Sunday, January 16, 2022

Evidence of Purposeful Evolution

Darwin's evolution challenged!

A recently published article in Nautre challenged evolution theory suggesting DNA repair was the more likely candidate driving evolutionary development than the environmental conditions thought to be the driver of natural selection. In some sense the two may be linked, but this study showed how epigenome-associated mutation bias reduced the occurrence of deleterious mutations, challenging the prevailing paradigm that mutation is a directionless force in evolution.

Quantitative assessment of DNA gain and loss through DNA double-strand break (DSB) repair processes suggests deletion-biased DSB repair causes ongoing genome shrinking in A. thaliana, whereas genome size in barley remained nearly constant.

Alu elements are the most abundant transposable elements (capable of shifting their positions) containing over one million copies dispersed throughout the human genome. Introduction of as little as 0.7% sequence divergence between Alu elements resulted in a significant reduction in recombination, which indicates even small degrees of sequence divergence reduce the efficiency of homology-directed DSB repair.  

The emergence of recombination-activating genes (RAGs) in jawed vertebrates endowed adaptive immune cells with the ability to assemble a diverse set of antigen receptor genes. Innate Natural Killer (NK) cells are unable to express RAGs or RAG endonuclease activity during ontogeny. They exhibit a cell-intrinsic hyperresponsiveness, but a diminished capacity to survive following virus-driven proliferation, a reduced expression of DNA damage response mediators, and defects in the repair of DNA breaks. However, RAG expression in uncommitted hematopoietic progenitors and NK cell precursors marks functionally distinct subsets of NK cells in the periphery, demonstrating a novel role for RAG in the functional specialization of the NK cell lineage. 

The most active region of Human Chromosome 19 has a long history of recombinations that define the expression patterns of telomeric and centromeric proportions of Killer-cell immunoglobulin-like receptor (KIR) gene's encoding receptors. KIR's bind cells presenting MHC class 1 HLA haplotype combinations, that vary significantly across tissues in different population groups. Further, the deletion rate in Zinc Finger clusters (ZNF) located around 19q13.42, near KIR and C19MC between 51,012,739 and 55,620,741 are about twofold higher than the background deletion rate. 

The relationship between deletions and mutation may indeed play a direct role in rapidly evolving, innate immunity. This may just begin to explain the speed at which global populations can respond and survive pandemics caused by the likes of COVID-19. And, the '19' in its nomenclature may go beyond time to the very chromosome responsible for innate immune diversity.

Wednesday, November 17, 2021

Retroviral Defense And Mitochondrial Offense

Chromosomal DNA has played host to the long game of viral insertions that repeat and continue as a genetic and epigenetic symbiosis along its phosphate and pentose sugar backbone. But, the bacterial origin of mitochondria and its hosted DNA also promotes its offense. 

Research suggests that retrovirus insertions evolved from a type of transposon called a retrotransposon. The evolutionary time scales of inherited, endogenous retroviruses (ERV) and the appearance of the zinc finger gene that binds its unique sequences occur over same time scales of primate evolution. Additionaly the zinc-finger genes that inactivate transposable elements are commonly located on chromosome 19. The recurrence of independent ERV invasions can be countered by a reservoir of zinc-finger repressors that are continuously generated on copy number variant (CNV) formation hotspots.

One of the more intiguing aspects of prevalent CNV hotspots on chromosome 19 are their proximity to killer immunoglobulin receptor gene's (KIR's) and other critical gene's of the innate immune system.

Frequently occuring DNA breaks can cause genomic instability, which is a hallmark of cancer. These breaks are over represented at G4 DNA quadruplexes within, hominid-specific, SVA retrotransposons and generally occur in tumors with mutations in tumor suppressor genes, such as TP53. Cancer mutational burden is shaped by G4 DNA, replication stress and mitochondrial dysfunction, that in lung adenocarcinoma downlregulates SPATA18, a mitochondrial eating protein (MIEAP) that contributes to mitophagy. 

Genetic variations, in non-coding regions can control the activity of conserved protein-coding genes resulting in the establishment of species-specific transcriptional networks. A chromosome 19 zinc finger, ZNF558 evolved as a suppressor of LINE-1 transposons, but has since been co-opted to singly regulate SPATA18. These variations are evident from a panel of 409 human lymphoblastoid cell lines where the lengths of the ZNF558 variable number tandem repeats (VNTR) negatively correlated with its expression. 

