Koryakov Dmitry E, Zhimulev Igor F
Institute of Molecular and Cellular Biology SB RAS, Novosibirsk State University, Novosibirsk, 630090, Russia,
Chromosoma. 2015 Mar;124(1):95-106. doi: 10.1007/s00412-014-0487-4. Epub 2014 Sep 26.
Drosophila cell lines are used extensively to study replication timing, yet data about DNA replication in larval and adult tissues are extremely limited. To address this gap, we traced DNA replication in polytene chromosomes from nurse cells of Drosophila melanogaster otu mutants using bromodeoxyuridine incorporation. Importantly, nurse cells are of female germline origin, unlike the classical larval salivary glands, that are somatic. In contrast to salivary gland polytene chromosomes, where replication begins simultaneously across all puffs and interbands, replication in nurse cells is first observed at several specific chromosomal regions. For instance, in the chromosome 2L, these include the regions 31B-E and 37E and proximal parts of 34B and 35B, with the rest of the decondensed chromosomal regions joining replication process a little later. We observed that replication timing of pericentric heterochromatin in nurse cells was shifted from late S phase to early and mid stages. Curiously, chromosome 4 may represent a special domain of the genome, as it replicates on its own schedule which is uncoupled from the rest of the chromosomes. Finally, we report that SUUR protein, an established marker of late replication in salivary gland polytene chromosomes, does not always colocalize with late-replicating regions in nurse cells.
果蝇细胞系被广泛用于研究复制时间，但有关幼虫和成虫组织中DNA复制的数据极为有限。为了填补这一空白，我们使用溴脱氧尿苷掺入法追踪了黑腹果蝇otu突变体的滋养细胞多线染色体中的DNA复制。重要的是，与经典的幼虫唾液腺（属于体细胞）不同，滋养细胞起源于雌性生殖系。与唾液腺多线染色体不同，在唾液腺多线染色体中，所有的疏松区和间带同时开始复制，而在滋养细胞中，复制首先在几个特定的染色体区域被观察到。例如，在2L染色体中，这些区域包括31B-E、37E以及34B和35B的近端部分，其余解聚的染色体区域稍后才加入复制过程。我们观察到，滋养细胞中着丝粒周围异染色质的复制时间从S期后期转移到了早期和中期。奇怪的是，4号染色体可能代表基因组的一个特殊区域，因为它按照自己的时间表进行复制，与其他染色体不同步。最后，我们报告称，SUUR蛋白是唾液腺多线染色体中晚期复制的一个既定标记，但它并不总是与滋养细胞中的晚期复制区域共定位。
