CTF19 Antibody

What is CTF19 and why is it important in chromosome biology?

CTF19 is a conserved kinetochore protein that forms part of the Ctf19 complex (Ctf19c), also known as the CCAN (Constitutive Centromere-Associated Network) in mammals. It plays fundamental roles in kinetochore assembly and chromosome segregation. Specifically, the Ctf19 complex functions as a critical suppressor of centromere-proximal crossover recombination during meiosis . This suppression is essential for proper chromosome segregation, as centromere-proximal crossovers are associated with an increased risk of aneuploidy, including conditions like Trisomy 21 in humans . The importance of CTF19 was initially suspected due to high-dosage lethality of Cbf3c in a ctf19 mutant background, suggesting its kinetochore function . CTF19 works within a protein complex that likely includes Mcm21 and Okp1, forming part of the structural foundation of the kinetochore .

Which commercial antibodies against CTF19 are most widely validated?

Based on the available research literature, several antibodies have been successfully used for CTF19 detection. The most commonly cited include anti-Flag antibodies when working with tagged versions of CTF19. Specifically, α-Flag M2 (1:1000 dilution; Sigma-Aldrich) and α-Flag (1:1000 dilution; Abcam) have been effectively used in western blotting applications involving Flag-tagged CTF19 constructs . For hemagglutinin (HA)-tagged versions of CTF19 or its interacting partners, α-HA antibodies (1:500 dilution from Biolegend or 1:1000 dilution from Sigma-Aldrich) have proven effective . Research teams frequently use epitope-tagged versions of CTF19 (typically with FLAG or HA tags) rather than antibodies targeting the native protein, possibly due to limitations in specific antibody availability for the unmodified protein.

How does CTF19 interact with other kinetochore components?

CTF19 serves as a core component of the COMA complex (comprising Ctf19, Okp1, Mcm21, and Ame1), which is a central hub of the inner kinetochore. Through co-immunoprecipitation studies, researchers have demonstrated that CTF19 directly interacts with Mcm21, as evidenced by the successful co-immunoprecipitation of Ctf19-33Flag-dCas9 and Mcm21-3HA . When targeted to an ectopic location, Ctf19 co-recruits Mcm21, suggesting they form a functional subcomplex .

What are the optimal conditions for using CTF19 antibodies in Western blotting?

For optimal Western blotting using CTF19 antibodies (typically against tagged versions), researchers should follow these methodological considerations:

• Sample preparation: Harvest cells from your experimental culture (typically 200ml of culture for meiotic studies). For TCA precipitation, centrifuge samples at 2700 rpm for 3 minutes, precipitate cell pellets in 5ml of 5% TCA, and wash with 800μl acetone. After overnight drying, resuspend in 200μl protein breakage buffer (4ml TE buffer with 20μl 1M DTT) .

• Cell lysis: Add 0.3g glass beads to the resuspended sample and lyse cells using a FastPrep-24 or equivalent mechanical disruption system .

• SDS-PAGE setup: Add 100μl of 3× SDS loading buffer to lysed samples and proceed with standard SDS-PAGE methodology .

• Antibody dilutions and incubation: For detecting FLAG-tagged CTF19, use α-Flag M2 antibody at 1:1000 dilution (Sigma-Aldrich) or α-Flag at 1:1000 dilution (Abcam). Include appropriate loading controls such as α-Pgk1 (1:1000; Thermo Fischer) .

• Detection system: Use an appropriate secondary antibody and detection system compatible with your primary antibody source species.

Standard Western blotting procedures apply, with particular attention to optimizing transfer conditions for the expected molecular weight of CTF19 fusion proteins (approximately 50-70 kDa for most tagged constructs).

How can CTF19 antibodies be used effectively in chromatin immunoprecipitation (ChIP)?

For effective chromatin immunoprecipitation of CTF19 or CTF19-associated proteins, follow this optimized protocol based on published research:

• Cross-linking: Harvest cells from a 100ml sporulation culture (ideally 4.5 hours post-inoculation for meiotic studies). Cross-link with 1% formaldehyde for optimal protein-DNA fixation .

• Chromatin preparation: After cross-linking, process samples through standard ChIP protocols including cell lysis, chromatin shearing (aim for fragments of 200-500bp), and preparation of input samples.

• Immunoprecipitation: For FLAG-tagged CTF19, use α-Flag M2 antibody (Sigma-Aldrich). For HA-tagged versions, use α-HA antibody (Biolegend or Sigma-Aldrich) at appropriate dilutions (typically 1:200-1:500 for ChIP applications) .

• Analysis: Perform qPCR with primers specific to centromeric regions and surrounding pericentromeric areas. Include primers for chromosome arms as controls to demonstrate enrichment specificity .

In studies assessing CTF19 recruitment to ectopic sites, researchers have successfully used ChIP-qPCR to confirm targeting of Ctf19-3xFlag-dCas9 to non-centromeric loci and to assess co-recruitment of interacting partners like Mcm21-3HA .

