36. Following statements were made about imprinting in the human genome.
A. Imprinting control centre (lC) harbors part of the SNRPN gene.
B. Imprinting of genes in an individual cannot be tissue specific.
C. Sperms and eggs exhibit identical pattern of genome methylation, except in the sex chromosomes.
D. At imprinted loci, expression depends on the parental origin.
Select the option with all the correct statements.
(1) A and D        (2) B and D
(3) A and C        (4) B and C

Following are the explanations and verification of each statement about imprinting in the human genome:

A. Imprinting control centre (IC) harbors part of the SNRPN gene.

• Correct. The SNRPN gene (small nuclear ribonucleoprotein polypeptide N) is located within the Prader-Willi Syndrome critical region on chromosome 15 and is imprinted. The imprinting control center (IC) is located in this region and includes part of the SNRPN gene. This locus is well-established as an imprinting control region regulating the paternal expression of genes in this cluster.​

B. Imprinting of genes in an individual cannot be tissue specific.

• Incorrect. Imprinting can be tissue specific. Epigenetic modifications such as DNA methylation and histone modification at imprinted loci can show variation in different tissues, leading to tissue-specific expression patterns of imprinted genes. Studies reveal that some imprinted genes may have different imprinting patterns depending on tissue type.​

C. Sperms and eggs exhibit identical pattern of genome methylation, except in the sex chromosomes.

• Incorrect. Sperm and egg genomes exhibit distinct methylation patterns, not identical. There are many differentially methylated regions between sperm and eggs, indicating parent-specific methylation signatures are established during gametogenesis. While both carry methylation marks, these are quite different even outside the sex chromosomes.​

D. At imprinted loci, expression depends on the parental origin.

• Correct. The fundamental definition of genomic imprinting is parent-of-origin specific expression, where genes are expressed only from the allele inherited from either the mother or the father, not both. This monoallelic expression is a hallmark of imprinting.​

Correct Option: (1) A and D

Introduction to Genomic Imprinting

Genomic imprinting is an epigenetic mechanism where gene expression depends on the parent from whom the gene is inherited. It involves DNA methylation and chromatin modifications that silence one parental allele while allowing the expression of the other. The imprinting control center (IC), such as the one harboring part of the SNRPN gene on chromosome 15, regulates this selective expression. This parent-of-origin effect is critical in normal development and diseases like Prader-Willi Syndrome.

Imprinting Control Centre and SNRPN

The imprinting control centre includes key regulatory elements in chromosome 15’s Prader-Willi critical region. This area contains the SNRPN gene, which is expressed solely from the paternal allele. The IC orchestrates allele-specific methylation patterns that define which parental gene copy is active, making SNRPN a central player in human imprinting mechanisms.

Tissue Specificity of Imprinting

Contrary to some beliefs, imprinting can be tissue specific. Epigenetic regulation allows certain imprinted genes to show differential expression depending on the tissue type. These variations contribute to the diverse roles imprinting plays across various biological processes in the body.

Distinct Methylation Patterns in Gametes

Methylation patterns in sperm and eggs differ significantly, reflecting their unique roles in development. These differences are not limited to sex chromosomes but extend throughout the genome, establishing parental epigenetic marks critical for imprinting following fertilization.

Parent-of-Origin Gene Expression

The defining feature of imprinting is expression based on parental origin, where only the maternal or paternal allele is expressed while the other is silenced. This monoallelic expression influences growth, development, and metabolism, underpinning many key genetic syndromes and traits.

This comprehensive view clarifies the correct statements regarding genomic imprinting mechanisms in humans, emphasizing the significance of the SNRPN gene and parent-origin dependent gene expression.

(Answer based on current scientific literature and data)