Abstract
Proper control of adult stem cells including their proliferation and differentiation is crucial in maintaining homeostasis of well-organized tissues/organs throughout an organism's life. The Drosophila adult midgut has intestinal stem cells (ISCs), which have been exploited as a simple model system to investigate mechanisms controlling adult tissue homeostasis. Here, we found that a viable mutant of βν integrin (βint-ν), encoding one of two Drosophila integrin β subunits, showed a short midgut and abnormal multilayered epithelia accompanied by an increase in ISC proliferation and misdifferentiation defects. The increase in ISC proliferation and misdifferentiation was due to frequent ISC duplication expanding a pool of ISCs, which was caused by depression of the Notch signalling, and up-regulation of unpaired (upd), a gene encoding an extracellular ligand in the JAK/STAT signalling pathway. In addition, we observed that abnormally high accumulation of filamentous actin (F-actin) was caused in the βint-ν mutant enterocytes. Furthermore, the defects were rescued by suppressing c-Jun N-terminal kinase (JNK) signalling, which was up-regulated in a manner correlated with the defect levels in the above-mentioned βint-ν mutant phenotype. These symptoms observed in young βint-ν mutant midgut were very similar to those in the aged midgut in wild type. Our results suggested that βint-ν has a novel function for the Drosophila adult midgut homeostasis under normal conditions and provided a new insight into possible age-related diseases caused by latent abnormality of an integrin function.
Highlights
In maintaining homeostasis of well-organized adult tissues/ organs, it is crucial to control proliferation and differentiation in adult stem cells, since adult stem cells constantly replenish new healthy differentiated cells constituting tissues/organs throughout an organism’s life [1,2]
Both in mammals and Drosophila, Intestinal stem cells (ISCs) proliferation and differentiation are regulated by similar signalling pathways/ factors including Wnt/wingless, Notch (N), epidermal growth factor (EGF), cytokines/JAK/STAT, c-Jun N-terminal kinase (JNK), Hippo and insulin in normal and regenerative conditions [8,9,10,11,12,13,14,15,16,17,18,19]
ISC overproliferation is often associated with induction of misdifferentiated EC-like polyploid cells that are continuously expressing EB markers [12,13],[16]. To determine whether these misdifferentiated EC-like cells appeared in bint-n mutants, we examined the expression of ISC and EB markers, i.e. 106STAT92E-GFP, Su(H)Gbe-lacZ, and a dual-phosphorylated form of ERK, that had respectively been used as monitors for JAK/STAT, N, and EGF signalling activities
Summary
In maintaining homeostasis of well-organized adult tissues/ organs, it is crucial to control proliferation and differentiation in adult stem cells, since adult stem cells constantly replenish new healthy differentiated cells constituting tissues/organs throughout an organism’s life [1,2]. These results indicated that the normal gene product of bint-n restricted the number of proliferating ISCs. The adult midgut was composed of ISCs, EBs, ECs, ees, and VMs (Figure 1A).
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