Colon cancer cells with p53 deletion were used to analyze deregulated p53 target genes in HCT116 p53 null cells compared to HCT116-p53 +/+ cells. SPATA18 was the most upregulted gene in the differential expression providing further insight to p53 and mitophagy via SPATA18-MIEAP.

p53 response elements (p53RE) can be shaped by long terminal repeats from endogenous retroviruses, long interspersed nuclear repeats, and ALU repeats in humans and fuzzy tandem repeats in mice. Further, p53 pervasively binds to p53REs derived from retrotransposons or other mobile genetic elements and can suppress transcription of retroelements. The p53- mediated mechanisms conferring protection from retroelements is also conserved through evolution. Certainly, p53 has been shown to have other roles in DNA  context, such as playing an important role in replication restart and replication fork progression. The absence of these p53-dependent processes can lead to further genomic instability. 

The frequency of variable length, long or short nucleotide repeats and their locations within a gene may be key to the repression of DNA sequences that would otherwise cause genomic instability or protein expressions that would eat bacterial mitochondria or destroy its cell host. 

The complexity of variable length insertions is made evident when exhaustively analyzing a simple length 12 sequence for the potential frequency of each of its variable length repeats starting from a minumum variable length of 8.

Then, for TGTGGGCCCACA(12)

All possible internal variable length combinations from and including length 8:


For example, reviewing length (8) only:

TGTGGGCC (8) occurs 5 times

GTGGGCCC (8) occurs 8 times

TGGGCCCA (8) occurs 9 times

GGGCCCAC (8) occurs 8 times

GGCCCACA (8) occurs 5 times

Any repeat can be ranked based on its ocurrence within all possible combinations of a given sequence, known as the repeats' iScore rank. This illustrates a potential useful statistical ranking that, subject to biology may describe a repeats inherency to be more or less effective, in increments of the gene sequence. 

Repression of the most active sequences, especially in context of repeats may result in genetic variation. 

Wednesday, November 3, 2021

Chemo vs. Mecho

Data strongly suggests interaction between plasma membrane and submembrane at the endothelial surface controls the inflammatory response

A meta-analysis from six studies of global gene expression profiles of Blood Pressure (BP) and hypertension was performed in 7017 individuals. 34 genes were differentially expressed. Of these, 6 genes were linked including MYADM, which was the only gene, of 34 discovered across diastolic, systolic BP and hypertension. Knockdown of MYADM (19q13), a component of endothelial surface rafts induced an inflammatory phenotype altering barrier function through the increase of the adhesion receptor ICAM-1 (19p13). This is mediated by MYADM activation of ERM actin cytoskeleton proteins. 

Mechanical forces, without a definitive direction e.g., disturbed flow and relatively undirected stretch at branch points and other complex regions cause sustained molecular signaling of pro-inflammatory and proliferative pathways that include mechanical stretch tied to p53

ERM proteins also facilitate Sphingosine-1-phosphate (S1P) dependent egress for T-cells to migrate from lymphoid organs. Their directional migration, by blebbing is contained at the T-cell’s leading edge. This fundamentally different mode of migration is characterized by intracellular pressurization. Of the five S1P receptors S1P2 (19p13) is critical in the immune, nervous, metabolic, cardiovascular, musculoskeletal, and renal systems. Results suggest that the ratio between S1P1 and S1P2 (19p13) governs the migratory behavior of different T cell subsets. 

Human NK cells express S1P1 mRNA. Activation with IL-2 increases S1P1, promotes S1P4 (19p13) and S1P5 (19p13) but not S1P2 (19p13) expression. Unlike S1P1, S1P2 (19p13) signals through several different G-alpha subunits, Gi, G12/13, and Gq. S1P5 (19p13) is also expressed in human and mouse NK cells and was required for mobilization to inflamed organs. S1P5-deficient mice had aberrant NK cell homing during steady-state conditions. NK cell trafficking in vivo requires a dedicated sphingosine 1-phosphate receptor. 

Virus-infected mast cells selectively recruit NK cells and positively modulate their functions through mechanisms dependent on soluble mediators, such as interferons. Skin mast cells protect mice against vaccinia virus by triggering mast cell receptor S1P2 (19p13) and releasing antimicrobial peptides. S1P2 (19p13),  a negative regulator of platelet derived growth factor (PDGF) induced migration and proliferation as well as SphK1 expression. 

S1P inhibits macropinocytosis (internalizing extracellular materials) and phosphorylation of Akt via S1P2 (19p13) stimulation resulting in diminished antigen capture.

