GO:0005790 smooth endoplasmic reticulum: Components, Assembly and Research Methods, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0005790 defines the smooth endoplasmic reticulum (smooth ER or SER), a ribosome-free subcompartment of the endoplasmic reticulum that receives proteins from the rough ER and is the principal site of lipid and phospholipid synthesis, glycoprotein processing, and detoxification of lipid-soluble drugs and metabolic byproducts.
• The smooth ER is functionally and physically coupled to mitochondria at membrane contact sites, where it regulates calcium and lipid exchange.
• In human oocytes, smooth ER aggregates (SERa) are a morphologically distinct phenotype that has been linked to neonatal birth defects in some meta-analyses, although ploidy and euploidy rates appear largely unaffected.
• SERa prevalence and reproductive outcomes may vary with IVF protocol, including progestin-primed versus GnRH antagonist regimens.
• Smooth ER function is essential for axonal transport and neuronal membrane homeostasis, as shown by early ultrastructural studies.
• Research on GO:0005790 spans oocyte biology, neurobiology, lipid metabolism, and drug detoxification, requiring integrated imaging, proteomic, and CRISPR-based approaches.
Description
The smooth endoplasmic reticulum (smooth ER or SER) is a ribosome-free subcompartment of the endoplasmic reticulum (ER) that carries out essential biosynthetic and detoxification functions in eukaryotic cells. Unlike the rough ER, the smooth ER lacks bound ribosomes and is the recipient of proteins synthesized in the rough ER; it also serves as the site of lipid and phospholipid synthesis, continues glycosylation of glycoproteins, and contains enzymes that detoxify lipid-soluble drugs and harmful metabolic products. The smooth ER is also physically and functionally coupled to mitochondria at membrane contact sites, where it participates in calcium and lipid exchange. Because of these roles, the smooth ER is central to cellular homeostasis and is increasingly recognized as a determinant of reproductive and neuronal physiology. In human oocytes, a morphologically distinct phenotype known as smooth ER aggregates (SERa) has been described, and its impact on reproductive outcomes has been examined in multiple clinical studies and meta-analyses. These studies highlight the clinical relevance of the smooth ER in assisted reproduction and the need for robust experimental models to dissect its function.
smooth endoplasmic reticulum At A Glance
| GO ID | GO:0005790 |
|---|---|
| GO term | smooth endoplasmic reticulum |
| Ontology | cellular_component |
| Synonym | SER, smooth ER |
| Major function | Lipid and phospholipid synthesis, glycoprotein processing, detoxification of lipid-soluble drugs and metabolic byproducts, and protein sorting from rough ER to Golgi, lysosomes, or back to rough ER |
| Ribosome status | No ribosomes attached |
| Relationship to rough ER | Receives proteins synthesized in the rough ER; returns resident proteins to rough ER |
| Relationship to Golgi and lysosomes | Passes export proteins to Golgi complex; passes lysosomal proteins to lysosomes after mannose phosphorylation |
| Detoxification role | Contains enzymes that detoxify lipid-soluble drugs and harmful metabolic products; phenobarbital increases smooth ER amount |
| Notable phenotype | Smooth ER aggregates (SERa) in human oocytes, studied in IVF and reproductive outcome research |
What Is GO:0005790?
GO:0005790 describes the smooth endoplasmic reticulum (smooth ER or SER), a subcompartment of the endoplasmic reticulum that has no ribosomes attached to it. According to the QuickGO definition, the smooth ER is the recipient of proteins synthesized in the rough ER; proteins destined for export are passed to the Golgi complex, resident proteins are returned to the rough ER, and lysosomal proteins are passed to lysosomes after phosphorylation of their mannose residues. Glycosylation of glycoproteins also continues in the smooth ER. The smooth ER is the site of synthesis of lipids, including phospholipids. Its membranes contain enzymes that catalyze a series of reactions to detoxify lipid-soluble drugs and harmful products of metabolism. Large quantities of certain compounds such as phenobarbital cause an increase in the amount of the smooth ER.
Why Is smooth endoplasmic reticulum Important in Cell Biology?
The smooth endoplasmic reticulum is essential for fundamental cellular processes including lipid biosynthesis, glycoprotein processing, and detoxification of xenobiotics and metabolic waste. Its dysfunction or morphological alteration has been linked to clinically relevant phenotypes such as smooth ER aggregates in oocytes, which have been associated with increased risk of neonatal birth defects in some meta-analyses. At the same time, other studies suggest that SERa may not affect embryo ploidy or euploidy rates, underscoring the need for further mechanistic research. The smooth ER also interacts with mitochondria at membrane contact sites, influencing calcium and lipid exchange, which is critical for neuronal function and axonal transport. Thus, GO:0005790 is important for understanding reproductive biology, neurobiology, lipid metabolism, and drug detoxification.
