Recombinant Xenopus tropicalis DnaJ homolog subfamily C member 15 (dnajc15)

How does Xenopus tropicalis DNAJC15 differ from mammalian DNAJC15?

While Xenopus tropicalis DNAJC15 shares functional homology with mammalian DNAJC15, there are several important differences to consider:

What experimental approaches can be used to study DNAJC15 function in Xenopus embryos?

Multiple experimental approaches have proven effective for studying DNAJC15 function in Xenopus:

• Gain-of-function studies: mRNA injection of DNAJC15 into Xenopus laevis eggs followed by analysis of phenotypic effects on pronephros development has been successfully employed. This approach revealed that DNAJC15 overexpression causes specific abnormalities in pronephric marker expression .

• Loss-of-function studies: Morpholino antisense oligonucleotides can be used to knockdown DNAJC15 expression in developing embryos.

• In situ hybridization: Whole mount in situ hybridization can be used to characterize the spatial and temporal expression patterns of DNAJC15 during development, particularly in the pronephric region .

• Immunostaining: Antibody staining can detect the protein localization within tissues and subcellular compartments.

• Mitochondrial function assays: Oxygen consumption rate measurements, mitochondrial membrane potential assays, and Complex I activity assays can be performed on isolated mitochondria from tissues expressing recombinant or endogenous DNAJC15 .

The combination of these approaches provides a comprehensive understanding of both the developmental and biochemical functions of DNAJC15 in Xenopus tropicalis.

How is DNAJC15 involved in pronephros development in Xenopus?

DNAJC15 plays a critical role in pronephros development in Xenopus, as demonstrated through functional screening approaches. The pronephros in Xenopus is the functional larval kidney and consists of two main components: the glomus and the pronephric tubules (which can be divided into four segments based on marker gene expression) .

Functional screening experiments involving the injection of mRNA pools from a non-redundant X. tropicalis full-length cDNA library into X. laevis eggs identified DNAJC15 as one of 31 genes (approximately 4% of screened clones) that affected pronephric marker expression .

Key findings regarding DNAJC15's role in pronephros development include:

• DNAJC15 shows a highly specific expression pattern in the pronephric region during development.

• Overexpression of DNAJC15 causes pronephric abnormalities with distinct temporal and spatial effects.

• DNAJC15 likely functions as part of a molecular pathway regulating kidney organogenesis in amphibians.

• The protein may act through its role in mitochondrial function, which is essential for the high energy demands of developing kidney structures .

These findings highlight DNAJC15 as a crucial component in the developmental program that establishes the primitive kidney structure in Xenopus, potentially through regulation of mitochondrial activity in developing pronephric cells.

What are optimal conditions for expressing and purifying recombinant Xenopus tropicalis DNAJC15?

Based on established protocols for recombinant DNAJC15 production, the following conditions are recommended:

Expression System Options:

• E. coli expression: The full-length Xenopus tropicalis DNAJC15 (amino acids 1-149) has been successfully expressed in E. coli with an N-terminal His tag .

• Mammalian expression: For applications requiring post-translational modifications, expression in HEK293 cells may be preferable, similar to protocols used for human DNAJC15 .

Purification Protocol:

• Lysis: Use a Tris/PBS-based buffer system (pH 8.0) containing appropriate protease inhibitors.

• Affinity Chromatography: His-tagged protein can be purified using Ni-NTA affinity chromatography.

• Quality Control: Verify purity via SDS-PAGE (expected >90% purity) .

Storage Conditions:

• Store the purified protein in Tris/PBS-based buffer with 6% trehalose at pH 8.0 .

• For long-term storage, lyophilize the protein or add glycerol (final concentration 30-50%) and store at -20°C/-80°C .

• Avoid repeated freeze-thaw cycles which can compromise protein integrity.

Reconstitution:

• Reconstitute lyophilized protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL .

• For applications requiring higher stability, addition of 5-50% glycerol is recommended .

These conditions have been demonstrated to yield functional recombinant Xenopus tropicalis DNAJC15 suitable for various research applications, including functional studies and antibody production.

For DNAJC15 Overexpression:

• mRNA Injection: Synthetic capped mRNA encoding DNAJC15 can be injected into Xenopus eggs or early embryos. This approach has been successfully used in functional screens for genes involved in pronephros development .

