Overview of Cell and Organelle Markers

Cellular elements are organized into membrane-bound and non-membrane bound structures called organelles as shown in the figure below. Every organelle has a distinct cellular structure with a specified biological function. Each function is determined by the enzymes or proteins the organelle contains. Each organelle performs explicit functions such as providing the shape and support for the cell, energy production, processing, transportation/storage of biomolecules, and DNA maintenance—to name a few.

Explore Organelle Marker Antibodies  Explore Cell Marker Antibodies

Cell and organelle marker antibodies are utilized mostly for the determination of the localization of novel proteins within complex structures, and aid in discerning the proximity of two proteins within the same subcellular assembly. They assist in analyzing alterations in protein localization and transport to provide insights on protein function and disease mechanisms. Cell and organelle marker antibodies also help monitor and provide information on the biochemical purity of organelle fractionation.

The following sections briefly summarize the characteristics and function of the major cellular structures—the cell membrane, nucleus, and cytoplasm. Each section provides data examples using well-characterized marker antibodies.

The cell membrane is a selectively permeable bilayer of phospholipid molecules that separates the intracellular components from the extracellular environment. Proteins specific to the membrane provide structural support, aid in cell signaling, anchor the cytoskeleton, and control the passage of materials in and out of the cells.

Proteins specific to the plasma membrane and cell junctions, such as ZO-1, ZO-3, and E-cadherin, serve as markers that help study and clarify the role of novel proteins which may act as receptors, transport channels, and/or enzymes. The antibodies represented in the figure below have been verified for target specificity using independent antibody validation.

The nucleus is a bilipid membrane-bound organelle encompassing the genetic material of the cell. Components of the nucleus include:

• Nuclear lamina—the structural scaffolding network
• Nucleolus—responsible for RNA transcription and ribosomal assembly
• Chromatin—consists of DNA, histones, and other associated proteins
• Nuclear pore proteins—facilitate the shuttle of molecules to and from the nucleus
• Centromere—part of a chromosome that aids in cellular division
• Proteins—nuclear proteins facilitate gene expression/silencing, DNA replication, repair, and nuclear organization

Antibodies targeting distinct proteins in the nucleus, like histones H3 and H4, LSD1, fibrillarin, lamin B1, and CENPA, serve as marker proteins that facilitate the study of morphology and dynamics of the nucleus and its constituents. Histone and histone-associated proteins involved in DNA compaction, chromatin regulation, and gene expression—such as H3, H4, and LSD1—function as markers for the chromatin and nucleus, while the histone H3 variant CENPA specifically serves as a marker for centromeres. Lamins B1, A, and C function as structural support to the nucleus and are involved in the regulation of transcription. All of these are good marker choices for studying the nuclear membrane. Fibrillarin, which is involved in the regulation of RNA transcription and processing, is best utilized as a nucleoli marker.

Each of the antibodies used in the above immunofluorescence experiment were validated for use in that application. Also, antibody specificity was demonstrated by siRNA-mediated knockdown of the target proteins. The western blots below are the data from that verification study.
 

The cytoplasm consists of organelles suspended in the cytosol where most of the cellular activities occur. The organelles of the cytoplasm can be membrane- or non-membrane-bound and have a definite structure and specific cellular function. The organelles of the cytoplasm and their function are in the table below, along with their target marker antibodies.

Cytoplasmic organelle antibody targets:

Organelle marker antibodies targeting diverse cytoplasmic constituents help clarify the organization of subcellular structures, function, and the role of novel proteins in different cellular processes. Below are some examples of antibody targets in various organelles and the antibodies that are specific and verified to detect them.

Catalase is a key peroxisomal marker protein and functions to protect the cells from the toxic effects of hydrogen peroxide. Golgi protein, GM130, is involved in multiple tasks including ER-Golgi transport, structural maintenance, and stacking of Golgi cisternae. The specificity of the catalase and GM130 antibodies was verified in a biological setting utilizing the cell’s natural machinery to effectively knock down the target gene expression as shown in the figure below.

Hexokinase 1, an enzyme kinase involved in the first step of the glycolysis, and LIMP2, a lysosomal receptor, act as markers for the outer mitochondrial membrane and lysosomes, respectively. The specificity of the hexokinase 1 (HK1) and LIMP2 antibodies was verified by co-localization experiments using organelle-specific stains. The data is shown below.
 

RPS6 is a part of the 40S subunit of the ribosome. It is a major substrate of protein kinases in the ribosome and is used as one of the markers for ribosomes. Cytochrome C is a key subunit involved in the mitochondrial electron transport chain and acts as a marker for the inner mitochondrial membrane.

Specificity of both targets is represented in the figures below.