Ubiquitin Ligase COP1 Suppresses Neuroinflammation by Degrading c/EBPß in Microglia.

Dysregulated microglia are intimately involved in neurodegeneration, including Alzheimer's disease (AD) pathogenesis, but the mechanisms controlling pathogenic microglial gene expression remain poorly understood. The transcription factor CCAAT/enhancer binding protein beta (c/EBPß) regulates pro-inflammatory genes in microglia and is upregulated in AD. We show expression of c/EBPß in microglia is regulated post-translationally by the ubiquitin ligase COP1 (also called RFWD2). In the absence of COP1, c/EBPß accumulates rapidly and drives a potent pro-inflammatory and neurodegeneration-related gene program, evidenced by increased neurotoxicity in microglia-neuronal co-cultures. Antibody blocking studies reveal that neurotoxicity is almost entirely attributable to complement. Remarkably, loss of a single allele of Cebpb prevented the pro-inflammatory phenotype. COP1-deficient microglia markedly accelerated tau-mediated neurodegeneration in a mouse model where activated microglia play a deleterious role. Thus, COP1 is an important suppressor of pathogenic c/EBPß-dependent gene expression programs in microglia.

IL-10 Signaling Remodels Adipose Chromatin Architecture to Limit Thermogenesis and Energy Expenditure.

Signaling pathways that promote adipose tissue thermogenesis are well characterized, but the limiters of energy expenditure are largely unknown. Here, we show that ablation of the anti-inflammatory cytokine IL-10 improves insulin sensitivity, protects against diet-induced obesity, and elicits the browning of white adipose tissue. Mechanistic studies define bone marrow cells as the source of the IL-10 signal and adipocytes as the target cell type mediating these effects. IL-10 receptor alpha is highly enriched in mature adipocytes and is induced in response to differentiation, obesity, and aging. Assay for transposase-accessible chromatin sequencing (ATAC-seq), ChIP-seq, and RNA-seq reveal that IL-10 represses the transcription of thermogenic genes in adipocytes by altering chromatin accessibility and inhibiting ATF and C/EBPß recruitment to key enhancer regions. These findings expand our understanding of the relationship between inflammatory signaling pathways and adipose tissue function and provide insight into the physiological control of thermogenesis that could inform future therapy.

Analysis of Genetically Diverse Macrophages Reveals Local and Domain-wide Mechanisms that Control Transcription Factor Binding and Function.

Non-coding genetic variation is a major driver of phenotypic diversity and allows the investigation of mechanisms that control gene expression. Here, we systematically investigated the effects of >50 million variations from five strains of mice on mRNA, nascent transcription, transcription start sites, and transcription factor binding in resting and activated macrophages. We observed substantial differences associated with distinct molecular pathways. Evaluating genetic variation provided evidence for roles of ∼100 TFs in shaping lineage-determining factor binding. Unexpectedly, a substantial fraction of strain-specific factor binding could not be explained by local mutations. Integration of genomic features with chromatin interaction data provided evidence for hundreds of connected cis-regulatory domains associated with differences in transcription factor binding and gene expression. This system and the >250 datasets establish a substantial new resource for investigation of how genetic variation affects cellular phenotypes.

Dissecting Immune Circuits by Linking CRISPR-Pooled Screens with Single-Cell RNA-Seq.

In multicellular organisms, dedicated regulatory circuits control cell type diversity and responses. The crosstalk and redundancies within these circuits and substantial cellular heterogeneity pose a major research challenge. Here, we present CRISP-seq, an integrated method for massively parallel single-cell RNA sequencing (RNA-seq) and clustered regularly interspaced short palindromic repeats (CRISPR)-pooled screens. We show that profiling the genomic perturbation and transcriptome in the same cell enables us to simultaneously elucidate the function of multiple factors and their interactions. We applied CRISP-seq to probe regulatory circuits of innate immunity. By sampling tens of thousands of perturbed cells in vitro and in mice, we identified interactions and redundancies between developmental and signaling-dependent factors. These include opposing effects of Cebpb and Irf8 in regulating the monocyte/macrophage versus dendritic cell lineages and differential functions for Rela and Stat1/2 in monocyte versus dendritic cell responses to pathogens. This study establishes CRISP-seq as a broadly applicable, comprehensive, and unbiased approach for elucidating mammalian regulatory circuits.

