Noncoding DNA

Slide 1 · Noncoding DNA

Molecular architecture, regulatory variation, and implications for pathology

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Classify the major functional non–protein-coding DNA elements.

Explain promoter–enhancer regulation and the distinction between sequence and expression.

Differentiate SNPs, linkage disequilibrium, and copy-number variants.

Interpret how noncoding variation can contribute to phenotype and disease.

Slide 3 · Molecular pathology begins before protein synthesis

DNA sequence

Regulatory context

RNA expression

Protein activity

Cell phenotype

Disease may arise from a changed regulatory program, even when the protein-coding sequence is intact.

Slide 4 · Human genome: Approximate scale

The human genome comprises approximately 3.2 billion DNA base pairs.

Approximately 20,000–25,000 protein-encoding genes.

Only about 1.5% of genomic DNA is protein-coding.

Slide 5 · Coding sequence ≠ all biologically important sequence

Protein-coding sequence

Specifies amino acid sequence

Altered coding can change protein structure

Occupies a small genomic fraction

Noncoding sequence

Can regulate transcription or RNA fate

Includes structural chromosomal regions

May influence gene expression without altering protein sequence

Slide 6 · Why gene number does not explain organismal complexity

Organisms with similar gene counts can display major phenotypic differences.

A gene can yield multiple transcripts and protein isoforms.

Cellular identity also depends on when, where, and how much each gene is expressed.

Slide 7 · “Genome dark matter”: A historical label

Noncoding does not mean transcriptionally silent or biologically irrelevant.

Pervasive transcription and gene-regulatory potential.

Many transcribed or biochemically active segments remain incompletely characterized.

Slide 8 · Biochemical activity versus proven biological function

Evidence of molecular activity

RNA transcription detected

Protein binding detected

Accessible chromatin detected

Stronger functional inference

Sequence perturbation changes output

Phenotypic impact is reproducible

Mechanism is supported in relevant cells

A biochemical signal alone is insufficient to establish essential organism-level function.

Slide 9 · A practical map of noncoding genomic elements

Regulatory DNA: Promoters and enhancers.

Chromatin-organization sites: Architecture and access.

Regulatory RNAs: Transcribed but not translated.

Structural regions: Telomeres, centromeres, repeats.

Mobile elements: Transposon-derived genomic sequence.

Slide 10 · Promoters: Local initiation control

Promoter regions recruit transcription machinery and associated regulatory proteins.

Their relationship to the transcription start site helps define gene-specific initiation.

A promoter can be present yet inactive in an inappropriate cellular context.

Slide 11 · From promoter occupancy to primary transcript

Transcription factors

Promoter engagement

RNA polymerase recruitment

Pre-mRNA synthesis

Simplified mechanism; Chromatin accessibility and signaling state can modify every step.

Slide 12 · Promoter variants alter transcription, not necessarily protein sequence

A noncoding substitution may modify a transcription-factor binding motif.

The resulting effect can increase, decrease, or leave expression unchanged.

Functional consequences depend on the relevant cellular environment.

Slide 13 · Enhancers regulate transcription at a distance

Enhancers recruit regulatory proteins and can influence transcription from remote genomic positions.

DNA looping that allows an enhancer to interact with a promoter.

Distance in the linear DNA sequence is not the same as distance in the folded nucleus.

Slide 14 · Enhancer–promoter coupling

Enhancer bound

Chromatin loop forms

Promoter contacted

Transcription modulated

The same coding gene may have multiple enhancer inputs.

Slide 15 · Cell-type specificity emerges from regulatory wiring

A regulatory sequence may be active in one cell type and inactive in another.

Cell lineage influences transcription-factor abundance and chromatin accessibility.

Identical genomes can generate different expression programs and cellular identities.

Slide 16 · Promoter versus enhancer

Promoter

Typically near its target initiation region

Central to assembly of transcription machinery

Initiation-site oriented

Enhancer

Can act across substantial genomic distances

Modulates promoter output

Often highly context-dependent

Slide 17 · Cis-regulatory versus trans-acting factors

Cis-regulatory element

DNA site located on the same DNA molecule

Examples: Promoter or enhancer

A local sequence variant may change binding

Trans-acting factor

Diffusible RNA or protein regulator

Often binds multiple DNA targets

Its altered abundance can affect many genes

Slide 18 · Silencers and insulators: Additional regulatory vocabulary

Silencers reduce expression in a context-dependent manner.

