MPP10 Antibody

What is MPP10 and what is its primary cellular localization?

MPP10 is a nucleolar protein that serves as a component of the human U3 small nucleolar ribonucleoprotein (snoRNP). By cell fractionation studies, almost all MPP10 protein is found in isolated nucleoli . Immunofluorescence studies show that MPP10 colocalizes with nucleolar fibrillarin and other known nucleolar proteins in interphase cells . Notably, when nucleoli are separated into fibrillar and granular domains by treatment with actinomycin D, MPP10 is primarily found in the fibrillar caps, which contain proteins involved in rRNA processing . Unlike fibrillarin, MPP10 is not detected in coiled bodies stained for either fibrillarin or p80 coilin, making its localization pattern unique among nucleolar proteins .

What is the molecular weight of MPP10 and how does phosphorylation affect it?

The non-phosphorylated form of MPP10 has a molecular weight of approximately 79 kDa, while the phosphorylated form runs at approximately 120 kDa on SDS-PAGE . This significant shift indicates extensive phosphorylation during M phase of the cell cycle. When analyzing MPP10 by Western blot, researchers should be aware of this variation and may observe both forms depending on the cell cycle phase of their samples .

What are the recommended protocols for immunoprecipitation of MPP10 with its RNA binding partners?

For immunoprecipitation of MPP10 with its RNA binding partners:

• Prepare cell sonicates in an appropriate buffer (150-400 mM salt concentration).

• Add anti-MPP10 antibodies to the sonicates.

• Isolate immune complexes using protein A/G beads.

• Extract bound RNAs using phenol-chloroform extraction.

• Label RNAs at their 3′ ends with 32P-labeled pCp for visualization.

• Alternatively, separate RNAs, transfer to a membrane, and probe with specific oligonucleotides.

In the published studies, MPP10 immunoprecipitation specifically pulls down U3 snoRNA but not other box C/D snoRNAs . The association between MPP10 and U3 snoRNA remains stable even in high salt conditions (400 mM), indicating a strong and specific interaction . For validation, perform parallel immunoprecipitations with anti-fibrillarin (which precipitates multiple snoRNAs) and anti-TMG cap antibodies (which precipitate several small nuclear RNAs) .

How can researchers distinguish between phosphorylated and non-phosphorylated forms of MPP10?

To distinguish between phosphorylated and non-phosphorylated forms of MPP10:

• Use SDS-PAGE with adequate resolution in the 70-120 kDa range.

• Run samples from both interphase and M-phase cells side by side.

• Perform Western blot using anti-MPP10 antibodies.

• The non-phosphorylated form appears at approximately 79 kDa, while the phosphorylated form appears at approximately 120 kDa .

• For confirmation, treat a portion of your lysate with lambda phosphatase before SDS-PAGE to collapse the 120 kDa band to 79 kDa.

• Use phospho-specific antibodies if available to specifically detect the phosphorylated form.

This approach allows researchers to monitor MPP10 phosphorylation status throughout the cell cycle or in response to specific treatments.

How does the Mpp10 complex contribute to ribosome biogenesis at the molecular level?

The Mpp10 complex plays a critical role in ribosome biogenesis by:

• Associating with Imp3 and Imp4 to form a complex essential for the normal production of 18S rRNA .

• Serving as a platform for the simultaneous interaction with multiple proteins in the 90S pre-ribosome .

• Binding to the ribosome biogenesis factor Utp3/Sas10 through two conserved motifs in its N-terminal region .

• Interacting with the ribosomal protein S5/uS7 using a short stretch within an acidic loop region .

Structurally, the interaction between Imp4 and Mpp10 involves a short helical element of Mpp10, as revealed by crystal structure analysis to a resolution of 1.88 Å . Functionally, depletion of the Mpp10 homologue in yeast causes an 18S rRNA processing defect similar to that obtained upon depletion of other U3 snoRNP components . Furthermore, mutations in yeast MPP10 suggest that it may be directly involved in cleavage at the pre-rRNA A1 and A2 sites . These findings indicate that Mpp10 serves as an essential scaffold that coordinates multiple protein-protein interactions required for proper ribosome assembly.

What experimental approaches are most effective for studying the dynamics of MPP10 during the cell cycle?

To study the dynamics of MPP10 during the cell cycle:

• Immunofluorescence microscopy:

  • Synchronize cells at different cell cycle stages (using thymidine block, nocodazole, etc.)

  • Fix and immunostain with anti-MPP10 antibodies

  • Co-stain with antibodies against fibrillarin or other nucleolar markers

  • Use confocal microscopy for high-resolution imaging

• Live-cell imaging:

  • Generate stable cell lines expressing MPP10-GFP fusion protein

  • Perform time-lapse confocal microscopy to track localization changes

  • Co-express RFP-tagged markers for nucleolar structures

• Biochemical analysis:

  • Synchronize cells and collect samples at different cycle stages

  • Analyze phosphorylation status by Western blot (79 kDa vs. 120 kDa forms)

  • Perform immunoprecipitation to assess protein-protein interactions at different stages

Based on published data, you should observe MPP10 strongly localized to nucleoli during interphase, relocating to chromosome surfaces during early to middle M phase, and found in nucleolus-derived bodies and prenucleolar bodies during telophase . Importantly, MPP10 arrives at the newly forming nucleolus later than fibrillarin during telophase, suggesting distinct roles in nucleolar reassembly .