  Protocol:

  • Clone the full-length DNAJC15 cDNA into an appropriate expression vector with a strong promoter (e.g., SP6 or T7).

  • Synthesize capped mRNA using in vitro transcription.

  • Inject 0.5-2 ng of mRNA into 1-2 cell stage embryos.

  • Assess phenotypes using appropriate markers.

• Transgenesis: The Tol2 transposon system or I-SceI meganuclease-mediated transgenesis can be used to create transgenic Xenopus tropicalis expressing DNAJC15 under tissue-specific promoters.

For DNAJC15 Knockout:

• CRISPR/Cas9 Genome Editing:

  • Design guide RNAs targeting the DNAJC15 gene.

  • Inject Cas9 protein or mRNA along with guide RNAs into fertilized eggs.

  • Screen for mutations using T7 endonuclease assay or direct sequencing.

  • Raise F0 mosaic animals and establish knockout lines through breeding.

• Morpholino Antisense Oligonucleotides:

  • Design morpholinos targeting the translation start site or splice junctions of DNAJC15.

  • Inject 4-10 ng of morpholino into 1-2 cell stage embryos.

  • Verify knockdown efficiency using Western blot or qRT-PCR.

• Dominant Negative Approach:

  • Express truncated versions of DNAJC15 that interfere with normal function.

  • This approach can be particularly useful for studying specific domains.

Each method has advantages and limitations, and the choice depends on experimental requirements, timeline, and whether transient or stable genetic modification is needed.

What evolutionary conservation exists in DNAJC15 function across vertebrate species?

DNAJC15 shows remarkable functional conservation across vertebrate species, despite some variation in sequence and size. This conservation reflects the fundamental importance of its role in mitochondrial function.

Evolutionary Conservation Analysis:

Across species, DNAJC15 maintains its core function as a negative regulator of mitochondrial respiration through interaction with Complex I of the electron transport chain . This is evidenced by studies showing that loss of DNAJC15/MCJ increases Complex I activity and promotes the formation of respiratory supercomplexes in multiple species .

The protein's role in development shows more variation between species. In Xenopus, it has a specialized role in pronephros development , while in mammals it appears to have broader functions including roles in adipose tissue metabolism and sexually dimorphic gonadal development .

These evolutionary differences provide valuable insights into both the core conserved functions of DNAJC15 and its adaptations to species-specific physiological requirements.

How does the mitochondrial localization of DNAJC15 affect its function in Xenopus cells?

The mitochondrial localization of DNAJC15 in Xenopus cells is critical for its function as a regulator of cellular energy metabolism and development. As in mammals, Xenopus DNAJC15 is a transmembrane protein embedded in the inner mitochondrial membrane, which positions it to interact with respiratory chain components .

Key Aspects of DNAJC15 Mitochondrial Function:

• Interaction with Respiratory Complexes: DNAJC15 acts as an endogenous negative regulator of Complex I of the electron transport chain, similar to its mammalian counterpart . This regulation affects ATP production capacity in energy-demanding developmental processes.

• Protein Import Regulation: DNAJC15 interacts with the TIMM23 translocase complex, enhancing the ATPase activity of mitochondrial heat shock protein 70 and facilitating the transport of proteins lacking a mitochondrial targeting sequence . This function is critical for mitochondrial biogenesis during development.

• Developmental Energy Requirements: The pronephros development in Xenopus requires precise regulation of energy metabolism. DNAJC15's mitochondrial localization allows it to fine-tune energy production during kidney organogenesis .

• Response to Metabolic Stress: The mitochondrial position of DNAJC15 enables it to act as a sensor and regulator during metabolic stress, potentially coordinating cellular responses to energy availability changes during development.

When DNAJC15 is cleaved by proteases like OMA1 (after amino acid 19), it becomes destabilized and rapidly degraded, which impairs mitochondrial protein import and can lead to stress responses including activation of the ATF6-mediated unfolded protein response pathway . This proteolytic regulation represents an important control mechanism for DNAJC15 function in mitochondria.

What signaling pathways are regulated by DNAJC15 in Xenopus tropicalis?

