Can Eukaryotic Gene Regulated by Hormones ? | Genetics

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Most of the hormones in human are either peptide or peptide derivatives in nature or steroid in nature. The peptide hormones do not normally enter cells because of their rela­tively large size. Their effects appear to be mediated by receptor proteins located in tar­get cell membranes and also by the intracellu­lar levels of cyclic AMP.

The steroid hormones on the other hand, are small molecules and readily enter cells through the plasma mem­brane. After entry the steroid hormones become tightly bound to specific receptor pro­teins. These receptor proteins are present only in the cytoplasm of target cells.

Following are the different views regard­ing the hormonal control of gene expression:

1. Some of the hormone receptor pro­tein complexes activate transcription of target genes by binding to specific DNA sequences present in the cis-acting regulatory regions of these genes.

2. The hormone receptor protein com­plexes interact with specific non-histone chro­mosomal proteins rather than directly with DNA. This interaction would then stimulate the transcription of the correct genes.

Remark:

In both the above cases hor­mone receptor protein complexes would func­tion as positive regulators or activators of transcription.

3. The nonhistone chromosomal pro­teins play important roles in the regulation of gene expression particularly in eukaryotes.

4. The regulation of transcription in eukaryotes may well involve specific interac­tion among DNA, histones and non-histone chromosomal proteins.

5. The hormone receptor protein com­plexes activates gene expression by interacting directly with the specific DNA sequences pre­sent within the enhancer or promoter regions that regulate the transcription of the target genes.

6. Some of the steroid hormones e.g. glucocorticoid, estrogen etc. act via enhancer elements which causes localized unwinding of the two DNA strands in the promoter regions.

7. Another most striking method of hor­monal control of gene expression is the selec­tive stabilization of hormone-stimulated tran­scripts against cytoplasmic degradation.

Remark:

Steroid hormones achieve massive accumulation of specific mRNAs by concerted manipulation of both transcriptional and post-transcriptional processes.