MEIS3 Human

What is MEIS3 and what protein family does it belong to?

MEIS3 belongs to the TALE/MEIS homeobox family of transcription factors. It contains a homeobox domain that enables DNA binding and transcriptional regulation . As part of the Three-Amino-acid-Loop-Extension (TALE) homeodomain superclass, MEIS3 typically functions by forming heterodimeric and heterotrimeric complexes with other transcription factors, including Pbx family members and Hox proteins . These complexes regulate gene expression during embryonic development and in adult tissues, with particularly important roles in hindbrain development and cell survival pathways .

What are the molecular characteristics of human MEIS3?

MEIS3 is encoded by the MEIS3 gene (Gene ID: 56917) and produces a protein of 421 amino acids with a calculated molecular weight of 46 kDa . The protein contains several functional domains:

The gene produces multiple transcript variants, with three documented isoforms of MEIS3 protein having molecular masses of 39, 41, and 46 kDa . The human MEIS3 gene is located on chromosome 19 and has UniProt ID Q99687 .

Where is MEIS3 expressed in human tissues?

MEIS3 shows a broad expression pattern across human tissues. According to the Human Protein Atlas, MEIS3 is expressed in:

• Brain regions (hippocampal formation, amygdala, basal ganglia, midbrain, cerebral cortex)

• Endocrine tissues (thyroid, adrenal, pituitary glands)

• Digestive organs (pancreas, liver, intestines)

• Reproductive tissues (testis, prostate, ovary)

• Immune tissues (bone marrow, lymph nodes, spleen)

Of particular significance is its abundant expression in pancreatic islets and β-cells, where it plays a critical role in cell survival .

What antibodies and molecular tools are available for MEIS3 research?

Researchers investigating MEIS3 have several validated tools at their disposal:

For genetic manipulation studies, siRNA approaches have been successfully used to knockdown MEIS3 expression in cell lines and primary islets . Additionally, expression plasmids for rescue experiments are available and have been employed in functional studies .

What experimental approaches are most effective for studying MEIS3 function?

Based on published research, several approaches have proven effective:

• Loss-of-function studies: siRNA-mediated knockdown has been successfully employed in Min6 cells (pancreatic β-cell line) and primary mouse islets to study MEIS3 function .

• Rescue experiments: Co-transfection with expression plasmids (e.g., PDK1) following MEIS3 knockdown has been used to identify downstream mediators of MEIS3 function .

• Apoptosis assays: Following MEIS3 manipulation, researchers have utilized:

  • Western blotting for caspase-3 cleavage

  • TUNEL staining for apoptotic cells

  • qPCR for expression of anti-apoptotic genes (e.g., Bcl-2)

• Gene expression analysis: qPCR has been used to measure changes in transcript levels of MEIS3, other MEIS family members, and potential target genes .

How can researchers distinguish between MEIS family members in experimental settings?

Distinguishing between MEIS family members (MEIS1, MEIS2, MEIS3) presents a significant challenge due to structural similarities. Effective approaches include:

• Using gene-specific primers for qPCR that target unique regions to ensure specificity of detection

• Employing specific siRNAs targeting non-conserved regions of MEIS3

• Validating knockdown specificity by measuring expression of all family members (as demonstrated in studies where MEIS3 knockdown did not affect MEIS1 or MEIS2 levels)

• Using isoform-specific antibodies when available

• Employing mass spectrometry for definitive protein identification

What are the primary molecular functions of MEIS3?

MEIS3 functions primarily as a transcription factor with several documented roles:

• DNA binding: MEIS3 contains a homeodomain that enables sequence-specific DNA binding .

• Transcriptional regulation: It is involved in positive regulation of transcription by RNA polymerase II .

• Developmental regulation: MEIS3 acts upstream of or within several developmental processes:

  • Enteric nervous system development

  • Exocrine pancreas development

  • Neural crest cell migration in autonomic nervous system development

• Cell survival regulation: MEIS3 promotes cell survival in pancreatic β-cells and certain cancer cell lines through regulation of pro-survival pathways .

How does MEIS3 regulate the PDK1-Akt survival pathway?

A key discovery in MEIS3 biology is its regulation of PDK1 (3-phosphoinositide-dependent protein kinase 1), a critical component of the PI3K-Akt signaling pathway:

• MEIS3 directly regulates PDK1 expression at the transcriptional level.

• In experimental models, MEIS3 depletion leads to:

  • Significant reduction in PDK1 protein and transcript levels

  • Increased caspase-3 cleavage

  • Reduced expression of anti-apoptotic gene Bcl-2

  • Increased apoptotic cell death

• The functional relationship has been experimentally validated through rescue experiments:

  • Co-transfection of PDK1 expression plasmids with MEIS3-targeted siRNA significantly restored PDK1 protein levels

  • This rescue reversed the apoptotic phenotype caused by MEIS3 depletion

• This regulatory module appears conserved across cell types, functioning in both pancreatic β-cells and ovarian carcinoma cells .