Excessive Polyamine Generation in Keratinocytes Promotes Self-RNA Sensing by Dendritic Cells in Psoriasis.

Psoriasis is a chronic inflammatory disease whose etiology is multifactorial. The contributions of cellular metabolism to psoriasis are unclear. Here, we report that interleukin-17 (IL-17) downregulated Protein Phosphatase 6 (PP6) in psoriatic keratinocytes, causing phosphorylation and activation of the transcription factor C/EBP-ß and subsequent generation of arginase-1. Mice lacking Pp6 in keratinocytes were predisposed to psoriasis-like skin inflammation. Accumulation of arginase-1 in Pp6-deficient keratinocytes drove polyamine production from the urea cycle. Polyamines protected self-RNA released by psoriatic keratinocytes from degradation and facilitated the endocytosis of self-RNA by myeloid dendritic cells to promote toll-like receptor-7 (TLR7)-dependent RNA sensing and IL-6 production. An arginase inhibitor improved skin inflammation in murine and non-human primate models of psoriasis. Our findings suggest that urea cycle hyperreactivity and excessive polyamine generation in psoriatic keratinocytes promote self-RNA sensation and PP6 deregulation in keratinocytes is a pivotal event that amplifies the inflammatory circuits in psoriasis.

Targeting Degradation of the Transcription Factor C/EBPß Reduces Lung Fibrosis by Restoring Activity of the Ubiquitin-Editing Enzyme A20 in Macrophages.

Although recent progress provides mechanistic insights into the pathogenesis of pulmonary fibrosis (PF), rare anti-PF therapeutics show definitive promise for treating this disease. Repeated lung epithelial injury results in injury-repairing response and inflammation, which drive the development of PF. Here, we report that chronic lung injury inactivated the ubiquitin-editing enzyme A20, causing progressive accumulation of the transcription factor C/EBPß in alveolar macrophages (AMs) from PF patients and mice, which upregulated a number of immunosuppressive and profibrotic factors promoting PF development. In response to chronic lung injury, elevated glycogen synthase kinase-3ß (GSK-3ß) interacted with and phosphorylated A20 to suppress C/EBPß degradation. Ectopic expression of A20 or pharmacological restoration of A20 activity by disturbing the A20-GSK-3ß interaction accelerated C/EBPß degradation and showed potent therapeutic efficacy against experimental PF. Our study indicates that a regulatory mechanism of the GSK-3ß-A20-C/EBPß axis in AMs may be a potential target for treating PF and fibroproliferative lung diseases.

Genomic Characterization of Murine Monocytes Reveals C/EBPß Transcription Factor Dependence of Ly6C- Cells.

Monocytes are circulating, short-lived mononuclear phagocytes, which in mice and man comprise two main subpopulations. Murine Ly6C+ monocytes display developmental plasticity and are recruited to complement tissue-resident macrophages and dendritic cells on demand. Murine vascular Ly6C- monocytes patrol the endothelium, act as scavengers, and support vessel wall repair. Here we characterized population and single cell transcriptomes, as well as enhancer and promoter landscapes of the murine monocyte compartment. Single cell RNA-seq and transplantation experiments confirmed homeostatic default differentiation of Ly6C+ into Ly6C- monocytes. The main two subsets were homogeneous, but linked by a more heterogeneous differentiation intermediate. We show that monocyte differentiation occurred through de novo enhancer establishment and activation of pre-established (poised) enhancers. Generation of Ly6C- monocytes involved induction of the transcription factor C/EBPß and C/EBPß-deficient mice lacked Ly6C- monocytes. Mechanistically, C/EBPß bound the Nr4a1 promoter and controlled expression of this established monocyte survival factor.

C/EBPß controls exercise-induced cardiac growth and protects against pathological cardiac remodeling.

The heart has the ability to grow in size in response to exercise, but little is known about the transcriptional mechanisms underlying physiological hypertrophy. Adult cardiomyocytes have also recently been proven to hold the potential for proliferation, a process that could be of great importance for regenerative medicine. Using a unique RT-PCR-based screen against all transcriptional components, we showed that C/EBPß was downregulated with exercise, whereas the expression of CITED4 was increased. Reduction of C/EBPß in vitro and in vivo resulted in a phenocopy of endurance exercise with cardiomyocyte hypertrophy and proliferation. This proliferation was mediated, at least in part, by the increased CITED4. Importantly, mice with reduced cardiac C/EBPß levels displayed substantial resistance to cardiac failure upon pressure overload. These data indicate that C/EBPß represses cardiomyocyte growth and proliferation in the adult mammalian heart and that reduction in C/EBPß is a central signal in physiologic hypertrophy and proliferation.

