Details for: CL0000746

Cell ID: CL0000746

Cell Name: cardiac muscle cell

Description: This class encompasses the muscle cells responsible for heart* contraction in both vertebrates and arthropods. The ultrastucture of a wide range of arthropod heart cells has been examined including spiders, horseshoe crabs, crustaceans (see Sherman, 1973 and refs therein) and insects (see Lehmacher et al (2012) and refs therein). According to these refs, the cells participating in heart contraction in all cases are transversely striated. Insects hearts additionally contain ostial cells, also transversely striated muscle cells, but which do not participate in heart contraction.

Synonyms: cardiac myocyte, cardiocyte, cardiomyocyte, heart muscle cell, cardiac muscle fiber

Selected Context(s): Overall

Gene Significance Landscape

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Score:
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Genes

Contexts:

Cell Significance Index (CSI) is uniquely calculated to reveal cell-specific gene markers. More info here

Significant Genes List

Genes with the highest and lowest Percentile Rank Scores (PRS) for cardiac muscle cell within the selected context(s).

Gene ID: A unique numerical identifier for this specific gene.
Symbol: Shortened abbreviation or name that represents this gene.
Ensembl Gene ID: A unique identifier assigned by Ensembl for genomic data mapping.
CSI Score: A combined effect size and statistical significance measure for cardiac muscle cell. Higher scores indicate a stronger, more significant difference in expression.
(Previously described as "Fold Change", but now represents Cliff's Delta × –log10(p).)

Gene ID: A unique numerical identifier for this specific gene.
Symbol: Shortened abbreviation or name that represents this gene.
Ensembl Gene ID: A unique identifier assigned by Ensembl for genomic data mapping.
CSI Score: A combined effect size and statistical significance measure for cardiac muscle cell. Higher scores indicate a stronger, more significant difference in expression.
Average CSI: csi sum / gene count
Cell network configuration

This network visualizes key genes for cardiac muscle cell. It primarily includes:
1. Top genes highly significant for this cell (Num. Top Cell Genes - based on the 'Min. CSI' setting).
2. Any additional specific 'Context Genes' you add below.
The final network is a combined view. Choose an Interaction Source (pathways or protein interactions) and optionally compare CSI scores with a Baseline Cell Type.

Maximum number of selected genes.
Select a context for the baseline cell.
Select a context for the target cell.
Target Cell for CSI:  cardiac muscle cell (CL0000746)

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Nodes (Genes):
 Query Gene
Node size also reflects Target Cell CSI magnitude.
Node Color (Target Cell CSI in specific network):
 Very High
 High
 Medium
 Low
 Very Low
 N/A or Not Sig.
Edges (Interactions):
 STRING (Protein-Protein)
 ONTOLOGY (Shared Pathway)
 Colors vary by pathway category; default arrow applies.

