prevented by restoring GAS6. Importantly, GAS6 protein microinjection in aged oocytes also rescued fertility. We conclude that GAS6 improves mitochondrial function to achieve sufficient cytoplasmic maturation and attenuates maternal age-related meiotic errors, thereby efficiently safeguarding oocyte quality and fertility.//////////////////Gas6 is a reciprocal regulator of mitophagy during mammalian oocyte maturation. Kim KH et al. (2019) Previously, we found that the silencing of growth arrest-specific gene 6 (Gas6) expression in oocytes impairs cytoplasmic maturation through mitochondrial overactivation with concurrent failure of pronuclear formation after fertilization. In this study, we report that Gas6 regulates mitophagy and safeguards mitochondrial activity by regulating mitophagy-related genes essential to the complete competency of oocytes. Based on RNA-Seq and RT-PCR analysis, in Gas6-silenced MII oocytes, expressions of mitophagy-related genes were decreased in Gas6-silenced MII oocytes, while mitochondrial proteins and Ptpn11, the downstream target of Gas6, was increased. Interestingly, GAS6 depletion induced remarkable MTOR activation. Gas6-depleted MII oocytes exhibited mitochondrial accumulation and aggregation caused by mitophagy inhibition. Gas6-depleted MII oocytes had a markedly lower mtDNA copy number. Rapamycin treatment rescued mitophagy, blocked the increase in MTOR and phosphorylated-MTOR, and increased the mitophagy-related gene expression in Gas6-depleted MII oocytes. After treatment with Mdivi-1, a mitochondrial division/mitophagy inhibitor, all oocytes matured and these MII oocytes showed mitochondrial accumulation but reduced Gas6 expression and failure of fertilization, showing phenomena very similar to the direct targeting of Gas6 by RNAi. Taken together, we conclude that the Gas6 signaling plays a crucial role in control of oocytes cytoplasmic maturation by modulating the dynamics and activity of oocyte mitochondria.//////////////////
Oocyte Cytoplasmic Gas6 and Heparan Sulfate (HS) are Required to Establish the Open Chromatin State in Nuclei During Remodeling and Reprogramming. Kim KH et al. (2018) Previously, we found that silencing of growth arrest-specific gene 6 (Gas6) in oocytes impaired cytoplasmic maturation, resulting in failure of sperm chromatin decondensation (SCD) and pronuclear (PN) formation after fertilization. Thus, we conducted this study to determine the effect of Gas6 RNAi on downstream genes and to elucidate the working mechanism of Gas6 on oocyte cytoplasmic maturation and SCD. Using RT-PCR, Western blot and immunofluorescence, the expression levels of various target genes and the localization of heparan sulfate (HS) were analyzed after Gas6 RNAi. The roles of Gas6 in HS biosynthesis, production of ATP and GSH, ROS generation and ΔΨm were also investigated. SCD and micrococcal nuclease (MNase) analyses were used to examine the effects of HS on the open chromatin state in sperm and somatic cell nuclei, respectively. Disruption of Gas6 expression led to the inhibition of HS biosynthesis through the reduction of several HS biosynthetic enzymes. The rescue experiment, HS treatment in vitro, significantly recovered SCD and PN formation, confirming that HS had the ability to induce sperm head remodeling during fertilization. Interestingly, excessive mitochondrial activation in Gas6-depleted MII oocytes caused ROS generation and glutathione (GSH) degradation via mitochondrial activation, such as elevated ΔΨm and ATP production. Indeed, HS-treated NIH3T3 cell nuclei showed an open chromatin state, as determined by diffuse DAPI staining and increased sensitivity to MNase. We propose that the addition of HS to sperm and/or oocyte maturation would improve the efficiency of in vitro fertilization and somatic cell nuclear transfer (SCNT) reprogramming.//////////////////
Gas6 Downregulation Impaired Cytoplasmic Maturation and Pronuclear Formation Independent to the MPF Activity. Kim KH et al. Previously, we found that the growth arrest-specific gene 6 (Gas6) is more highly expressed in germinal vesicle (GV) oocytes than in metaphase II (MII) oocytes using annealing control primer (ACP)-PCR technology. The current study was undertaken to investigate the role of Gas6 in oocyte maturation and fertilization using RNA interference (RNAi). Interestingly, despite the specific and marked decrease in Gas6 mRNA and protein expression in GVs after Gas6 RNAi, nuclear maturation including spindle structures and chromosome segregation was not affected. The only discernible effect induced by Gas6 RNAi was a change in maturation promoting factor (MPF) activity. After parthenogenetic activation, Gas6 RNAi-treated oocytes at the MII stage had not developed further and arrested at MII (90.0%). After stimulation with Sr(2+), Gas6-silenced MII oocytes had markedly reduced Ca(2+) oscillation and exhibited no exocytosis of cortical granules. In these oocytes, sperm penetration occurred during fertilization but not pronucleus (PN) formation. By roscovitine and colcemid treatment, we found that the Gas6 knockdown affected cytoplasmic maturation directly, independent to the changed MPF activity. These results strongly suggest that 1) the Gas6 signaling itself is important to the cytoplasmic maturation, but not nuclear maturation, and 2) the decreased Gas6 expression and decreased MPF activity separately or mutually influence sperm head decondensation and PN formation.
|