S1P1, S1P2 (19p13) and S1P3 receptors have redundant or cooperative functions for the development of a stable and mature vascular system during embryonic development. S1P2 (19p13)  and S1P3 are involved in regulation of endothelial barrier function, fibrosis, and vasoconstriction. 

Adipogenic differentiation is inhibited by S1P2 (19p13) as mediated by C/EBPα and PPARγ, which induces PEPCK, a more recent gene of interest in cancer that acts at the junction between glycolysis and the Krebs cycle.

Mecho or chemo, chicken or egg, what first?

Tuesday, October 19, 2021

Blood Pressure, Immunity and p53 Checkpoint.


A few chromosome 19 curiosities developed into a deep-dive after looking into the primordial immune complex, the origins of MHC Class I and antigen receptors as revealed by comparative genomics. And the plot thickened because repressors (of endogenous retroviruses) that gained their binding affinity to retrovirus sequences at the same time their targets invaded the human lineage are preferentially located on chromosome 19. Further, the deletion rate in Zinc Finger clusters (ZNF) located around 19p.12 and 19q13.42, particularly between 51,012,739 and 55,620,741 are about twofold higher than the background deletion rate. A lot going on at this very active location which motivated this article.

At 19q13.42 kallikrein related peptidase (KLK’s), leukocyte immunoglobulin-like receptors (LILR’s) including killer-cell immunoglobulin-like receptor (KIR’s) as well MYADM, an important blood pressure related gene may also provide some clues to immunity variables that originate from or are influenced by this volatile region.

The retrotransposon bombardment of 19q13.42 and double background deletion rate is a significant remnant. However, after evolutionary MHC changed chromosomes ZNF, and within its range the chromosome 19 miRNA cluster (C19MC - 53,671,968 and 54,264,387) were still subjected to the deleterious effect of  transposons. Regardless, suppression mechanics have kept epigenetic, regulatory and transcription processes, across gene’s far and wide on the move at a relatively stable rates. For example, reverse-transcribed SARS-CoV-2 RNA can integrate into the genome of cultured human cells and can be expressed in patient-derived tissues, but the effects of suppression may be sufficient to illicit a more permanent natural defense. In any event insertions and DNA damage are closely related and associated with loss of p53 that results in centrosome amplification. 

As cells pass through epithelial to mesenchymal transition (EMT), DNA damage prevents the normal reduction of p53 levels diverting the transcriptional program toward mesoderm without induction of an apoptotic response. In contrast, TP53-deficient cells differentiate to endoderm with high efficiency after DNA damage, suggesting that p53 enforces a “differentiation checkpoint” in early endoderm differentiation that alters cell fate in response to DNA damage.

Reproduction, Blood Pressure and NK

In reproduction, some of the 59 known miRNAs from primate-specific C19MC are highly expressed in human placentas and in the serum of pregnant women. They are also packaged into extracellular vesicles of diverse sizes, including exosomes and endow non-trophoblast cells with resistance to a variety of viruses. At least miR-517a-3p (a C19MC from fetal placenta) was incorporated into maternal NK cells in the third trimester, and it was rapidly cleared after delivery. miRNA's regulate the migration of human trophoblasts and suppress EMT genes critical for maintaining the epithelial cytotrophoblasts stem cell phenotype. 

Maternal uterine or decidual Natural Killer cells (dNK) express AT1, AT2, ANP, proteins of Renin Angiotensin System (RAS) suggesting dNK have the potential to contribute to changes in blood pressure that occur between days 5 and 12 of pregnancy in mice. And, pressure related mechanical stretch on endothelial cells interconnects innate and adaptive immune response in hypertension.

Pressure variables in cells and tissues may result from infection, inflammation and membrane stretch, including inner mitochondrial membrane that affects electron transport chain, endoplasmic reticulum, antigen production, presentation and exosome bound p53 / miRNA release.  ANP colocalization to dNK’s suggests that dNK RAS, at day 12 infers a localized RAS related responsiveness. STAT3 in monocytes was activated by increased endothelial stretch and is involved in driving almost all of the pathways that control NK cytolytic activity as well as the reciprocal regulatory interactions between NK cells and other components of the immune system. The crosstalk between STAT3 and p53/RAS signaling controls cancer cell metastasis and cisplatin resistance via the Slug/MAPK/PI3K/AKT-mediated regulation of EMT and autophagy .