Insulator/boundary-associated elements can constrain inappropriate enhancer–promoter interactions.

Their effects reflect the interplay of sequence, proteins, and three-dimensional chromatin.

Slide 19 · One pathogenic regulatory route

Noncoding variant

Factor binding altered

Target expression changed

Cell behavior altered

Disease phenotype

A change in expression can be clinically important even without a coding mutation.

Slide 20 · A regulatory variant can act by gain or loss

Gain: Create or strengthen an activating motif.

Loss: Disrupt an activating motif or a regulatory contact.

Direction of gene-expression change is empirical; It cannot be inferred from variant location alone.

Slide 21 · The gene nearest a variant is not always its target

Long-range regulation can connect a distal element with a non-neighboring gene.

Physical proximity in linear genome coordinates is an unreliable sole targeting rule.

Experimental or multi-omic evidence helps connect the variant to its effector gene.

Slide 22 · Regulatory variant interpretation: Causal logic

Variant observed

Regulatory locus implicated

Target gene identified

Expression consequence shown

Phenotype linked

Association, regulatory localization, and functional validation are distinct evidentiary steps.

Slide 23 · Chromatin organization is not merely packaging

Genomic sites that organize and maintain higher-order chromatin.

DNA folding can influence which regulatory elements contact one another.

Architecture shapes access of regulatory proteins to genomic sequences.

Slide 24 · Euchromatin and heterochromatin

Euchromatin

Relatively dispersed on light microscopy

Generally accessible and transcriptionally permissive

Can support active gene expression

Heterochromatin

Densely packed chromatin

Often transcriptionally repressed

Important for chromosome organization

Slide 25 · Three-dimensional contacts complicate linear maps

Enhancers and target promoters may be far apart along the DNA strand.

Folding changes physical proximity within a nucleus.

A regulatory variant may influence a gene outside its nearest annotated locus.

Slide 26 · Chromatin state connects DNA to transcription

DNA sequence

Chromatin access

Transcription factor binding

Promoter activity

RNA output

Slide 27 · Interpretation pitfall: One regulatory map is not universal

Chromatin and transcription-factor profiles vary across tissues and states.

A candidate enhancer should be evaluated in the biologically relevant cell population.

Absence of activity in one assay does not prove inactivity across all tissues.

Slide 28 · Noncoding DNA can encode functional RNA

Noncoding regulatory RNAs as a major class of noncoding elements.

The source specifically highlights microRNAs and long noncoding RNAs.

These RNAs regulate gene output without being translated into proteins.

Slide 29 · MicroRNA: A post-transcriptional control route

MiRNA generated

Target mRNA recognized

Translation reduced / RNA destabilized

Protein output modified

A single miRNA can participate in a network of mRNA targets.

Slide 30 · MicroRNA: Implications for cellular phenotype

MicroRNAs frequently fine-tune rather than switch gene expression absolutely.

One regulatory RNA can influence multiple components of a pathway.

Dysregulation can contribute to changes in cell differentiation, survival, or proliferation.

Slide 31 · Long noncoding RNA: Diverse mechanisms

Long noncoding RNAs are a heterogeneous group, not one mechanistic category.

Some participate in chromatin-associated regulatory complexes.

Others act through RNA–protein or RNA–RNA interactions; Function must be established case by case.

Slide 32 · Regulatory RNA versus untranslated region

Regulatory noncoding RNA

Transcribed as its own RNA product

Can regulate other transcripts or chromatin

Examples: MiRNA, lncRNA

UTR of a coding mRNA

Part of a protein-coding transcript

Not itself translated into amino acids

Can affect stability, localization, and translation

Slide 33 · Why widespread transcription requires careful interpretation

RNA detection reveals transcription, not automatically necessity.

Noise, transient intermediates, and functional products must be distinguished.

Perturbation plus appropriate phenotype provides stronger causal support.

Slide 34 · Noncoding sequence can have structural functions

Telomeres protect chromosome termini.

Centromeres support chromosome segregation machinery.

Satellite repeats contribute to centromeric and heterochromatic organization.

Slide 35 · Telomeres: Protective chromosome termini

Telomeres comprise repetitive DNA at the ends of linear chromosomes.

They distinguish physiological chromosome ends from DNA breaks.

Changes in telomere maintenance are relevant to replicative capacity and genome stability.