What controls should be included when performing co-immunoprecipitation with CTF19 antibodies?

When performing co-immunoprecipitation (Co-IP) experiments to study CTF19 interactions, the following controls and considerations are essential:

• Input controls: Always include input samples (pre-immunoprecipitation) to verify the presence of proteins of interest in your starting material .

• Negative controls: Include:

  • Non-specific antibody control (same isotype as your experimental antibody)

  • Untagged strain control when using epitope-tagged proteins

  • Non-interacting protein control (e.g., Mtw1-GFP has been used as a non-Ctf19C kinetochore factor that demonstrates specificity)

• Positive controls: Include known interacting partners. For example, when immunoprecipitating Ctf19-33Flag-dCas9, detection of Mcm21-3HA serves as a positive control for a known interaction .

• Loading controls: Western blot analysis should include loading controls such as Pgk1 and Histone H3 .

• Sample timing: For meiotic studies, samples are typically taken during prophase (approximately 5 hours into the meiotic program) to capture relevant interactions .

Researchers have successfully used Co-IP to demonstrate interactions between Ctf19-33Flag-dCas9 and Mcm21-3HA during meiotic prophase, confirming that fusion of dCas9 to CTF19 does not disrupt its ability to form native protein complexes .

How can CTF19 function be assessed through genetic and cytological approaches?

Beyond biochemical approaches using antibodies, CTF19 function can be comprehensively assessed through combined genetic and cytological methods:

• Genetic recombination assays: Map distances (in centiMorgans) can be determined for chromosomal intervals in cells expressing CTF19 variants or in CTF19 mutant backgrounds. These assays directly quantify the effect of CTF19 on crossover suppression .

• Microscopy-based approaches: After tetrad formation, researchers can quantify spore viability and chromosome segregation patterns using fluorescently-labeled chromosomes. For detailed analysis, use a Delta Vision Ultra High Resolution Microscope with appropriate filters (CFP, mCherry, Green channels). Process images with software like ImageJ, counting only tetrads with four visible spores in the CFP channel to prevent confounding effects due to meiotic chromosome missegregation .

• Statistical analysis: Calculate map distance (cM) and standard errors using established tools (such as those provided at http://elizabethhousworth.com/StahlLabOnlineTools/EquationsMapDistance.html). Statistical significance can be assessed using Fisher's exact test .

• dCas9-based targeting systems: An innovative approach involves using a dCas9/CRISPR-based system to target CTF19 to non-centromeric chromosomal locations. This allows researchers to determine whether CTF19's functions are intrinsic to the protein or dependent on its centromeric context .

How can phosphorylation status of CTF19 be monitored and what is its functional significance?

The phosphorylation status of CTF19 plays a crucial role in its function, particularly in cohesin recruitment and crossover suppression:

• Key phosphorylation sites: The amino-terminal (NH2-terminal) region of CTF19, specifically the first 30 amino acids, contains nine serine/threonine residues that are phosphorylated by the Cdc7/Dbf4 kinase (DDK) . Mutation of these residues to non-phosphorylatable alanines (in the ctf19-9A allele) impairs Scc2-Scc4 recruitment and affects cohesin function .

• Functional significance: Phosphorylation of these residues is essential for CTF19's role in crossover suppression. When a non-phosphorylatable Ctf19-9A variant was targeted to a chromosome arm locus, it failed to suppress recombination frequencies, suggesting that phosphorylation is critical for this function .

• Monitoring methods:

  • Western blotting with phospho-specific antibodies (when available)

  • Mobility shift assays to detect phosphorylated forms

  • Mass spectrometry for comprehensive phosphorylation site mapping

  • Functional assays comparing wild-type CTF19 with phospho-mutant variants

• Structural implications: Phosphorylation of the N-terminal region of CTF19 creates binding sites for the Scc2-Scc4 cohesin loader complex, which in turn influences cohesin distribution throughout pericentromeric regions .

What are common issues when working with CTF19 antibodies and how can they be resolved?

Researchers commonly encounter several challenges when working with CTF19 antibodies:

• High background in Western blots:

  • Solution: Optimize blocking conditions (try 5% BSA instead of milk for phospho-specific detection)

  • Increase washing stringency with higher salt concentrations in TBST

  • Dilute primary antibody further (test range from 1:500 to 1:5000)

• Weak or absent signal in immunoprecipitation:

  • Solution: Ensure sufficient starting material (at least 200ml of meiotic culture)

  • Consider using epitope-tagged versions of CTF19 for more efficient pulldown

  • Optimize lysis conditions to ensure complete protein extraction

• Non-specific bands in Western blots:

  • Solution: Include appropriate controls (knockout/knockdown samples)

  • Test multiple antibodies when available

  • Use gradient gels for better resolution around the expected molecular weight

• Cross-reactivity issues:

  • Solution: Pre-absorb antibody with cell lysates from CTF19-deleted strains

  • Validate antibody specificity using recombinant protein controls

  • Consider using more specific monoclonal antibodies if available

How can researchers distinguish between direct and indirect effects when studying CTF19 function?

