Regional signals in the planarian body guide stem cell fate in the presence of DNA instability

Abstract

Cellular fate decisions are influenced by their topographical location in the adult body. For instance, tissue repair and neoplastic growth are greater in anterior than in posterior regions of adult animals. However, the molecular underpinnings of these regional differences are unknown. We identified a regional switch in the adult planarian body upon systemic disruption of homologous recombination with RNAinterference of Rad51. Rad51 knockdown increases DNA doublestrand breaks (DSBs) throughout the body, but stem cells react differently depending on their location along the anteroposterior axis. In the presence of extensive DSBs, cells in the anterior part of the body resist death, whereas cells in the posterior region undergo apoptosis. Furthermore, we found that proliferation of cells with DNA damage is induced in the presence of brain tissue and that the retinoblastoma pathway enables overproliferation of cells with DSBs while attending to the demands of tissue growth and repair. Our results implicate both autonomous and non-autonomous mechanisms as key mediators of regional cell behavior and cellular transformation in the adult body.

SUMOylation controls stem cell proliferation and regional cell death through Hedgehog signaling in planarians

“…To assess DNA integrity in Ubc9(RNAi) animals, we collected cells at different dpf and performed (1) COMET assay, (2) karyotyping and (3) immunostaining against markers required for early DNA damage response and repair through homologous recombination (HR). COMET assay was adjusted to detect DSBs [9,31] and our results confirmed an increase in DNA damage equally distributed along the AP axis and is present as early as 10 dpf (Fig. 5a).…”

“…To investigate the cause of regional tissue loss after Ubc9(RNAi), we analyzed cell death through whole-mount immunostaining and FACS [9,23]. First, immunostaining assay with cell death marker caspase-3; which has been previously characterized in planarians [29], revealed an increase in cell death throughout the animal, with a prominent expression in the posterior region 25 dpf (Fig.…”

“…Ubc9 downregulation in planarians resembles regional features of the Rad51 phenotype, which is characterized by an increase in DNA double stranded breaks (DSBs) throughout the body [9]. To assess DNA integrity in Ubc9(RNAi) animals, we collected cells at different dpf and performed (1) COMET assay, (2) karyotyping and (3) immunostaining against markers required for early DNA damage response and repair through homologous recombination (HR).…”

“…Signals influencing cellular behavior during adult tissue maintenance, repair, and cancer are evolutionarily conserved between planaria and mammals [2][3][4][5][6][7][8]. Systemic disruption of homologous recombination in S. mediterranea leads to dramatic increases in DNA doublestrand breaks (DSBs) throughout the body [9]. Intriguingly, cells in the anterior region of the body survive and continue dividing with DSBs, while most cells in the posterior region of the planarian body undergo cell death.…”

“…Intriguingly, cells in the anterior region of the body survive and continue dividing with DSBs, while most cells in the posterior region of the planarian body undergo cell death. Brain signals and the retinoblastoma pathway contribute to the survival of cells with DNA damage in the anterior region [9]. However, it remains elusive which mechanisms operate in the posterior region, where cells with DSB are collectively eliminated by apoptosis.…”