• Smooth ER aggregates in oocytes have been associated with increased risk of neonatal birth defects in a meta-analysis.
• A separate meta-analysis examined the effects of smooth ER aggregation on birth outcomes, highlighting clinical relevance.
• SERa presence may not affect embryo ploidy, suggesting that morphological assessment alone may not predict chromosomal status.
• Oocytes with SERa may not impact blastocyst euploidy rate, according to a 2022 study.
• IVF protocols, such as progestin-primed versus GnRH antagonist, may influence SERa prevalence.
• Management of oocytes affected by SERa remains debated, as discussed by Ferreux et al. (2019).
• The smooth ER interacts with mitochondria, affecting calcium and lipid exchange relevant to neuronal function.
• Smooth ER and axonal transport are linked, as shown by Rambourg et al. (1980).
• Smooth ER is the site of lipid and phospholipid synthesis, critical for membrane biogenesis.
• Detoxification enzymes in the smooth ER metabolize lipid-soluble drugs and harmful products, influencing drug response.
What Happens During smooth endoplasmic reticulum?
Protein sorting and transport from the rough ER
In simple terms: The smooth ER receives proteins made in the rough ER and decides where they go next.
According to the QuickGO definition, the smooth ER is the recipient of proteins synthesized in the rough ER. Proteins destined for export are passed to the Golgi complex, resident proteins are returned to the rough ER, and lysosomal proteins are passed to lysosomes after phosphorylation of their mannose residues. This sorting function is fundamental to the secretory pathway and ensures that proteins reach their correct destinations.
Glycoprotein processing
In simple terms: Sugar chains on proteins are further modified in the smooth ER.
The QuickGO definition states that glycosylation of glycoproteins continues in the smooth ER. This processing step is essential for protein folding, stability, and function, and it links the smooth ER to the broader glycosylation machinery of the cell.
Lipid and phospholipid synthesis
In simple terms: The smooth ER is a factory for making fats and membrane lipids.
The smooth ER is the site of synthesis of lipids, including phospholipids, as stated in the QuickGO definition. These lipids are critical for membrane biogenesis, energy storage, and signaling, and their production is a core function of the smooth ER.
Detoxification of drugs and metabolic products
In simple terms: The smooth ER contains enzymes that break down drugs and harmful chemicals.
The membranes of the smooth ER contain enzymes that catalyze a series of reactions to detoxify both lipid-soluble drugs and harmful products of metabolism. Large quantities of certain compounds such as phenobarbital cause an increase in the amount of the smooth ER, reflecting an adaptive response to xenobiotic exposure.
Interaction with mitochondria
In simple terms: The smooth ER communicates with mitochondria to exchange calcium and lipids.
The smooth ER interacts with mitochondria at membrane contact sites, as reviewed by Goetz et al. (2006). This interaction is important for calcium signaling and lipid transfer, and it influences neuronal function and axonal transport.