DNA demethylase activity maintains intestinal cells in an undifferentiated state following loss of APC.

Although genome-wide hypomethylation is a hallmark of many cancers, roles for active DNA demethylation during tumorigenesis are unknown. Here, loss of the APC tumor suppressor gene causes upregulation of a DNA demethylase system and the concomitant hypomethylation of key intestinal cell fating genes. Notably, this hypomethylation maintained zebrafish intestinal cells in an undifferentiated state that was released upon knockdown of demethylase components. Mechanistically, the demethylase genes are directly activated by Pou5f1 and Cebpß and are indirectly repressed by retinoic acid, which antagonizes Pou5f1 and Cebpß. Apc mutants lack retinoic acid as a result of the transcriptional repression of retinol dehydrogenase l1 via a complex that includes Lef1, Groucho2, Ctbp1, Lsd1, and Corest. Our findings imply a model wherein APC controls intestinal cell fating through a switch in DNA methylation dynamics. Wild-type APC and retinoic acid downregulate demethylase components, thereby promoting DNA methylation of key genes and helping progenitors commit to differentiation.

Exosomal long non-coding RNA AU020206 alleviates macrophage pyroptosis in atherosclerosis by suppressing CEBPB-mediated NLRP3 transcription.

Recent studies have suggested exosomes (EXO) as potential therapeutic tools for cardiovascular diseases, including atherosclerosis (AS). This study investigates the function of bone marrow stem cell (BMSC)-derived exosomes (EXO) on macrophage pyroptosis in AS and explores the associated mechanism. BMSC-EXO were isolated from healthy mice and identified. RAW264.7 cells (mouse macrophages) were exposed to oxLDL to simulate an AS condition. BMSC-EXO treatment enhanced viability and reduced lactate dehydrogenase release of macrophages. An animal model of AS was established using ApoE-/- mice. BMSC-EXO treatment suppressed plaque formation as well as macrophage and lipid infiltration in mouse aortic tissues. Moreover, BMSC-EXO decreased concentrations of pyroptosis-related markers interleukin (IL)-1ß, IL-18, cleaved-caspase-1 and gasdermin D in vitro and in vivo. Long non-coding RNA AU020206 was carried by the BMSC-EXO, and it bound to CCAAT enhancer binding protein beta (CEBPB) to block CEBPB-mediated transcriptional activation of NLR family pyrin domain containing 3 (NLRP3). Functional assays revealed that silencing of AU020206 aggravated macrophage pyroptosis and exacerbated AS symptoms in mice. These exacerbations were blocked upon CEBPB silencing but then restored after NLRP3 overexpression. In conclusion, this study demonstrates that AU020206 delivered by BMSC-EXO alleviates macrophage pyroptosis in AS by blocking CEBPB-mediated transcriptional activation of NLRP3.

PARP-1 Controls the Adipogenic Transcriptional Program by PARylating C/EBPß and Modulating Its Transcriptional Activity.

Poly(ADP-ribosyl)ation (PARylation) is a post-translational modification of proteins mediated by PARP family members, such as PARP-1. Although PARylation has been studied extensively, few examples of definitive biological roles for site-specific PARylation have been reported. Here we show that C/EBPß, a key pro-adipogenic transcription factor, is PARylated by PARP-1 on three amino acids in a conserved regulatory domain. PARylation at these sites inhibits C/EBPß's DNA binding and transcriptional activities and attenuates adipogenesis in various genetic and cell-based models. Interestingly, PARP-1 catalytic activity drops precipitously during the first 48 hr of differentiation, corresponding to a release of C/EBPß from PARylation-mediated inhibition. This promotes the binding of C/EBPß at enhancers controlling the expression of adipogenic target genes and continued differentiation. Depletion or chemical inhibition of PARP-1, or mutation of the PARylation sites on C/EBPß, enhances these early adipogenic events. Collectively, our results provide a clear example of how site-specific PARylation drives biological outcomes.