Slide 36 · Telomere failure: Conceptual consequence

Telomere protection lost

Chromosome end appears damaged

Damage responses / end joining

Genome instability risk

Slide 37 · Centromeres: Chromosome-segregation sites

Centromeric DNA is associated with kinetochore formation.

Kinetochore machinery mediates interaction with the mitotic spindle.

Centromere function is therefore central to accurate chromosome segregation.

Slide 38 · Satellite DNA: Repeating structural sequence

Arrays of short repeated units that can extend for large distances.

Satellite repeats are prominent in centromeric regions.

Their structural roles should not be confused with classic protein-coding functions.

Slide 39 · Telomere versus centromere

Telomere

Chromosome end

Protects terminal DNA

Relates to replication and end stability

Centromere

Chromosome segregation region

Associated with kinetochore

Relates to spindle attachment and partitioning

Slide 40 · Mobile genetic elements occupy a major genomic fraction

Mobile elements as accounting for more than one third of the human genome.

Their historical movement contributed to genomic rearrangement and diversity.

Many copies are no longer capable of autonomous mobility.

Slide 41 · Transposon-derived change: Possible trajectories

Mobile element sequence

Insertion / rearrangement

Local genomic context changes

Neutral or regulatory effect

The outcome depends on the element, its activity, and insertion site.

Slide 42 · Possible biological consequences of mobile DNA

Insertion may disrupt a coding or regulatory region.

Mobile-element sequence may contribute regulatory motifs.

Repeated elements can facilitate genomic rearrangements and structural diversity.

Slide 43 · Repeat-rich DNA does not imply a single function

Structural or regulatory repeat

Can support chromosome architecture

May form regulatory binding environments

Function can be context-specific

Mobile-element-derived repeat

Originates from transposon activity

Many copies are inactive remnants

A subset affects gene regulation or rearrangement

Slide 44 · Most inherited genomic differences are small—but consequential

Human genomes are overwhelmingly sequence-identical.

A relatively small differing fraction still represents many variable sites.

Phenotypic differences reflect variants interacting with regulatory and environmental context.

Slide 45 · Single-nucleotide polymorphism: Definition

An SNP is variation at one nucleotide position among individuals.

Common SNP loci as typically biallelic.

SNPs occur in exons, introns, and intergenic sequence.

Slide 46 · Coding SNP versus noncoding SNP

Coding-region SNP

Can be synonymous or change an amino acid

May influence protein structure or function

Interpret through transcript and protein context

Noncoding SNP

May influence transcription or RNA processing

Often requires tissue-specific regulatory context

Can be benign, causal, or a correlated marker

Slide 47 · Not every noncoding SNP changes gene expression

Many variants are functionally neutral in the tested context.

Some alter a regulatory motif without measurable phenotypic effect.

Variant classification requires evidence beyond genomic coordinates.

Slide 48 · Linkage disequilibrium: Correlation between variants

Variants physically near each other may be inherited together.

A neutral SNP can tag a nearby functional variant.

Thus, a strong association signal may not identify the causal nucleotide.

Slide 49 · Genome-wide association: Avoid the causal leap

Association at locus

Correlated variants defined

Candidate function prioritized

Experimental validation

Linkage disequilibrium is central to the gap between association and mechanism.

Slide 50 · A marker SNP versus a causal regulatory SNP

Marker / tag SNP

Statistically associated with a phenotype

May be inherited with the causal allele

Not necessarily a functional DNA change

Causal regulatory SNP

Sequence alters a functional element

Changes target expression in relevant cells

Mechanism connects to phenotype

Slide 51 · Population differences require careful interpretation

SNP allele frequencies can vary across ancestral populations.

Linkage patterns can also vary; A useful marker need not transfer identically between groups.

Group-level variation cannot substitute for individual functional or clinical evidence.

Slide 52 · Copy-number variation: Definition and scale

CNVs involve deletion or duplication of contiguous genomic segments.

A scale from roughly 1 kilobase to millions of bases.

A CNV may include coding genes, regulatory DNA, or both.

Slide 53 · Copy-number variation: A dosage framework

Genomic segment deleted/duplicated

Sequence dosage changes

Expression may be altered

Phenotype may emerge

A CNV is not automatically pathogenic; Content, size, inheritance, and context matter.