Does MEIS3 functionally interact with other TALE homeodomain factors?

While direct evidence for MEIS3-specific interactions is limited, TALE homeodomain proteins typically function through protein-protein interactions:

• MEIS proteins generally form heterodimeric and heterotrimeric complexes with Pbx family members and/or Hox proteins .

• These complexes confer enhanced DNA-binding specificity and transcriptional activation.

• In prostate cancer research, a germline mutation in HOXB13 (84G→E) that disrupts interaction with MEIS1 has been identified in familial disease, suggesting functional importance of MEIS-HOX interactions .

• The specific interaction partners of MEIS3 may vary by tissue context and developmental stage, potentially explaining some of the contradictory findings in different research models.

What role does MEIS3 play in embryonic development?

MEIS3 has several documented roles in vertebrate embryonic development:

• Hindbrain development: MEIS3 is a key regulator of hindbrain formation and patterning .

• Neural development: MEIS3 is expressed in neural structures during development, including:

  • Neural plate

  • Neural keel

  • Posterior neural tube

• Enteric nervous system: MEIS3 acts upstream of or within enteric nervous system development .

• Pancreatic development: MEIS3 is involved in exocrine pancreas development .

• Neural crest cell migration: MEIS3 regulates neural crest cell migration involved in autonomic nervous system development .

These roles highlight MEIS3's importance as a developmental regulator with functions beyond the traditional roles of TALE homeodomain factors in embryogenesis.

How does MEIS3 function in pancreatic β-cells?

MEIS3 plays a critical role in pancreatic β-cell survival through several mechanisms:

• Abundant expression: MEIS3 is highly expressed in pancreatic islets and β-cells .

• Pro-survival function: Depletion of MEIS3 in Min6 cells (a β-cell line) results in:

  • Increased cell death

  • Enhanced caspase-3 cleavage

  • Reduced procaspase-3 levels

  • Increased apoptotic cells (confirmed by TUNEL staining)

  • Decreased expression of anti-apoptotic gene Bcl-2

• PDK1 regulation: MEIS3 directly regulates the expression of PDK1, a key component of the PI3K-Akt survival pathway .

• Conservation in primary islets: The MEIS3-PDK1 regulatory axis is conserved in primary mouse islets, where reduction in MEIS3 transcripts leads to significant decrease in PDK1 transcript levels .

This role in β-cell survival suggests potential relevance to diabetes research, though direct links to diabetes pathology remain to be fully established.

What is the evidence linking MEIS3 to cancer development?

Evidence connecting MEIS3 to cancer development includes:

• Expression in cancer: MEIS genes, including MEIS3, are expressed in various cancers:

  • Ovarian carcinomas show extensive expression of MEIS proteins

  • Neuroblastoma exhibits MEIS gene expression and occasional amplification

• Cell survival regulation: The MEIS3-PDK1 regulatory module identified in β-cells also functions in ovarian carcinoma cells, suggesting a role in cancer cell survival .

• Family history: MEIS family members were first identified through their association with tumorigenesis in a murine leukemia model .

• Contradictory evidence: Research on MEIS genes in cancer shows contradictory results:

  • In prostate cancer, studies testing the hypothesis that MEIS1 plays a role in cancer initiation have been largely inconclusive

  • In neuroblastoma, evidence regarding the role of MEIS genes is contradictory despite abundant expression

These contradictions suggest context-dependent functions of MEIS proteins in cancer, with potential roles as both oncogenes and tumor suppressors depending on the cellular context.

What are the major contradictions in MEIS3 research findings?

Several contradictions exist in the literature regarding MEIS3 and related family members:

• Cancer role discrepancies: Evidence regarding the role of MEIS genes in cancer is contradictory:

  • In prostate cancer, functional studies testing the hypothesis that MEIS1 contributes to cancer initiation have been largely inconclusive despite genetic evidence suggesting its involvement

  • In neuroblastoma, contradictory evidence exists regarding the role of MEIS genes

• Functional overlap: The degree of functional redundancy between MEIS family members (MEIS1, MEIS2, MEIS3) remains unclear and may contribute to contradictory findings across studies.

• Context-dependent functions: MEIS3 appears to have different roles depending on cellular context, developmental stage, and disease state, complicating interpretation of research findings.

• Technical limitations: Variations in experimental approaches, models, and reagent specificity may contribute to seemingly contradictory results.

How can researchers address functional redundancy between MEIS family members?

