Honeybees (Apis mellifera) provide a striking example of...

Honeybees (Apis mellifera) provide a striking example of environmental effects on eukaryotic gene expression and thus phenotype. Fertile queens and sterile workers are both female bees with the same diploid genomes. However, their morphologies and behaviors are different.It turns out that the diet of the larval (larvae are young developing insects) females controls their development as either workers or queens. When the hive needs new queens, a few female larvae are fed royal jelly, a substance secreted by worker bees, instead of the normal diet of nectar and pollen. Investigators determined that many genes are more highly CpG-methylated in the larval-stage workers than in the larval-stage queens. a. Describe an experiment you could do to determine if DNA methylation correlates with differences in gene expression in workers and queens. b. Researchers were able to mimic the effect of royal jelly by knocking down the expression in female larvae of a DNA methyltransferase enzyme called $D N M T 3$. (The knockdown was accomplished through a technique called $R N A$ interference that is described in a later problem; the details are unimportant here.) Remarkably, when fed a normal diet, most of these larvae developed as queens. Based on the description of the transgenerational silencing of the $A^{Y}$ allele of the mouse agouti gene presented in Fig. 17.24 suggest a simple hypothesis that accounts for the different effects on female honeybee larval development of normal versus royal jelly diets.

Honeybees (Apis mellifera) provide a striking example of environmental effects on eukaryotic gene expression and thus phenotype. Fertile queens and sterile workers are both female bees with the same diploid genomes. However, their morphologies and behaviors are different.It turns out that the diet of the larval (larvae are young developing insects) females controls their development as either workers or queens. When the hive needs new queens, a few female larvae are fed royal jelly, a substance secreted by worker bees, instead of the normal diet of nectar and pollen. Investigators determined that many genes are more highly CpG-methylated in the larval-stage workers than in the larval-stage queens.
a. Describe an experiment you could do to determine if DNA methylation correlates with differences in gene expression in workers and queens.
b. Researchers were able to mimic the effect of royal jelly by knocking down the expression in female larvae of a DNA methyltransferase enzyme called $D N M T 3$. (The knockdown was accomplished through a technique called $R N A$ interference that is described in a later problem; the details are unimportant here.) Remarkably, when fed a normal diet, most of these larvae developed as queens. Based on the description of the transgenerational silencing of the $A^{Y}$ allele of the mouse agouti gene presented in Fig. 17.24 suggest a simple hypothesis that accounts for the different effects on female honeybee larval development of normal versus royal jelly diets.

Key Concepts

DNA Methylation

DNA methylation is an epigenetic mechanism that involves the addition of a methyl group to the cytosine residues in CpG dinucleotides. This modification can alter gene expression by affecting the accessibility of the DNA to transcriptional machinery, and it is a key process by which cells can regulate gene expression without changing the underlying genetic code.

Epigenetics

Epigenetics refers to the study of heritable changes in gene function that do not involve alterations in the DNA sequence. These changes, which include DNA methylation and other modifications, allow environmental factors—such as diet—to influence phenotype by regulating gene expression in a dynamic and reversible manner.

Gene Expression Regulation

Gene expression regulation encompasses the various mechanisms by which a cell controls the timing, location, and amount of a gene product (RNA or protein) produced. Understanding how external factors like environmental inputs or molecular modifications (e.g., methylation) influence the transcription of genes is fundamental to linking genetic and phenotypic outcomes.

RNA Interference

RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression, typically by causing the degradation of specific mRNA molecules. It serves as a tool in research to selectively knock down the expression of target genes, thereby illuminating the roles of these genes in development and disease.

Environmental Influence on Phenotype

The environmental influence on phenotype involves how external factors, such as diet or stress, can lead to changes in gene expression and subsequent developmental outcomes. This concept is central to understanding how identical genomes can lead to diverse phenotypes based on variations in external conditions, mediated in part by epigenetic mechanisms.

Transgenerational Epigenetic Inheritance

Transgenerational epigenetic inheritance describes the transmission of epigenetic marks, such as DNA methylation patterns, from one generation to the next. This concept is important for explaining how environmental factors experienced by one generation can have lasting effects on the gene expression and phenotype of subsequent generations, without altering the DNA sequence itself.

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