MYL9 Human

What is MYL9 and what are its primary functions in human cells?

MYL9 is a regulatory component of myosin protein belonging to the myosin light chain family with high homology to Myl12a (93%) and Myl12b (93%) . It functions as a myosin regulatory subunit that plays a critical role in regulating both smooth muscle and nonmuscle cell contractile activity via phosphorylation . MYL9 is implicated in essential cellular processes including cytokinesis, receptor capping, and cell locomotion . In myoblasts, it may regulate PIEZO1-dependent cortical actomyosin assembly involved in myotube formation .

What nomenclature and alternative identifiers exist for MYL9?

MYL9 is also known by several alternative names in the literature:

• MLC2 (Myosin Light Chain 2)

• MRLC1 (Myosin Regulatory Light Chain 1)

• MYRL2

• 20 kDa myosin light chain

• MLC-2C

• Myosin RLC

• LC20

This diversity in nomenclature should be considered when conducting comprehensive literature searches.

How is MYL9 expression regulated in different human tissues and under physiological conditions?

MYL9 exhibits tissue-specific and age-dependent regulation patterns. Studies in rat models have demonstrated that MYL9 expression increases with age in both smooth muscle and endothelial layers of arteries . Dynamic regulation of MYL9 has been observed in response to vascular injury, with MYL9 being the only gene differentially expressed in aged versus young injured arteries at all time points studied . The increased endothelial MYL9 may explain morphological changes of endothelial cells associated with aging, which could account for altered vascular reactivity .

How does MYL9 contribute to genetic disorders and what methodologies are optimal for mutation screening?

MYL9 has been identified as one of five genes linked to megacystis–microcolon–intestinal hypoperistalsis syndrome (MMIHS), a severe early-onset disorder characterized by impaired muscle contractility in the bladder and intestines . Research has demonstrated that compound heterozygous loss-of-function variants in MYL9 can cause MMIHS . In a documented case, a three-year-old girl with MMIHS had two heterozygous loss-of-function variants in MYL9: an exon 4 deletion and a nine base pair deletion that removes the canonical splicing donor site at exon 2 (NM_006097.5:c.184+2_184+10del) .

For mutation screening, the recommended methodology includes:

• Initial sequencing of more common MMIHS-associated genes (e.g., ACTG2)

• Followed by comprehensive sequencing and deletion/duplication testing of MYL9

• Confirmation of variants through parental testing to establish trans configuration

• Inclusion of MYL9 on genetic testing panels for smooth muscle myopathies

What is the role of MYL9 in cancer progression and metastasis?

MYL9 plays a significant role in cancer progression, particularly in colorectal cancer. Research indicates that MYL9 expression is elevated in colorectal cancer cell lines and early-stage and recurrent colorectal cancer tissues . Functional studies have demonstrated that MYL9 overexpression promotes cell proliferation, invasion, migration, and angiogenesis, while silencing of MYL9 exerts the opposite effects .

Mechanistically, MYL9 affects cancer progression through:

• Binding to Yes-associated protein 1 (YAP1), as demonstrated by co-immunoprecipitation assays

• Activating Hippo signaling pathways

• Affecting the expression of YAP1 and its downstream signaling proteins including connective tissue growth factor and cysteine-rich angiogenic inducer 61

Experimental verification of MYL9 knockdown or the addition of Hippo antagonists inhibits the proliferation, invasion, migration, and angiogenesis of colorectal cancer cells, confirming the YAP1-Hippo signaling pathway as the primary mechanism .

How does MYL9 contribute to vascular inflammation and thrombosis in diseases like COVID-19?

MYL9 has emerged as an important factor in the pathogenesis of COVID-19-associated vascular complications. Studies have revealed that SARS-CoV-2 accumulates in pulmonary vessels, causing exudative vasculitis accompanied by:

• Emergence of thrombospondin-1-expressing noncanonical monocytes

• Formation of Myl9-containing microthrombi in the lungs of COVID-19 patients with fatal disease

SARS-CoV-2-induced platelet activation causes an increase in plasma MYL9 levels, which is closely correlated with clinical severity . This suggests that MYL9 not only serves as a biomarker but also plays a direct pathogenic role in COVID-19-associated thrombotic complications.

Similarly, in Kawasaki disease (an acute systemic vasculitis that predominantly affects children), MYL9 expression is significantly increased during vasculitis . This condition is known to be associated with an aberrant immune response and abnormal platelet activation, with MYL9 potentially serving as a useful biomarker to estimate inflammation .

