38. Which one of the following statements is correct?
(1) Epigenetic memory depends on DNA acetylation by trithorax group of proteins
(2) An epigenetic change could be inherited from a cell to a daughter cell
(3) Parental origin does not influence the expression level of imprinted loci
(4) Epigenetic changes do not alter the chromatin landscape

Epigenetic memory is linked to DNA methylation and histone modifications, notably methylation by trithorax group proteins rather than acetylation. Epigenetic changes can indeed be inherited from a cell to its daughter cells, preserving gene expression states across cell divisions. Parental origin strongly influences the expression of imprinted loci, meaning that genes expressed depend on whether they are inherited from the mother or father. Epigenetic changes do alter the chromatin landscape by modifying DNA and histones, affecting gene expression without changing the DNA sequence.

Explanation of Each Option

1. Epigenetic memory depends on DNA acetylation by trithorax group of proteins
   This statement is incorrect because trithorax group proteins mainly mediate methylation of histone tail residues (such as H3K4me), which maintains active gene states, rather than acetylation. Acetylation is usually performed by other enzymes like histone acetyltransferases (HATs), not directly by trithorax group proteins.​

2. An epigenetic change could be inherited from a cell to a daughter cell
   This is correct. Epigenetic modifications like DNA methylation and histone modifications can be faithfully propagated through mitosis, allowing daughter cells to maintain gene expression patterns inherited from the parent cell. This inheritance is fundamental to cellular memory and differentiation.​

3. Parental origin does not influence the expression level of imprinted loci
   This is false. Genomic imprinting is a classic epigenetic phenomenon where only one allele of a gene is expressed depending on its parental origin (maternal or paternal). This parent-of-origin effect is critical for correct gene regulation and development.​

4. Epigenetic changes do not alter the chromatin landscape
   This is incorrect. Epigenetic changes such as DNA methylation, histone modification, and chromatin remodeling directly alter the chromatin structure and accessibility, thereby influencing gene expression without sequence mutation.​

Introduction

Epigenetic memory is a vital cellular mechanism that allows changes in gene expression to be maintained without altering the DNA sequence. This process involves modifications to DNA and histones which can be inherited through cell divisions and can influence traits depending on parental origin, especially in imprinted genes. Understanding how epigenetic changes affect the chromatin landscape is crucial for studying gene regulation and development.

This article explains the correct and incorrect statements related to epigenetic memory, inheritance of epigenetic changes, imprinting, and chromatin changes, clarifying common misconceptions.

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