What are the technical considerations when using MPP10 antibodies for immunofluorescence studies?

When using MPP10 antibodies for immunofluorescence:

• Antibody selection:

  • Choose antibodies validated for immunofluorescence

  • Be aware that antibodies recognizing human MPP10 may not work in other species for this application

• Fixation method:

  • Paraformaldehyde (4%) is typically suitable for preserving nucleolar structures

  • For detailed nucleolar substructure studies, compare multiple fixation methods

• Permeabilization:

  • Use optimal detergent concentration to maintain nucleolar integrity while allowing antibody access

• Controls and co-staining:

  • Include fibrillarin co-staining to identify nucleolar regions

  • For studies of nucleolar segregation, treat cells with actinomycin D to separate fibrillar and granular components

• Expected patterns:

  • In interphase: strong nucleolar staining

  • In M phase: chromosome surface localization

  • In telophase: localization to nucleolus-derived bodies and prenucleolar bodies

  • Not detected in coiled bodies (unlike fibrillarin)

• Image acquisition:

  • Use confocal microscopy for precise co-localization studies

  • Collect Z-stacks for complete nucleolar visualization

How can researchers validate the specificity of MPP10 antibodies in their experimental system?

To validate MPP10 antibody specificity:

• Western blot validation:

  • Observe bands at expected molecular weights (~79 kDa unphosphorylated, ~120 kDa phosphorylated)

  • Test lysates from multiple species if cross-reactivity is desired

  • Include positive controls from tissues with high nucleolar activity

• Knockdown/knockout controls:

  • Perform siRNA knockdown or CRISPR knockout of MPP10

  • Confirm reduction/elimination of signal in Western blot and immunofluorescence

• Immunoprecipitation specificity:

  • Verify that MPP10 antibodies specifically pull down U3 snoRNA but not other snoRNAs

  • Test salt stability of interactions (should remain stable at 400 mM salt)

• Cross-species reactivity:

  • Test the antibody against samples from various species

  • Be aware that immunoblot cross-reactivity doesn't guarantee functionality in other applications

• Peptide competition:

  • Pre-incubate antibody with the immunizing peptide (e.g., amino acids 126-171 of human MPP10 for A28041)

  • Confirm signal reduction in pre-absorbed samples

How might MPP10 dysfunction contribute to nucleolar stress and disease states?

While the search results don't directly address MPP10 in disease, its essential role in ribosome biogenesis suggests potential pathological implications:

• Ribosomopathies:

  • MPP10 dysfunction could potentially contribute to disorders characterized by defective ribosome biogenesis

  • Investigate MPP10 expression and function in relevant disease models

• Cancer research applications:

  • Many cancers show nucleolar abnormalities and altered ribosome biogenesis

  • Examine MPP10 expression, localization, and phosphorylation in cancer cell lines

  • Assess correlation between MPP10 status and cancer cell proliferation

• Experimental approaches:

  • Compare MPP10 expression levels across normal and disease tissues

  • Analyze MPP10 phosphorylation status in disease states

  • Examine co-localization with other nucleolar stress markers

  • Evaluate effects of MPP10 knockdown on pre-rRNA processing and cell viability

What are the most reliable methods for quantifying MPP10 expression levels in different experimental conditions?

For reliable quantification of MPP10 expression:

• Western blot:

  • Use purified MPP10 protein standards for quantitative comparison

  • Include housekeeping protein controls (β-actin, GAPDH)

  • Be aware of the different molecular weights for phosphorylated and non-phosphorylated forms

  • Use digital image analysis software for densitometry

• qRT-PCR:

  • Design primers specific to MPP10 mRNA

  • Validate primer efficiency using standard curves

  • Use multiple reference genes for normalization

  • Calculate relative expression using the 2^-ΔΔCt method

• Proteomics approaches:

  • Use SILAC or TMT labeling for comparative proteomics

  • Include MPP10-specific peptides in targeted mass spectrometry assays

  • Distinguish between phosphorylated and non-phosphorylated forms

• Considerations:

  • Account for cell cycle phase in your experimental design (due to phosphorylation changes)

  • Include appropriate positive controls (tissues with high nucleolar activity)

  • For nuclear vs. cytoplasmic distribution, perform cellular fractionation before analysis

What are potential approaches to study the MPP10 interactome beyond its known binding partners?

To expand our understanding of the MPP10 interactome:

• Proximity labeling approaches:

  • Generate BioID or TurboID fusions with MPP10

  • Identify proteins in close proximity to MPP10 in living cells

  • Compare interactomes across different cell cycle stages

• Crosslinking mass spectrometry:

  • Use protein crosslinkers followed by immunoprecipitation

  • Identify crosslinked peptides by mass spectrometry

  • Map interaction interfaces at amino acid resolution

• Cryo-EM structural analysis:

  • Purify native MPP10-containing complexes

  • Determine structures by cryo-electron microscopy

  • Place in context of the 90S pre-ribosome structure

• In vitro reconstitution:

  • Express and purify recombinant MPP10 and its binding partners

  • Reconstitute complexes in vitro

  • Perform functional assays for rRNA processing

• Yeast genetic screens:

  • Use yeast MPP10 as bait in two-hybrid or genetic suppressor screens

  • Validate mammalian homologs of identified interactors