Tissue-specific schedule of selective replication in Drosophila nasutoides

Area of Science:

• * Developmental Biology
• * Genetics
• * Molecular Biology

Background:

• * DNA content changes significantly between post-mitotic, mitotic, and germ line nuclei during organism development.
• * Drosophila nasutoides has n=4 chromosomes with distinct DNA proportions in diploid nuclei.
• * Previous studies on Drosophila genomes show under-replicating DNA dispersed across elements.

Purpose of the Study:

• * To quantify DNA content in Drosophila nasutoides nuclei.
• * To investigate the under-replication of DNA in polytene nuclei.
• * To determine the tissue-specific timing of DNA under-replication.

Main Methods:

• * Microphotometry was used to quantify DNA in female Drosophila nasutoides.
• * Diploid DNA content was calculated using brain metaphases and calibrated with hen erythrocyte nuclei.
• * Feulgen DNA content was analyzed in polytene nuclei of larval salivary glands.

Main Results:

• * The diploid DNA content of Drosophila nasutoides is 0.79 pg (7.7×10^8 nucleotide pairs).
• * Chromosome 4 constitutes 62% of the total DNA complement in diploid nuclei.
• * In polytene nuclei, chromosome 4 contained only 1.55% of total Feulgen DNA after 11 endoreplication cycles.
• * Under-replicating DNA in Drosophila nasutoides is concentrated in chromosome 4, unlike other Drosophila species.
• * Tissue-specific under-replication timing was observed, with variations between larval hind gut, salivary duct, adult/larval salivary glands, and Malpighian tubules.

Conclusions:

• * Drosophila nasutoides exhibits a unique pattern of DNA under-replication, localized to chromosome 4.
• * The timing of DNA under-replication is tissue-specific, initiating at different endocycle stages.
• * This localized under-replication allows for precise temporal analysis within single cells.