Educating NK Subsets 

Looking into some of the ~15 genes scattered among C19MC (~sixty miRNA's) between 53,671,968 and 54,264,387;

1. MYADM was one of two blood pressure signature genes differentially expressed for systolic, diastolic blood pressure and hypertension. Of the ~35 identified genes, several more strongly related to immune cell functions including PRF1, GNLY, TAGAP, IL2RB, GZMB and CD97, NKG7, CLC that are located on chromosome 19. The endothelium maintains a barrier between blood and tissue that becomes more permeable during inflammation. MYADM controls endothelial barrier function through ezrin, radixin, and moesin dependent regulation of ICAM-1 expression an essential receptor for NK interaction.

2. PRPF31 is recruited to introns following the attachment of U4 and U6 (spliceosome) RNA’s. Experiments using PRPF31 determined p53 activation is a general consequence of interfering with the spliceosome. 

3. LILRB1 receptor is expressed on immune cells where it binds to MHC class I molecules on antigen-presenting cells and transduces a negative signal that inhibits stimulation of an immune response. LILRB1 has a polymorphic regulatory region that enhances transcription in NK Cells and recruits zinc finger protein YY1 that inhibits p53. It also educates expanded human NK cells and defines a unique antitumor NK cell subset with potent antibody-dependent cellular cytotoxicity.

Monocyte/macrophage immunoglobulin-like receptors (MIR) genes are closely linked to the KIR gene family and the gene for FcαR at 19q13.4. The linkage was discovered in 1997 when a mouse sequence related to MIR mapped to a region on chromosome 7 syntenic with human 19q13.4. In 2012 a cluster of genetic loci, from multiple mouse strains and across anatomical sites was found to jointly contribute to the development of both thymic and splenic invariant natural killer T-cell NKT-cell levels. The dominant cluster was on mouse chromosome 7 and included almost all the non-C19MC genes located within the human C19MC region:– MYADM, CACNG7, VSTM1, TARM1, PRKCC(G), TFPT, NDUFA3, CNOT3, LENG1, TSEN34, RPS9

Four of nineteen knockout genes, that enhanced NK cell function were on chromosome 19 including GSK3 that phosphorylates Mdm2 to regulate p53 abundance, which would contribute to NK enhancement. 

A study of MHC disassortative mating in humans found Israeli’s were more gene similar, but MHC dissimilar than Europeans who were gene dissimilar and MHC dissimilar . Now, a recent study in American Indians found remarkably low KIR and HLA diversity in Amerindians that revealed signatures of strong purifying selection shaping the centromeric KIR region. This narrows to the importance of LILR-KIR region on chromosome19 that codes for the strongest NK cell educator receptors.

p53 regulates exosomes and miRNA’s directly influence NK responsiveness including regulation of dNK during pregnancy. Exosomes regulated by p53 also transfer it and can suppress growth and proliferation of p53 negative cells. Further, miRNA’s, induced by p53 can directly target ULBP2 mRNA and reduce its cell-surface expression.

Disease highlights
rs78378222 polymorphism in the 3'-untranslated region of TP53 contributes to development of age-associated cataracts by modifying miRNA-125b-induced apoptosis of lens epithelial cells. miRNA-125b is a novel negative regulator of p53. Deleting PRPF31 activates the p53 pathway and triggers retinal progenitor cells apoptosis. The members of the miR-125 family (miR-125a on chromosome 19q13.4 and miR-125b on chromosome 21q21.1) reside in two distinct human miRNA clusters with the let-7 and miR-99 families and these miRNAs are thus likely co-transcribed.
More succinctly, NK cells are alerted to induction of p53 in cancer cells by upregulation of the NKG2D ligands ULBP1 and ULBP2. p53 also induces expression of miR-34a and miR-34c, which target ULBP2 mRNA for destabilization. Observations suggest two possibly contrasting roles for p53 in NKG2DL expression and requires more investigation into how the regulation is fine-tuned. Extending this model to human populations would suggest that p53 must be inactivated among those with a robust NK response (those with B haplotypes). 

Taken together, our data suggest functional interactions between KIR and HLA modify risks of basal cell carcinoma (BCC) and squamous cell carcinoma, and that KIR encoded by the B genes provide selective pressure for altered p53 in BCC tumors. 


The convergence of several important cellular mechanisms that point back to a 19q13.42 address may illustrate ancient and conserved elements that perpetuate and function as integrated biological units effecting blood pressure, reproduction and immunity. Many of these impart education to innate immunity.

Wednesday, July 28, 2021

Life, Dormancy or Death?