The paracrine isthmin1 transcriptionally regulated by C/EBPß exacerbates pulmonary vascular leakage in murine sepsis.

It is known that pulmonary vascular leakage, a key pathological feature of sepsis-induced lung injury, is largely regulated by perivascular cells. However, the underlying mechanisms have not been fully uncovered. In the present study, we aimed to evaluate the role of isthmin1, a secretory protein originating from alveolar epithelium, in the pulmonary vascular leakage during sepsis and to investigate the regulatory mechanisms of isthmin1 gene transcription. We observed an elevated isthmin1 gene expression in the pulmonary tissue of septic mice induced by cecal ligation and puncture (CLP), as well as in primary murine alveolar type II epithelial cells (ATII) exposed to lipopolysaccharide (LPS). Furthermore, we confirmed that isthmin1 derived from ATII contributes to pulmonary vascular leakage during sepsis. Specifically, adenovirus-mediated isthmin1 disruption in ATII led to a significant attenuation of the increased pulmonary microvascular endothelial cell (PMVEC) hyperpermeability in a PMVEC/ATII coculture system when exposed to LPS. In addition, adeno-associated virus 9 (AAV9)-mediated knockdown of isthmin1 in the alveolar epithelium of septic mice significantly attenuated pulmonary vascular leakage. Finally, mechanistic studies unveiled that nuclear transcription factor CCAAT/enhancer binding protein (C/EBP)ß participates in isthmin1 gene activation by binding directly to the cis-regulatory element of isthmin1 locus and may contribute to isthmin1 upregulation during sepsis. Collectively, the present study highlighted the impact of the paracrine protein isthmin1, derived from ATII, on the exacerbation of pulmonary vascular permeability in sepsis and revealed a new regulatory mechanism for isthmin1 gene transcription.NEW & NOTEWORTHY This article addresses the role of the alveolar epithelial-secreted protein isthmin1 on the exacerbation of pulmonary vascular permeability in sepsis and identified nuclear factor CCAAT/enhancer binding protein (C/EBP)ß as a new regulator of isthmin1 gene transcription. Targeting the C/EBPß-isthmin1 regulatory axis on the alveolar side would be of great value in the treatment of pulmonary vascular leakage and lung injury induced by sepsis.

rs822336 binding to C/EBPß and NFIC modulates induction of PD-L1 expression and predicts anti-PD-1/PD-L1 therapy in advanced NSCLC.

Efficient predictive biomarkers are needed for immune checkpoint inhibitor (ICI)-based immunotherapy in non-small cell lung cancer (NSCLC). Testing the predictive value of single nucleotide polymorphisms (SNPs) in programmed cell death 1 (PD-1) or its ligand 1 (PD-L1) has shown contrasting results. Here, we aim to validate the predictive value of PD-L1 SNPs in advanced NSCLC patients treated with ICIs as well as to define the molecular mechanisms underlying the role of the identified SNP candidate. rs822336 efficiently predicted response to anti-PD-1/PD-L1 immunotherapy in advanced non-oncogene addicted NSCLC patients as compared to rs2282055 and rs4143815. rs822336 mapped to the promoter/enhancer region of PD-L1, differentially affecting the induction of PD-L1 expression in human NSCLC cell lines as well as their susceptibility to HLA class I antigen matched PBMCs incubated with anti-PD-1 monoclonal antibody nivolumab. The induction of PD-L1 expression by rs822336 was mediated by a competitive allele-specificity binding of two identified transcription factors: C/EBPß and NFIC. As a result, silencing of C/EBPß and NFIC differentially regulated the induction of PD-L1 expression in human NSCLC cell lines carrying different rs822336 genotypes. Analysis by binding microarray further validated the competitive allele-specificity binding of C/EBPß and NFIC to PD-L1 promoter/enhancer region based on rs822336 genotype in human NSCLC cell lines. These findings have high clinical relevance since identify rs822336 and induction of PD-L1 expression as novel biomarkers for predicting anti-PD-1/PD-L1-based immunotherapy in advanced NSCLC patients.

MiR-320 inhibits PRRSV replication by targeting PRRSV ORF6 and porcine CEBPB.