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## Summary The [cardiac muscle cell](/details-cell/CL0000746), or cardiomyocyte, is a highly specialized, terminally differentiated cell responsible for the contractile force of the heart. Analysis of its gene expression specificity reveals a dual identity. While expected contractile and structural proteins such as [MYOZ2](/details-gene/51778) and [MYLK3](/details-gene/91807) are significant markers, the cell's unique transcriptional landscape is overwhelmingly defined by a complex machinery of post-transcriptional regulation. The long non-coding RNA [NEAT1](/details-gene/283131) is the single most specific marker, and numerous RNA-binding proteins and splicing factors like [DDX17](/details-gene/10521) and [PNISR](/details-gene/25957) rank among the top identifiers. This suggests that the cardiomyocyte's identity and function are maintained not just by the presence of muscle proteins, but by a highly specialized and continuously active system of RNA processing and nuclear organization. ## Key Characteristics and Function **Overall**, the gene significance profile of the [cardiac muscle cell](/details-cell/CL0000746) points to a sophisticated integration of structural mechanics, nuclear regulation, and signaling. Key functional clusters emerge from its top specificity markers. * **Contractile and Sarcomeric Machinery:** As expected for a muscle cell, several top markers are integral to the sarcomere and its function. [MYOZ2](/details-gene/51778), a Z-disc protein that binds calcineurin ([Link](https://doi.org/10.1073/pnas.260501097)), and [MYLK3](/details-gene/91807) (cardiac myosin light-chain kinase), are highly specific, underscoring their critical roles in calcium-mediated contraction. The expression of [MYL12A](/details-gene/10627), a myosin regulatory light chain, and [TRIM54](/details-gene/57159), a muscle-specific ring finger protein that interacts with the titin kinase domain ([Link](https://doi.org/10.1006/jmbi.2001.4448)), further cements the importance of a finely tuned contractile apparatus. * **Nuclear Organization and Post-Transcriptional Regulation:** A striking feature of the cardiomyocyte is the exceptional specificity of genes involved in RNA processing and nuclear architecture. The top marker, [NEAT1](/details-gene/283131), is a lncRNA that serves as a core structural component of paraspeckles, nuclear bodies involved in sequestering proteins and regulating gene expression. This is complemented by a suite of highly specific RNA helicases and binding proteins, including [DDX17](/details-gene/10521), [PNISR](/details-gene/25957), [HNRNPA1](/details-gene/3178), [RBM39](/details-gene/9584), [HNRNPC](/details-gene/3183), and [DDX5](/details-gene/1655). The prominence of this group strongly suggests that alternative splicing and mRNA stability are critical, specialized functions that allow these long-lived cells to adapt their proteome in response to physiological demands. * **Signaling and Metabolism:** The cell's interaction with its environment is highlighted by the specific expression of [CHRM2](/details-gene/1129), the muscarinic M2 acetylcholine receptor, which is fundamental to the parasympathetic regulation of heart rate. Furthermore, the significant specificity of [TXNIP](/details-gene/10628), an inhibitor of the antioxidant protein thioredoxin, points to a tightly controlled redox signaling environment, essential for managing the high metabolic load and oxidative stress inherent to cardiac function. * **Defining by Absence (Anti-Markers):** The list of anti-markers is dominated by genes encoding core components of the mitochondrial electron transport chain, such as [CYTB](/details-gene/4519), [ND4](/details-gene/4538), [COX1](/details-gene/4512), and [ATP6](/details-gene/4508). The low `csi_z` score for these genes is not indicative of low mitochondrial content; on the contrary, cardiomyocytes are rich in mitochondria. Instead, it demonstrates that high-level expression of these genes is not unique to cardiomyocytes, as many other cell types share a heavy reliance on aerobic respiration. This highlights that while mitochondrial function is vital, it is not a *distinguishing* feature that sets the cardiomyocyte apart from all other cells at the level of expression specificity. ## Clinical Significance and Contextual Roles While this analysis provides an `Overall` view without a direct disease comparison, the key specific markers of the [cardiac muscle cell](/details-cell/CL0000746) have profound clinical implications. The high specificity of sarcomeric proteins like [MYOZ2](/details-gene/51778) and [MYLK3](/details-gene/91807) aligns with their established roles in inherited cardiomyopathies. Mutations in genes encoding components of the contractile apparatus are a primary cause of hypertrophic and dilated cardiomyopathies. The specific expression of these genes in cardiac muscle, as confirmed by this analysis and supporting literature ([Link](https://doi.org/10.1006/geno.2000.6399)), makes them prime targets for both diagnostic screening and therapeutic development. Perhaps more significantly, the data suggest that dysregulation of RNA processing may be a central, underappreciated mechanism in cardiac disease. The high specificity of numerous splicing factors ([DDX17](/details-gene/10521), [RBM39](/details-gene/9584), [HNRNPA1](/details-gene/3178)) implies that aberrant splicing events could be a major contributor to pathology. Splicing defects in genes like Titin (TTN) are already known to cause cardiomyopathy. This analysis suggests that the machinery controlling these events is itself a highly specific feature of the cardiomyocyte, and therefore a potential point of vulnerability. Similarly, the role of [NEAT1](/details-gene/283131) in cardiac pathophysiology is an area of growing interest, with studies linking its expression to cardiac hypertrophy and fibrosis. Its position as the top specificity marker underscores its potential as a biomarker and therapeutic target. ## Potential Mechanisms and Research Directions 1. **Hypothesis:** The high specificity of a large cohort of RNA-binding proteins and helicases (e.g., [DDX17](/details-gene/10521), [PNISR](/details-gene/25957), [HNRNPA1](/details-gene/3178)) indicates that cardiac muscle cells employ a unique, cell-type-specific "splicing code" to generate a proteome optimized for extreme mechanical and metabolic stress. This specialized post-transcriptional regulation is likely critical for both long-term homeostasis and adaptive responses, and its failure may precede the onset of contractile dysfunction in heart disease. * **Surprising Findings:** The fact that the specificity of RNA processing factors rivals or exceeds that of many canonical muscle-specific structural proteins is unexpected. It elevates the importance of post-transcriptional regulation from a general cellular process to a core identity feature of the cardiomyocyte. * **Testable Questions:** Using long-read sequencing on isolated human cardiomyocytes, can a comprehensive, cardiomyocyte-specific isoform catalog be created? Furthermore, does siRNA-mediated knockdown of top-ranked splicing factors like [DDX17](/details-gene/10521) in iPSC-cardiomyocytes lead to a predictable shift in the splicing of key sarcomeric or metabolic transcripts, and does this correlate with altered calcium handling or contractility? 2. **Hypothesis:** As the most specific gene marker, the long non-coding RNA [NEAT1](/details-gene/283131) forms the structural core of nuclear paraspeckles that function as dynamic regulatory hubs in [cardiac muscle cells](/details-cell/CL0000746). These domains may act to sequester and buffer the activity of specific transcription factors or RNA-binding proteins, thereby maintaining the stable yet responsive gene expression program required for cardiac function and preventing pathological remodeling. * **Surprising Findings:** The premier marker of a cell defined by physical contraction is not a protein but a non-coding structural RNA. This challenges a protein-centric view of cell identity and points toward the critical role of nuclear architecture in maintaining the phenotype of a terminally differentiated cell. * **Testable Questions:** Does the number, size, or protein composition of [NEAT1](/details-gene/283131)-defined paraspeckles change in cardiomyocytes subjected to hypertrophic stimuli (e.g., endothelin-1 treatment)? Does targeted degradation of [NEAT1](/details-gene/283131) in a mouse model using AAV-delivered antisense oligonucleotides result in cardiac dysfunction or an exaggerated response to pressure-overload stress?