Histone H3 availability is more important for development than H3.2 versus H3.3 subtype identity.

Area of Science:

• Molecular Biology
• Genetics
• Developmental Biology

Background:

• The roles of replication-dependent and replication-independent histones in development and genome regulation are not fully understood.
• Histone H3 has distinct subtypes, including H3.2 (replication-dependent) and H3.3 (replication-independent), with potentially different functions.

Purpose of the Study:

• To investigate the specific contributions of histone H3.2 and H3.3 protein identities to development and gene regulation in Drosophila.
• To determine the necessity of replication-independent H3.3 for various life processes and genome functions.

Main Methods:

• Comparative analysis of Drosophila mutants: one with H3.3 genes producing H3.2 protein, and another with H3.3 gene deletions.
• Assessment of fertility, adult behavior, longevity, chromatin accessibility, and gene expression patterns.

Main Results:

• Replication-independent H3.3 is crucial for Drosophila fertility, adult locomotor behavior, and longevity.
• Development to adulthood is not dependent on the specific replication-independent H3 subtype expressed from H3.3 loci.
• Replication-independent H3.3 is not essential for global chromatin accessibility or gene expression in the adult brain.
• H3.2 expression from the HisC locus is vital in post-replicative cells when H3.3 is absent.
• The HIRA histone chaperone complex plays a key role in maintaining genome function upon H3.3 deletion.

Conclusions:

• An available pool of histone H3 is more critical for genome function than the specific identity of the H3 subtype.
• The HIRA complex is essential for genome integrity when replication-independent H3.3 is compromised.