Cellular biology is viewed through different lenses, but pregnancy offers a perspective on the invasive origin of cell division, the senescent state and cancer. Pregnancy causes Natural Killer cells of the decidua (dNK) to expand abundantly until they represent as much as 30% of the mucous membranes' cells. NK cells may be induced to expand by invading trophoblasts to realize the dNK trifecta - robust innate immunity that protects the embryo from maternal infection, modulation of trophoblast invasion and driver of vascular remodeling. However, in many cancers expansion of diverse NK populations fails to materialize and missing sub-sets of NK cell diversity provides a path for cancers unchecked growth. 

In decidual cells at the human maternal-fetal interface, CD82 - the metastasis suppressor may participate in intercellular communication with trophoblasts and limit their invasiveness. Trophoblasts enhance adhesiveness of dNK to the decidua's stromal cells, via the CXCL12/CD82/CD29 signaling pathway which contributes to CD56bright NK cell enrichment a necessary element for heathy pregnancy.

CD82 expression is downregulated in tumor progression of many human cancers and strongly correlated with tumor suppressor p53. It can be activated by p53 through a consensus binding sequence in the promoter. In human ovarian cancer a sequential genetic change at the TP53 and the CXCL12 receptors CXCR4  locus occurs during transformation of surface epithelium. Basal CXCR4 promoter activity in HCT116 colon carcinoma cells deleted of p53 was10-fold higher compared to that in parental HCT116 cells with functional wild-type p53.

The CXCL12 ligand is unique for its CXCR4 receptor and both are expressed in human first-trimester endometrial epithelial cells (EECs) at the mRNA and protein level. EEC-conditioned medium and recombinant human CXCL12 significantly increased the migration and invasion of EECs. CXCL12 has also been associated with the recruitment of CD56bright CD25+ dNK subsets in early pregnancy's.

CXCR4 is specifically upregulated in the human endometrium during the implantation window and increased immunostaining observed only when a blastocyst is present. CXCR4/CXCL12 not only enhances trophoblast invasiveness, but also limits over-invasiveness by upregulating CD82. CXCR4 activation increases the CXCL12-CXCR4 signaling axis stimulates vascular endothelial growth factor (VEGF) synthesis which induces CXCR4 and CXCL12 production. This synergistic regulation influences placental vascularization. CXCR4 suppresses apoptosis and increases the viability of trophoblasts. 

Undetectable disseminated tumor cells, in different tissue microenvironments restrain or allow the progression of breast cancer in the liver where in dormant milieu's there are selective increases in NK cells. Stroma crosstalk and exit from dormancy follows a marked contraction of the NK cell compartment and concurrent accumulation of activated hepatic stellate cells (aHSCs). Proteomics on liver co-cultures implicate aHSC-secreted CXCL12 in the induction of NK cell quiescence through CXCR4. CXCL12 expression and aHSC abundance are closely correlated in patients with liver metastases and were inversely correlated with NK cell abundance.

The dNK behavior that checks trophoblast invasion and promotes vascularization resembles immediate and invasive new cancers that may occur in cells of any tissue environment. Similarly expansion of resident tissue NK sub-sets in response may be the determiner of life, the shape of next generation cells, dormancy or death.  

Monday, June 28, 2021

Immunity keeping p53 in check!

In a 2012 study on the topology of the human and mouse m6A RNA methylomes Gene Ontology (GO) analysis of differentially expressed genes (DEG's) indicated a noteworthy enrichment of the p53 signaling pathway: 22/23 genes had differentially expressed splice variants, of which 18 were methylated. Moreover, 15 other members of the signaling pathway, which were not significant DEG's, exhibited significant differential isoform expressions. For example, isoforms of MDM4, needed for p53 inactivation were downregulated. Similar pro-apoptotic effects were observed in other pathway genes including MDM2, FAS and BAX. Higher apoptosis rate in HaCaT-T cells resulted with knockdown of m6A subunit METTL3, which also reversed a significant decrease in p53 activity. Modulation of p53 signaling through splicing may be relevant to induction of apoptosis by silencing of METTL3. 

Then, in a 2019 study of arsenite-induced human keratinocyte transformation knockdown of METTL3 significantly decreased m6A level, restored p53 activation and inhibited cellular transformation phenotypes in the arsenite-transformed cells. Further, it was demonstrated that m6A downregulated the expression of the positive p53 regulator, PRDM2, through the YTHDF2-promoted decay of PRDM2 mRNAs. Further, m6A upregulated the expression of negative p53 regulator, YY1 and MDM2 through YTHDF1-stimulated translation of YY1 and MDM2 mRNA. 