Key Genes Involved in GO:0005790 smooth endoplasmic reticulum
The following genes and proteins are functionally associated with the smooth endoplasmic reticulum (GO:0005790) based on the QuickGO definition and the verified literature, including roles in lipid synthesis, detoxification, protein sorting, and oocyte biology.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CYP2B6 | Cytochrome P450 enzyme involved in drug metabolism and detoxification in the smooth ER | Phenobarbital-induced smooth ER proliferation and drug metabolism studies |
| CYP3A4 | Major drug-metabolizing enzyme localized to the smooth ER | Detoxification of lipid-soluble drugs and xenobiotics |
| CYP2C9 | Cytochrome P450 enzyme in the smooth ER | Metabolism of drugs and endogenous compounds |
| UGT1A1 | UDP-glucuronosyltransferase involved in phase II detoxification in the ER | Glycosylation and detoxification pathways |
| SAR1A | Small GTPase involved in ER-to-Golgi transport | Protein sorting from smooth ER to Golgi |
| SEC23A | COPII coat component mediating ER export | Vesicle formation at ER exit sites |
| SEC24A | COPII cargo receptor for ER export | Sorting of proteins from ER to Golgi |
| LMAN1 | Mannose-specific lectin involved in ER-to-Golgi transport of lysosomal proteins | Lysosomal protein sorting after mannose phosphorylation |
| M6PR | Mannose-6-phosphate receptor that directs lysosomal proteins | Lysosomal protein targeting from the smooth ER |
| ATP2A2 | SERCA2 calcium pump in the ER membrane | Calcium homeostasis and ER-mitochondria contact |
| VAPB | Vesicle-associated membrane protein associated with ER-mitochondria contacts | Membrane contact sites and lipid exchange |
| MFN2 | Mitofusin 2 involved in ER-mitochondria tethering | Interaction of smooth ER and mitochondria |
| DGAT1 | Diacylglycerol O-acyltransferase 1 in lipid droplet formation at the ER | Lipid synthesis and storage |
| DGAT2 | Diacylglycerol O-acyltransferase 2 involved in triglyceride synthesis | Lipid metabolism in the smooth ER |
| PLIN2 | Perilipin 2 associated with lipid droplets originating from the ER | Lipid storage and smooth ER function |
| KIF5B | Kinesin motor protein involved in axonal transport | Smooth ER and axonal transport |
| DYNC1H1 | Dynein heavy chain involved in retrograde axonal transport | Smooth ER dynamics in neurons |
| BSCL2 | Seipin involved in lipid droplet formation at the ER | Lipid metabolism and smooth ER |
How Is smooth endoplasmic reticulum Regulated?
The smooth endoplasmic reticulum is regulated at multiple levels. According to the QuickGO definition, large quantities of certain compounds such as phenobarbital cause an increase in the amount of the smooth ER, indicating that xenobiotic exposure can induce smooth ER proliferation. This adaptive response is linked to the induction of detoxification enzymes in the smooth ER membrane. Additionally, the interaction between the smooth ER and mitochondria is regulated by tethering proteins such as VAPB and MFN2, which influence calcium and lipid exchange. In oocytes, the presence of smooth ER aggregates (SERa) may be influenced by IVF protocols, as suggested by a comparison of progestin-primed and GnRH antagonist regimens. However, the precise molecular regulation of smooth ER biogenesis and dynamics remains an active area of research.
smooth endoplasmic reticulum and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CYP2B6 | Drug metabolism and detoxification in the smooth ER | Knockout or overexpression in hepatocyte-like cells |
| CYP3A4 | Xenobiotic metabolism and drug-induced smooth ER proliferation | CRISPR knockout in HepG2 cells |
| VAPB | ER-mitochondria contact and neuronal function | Point mutation knock-in in neuronal cells |
| MFN2 | Mitochondrial dynamics and ER-mitochondria tethering | Knockout in fibroblasts or neurons |
| KIF5B | Axonal transport and smooth ER dynamics | Knockout in primary neurons |
Smooth ER aggregates and reproductive outcomes
Smooth ER aggregates (SERa) in human oocytes have been studied for their association with neonatal birth defects. A meta-analysis by Long et al. (2024) found that SERa in oocytes were associated with increased risk of neonatal birth defects. Another meta-analysis by Zhang et al. (2021) examined the effects of smooth ER aggregation on birth outcomes. However, other studies have reported that SERa presence does not affect embryo ploidy or blastocyst euploidy rate. The management of oocytes affected by SERa remains debated, as discussed by Ferreux et al. (2019). IVF protocol may influence SERa prevalence, with differences observed between progestin-primed and GnRH antagonist protocols.
Smooth ER and neurodegenerative processes
The smooth ER is involved in axonal transport and interacts with mitochondria, processes that are critical for neuronal function. Rambourg et al. (1980) described the relationship between the smooth endoplasmic reticulum and axonal transport, highlighting its role in neuronal membrane dynamics. Goetz et al. (2006) reviewed the interaction of the smooth ER and mitochondria, which is relevant to calcium homeostasis and lipid metabolism in neurons. Dysregulation of these interactions may contribute to neurodegenerative conditions, although direct disease associations require further investigation.
Smooth ER and drug metabolism
The smooth ER contains enzymes that detoxify lipid-soluble drugs and harmful products of metabolism. This function is critical for drug clearance and protection against xenobiotic toxicity. Induction of smooth ER proliferation by compounds such as phenobarbital can alter drug metabolism and potentially influence drug efficacy and toxicity. Understanding smooth ER function is therefore relevant to pharmacology and toxicology.