Porcine reproductive and respiratory syndrome (PRRS), a highly contagious disease caused by Porcine reproductive and respiratory syndrome virus (PRRSV), results in huge economic losses to the world pig industry. MiRNAs have been reported to be involved in regulation of viral infection. In our study, miR-320 was one of 21 common differentially expressed miRNAs of Meishan, Pietrain, and Landrace pig breeds at 9-h post-infection (hpi). Bioinformatics and experiments found that PRRSV replication was inhibited by miR-320 through directly targeting PRRSV ORF6. In addition, the expression of CCAAT enhancer binding protein beta (CEBPB) was also inhibited by miR-320 by targeting the 3' UTR of CEBPB, which significantly promotes PRRSV replication. Intramuscular injection of pEGFP-N1-miR-320 verified that miR-320 significantly inhibited the replication of PRRSV and alleviated the symptoms caused by PRRSV in piglets. Taken together, miR-320 have significant roles in the infection and may be promising therapeutic target for PRRS.

Med1 Controls Effector CD8+ T Cell Differentiation and Survival through C/EBPß-Mediated Transcriptional Control of T-bet.

Effector CD8+ T cells are crucial players in adaptive immunity for effective protection against invading pathogens. The regulatory mechanisms underlying CD8+ T cell effector differentiation are incompletely understood. In this study, we defined a critical role of mediator complex subunit 1 (Med1) in controlling effector CD8+ T cell differentiation and survival during acute bacterial infection. Mice with Med1-deficient CD8+ T cells exhibited significantly impaired expansion with evidently reduced killer cell lectin-like receptor G1+ terminally differentiated and Ly6c+ effector cell populations. Moreover, Med1 deficiency led to enhanced cell apoptosis and expression of multiple inhibitory receptors (programmed cell death 1, T cell Ig and mucin domain-containing-3, and T cell immunoreceptor with Ig and ITIM domains). RNA-sequencing analysis revealed that T-bet- and Zeb2-mediated transcriptional programs were impaired in Med1-deficient CD8+ T cells. Overexpression of T-bet could rescue the differentiation and survival of Med1-deficient CD8+ effector T cells. Mechanistically, the transcription factor C/EBPß promoted T-bet expression through interacting with Med1 in effector T cells. Collectively, our findings revealed a novel role of Med1 in regulating effector CD8+ T cell differentiation and survival in response to bacterial infection.

BCR-Associated Protein 31 Regulates Macrophages Polarization and Wound Healing Function via Early Growth Response 2/C/EBPß and IL-4Rα/C/EBPß Pathways.

The BCR-associated protein 31 (BAP31), a transmembrane protein in the endoplasmic reticulum, participates in the regulation of immune cells, such as microglia and T cells, and has potential functions in macrophages that remain to be unexplored. In this study, we designed and bred macrophage-specific BAP31 knockdown mice to detect the polarization and functions of macrophages. The results revealed that M2 macrophage-associated genes were suppressed in mouse bone marrow-derived macrophages of Lyz2 Cre-BAP31flox/flox mice. Multiple macrophage-associated transcription factors were demonstrated to be able to be regulated by BAP31. Among these factors, C/EBPß was the most significantly decreased and was regulated by early growth response 2. BAP31 could also affect C/EBPß via modulating IL-4Rα ubiquitination and proteasome degradation in IL-4-stimulated macrophages. Furthermore, we found that BAP31 affects macrophages functions, including angiogenesis and skin fibrosis, during the wound healing process through IL-4Rα, as confirmed by infection with adeno-associated virus-short hairpin (sh)-IL-4Rα in Lyz2 Cre-BAP31flox/flox mice. Our findings indicate a novel mechanism of BAP31 in regulating macrophages and provide potential solutions for the prevention and treatment of chronic wounds.

Suppression of lipopolysaccharide-induced COX-2 expression via p38MAPK, JNK, and C/EBPß phosphorylation inhibition by furomagydarin A, a benzofuran glycoside from Magydaris pastinacea.

The phytochemical investigation of the methanol extract of the seeds of Magydaris pastinacea afforded two undescribed benzofuran glycosides, furomagydarins A-B (1, 2), together with three known coumarins. The structures of the new isolates were elucidated after extensive 1D and 2D NMR experiments as well as HR MS. Compound 1 was able to inhibit the COX-2 expression in RAW264.7 macrophages exposed to lipopolysaccharide, a pro-inflammatory stimulus. RT-qPCR and luciferase reporter assays suggested that compound 1 reduces COX-2 expression at the transcriptional level. Further studies highlighted the capability of compound 1 to suppress the LPS-induced p38MAPK, JNK, and C/EBPß phosphorylation, leading to COX-2 down-regulation in RAW264.7 macrophages.

