PAX6 (MSVA-706M)

PAX6 (paired box protein 6) is a 46 KDa transcription factor protein coded by the PAX6 gene on chromosome 11p13. PAX6 is a key molecule for neural development. It is involved in the regulation of brain patterning and the balance between cell proliferation and neural differentiation in an appropriate manner to developmental timing. PAX6 also plays a role in the development of the pancreas, pituitary gland, and the testes. The function of the PAX6 protein and the factors that regulate its expression are not well known. In the cortex of the brain, PAX6 controls the responsiveness to some secreted molecules such as sonic hedgehog and BMP. Because of its critical role in eye development, the protein has also been termed aniridia type II protein (AN2) or oculorhombin. Heterozygous mutants produce a wide spectrum of ocular defects such as aniridia in humans. In animal models, mutations cause various neurodevelopmental disorders.

Images describing the PAX6 staining pattern in normal tissues obtained by the antibody MSVA-706M are shown in our “Normal Tissue Gallery”.

These findings are largely consistent with the RNA data described in the Human Protein Atlas (Tissue expression PAX6)

All organs with documented PAX6 RNA expression (brain, pituitary gland, pancreas, stomach, duodenum, testis) showed IHC positivity for MSVA-706M which was restricted to specific cell types. 

Positive control = Pancreas: A strong PAX6 positivity should be seen in the cells of islets of Langerhans.

Negative control = Tonsil: PAX6 immunostaining should be absent in all cells.

Normal tissue gallery

The TCGA findings on PAX6 RNA expression in different tumor categories have been summarized in the Human Protein Atlas.

Cancer tissue gallery

No data available at the moment

IHC users have different preferences on how the stains should look like. Some prefer high staining intensity of the target stain and even accept some background. Others favor absolute specificity and lighter target stains. Factors that invariably lead to more intense staining include higher concentration of the antibody and visualization tools, longer incubation time, higher temperature during incubation, higher temperature and longer duration of the heat induced epitope retrieval (slide pretreatment). The impact of the pH during slide pretreatment has variable effects and depends on the antibody and the target protein.

All images and data shown here and in our image galleries are obtained by the manual protocol described below. Other protocols resulting in equivalent staining are described as well.

Manual protocol

Freshly cut sections should be used (less than 10 days between cutting and staining). Heat-induced antigen retrieval for 5 minutes in an autoclave at 121°C in pH 7,8 Target Retrieval Solution buffer. Apply MSVA-706M at a dilution of 1:150 at 37°C for 60 minutes. Visualization of bound antibody by the EnVision Kit (Dako, Agilent) according to the manufacturer’s directions.

• The function of PAX6 and its interaction partners are unknown.
• The role of PAX6 in cancer needs to be further investigated.
• The diagnostic utility of PAX6 immunohistochemistry is unclear.

There are two ways how the specificity of antibodies can be documented for immunohistochemistry on formalin fixed tissues. These are: 1. Comparison with a second independent method for target expression measurement across a large number of different tissue types (orthogonal strategy), and 2. Comparison with one or several independent antibodies for the same target and showing that all positive staining results are also seen with other antibodies for the same target (independent antibody strategy). 

Orthogonal validation: For the antibody MSVA-706M, specificity is suggested by the strong concordance of the immunostaining data with data from three independent RNA screening studies, including the Human Protein Atlas (HPA) RNA-seq tissue dataset, the FANTOM5 project, and the Genotype-Tissue Expression (GTEx) project, which are all summarized in the Human Protein Atlas (Tissue expression PAX6). Most organs with documented PAX6 RNA expression (brain, pituitary gland, pancreas, stomach, duodenum) showed IHC positivity for MSVA-706M. positivity. Additional PAX6 staining was detected by MSV-xxx in neuroendocrine cells in other gastrointestinal mucosa samples. Given the small number of PAX6 positive cells in these tissues, PAX6 RNA probably remained undetected in analyses involving large tissue samples. Despite of some PAX6 RNA expression in normal testis, MSVA-706M did not show any staining of testicular structures.

Comparison of antibodies: True expression of PAX6 in all cell types for which a nuclear PAX6 staining had been detected by MSVA-706M (brain, pituitary gland, pancreas, gastrointestinal mucosa, paranasal sinus mucosa) was confirmed by comparison with a commercially available independent second antibody (termed “validation antibody”). Similar as MSVA-706M, the validation antibody did not stain any testicular structures.

Normal tissue gallery