From smooth endoplasmic reticulum-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of CYP2B6 affect smooth ER detoxification capacity? | CRISPR knockout in HepG2 or primary hepatocytes |
| Does a point mutation in VAPB alter ER-mitochondria contact? | Point mutation knock-in in neuronal cell lines |
| Can tagged MFN2 be used to visualize ER-mitochondria tethering? | Knock-in of fluorescent tag at endogenous locus |
| Does overexpression of DGAT1 increase lipid droplet formation from the smooth ER? | Overexpression in HeLa or COS-7 cells |
| Does knockout of KIF5B disrupt smooth ER axonal transport? | Knockout in primary hippocampal neurons |
| Does CYP3A4 induction by phenobarbital increase smooth ER amount? | Overexpression or reporter knock-in in hepatocytes |
How to Study the smooth endoplasmic reticulum Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Transmission electron microscopy | Ultrastructure of smooth ER and aggregates | Oocyte and neuronal morphology |
| Immunofluorescence | Localization of smooth ER markers and contact sites | ER-mitochondria interaction studies |
| Live-cell imaging | Dynamic changes in smooth ER structure | Real-time ER remodeling |
| Proteomics | Protein composition of smooth ER fractions | Identification of detoxification and lipid enzymes |
| Lipidomics | Lipid species synthesized by smooth ER | Phospholipid and neutral lipid profiling |
| RNA-seq | Transcriptional changes in smooth ER-related genes | Drug treatment or genetic perturbation |
| CRISPR knockout screening | Genes required for smooth ER function | Functional genomics |
| Meta-analysis of clinical data | Association of SERa with birth outcomes | Reproductive epidemiology |
Electron microscopy and imaging
Transmission electron microscopy (TEM) is a classic method to visualize the smooth ER and its aggregates in oocytes, as described in studies of SERa. Immunofluorescence with markers such as calreticulin or SERCA2 can reveal smooth ER distribution and its contact with mitochondria. Live-cell imaging using fluorescently tagged ER proteins enables dynamic studies of smooth ER remodeling.
Proteomics and lipidomics
Mass spectrometry-based proteomics can identify proteins enriched in smooth ER fractions, including detoxification enzymes and lipid synthesis enzymes. Lipidomics can quantify phospholipid and neutral lipid species produced by the smooth ER, providing functional readouts.
Transcriptomics and CRISPR screening
RNA-seq can measure expression changes in smooth ER-related genes upon drug treatment or genetic perturbation. CRISPR knockout screens can identify genes required for smooth ER function, such as those involved in lipid synthesis or detoxification.
Clinical and reproductive studies
Meta-analyses and cohort studies have assessed the impact of smooth ER aggregates on birth outcomes and embryo ploidy. These studies use IVF databases and morphological scoring of oocytes, sometimes combined with genetic testing for ploidy.
How CRISPR Can Be Used to Study GO:0005790 smooth endoplasmic reticulum
Knockout
CRISPR knockout of genes such as CYP2B6, CYP3A4, or DGAT1 can be used to test their roles in smooth ER detoxification and lipid synthesis. Knockout of KIF5B or DYNC1H1 can reveal effects on smooth ER axonal transport. These models help establish causality between specific genes and smooth ER functions.
Point Mutation
Point mutation knock-in of disease-associated variants in genes like VAPB or MFN2 can model altered ER-mitochondria contact and calcium exchange. Such models are valuable for studying subtle functional changes without complete loss of protein.
Knock-in
Tagged knock-in of fluorescent proteins (e.g., GFP or mCherry) into endogenous loci such as VAPB or MFN2 allows visualization of smooth ER and its contact sites in live cells. This approach preserves endogenous regulation and enables dynamic imaging.
Overexpression
Overexpression of lipid synthesis enzymes like DGAT1 or DGAT2 can increase smooth ER-derived lipid droplet formation, providing a gain-of-function model. Overexpression of detoxification enzymes can enhance drug metabolism and protect against xenobiotic toxicity.
How EDITGENE Supports smooth endoplasmic reticulum Research
Researchers studying smooth endoplasmic reticulum-related genes often need to determine whether a candidate gene is causally involved in lipid synthesis, detoxification, protein sorting, or oocyte biology. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models for such functional studies.
Contact EDITGENE today to design your custom CRISPR model for smooth endoplasmic reticulum research.
Frequently Asked Questions About smooth endoplasmic reticulum
What is the smooth endoplasmic reticulum (GO:0005790)?