What experimental approaches should be used to study MYL9 phosphorylation dynamics?

MYL9 phosphorylation is critical for its function in regulating cellular contractility. To effectively study MYL9 phosphorylation, researchers should employ a combination of techniques:

Table 1: Techniques for Studying MYL9 Phosphorylation

For reliable results, phosphatase inhibitors must be included during sample preparation to prevent dephosphorylation artifacts.

How can researchers effectively measure plasma MYL9 as a biomarker, and what standardization is required?

Plasma MYL9 has shown promise as a biomarker in several conditions, including COVID-19 severity and Kawasaki disease inflammation . For effective measurement and standardization:

• Assay Development:

  • Develop specific ELISA or other immunoassays targeting human MYL9

  • Validate against recombinant MYL9 protein

  • Check for cross-reactivity with homologous proteins (MYL12a, MYL12b)

• Sample Collection Protocol:

  • Standardize collection tubes (citrate vs. EDTA)

  • Establish consistent processing timeframes to prevent ex vivo release from platelets

  • Consider platelet-free plasma preparation for highest accuracy

• Reference Range Establishment:

  • Determine age-specific reference ranges

  • Account for comorbidities that may affect baseline levels

  • Establish thresholds for clinical decision-making

• Multimarker Approach:

  • Combine MYL9 with other markers for enhanced diagnostic accuracy

  • In COVID-19, combining plasma MYL9 with other markers allowed more accurate prediction of disease severity

What animal and cellular models are most appropriate for studying MYL9 function in different contexts?

Table 2: Research Models for MYL9 Studies

When selecting models, researchers should consider the specific aspect of MYL9 biology being studied and choose models that best recapitulate the relevant physiology or pathology.

How does age-related upregulation of MYL9 contribute to vascular pathophysiology?

Research has demonstrated that MYL9 is dynamically regulated with aging and injury in vascular tissues. Studies in rat iliac arteries revealed that MYL9 was the only gene differentially expressed in aged versus young injured arteries at all time points studied, with peak expression at day 3 after injury (4.6-fold upregulation) in the smooth muscle cell layers .

Immunohistochemistry studies confirmed that in both healthy and injured (30 days post-injury) arteries, MYL9 expression increased with age in the endothelial layers . This age-dependent upregulation may contribute to:

• Altered vascular reactivity and increased stiffness

• Modified endothelial cell morphology

• Increased susceptibility to vascular injury

• Changes in wound healing and tissue repair mechanisms

These findings suggest that MYL9 could be a target for interventions aimed at preventing age-related vascular dysfunction .

What are the technical challenges in differentiating MYL9 from its homologs in research applications?

MYL9 shares high sequence homology with related myosin light chain family members, particularly MYL12a and MYL12b (both with 93% homology) . This creates several technical challenges:

• Antibody Specificity:

  • Commercial antibodies may cross-react with homologs

  • Validation using knockout/knockdown controls is essential

  • Peptide competition assays can confirm specificity

• Gene Expression Analysis:

  • PCR primers must target unique regions

  • RNA-seq analysis requires careful mapping parameters

  • qPCR requires validation with multiple primer sets

• Genetic Manipulation:

  • CRISPR-Cas9 guide RNA design must avoid homologous regions

  • siRNA/shRNA knockdown may affect homologs

  • Phenotypic effects must be validated by rescue experiments

• Functional Redundancy:

  • Experimental design must account for potential compensation by homologs

  • Combined knockdown approaches may be necessary

  • Tissue-specific expression patterns should be considered

Researchers must carefully validate their tools and methodologies to ensure specific targeting of MYL9 rather than its homologs.

What are the most promising clinical applications of MYL9 research?

Based on current research, several promising clinical applications for MYL9 research have emerged:

• Diagnostic Biomarkers:

  • Plasma MYL9 levels as a severity marker in COVID-19

  • Inflammation indicator in Kawasaki disease

  • Potential early detection marker for colorectal cancer

• Therapeutic Targets:

  • Inhibition of MYL9-YAP1 interaction for cancer therapy

  • Anti-thrombotic approaches targeting MYL9-mediated microthrombi formation

  • Modulation of MYL9 to address age-related vascular dysfunction

• Genetic Testing:

  • Inclusion of MYL9 in genetic testing panels for MMIHS and related smooth muscle myopathies

  • Carrier testing for families with history of MMIHS

• Personalized Medicine:

  • MYL9 expression levels as potential predictors of treatment response

  • Stratification of patients based on MYL9-related pathways