EvoGenExpression

• cis - change in regulatroy sequence linked to the target gene

• trans - change in different, unlinked gene effects expression of target gene

pyrosequencing or NGS

• expression differences between parents caused from trans -> two alleles in hybird equally expressed in hybrids

• expression differences between partens caused from cis -> two alleles should be expressed differently in hybird & match expression difference between parents

Gene expression differences between species are caused mainly by cis but trans equally involved

environmental conditions/media

1. 
   

   • The Mechanism: Resistance is driven by the overexpression of a single detoxification gene, Cyp6g1 (a Cytochrome P450 enzyme), not by a change in the protein sequence itself.

   • The Genetic Driver: An insertion of a transposable element (Accord) into the gene's cis-regulatory (promoter) region acts as a massive transcriptional enhancer.

   • Evolutionary Takeaway: It proves that rapid adaptation to strong selective pressures (like pesticides) can occur purely through regulatory evolution (altering the "volume" of gene expression) rather than structural evolution of proteins.

cytochrome P450 gene, Cyp6g1

-> involved in the metabolism of many compounds

transposable element inserstion ar 5’ end of Cyp6g1 gene

-> lead to higher expression

Microarrays & RNA seq

gene expression

-> lies between genotype and organismal phenotype that ultimately responds to selection

Definition: The study of variation in gene expression levels among individuals within or between natural populations.

1. If a cis-regulatory mutation caused recent adaptation in a new environment (e.g., Europe), it leaves two distinct signatures in the DNA:

   1. Selective Sweep: A massive reduction in DNA sequence polymorphism in or near the gene within the adapted population.

   2. High Allele Frequency Divergence: Specific sequence variants will be at a very high frequency (fixed) in one population but absent or rare in the other.

• More expression differences in the brain btw population than bte sexes

• Genes that differed in expression btw population had same patter

involved in heavy metal detoxification and oxidative stress tolerance.

The Function: MtnA is involved in heavy metal detoxification and oxidative stress tolerance in the brain.

1. The Mutation: A deletion in the 3' UTR removes a negative regulatory element (likely a microRNA binding site), leading to increased gene expression.

   • The Evolutionary Forces:

     1. Positive/Clinal Selection: The deletion frequency increases with distance from the equator (providing adaptation to cold/stress outside Africa).

     2. Balancing Selection: It remains polymorphic due to a selective trade-off (evolutionary costs), preventing complete fixation.

• The Expression Shift: European ("cosmopolitan") flies show 2–3x higher expression of CG9509 compared to ancestral African flies.

• The Genomic Evidence: The genomic region directly upstream of the gene displays:

  1. A complete absence of sequence polymorphism (Signal of a Selective Sweep).

  2. Several fixed sequence differences between the European and African populations.

• Conclusion: Selection favored mutations in the 5'-upstream regulatory region to explicitly drive the adaptive up-regulation of CG9509 in Europe.

1. 
   

   • The Method (In Vitro & In Vivo):

     1. Clone the CG9509 upstream (promoter) region from both an African and a European allele.

     2. Place them in front of a reporter gene (E. coli lacZ, encoding β-galactosidase).

     3. Insert both constructs into the exact same genomic location of D. melanogaster using PhiC31 site-specific integration.

   • The Logic: Testing them in the identical genetic background eliminates all trans-acting variables.

   • The Result: The European upstream region drove 2–3x higher expression than the African one, proving that cis-regulatory sequence divergence fully explains the natural population differences.

1. The Clash: The classical sweep model predicts that the adaptive allele should be fixed (100% frequency) in Europe.

2. The Reality: The causative SNP with the largest effect is only at an intermediate frequency (40–50%) in cosmopolitan populations (and nearly absent, 0–5%, in Africa).

3. The Conclusion: Instead of a hard selective sweep, this polymorphism is likely maintained outside of Africa by balancing selection (due to a selective trade-off).

Function: Predicted to encode a choline dehydrogenase involved in ecdysteroid (growth hormone) metabolism and stress tolerance.

Tissue: Specifically expressed in the Malpighian tubules (the insect equivalent of kidneys).

The "Fezzik" Phenotype: Knock-out or RNAi knockdown of the gene results in larger flies than the wild type (named after the giant character in The Princess Bride). Thus, higher expression in Europe restricts growth/influences size.

1. The Global Trend: Overall, much more expression variation within natural populations is explained by trans-acting factors than cis-acting factors.

   The Big Exception: There is a strong enrichment of cis-acting variation specifically in Cytochrome P450 genes(which are crucial for detoxification, like the Cyp6g1 DDT-resistance gene).

   Method Insight: This was quantified by measuring global gene expression in both parental populations alongside Allele-Specific Expression (ASE) in their F1​ offspring.

The Location: Transgenic reporter gene assays proved that most functional cis-variants are localized in the immediate upstream promoter region.

The Window: They map specifically within 2 kb of the start codon (ATG) of the P450 genes.

Significance: This confirms that rapid, adaptive expression changes in metabolic/detoxification genes are tightly packed near the core transcriptional switches.