The smooth endoplasmic reticulum (smooth ER or SER) is a ribosome-free subcompartment of the endoplasmic reticulum that receives proteins from the rough ER, synthesizes lipids and phospholipids, continues glycoprotein glycosylation, and detoxifies lipid-soluble drugs and metabolic products.
What genes are involved in smooth endoplasmic reticulum function?
Genes involved include CYP2B6, CYP3A4, CYP2C9, UGT1A1, SAR1A, SEC23A, SEC24A, LMAN1, M6PR, ATP2A2, VAPB, MFN2, DGAT1, DGAT2, PLIN2, KIF5B, DYNC1H1, and BSCL2, based on their roles in lipid synthesis, detoxification, protein sorting, and ER-mitochondria contact.
What are smooth ER aggregates in oocytes?
Smooth ER aggregates (SERa) are a morphological phenotype observed in human oocytes, characterized by clusters of smooth endoplasmic reticulum, and have been studied for their association with reproductive outcomes.
Do smooth ER aggregates affect birth outcomes?
A meta-analysis found that SERa in oocytes were associated with increased risk of neonatal birth defects, while another meta-analysis examined effects on birth outcomes. However, other studies suggest no impact on embryo ploidy or euploidy rate.
How is the smooth endoplasmic reticulum studied?
Common methods include transmission electron microscopy, immunofluorescence, live-cell imaging, proteomics, lipidomics, RNA-seq, and CRISPR screening.
What is the relationship between smooth ER and mitochondria?
The smooth ER interacts with mitochondria at membrane contact sites, regulating calcium and lipid exchange, which is important for neuronal function and axonal transport.
Can CRISPR be used to study smooth ER genes?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models can be used to study genes involved in smooth ER function, such as CYP2B6, VAPB, and MFN2.
What is the role of smooth ER in drug detoxification?
The smooth ER contains enzymes that detoxify lipid-soluble drugs and harmful metabolic products, and compounds like phenobarbital can increase the amount of smooth ER.
Does IVF protocol affect smooth ER aggregates?
A comparison of progestin-primed and GnRH antagonist IVF protocols suggested that protocol may influence SERa prevalence.
What is the clinical significance of smooth ER aggregates?
The management of oocytes affected by SERa remains debated, and further research is needed to understand their impact on reproductive outcomes.
Conclusion
The smooth endoplasmic reticulum (GO:0005790) is a multifunctional cellular component essential for lipid synthesis, protein sorting, glycoprotein processing, and detoxification. Its interaction with mitochondria and its role in oocyte biology underscore its importance in reproductive and neuronal physiology. While clinical studies have yielded mixed findings on the impact of smooth ER aggregates on birth outcomes and ploidy, the need for mechanistic research using advanced CRISPR models is clear. EDITGENE provides comprehensive services to support such research, from knockout and knock-in models to library screening and bioinformatics.
References
- 1. Long R et al.. 2024. Smooth endoplasmic reticulum aggregates in oocytes associated with increased risk of neonatal birth defects: A meta-analysis.. Acta Obstet Gynecol Scand 103(11):2163-2170 PMID: 38961609
- 2. Wu HM et al.. 2025. Smooth endoplasmic reticulum aggregates in oocytes: a comparison of progestin-primed and GnRH antagonist IVF protocols.. J Ovarian Res 18(1):181 PMID: 40796874
- 3. Zhang H et al.. 2021. Meta-analysis of the effects of smooth endoplasmic reticulum aggregation on birth outcome.. BMC Pregnancy Childbirth 21(1):374 PMID: 33980189
- 4. Rambourg A et al.. 1980. Smooth endoplasmic reticulum and axonal transport.. J Neurochem 35(1):16-25 PMID: 6161215
- 5. Mizobe Y et al.. 2023. Smooth endoplasmic reticulum cluster presence does not affect embryo ploidy.. Arch Gynecol Obstet 307(5):1607-1612 PMID: 36799921
- 6. Ferreux L et al.. 2019. Is it time to reconsider how to manage oocytes affected by smooth endoplasmic reticulum aggregates?. Hum Reprod 34(4):591-600 PMID: 30805638
- 7. Goetz JG et al.. 2006. Interaction of the smooth endoplasmic reticulum and mitochondria.. Biochem Soc Trans 34(Pt 3):370-3 PMID: 16709164
- 8. Xu J et al.. 2022. Oocytes With Smooth Endoplasmic Reticulum Aggregates May Not Impact Blastocyst Euploidy Rate.. Front Endocrinol (Lausanne) 13:851370 PMID: 36093069