While the complete signaling network influenced by DNAJC15 in Xenopus tropicalis is still being elucidated, several key pathways have been identified based on functional studies and comparisons with mammalian systems:

Primary Signaling Pathways:

• Mitochondrial Respiration Regulation:

  • DNAJC15 negatively regulates Complex I activity in the electron transport chain

  • Influences ATP production and mitochondrial membrane potential

  • Affects the formation of respiratory supercomplexes

• Protein Folding and Import Pathways:

  • Interacts with the TIMM23 translocase complex

  • Enhances ATPase activity of mitochondrial heat shock protein 70

  • Facilitates import of specific mitochondrial proteins

• Pronephros Development Signaling:

  • Influences expression of pronephric marker genes

  • May interact with other factors identified in pronephros development screens

  • Temporal and spatial effects suggest stage-specific pathway regulation

• Stress Response Pathways:

  • Loss of DNAJC15 can trigger the ATF6-mediated unfolded protein response

  • Impaired mitochondrial protein import leads to accumulation of preproteins at the ER

  • This accumulation disrupts ER proteostasis and activates stress responses

• Lipid Metabolism:

  • By analogy with mammalian systems, likely involved in lipid metabolism regulation

  • May influence lipid peroxidation processes

  • Potential role in thermogenesis regulation (as seen in mammals)

The interconnection of these pathways demonstrates how DNAJC15 functions as a central regulator that coordinates mitochondrial activity with developmental processes and stress responses in Xenopus tropicalis.

What experimental challenges exist when working with recombinant Xenopus tropicalis DNAJC15?

Working with recombinant Xenopus tropicalis DNAJC15 presents several unique challenges that researchers should anticipate:

Production Challenges:

• Membrane Protein Expression: As a transmembrane protein, DNAJC15 can be difficult to express in soluble, correctly folded form. Expression in E. coli may yield inclusion bodies requiring refolding protocols .

• Post-translational Modifications: If Xenopus-specific modifications are critical for function, bacterial expression systems may be inadequate, necessitating eukaryotic expression systems.

• Protein Stability: DNAJC15 is subject to proteolytic regulation (e.g., cleavage by OMA1 after amino acid 19), which can lead to rapid degradation . Protease inhibitors and careful handling are essential.

Functional Assay Challenges:

• Mitochondrial Targeting: Assessing proper mitochondrial localization requires specialized subcellular fractionation or imaging techniques.

• Activity Assessment: Measuring the impact on Complex I activity requires isolated, functional mitochondria or sophisticated respirometry assays.

• Developmental Studies: Correlating biochemical functions with developmental phenotypes requires precise timing and dosage in microinjection experiments.

Technical Solutions:

• Expression Optimization:

  • Use fusion tags that enhance solubility (e.g., SUMO, MBP)

  • Consider codon optimization for the expression system

  • Explore insect cell or mammalian expression systems for properly folded protein

• Stability Enhancement:

  • Include 6% trehalose in storage buffers

  • Use glycerol (30-50%) for long-term storage

  • Avoid repeated freeze-thaw cycles

• Functional Validation:

  • Develop in vitro reconstitution systems with purified mitochondrial complexes

  • Use fluorescent reporters for mitochondrial import assays

  • Establish clear readouts for pronephros development in Xenopus embryos

Addressing these challenges requires careful experimental design and may necessitate combining multiple approaches to fully characterize the recombinant protein's properties and functions.

How does DNAJC15 expression vary during Xenopus development and across different tissues?

DNAJC15 exhibits distinct temporal and spatial expression patterns during Xenopus development, with particular relevance to pronephros formation and potentially other developmental processes:

Developmental Expression Timeline:

Tissue-Specific Expression:

DNAJC15 shows a highly specific expression pattern in the pronephric region during Xenopus development, as demonstrated by whole mount in situ hybridization . This specificity suggests a specialized role in kidney development rather than a general housekeeping function.

Comparative Expression:

By analogy with mammalian systems, DNAJC15 expression may be sexually dimorphic in certain tissues. In mice, DNAJC15 is expressed more highly in female gonads than male gonads during embryonic development (E12.5-E15.5) , suggesting potential sex-specific roles that might also exist in Xenopus.