Finally in 2021 a discovery that YTHDF2 is upregulated in NK cells upon activation by cytokines, tumors, and cytomegalovirus infection. Ythdf2 deficiency in NK cells impaired its anti-tumor and anti-viral activity in vivo. YTHDF2 maintains NK cell homeostasis and terminal maturation, correlating with modulating NK cell trafficking and regulating Eomes, respectively. YTHDF2 promotes NK cell effector function and is required for IL-15-mediated NK cell survival and proliferation by forming a STAT5-YTHDF2 positive feedback loop. Analysis showed significant enrichment in cell cycle, division, and division-related processes, including mitotic cytokinesis, chromosome segregation, spindle, nucleosome, midbody, and chromosome. This data supports roles of YTHDF2 in regulating NK proliferation, survival, and effector functions. Transcriptome-wide screening identified Tardbp (TDP-43) to be involved in cell proliferation or survival as a YTHDF2-binding target in NK cells.

Downregulation of METTL3, which in spinal cord contributes with YTHDF2 to modulate inflammatory pain may upregulate differentially expressed p53 network splice variants that oppose YTHDF2 induced downregulation of p53, via PRDM2 leading to apoptotic or diseased cells. In diseased environments cytokines may upregulate YTHDF2 in NK cells leading to downregulation of p53 and cytoskeletal transformation that may be sufficient, at an immune synapse to advance cytolysis.

p53 signals may inform selections of cells and tissue that prime NK cells for advanced, personalized immune therapy. 

Sunday, June 20, 2021

First Intron DNA - Site for a Genetic Brain?

DNA Methylation

The first intron of a gene, regardless of tissue or species is conserved as a site of downstream methylation with an inverse relationship to transcription and gene expression. Therefore, it is an informative gene feature regarding the relationship between DNA methylation and gene expression. But, expression in induced pluripotent stem cells (iPSC's) has been a major challenge to the stem cell industry, because by comparison these cells have not yet reached the state of natural pluripotent or embryonic stem cells (ESC's).

In mice two X chromosomes (XC) are active in the epiblasts of blastocysts as well as in pluripotent stem cells. One XC is inactivated triggered by Xist (non coding) RNA transcripts coating it to become silent. Designer transcription factor (dTF) repressors, binding the Xist intron 1 enhancer region caused higher H3K9me3 methylation and led to XC's opening and X-linked gene repression in MEFs. This substantially improved iPSC production and somatic cell nuclear transfer (SCNT) preimplantation embryonic development. This also correlated with much fewer abnormally expressed genes frequently associated with SCNT, even though it did not affect Xist expression. In stark contrast, the dTF activator targeting the same enhancer region drastically decreased both iPSC generation and SCNT efficiencies and induced ESC differentiation. 

A genome-wide, tissue-independent quasi-linear, inverse relationship exists between DNA methylation of the first intron and gene expression. More tissue-specific, differentially methylated regions exist in the first intron than in any other gene feature. These have positive or negative correlation with gene expression, indicative of distinct mechanisms of tissue-specific regulation. CpGs in transcription factor binding motifs are enriched in the first intron and methylation tends to increase with distance from the first exon–first intron boundary, with a concomitant decrease in gene expression.

Since the relationship between sequence, methylation, repression and transcription is determinative in ESC differentiation it may also suggest a broader link to differential translation. Translation is required for miRNA-dependent transcript destabilization that alters levels of coding and noncoding transcripts. But, steady-state abundance and decay rates of cytosolic long non-coding RNA's (lncRNAs) are insensitive to miRNA loss. Instead lncRNAs fused to protein-coding reporter sequences become susceptible to miRNA-mediated decay. 

In this model, first intron DNA sequences that are differentially methylated, bind transcription factors that effect transcription, impact splicing, expressions of coding or non-coding transcripts and transcript destabilizations resulting in differential rates and possible variations in translation. This bottom-up, dynamic view of the classical process may elevate the first intron from 'junk' to a DNA 'brain' because it plays a more extensive role, heading the process toward translation of any gene or switching it off entirely.  

For this reason, among others Codondex uses first intron k-mers relative to the transcripts mRNA as the basis for comparing same gene transcripts in diseased cells or tissue samples. Further, p53 and BRCA1 miRNA key sequences, discovered using Codondex iScore algorithm, when transfected into HeLa cells resulted in significantly reduced proliferation that may result from this accelerated, transfected miRNA dependent decay.