Distinguishing direct from indirect effects is crucial for accurate interpretation of CTF19 functional studies:

• Temporal manipulation strategies: Use anchor-away or degron systems to remove CTF19 at specific time points during meiosis. This approach has revealed that targeting CTF19 before versus after DNA replication has differential effects on cohesin establishment and DSB formation .

• Domain-specific analysis: Studies have shown that the first 30 NH2-terminal amino acids of CTF19 (when fused to dCas9) are sufficient to instigate crossover suppression, indicating a direct effect through this domain .

• Genetic epistasis analysis: Perform experiments in backgrounds lacking other kinetochore components. For example, targeting of Ctf19-33Flag-dCas9 in iml3Δ cells led to an equal reduction in recombination rates as in wild-type, suggesting Ctf19's effect is independent of Iml3 .

• Ectopic targeting approaches: The dCas9/CRISPR-based targeting system allows researchers to recruit CTF19 to non-centromeric locations, helping distinguish intrinsic functions from those dependent on centromeric context .

• Protein-protein interaction mapping: Detailed co-immunoprecipitation studies followed by mass spectrometry can reveal direct binding partners versus components of larger complexes .

What experimental design considerations are crucial for accurately interpreting CTF19 antibody-based results?

For robust experimental design and accurate interpretation of CTF19 antibody-based studies:

• Appropriate controls: Include all necessary controls as outlined in section 2.3, with particular emphasis on specificity controls that demonstrate antibody selectivity.

• Genetic background considerations: Create and use isogenic strains that differ only in the targeted variable. This is especially important when comparing wild-type CTF19 function with mutant variants .

• Temporal considerations: For meiotic studies, precise timing of sample collection is critical. Most studies examine CTF19 function approximately 4-5 hours into the meiotic program (prophase) .

• Quantification methods: Use appropriate quantification for Western blots and ChIP experiments. For ChIP-qPCR, normalize to input and unbound fractions, and include multiple primer sets covering regions of interest and control regions .

• Validation through orthogonal approaches: Confirm antibody-based findings using complementary techniques:

  • Genetic approaches (mutant phenotypes)

  • Cytological methods (microscopy)

  • Functional assays (genetic recombination measurement)

  • Direct protein interaction studies (yeast two-hybrid or proximity labeling)

How can CTF19 antibodies be used in studying meiotic recombination control mechanisms?

CTF19 antibodies enable detailed investigation of mechanisms controlling meiotic recombination:

• Mapping binding sites and spreading patterns: ChIP-seq approaches using CTF19 antibodies can map the protein's binding distribution throughout the genome during meiosis, providing insights into potential long-range effects on chromatin organization .

• Co-localization studies: Combined with antibodies against recombination machinery components (e.g., Spo11, Rec8), CTF19 antibodies can reveal spatial and temporal relationships between kinetochore proteins and recombination events .

• Investigating regulatory events: Given CTF19's role in suppressing pericentromeric DSB formation independently of cohesin recruitment, antibodies can help dissect the molecular pathways involved in this regulation .

• Chromatin conformation studies: When combined with chromosome conformation capture techniques, CTF19 antibody-based approaches can reveal how kinetochore proteins influence 3D chromatin organization in the pericentromere .

• Temporal dynamics: Using synchronized meiotic cultures and time-course sampling, researchers can track CTF19's localization and modification state throughout meiosis, correlating changes with critical events in recombination control .

What are the latest advances in CTF19 research enabled by innovative antibody applications?

Recent research has revealed several innovative applications for CTF19 antibodies:

• dCas9-based targeting systems: By fusing dCas9 to CTF19 and using specific sgRNAs, researchers have developed systems to target CTF19 to non-centromeric locations. This approach, detectable with standard antibodies against tagged CTF19, has revealed that CTF19 can suppress crossovers when recruited to chromosome arm regions .

• Dissection of functional domains: Studies using antibodies against tagged CTF19 variants have identified that the first 30 amino acids of CTF19 are sufficient for crossover suppression, highlighting the importance of this region in recruiting cohesin loaders .

• Multi-layered recombination control: Antibody-based studies have uncovered that CTF19 suppresses pericentromeric recombination through multiple mechanisms operating across distinct chromosomal distances - preventing meiotic DNA break formation near centromeres and independently driving cohesin enrichment throughout the broader pericentromere .

• Structure-function relationships: The combination of structural studies with functional analyses using antibodies has begun to reveal how the Ctf19 complex's architecture relates to its diverse functions in kinetochore assembly and chromosome dynamics .