Additionally, based on mammalian studies, DNAJC15 expression might be dynamically regulated in response to metabolic states, as seen in the decreased expression observed during obesity in mammals . Similar metabolic regulation could occur in Xenopus tissues with high energy demands.

Potential Applications in Disease Modeling:

• Kidney Disease Models:
  Given DNAJC15's role in pronephros development , manipulation of this gene can serve as a model for developmental kidney disorders. Xenopus pronephros shares structural and functional similarities with the human nephron, making it relevant for modeling human kidney diseases.

• Mitochondrial Dysfunction Disorders:
  As a negative regulator of Complex I , DNAJC15 manipulation can model aspects of mitochondrial respiratory chain disorders. Overexpression might mimic Complex I deficiency states, while knockdown could potentially reveal compensatory mechanisms.

• Cancer Chemoresistance Models:
  In humans, DNAJC15 loss correlates with cisplatin resistance in ovarian cancer . Similar mechanisms could be explored in Xenopus cells to understand the fundamental biology of chemoresistance.

• Metabolic Disease Models:
  Based on mammalian studies showing DNAJC15's role in obesity and brown adipose tissue function , Xenopus models with altered DNAJC15 expression could provide insights into conserved mechanisms of metabolic regulation.

Methodological Approaches:

• CRISPR/Cas9 Genome Editing:
  Generation of DNAJC15-deficient Xenopus lines can serve as disease models.

• Transgenic Rescue Experiments:
  Human disease-associated DNAJC15 variants could be expressed in DNAJC15-deficient Xenopus to assess functional conservation and pathogenic mechanisms.

• Drug Screening Platforms:
  Xenopus embryos with DNAJC15 modifications could be used for high-throughput screening of compounds that modulate mitochondrial function in disease contexts.

These approaches leverage the advantages of Xenopus as a model system—including external development, large embryo size, and rapid development—to provide insights into mitochondrial disease mechanisms that may be translatable to human conditions.

How does DNAJC15 interact with the mitochondrial protein import machinery in Xenopus?

DNAJC15 in Xenopus, like its mammalian counterpart, functions as an integral component of the mitochondrial protein import system, particularly through its interaction with the TIMM23 translocase complex:

Key Components and Interactions:

• TIMM23 Complex Association:
  DNAJC15 is localized to the inner mitochondrial membrane where it interacts with the TIMM23 translocase complex . This complex is the main entry gate for proteins destined for the matrix or inner membrane.

• Regulation of mtHSP70 Activity:
  DNAJC15 enhances the ATPase activity of mitochondrial heat shock protein 70 (mtHSP70) , which provides the driving force for protein translocation into the mitochondrial matrix.

• Import of Non-Canonical Proteins:
  DNAJC15 particularly facilitates the transport of proteins lacking a conventional mitochondrial targeting sequence , broadening the range of proteins that can be imported into mitochondria.

Functional Consequences of Disrupted Interaction:

When DNAJC15 function is compromised (e.g., through proteolytic cleavage by OMA1) , several consequences occur:

• Impaired Mitochondrial Protein Import:
  Loss of DNAJC15 leads to inefficient protein import into mitochondria .

• Preprotein Accumulation:
  Mitochondrial preproteins accumulate at the endoplasmic reticulum .

• ER Stress Response Activation:
  The accumulation of mitochondrial preproteins at the ER disrupts ER proteostasis and triggers an ATF6-mediated unfolded protein response .

• Secondary Mitochondrial Dysfunction:
  The disruption of proper protein import leads to broader mitochondrial dysfunction affecting multiple mitochondrial processes.

This intricate relationship between DNAJC15 and the protein import machinery highlights how a single protein can coordinate mitochondrial biogenesis with cellular stress responses, ensuring proper organelle function during development and homeostasis in Xenopus cells.

How can recombinant DNAJC15 be used to study ferroptosis mechanisms in Xenopus models?

Recombinant DNAJC15 provides a valuable tool for investigating ferroptosis—a form of regulated cell death characterized by iron-dependent lipid peroxidation—in Xenopus models. This application is particularly relevant given recent findings linking DNAJC15 to ferroptosis sensitivity in mammalian cells .