Addressing functional redundancy between MEIS1, MEIS2, and MEIS3 requires sophisticated experimental approaches:

• Specific targeting strategies:

  • Design siRNAs or shRNAs targeting unique regions of each MEIS family member

  • Validate specificity by measuring expression of all family members

  • Studies on MEIS3 in β-cells demonstrated that knockdown of MEIS3 did not affect MEIS1 or MEIS2 transcripts, confirming specificity

• Combinatorial approaches:

  • Simultaneous knockdown of multiple family members to identify synergistic or redundant functions

  • Sequential depletion experiments to detect compensatory mechanisms

• Genome editing:

  • CRISPR-Cas9 approaches to create specific mutations or deletions

  • Generation of conditional knockout models to address developmental lethality

• Domain-specific analysis:

  • Identification of unique functional domains that distinguish MEIS3 from other family members

  • Creation of chimeric proteins to identify domain-specific functions

What future research directions might resolve current gaps in MEIS3 understanding?

Several research directions could advance our understanding of MEIS3 biology:

• Comprehensive target identification:

  • ChIP-seq studies to identify direct transcriptional targets of MEIS3 across different cell types

  • RNA-seq following MEIS3 manipulation to identify context-specific gene regulatory networks

• Structural studies:

  • Detailed structural analysis of MEIS3-DNA and MEIS3-protein interactions

  • Structure-function studies to identify critical residues for specific interactions

• Physiological models:

  • Development of conditional knockout mouse models to study MEIS3 function in specific tissues

  • Organoid models to better recapitulate in vivo context while maintaining experimental accessibility

• Clinical correlations:

  • Analysis of MEIS3 expression, mutations, or polymorphisms in patient cohorts

  • Investigation of potential links to diabetes and pancreatic disorders given MEIS3's role in β-cell survival

• Single-cell approaches:

  • Single-cell transcriptomics to identify cell-specific functions of MEIS3

  • Spatial transcriptomics to understand context-dependent regulation in tissues

• Therapeutic targeting:

  • Development of specific modulators of MEIS3 function

  • Evaluation of MEIS3 as a potential therapeutic target in diseases where it plays a causal role

What are the technical challenges in studying MEIS3 protein interactions?

Investigating MEIS3 protein interactions presents several technical challenges:

• Antibody specificity:

  • Ensuring antibodies discriminate between MEIS3 and other MEIS family members

  • Validation across multiple experimental systems and applications

• Transient interactions:

  • MEIS3 likely forms dynamic complexes with various partners

  • Capturing these interactions may require crosslinking or proximity-based approaches

• Context-dependency:

  • Interaction partners may vary by cell type, developmental stage, or disease state

  • Comprehensive mapping requires analysis across multiple contexts

• Functional validation:

  • Distinguishing biologically relevant interactions from technical artifacts

  • Correlating interaction data with functional outcomes

Approaches to address these challenges include:

• Proximity labeling techniques (BioID, APEX)

• Mass spectrometry-based interactomics

• Co-immunoprecipitation with stringent controls

• Split reporter systems (yeast two-hybrid, mammalian two-hybrid)

How should researchers approach MEIS3 functional studies in diverse cellular contexts?

Given the context-dependent functions of MEIS3, researchers should consider:

• Multi-system validation:

  • Test hypotheses across multiple cell types and experimental systems

  • Compare findings in cell lines, primary cells, and in vivo models when possible

• Careful control selection:

  • Include related MEIS family members as controls

  • Measure expression of all family members to detect compensatory changes

• Physiologically relevant models:

  • Use disease-relevant cell types or patient-derived samples

  • Consider three-dimensional culture systems or organoids that better recapitulate tissue environment

• Integrative analysis:

  • Combine multiple methodologies (genomic, transcriptomic, proteomic)

  • Correlate molecular changes with functional outcomes

• Dose-dependent effects:

  • Test varying levels of MEIS3 depletion or overexpression

  • Consider physiological expression levels when interpreting results

What considerations apply to translating MEIS3 research findings to clinical applications?

Translating MEIS3 research to clinical applications requires addressing several considerations:

• Specificity challenges:

  • Developing interventions that specifically target MEIS3 without affecting other MEIS family members

  • Identifying unique binding sites or interaction surfaces for selective targeting

• Context-dependent functions:

  • Accounting for potentially different roles of MEIS3 in various tissues

  • Avoiding unintended consequences in tissues where MEIS3 has essential functions

• Patient stratification:

  • Identifying patient populations most likely to benefit from MEIS3-targeted approaches

  • Developing biomarkers to predict response to MEIS3 modulation

• Therapeutic approaches:

  • Exploring small molecule inhibitors of protein-protein interactions

  • Considering RNA-based approaches for selective targeting

  • Investigating downstream effectors (e.g., PDK1) as alternative targets

• Disease relevance:

  • Prioritizing conditions with strongest evidence for MEIS3 involvement

  • Current data suggests potential relevance to pancreatic β-cell disorders and certain cancers