Question

How does \(X\) chromosome dosage compensation in Drosophila differ from that process in humans?

Short answer

Answer: The major differences in X chromosome dosage compensation between Drosophila and humans are the mechanism and the regulating complexes. Drosophila upregulates gene expression on the single X chromosome in males through the Male-Specific Lethal (MSL) complex, while humans equalize expression using X-inactivation in female cells, regulated by the long non-coding RNA Xist.

Step-by-step solution

Understand dosage compensation

Dosage compensation is the process by which organisms balance the expression of genes on the sex chromosomes (X and Y) in males and females. In organisms with sex chromosome systems like humans and Drosophila, males have one X and one Y chromosome, while females have two X chromosomes. To ensure equal gene expression levels between sexes, dosage compensation mechanisms have evolved to equalize X-linked gene expression between males and females.

Dosage compensation in Drosophila

In Drosophila, dosage compensation is achieved by upregulating the expression of the single X chromosome in males to reach the same levels as in females with two X chromosomes. The Male-Specific Lethal (MSL) complex, a group of proteins and non-coding RNAs, is responsible for this upregulation. The MSL complex specifically binds to the male X chromosome, modifying its chromatin structure, and consequently enhancing transcription of the X-linked genes.

Dosage compensation in humans

In humans, dosage compensation is primarily accomplished by the process of X-inactivation. X-inactivation results in the inactivation of one of the two X chromosomes in female cells, equalizing gene expression levels between males and females. The inactivated X chromosome forms a condensed structure called a Barr body, which prevents transcription of its genes. This process is regulated by a long non-coding RNA called Xist, which coats the inactivated X chromosome and initiates the formation of the Barr body.

Major differences between Drosophila and humans

There are two key differences in the processes of X chromosome dosage compensation between Drosophila and humans: 1. The mechanism: Drosophila upregulates gene expression on the single X chromosome in males to equalize expression with females, while humans inactivate one of the X chromosomes in female cells via X-inactivation. 2. The regulating complexes: Drosophila dosage compensation is mediated by the MSL complex, which binds to and modifies the male X chromosome to enable gene upregulation. In humans, the process is regulated by the long non-coding RNA Xist, which initiates the inactivation of one X chromosome in females by coating it and leading to the formation of a Barr body.