Human DNA methylation signatures differentiate persistent from resolving MRSA bacteremia.

Persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is life threatening and occurs in up to 30% of MRSA bacteremia cases despite appropriate antimicrobial therapy. Isolates of MRSA that cause antibiotic-persistent methicillin-resistant S. aureus bacteremia (APMB) typically have in vitro antibiotic susceptibilities equivalent to those causing antibiotic-resolving methicillin-resistant S. aureus bacteremia (ARMB). Thus, persistence reflects host-pathogen interactions occurring uniquely in context of antibiotic therapy in vivo. However, host factors and mechanisms involved in APMB remain unclear. We compared DNA methylomes in circulating immune cells from patients experiencing APMB vs. ARMB. Overall, methylation signatures diverged in the distinct patient cohorts. Differentially methylated sites intensified proximate to transcription factor binding sites, primarily in enhancer regions. In APMB patients, significant hypomethylation was observed in binding sites for CCAAT enhancer binding protein-ß (C/EBPß) and signal transducer/activator of transcription 1 (STAT1). In contrast, hypomethylation in ARMB patients localized to glucocorticoid receptor and histone acetyltransferase p300 binding sites. These distinct methylation signatures were enriched in neutrophils and achieved a mean area under the curve of 0.85 when used to predict APMB using a classification model. These findings validated by targeted bisulfite sequencing (TBS-seq) differentiate epigenotypes in patients experiencing APMB vs. ARMB and suggest a risk stratification strategy for antibiotic persistence in patients treated for MRSA bacteremia.

Neurotrophic signaling deficiency exacerbates environmental risks for Alzheimer's disease pathogenesis.

The molecular mechanism of Alzheimer's disease (AD) pathogenesis remains obscure. Life and/or environmental events, such as traumatic brain injury (TBI), high-fat diet (HFD), and chronic cerebral hypoperfusion (CCH), are proposed exogenous risk factors for AD. BDNF/TrkB, an essential neurotrophic signaling for synaptic plasticity and neuronal survival, are reduced in the aged brain and in AD patients. Here, we show that environmental factors activate C/EBPß, an inflammatory transcription factor, which subsequently up-regulates δ-secretase that simultaneously cleaves both APP and Tau, triggering AD neuropathological changes. These adverse effects are additively exacerbated in BDNF+/- or TrkB+/- mice. Strikingly, TBI provokes both senile plaque deposit and neurofibrillary tangles (NFT) formation in TrkB+/- mice, associated with augmented neuroinflammation and extensive neuronal loss, leading to cognitive deficits. Depletion of C/EBPß inhibits TBI-induced AD-like pathologies in these mice. Remarkably, amyloid aggregates and NFT are tempospatially distributed in TrkB+/- mice brains after TBI, providing insight into their spreading in the progression of AD-like pathologies. Hence, our study revealed the roles of exogenous (TBI, HFD, and CCH) and endogenous (TrkB/BDNF) risk factors in the onset of AD-associated pathologies.

Identification of a distal enhancer that determines the expression pattern of acute phase marker C-reactive protein.

C-reactive protein (CRP) is a major acute phase protein and inflammatory marker, the expression of which is largely liver specific and highly inducible. Enhancers are regulatory elements critical for the precise activation of gene expression, yet the contributions of enhancers to the expression pattern of CRP have not been well defined. Here, we identify a constitutively active enhancer (E1) located 37.7 kb upstream of the promoter of human CRP in hepatocytes. By using chromatin immunoprecipitation, luciferase reporter assay, in situ genetic manipulation, CRISPRi, and CRISPRa, we show that E1 is enriched in binding sites for transcription factors STAT3 and C/EBP-ß and is essential for the full induction of human CRP during the acute phase. Moreover, we demonstrate that E1 orchestrates with the promoter of CRP to determine its varied expression across tissues and species through surveying activities of E1-promoter hybrids and the associated epigenetic modifications. These results thus suggest an intriguing mode of molecular evolution wherein expression-changing mutations in distal regulatory elements initiate subsequent functional selection involving coupling among distal/proximal regulatory mutations and activity-changing coding mutations.