Slide 54 · SNP versus CNV

SNP

Single nucleotide coordinate

Usually described as alternate alleles

Can change coding or regulatory sequence

CNV

Larger DNA interval

Different copy counts across individuals

Can involve one or many genes / elements

Slide 55 · Some CNVs act through regulatory elements

A copy-number change can alter enhancer dosage or topology.

The resulting effect can depend on which gene is controlled.

A CNV can be significant even without deleting an entire coding gene.

Slide 56 · From genomic finding to disease mechanism

An observed variant is not equivalent to an established cause.

Interpret the sequence, genomic context, inheritance, phenotype, and functional data together.

Regulatory variants often demand target-gene and tissue-specific evidence.

Slide 57 · Workup for a candidate noncoding variant

Describe variant

Map regulatory context

Identify target gene

Assess RNA / functional data

Integrate phenotype

Slide 58 · Clinical example: TERT promoter variants in cancer

Somatic TERT promoter mutations occur in several cancer types.

They can create or modify transcription-factor binding and increase TERT transcription.

This is a direct example of a pathogenic effect from noncoding sequence.

Slide 59 · TERT example: Causal chain

Promoter mutation

New regulatory binding

TERT expression increases

Telomerase activity supported

Proliferative capacity affected

Slide 60 · What the TERT example does not establish

A TERT promoter mutation is not present in all malignancies.

Detection alone does not establish a particular stage, grade, or prognosis.

Clinical utility depends on tumor classification, assay, and validated evidence.

Slide 61 · Case 1: A promoter variant

A tumor has a somatic nucleotide substitution upstream of a protein-coding gene. The gene’s exons remain unchanged, but RNA output is increased. Which mechanism is most direct?

A. Altered promoter regulation

B. Missense substitution

C. Protein truncation

D. Chromosomal nondisjunction

Slide 62 · Case 1: Interpretation

A. Altered promoter regulation

Promoter mutations can change transcription-factor occupancy.

Protein sequence may be completely unchanged.

The effect requires gene-expression and context-specific validation.

Slide 63 · Case 2: Association is not proof

A GWAS SNP is strongly associated with disease, but the nearest gene has no detectable expression change. What is the best next inference?

A. The SNP is necessarily causal

B. Search linked variants and distal targets

C. The GWAS signal is invalid

D. A coding mutation must explain it

Slide 64 · Case 2: Interpretation

B. Search linked variants and distal targets

Linkage disequilibrium can make a noncausal SNP a strong marker.

Enhancers may act on distal genes; The nearest gene is not always the target.

Fine-mapping and functional experiments can clarify mechanism.

Slide 65 · Case 3: Interpreting a deletion

A microdeletion removes an intergenic regulatory element but leaves nearby coding exons intact. Which statement is defensible?

A. No effect is possible because no exon is deleted

B. A gene-expression effect is plausible

C. All deletions cause the same phenotype

D. Pathogenicity is proven from location alone

Slide 66 · Case 3: Interpretation

B. A gene-expression effect is plausible

Regulatory dosage and chromatin contacts may be disrupted.

Target-gene assignment and phenotype must be evaluated.

Genomic location alone cannot establish pathogenicity.

Slide 67 · Common misconceptions in noncoding genomics

“Noncoding” does not mean “nonfunctional.”

“Transcribed” does not automatically mean “necessary.”

“Associated” does not automatically mean “causal.”

“Nearest gene” does not automatically mean “target gene.”

Slide 68 · Integrated comparison: Sequence, regulation, phenotype

Protein-coding variants may alter the properties of protein products.

Regulatory variants can alter the abundance, timing, or cellular distribution of otherwise normal proteins.

Copy-number changes can affect both coding content and regulatory architecture.

Slide 69 · Take-home framework

Recognize five broad noncoding element classes.

Ask which molecular output a variant could change: Transcription, RNA fate, structure, or dosage.

Connect molecular effect to a disease-relevant cell type.

Demand causal evidence before converting genetic association into mechanistic certainty.

Slide 70 · Selected references

Primary textbook

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11e (2026), Ch. 1, pp. 1–3

Supplementary genetics

MedlinePlus Genetics: Noncoding DNA; copy-number variation

Regulatory RNAs

Lee & Kim, Cell (2024); PMID 39547208

Function caveat

Doolittle, PNAS (2013); PMC3619371

Clinical example

Rachakonda et al., Int J Cancer (2021); PMID 34313327

Fine-mapping

Li & Zhou, Nat Rev Genet (2025); doi:10.1038/s41576-025-00869-4