Experimental Approaches:

• Overexpression Studies:

  • Inject mRNA encoding recombinant DNAJC15 into Xenopus embryos

  • Assess lipid peroxidation using BODIPY-C11 or other lipid peroxidation sensors

  • Measure ferroptosis markers (e.g., glutathione depletion, iron accumulation)

  • Test sensitivity to ferroptosis inducers (e.g., erastin, RSL3) with and without DNAJC15 overexpression

• Structure-Function Analysis:

  • Create recombinant DNAJC15 variants with mutations in key domains

  • Determine which domains are essential for promoting ferroptosis sensitivity

  • Assess how these mutations affect mitochondrial localization and function

• Interaction Studies:

  • Use purified recombinant DNAJC15 for pull-down assays to identify protein interactions

  • Investigate interactions with known ferroptosis regulators (e.g., GPX4, FSP1)

  • Determine if DNAJC15 directly affects lipid metabolism enzymes

Relevance to Disease Models:

The connection between DNAJC15, ferroptosis, and chemoresistance in cancer suggests several applications:

• Cancer Treatment Resistance:

  • Higher DNAJC15 levels are associated with increased cisplatin sensitivity in ovarian cancer through ferroptosis induction

  • Xenopus models can help determine if this mechanism is evolutionarily conserved

  • Potential for identifying new therapeutic targets

• Lipid Metabolism Regulation:

  • DNAJC15 affects lipid droplet accumulation

  • Recombinant protein can be used to study how mitochondrial function influences lipid storage

  • May reveal fundamental mechanisms connecting mitochondrial activity and lipid homeostasis

• Protective Mechanisms:

  • Ferrostatin-1 treatment reduces DNAJC15-induced ferroptosis

  • Using recombinant DNAJC15 can help identify additional protective factors

  • These studies could suggest new cytoprotective strategies

This research direction connects DNAJC15's known roles in mitochondrial function with emerging understanding of ferroptosis pathways, potentially revealing new mechanisms of regulated cell death in development and disease.

How do post-translational modifications affect DNAJC15 function in Xenopus?

Post-translational modifications (PTMs) play crucial roles in regulating DNAJC15 function, stability, and interactions in Xenopus. Although specific PTMs of Xenopus DNAJC15 are not comprehensively characterized, insights from mammalian studies and limited Xenopus data suggest several important modification mechanisms:

Key Post-translational Modifications:

• Proteolytic Processing:

  • DNAJC15 can be cleaved by the mitochondrial protease OMA1 after amino acid 19

  • This cleavage leads to destabilization and rapid degradation of DNAJC15

  • Functions as a regulatory mechanism during mitochondrial stress

• Potential Phosphorylation:

  • Sequence analysis reveals potential phosphorylation sites in the N-terminal region

  • Phosphorylation could affect membrane insertion or protein-protein interactions

  • May be regulated by kinases responding to metabolic or developmental signals

• Potential Ubiquitination:

  • As a regulator of protein quality control, DNAJC15 itself may be subject to ubiquitin-mediated regulation

  • Could control protein levels during different developmental stages

Experimental Approaches to Study PTMs:

• Mass Spectrometry Analysis:

  • Identify specific modification sites on recombinant or endogenous DNAJC15

  • Compare PTM patterns under different developmental or stress conditions

  • Use recombinant standards with C13 and N15 labeling for accurate quantification

• Site-Directed Mutagenesis:

  • Generate mutants at potential modification sites

  • Assess effects on protein stability, localization, and function

  • Determine if modifications are necessary for developmental functions

• Crosslinking Studies:

  • Use DSP (dithiobis(succinimidyl propionate)) or similar crosslinkers to capture dynamic interactions

  • Determine if PTMs affect interaction partners

  • Identify changes in the DNAJC15 interactome under different conditions

Functional Consequences of PTMs:

The impact of these modifications extends to multiple aspects of DNAJC15 function:

• Stability and Turnover:
  PTMs regulate the half-life of DNAJC15, allowing rapid adaptation to changing cellular needs.

• Subcellular Localization:
  Modifications may affect targeting to the inner mitochondrial membrane and insertion orientation.

• Protein-Protein Interactions:
  PTMs likely modulate interactions with the TIMM23 complex, mtHSP70, and respiratory chain components.

• Developmental Regulation: A ccurate timing of DNAJC15 activity during pronephros development may depend on precise PTM control.