# Dual role of PpV in Drosophila crystal cell proliferation and survival

## TL;DR

This study shows that PpV in fruit flies controls crystal cell growth and survival, playing a key role in immune response and wound healing.

## Contribution

PpV is identified as a novel dual regulator of crystal cell proliferation and survival in Drosophila.

## Key findings

- PpV accumulates in crystal cells and prevents their proliferation independently of Notch signaling.
- PpV inhibits crystal cell rupture and supports survival during injury, depending on Notch signaling.
- PpV contributes to wound healing by maintaining crystal cell integrity in lymph glands.

## Abstract

Drosophila melanogaster crystal cells are a specialized type of blood cells for the innate immune process upon injury. Under normal conditions, crystal cells rarely proliferate and constitute a small proportion of fly blood cells. Notch signaling has been known to guide the cell fate determination of crystal cells and maintain their survival. Here, we reported that protein phosphatase V (PpV), the unique catalytic subunit of protein phosphatase 6 in Drosophila, is a novel regulator of crystal cell proliferation and integrity. We found that PpV proteins highly accumulated in crystal cells in the larval hematopoietic organ termed the lymph gland. Silencing PpV using RNA interference led to increased crystal cell proliferation in a Notch-independent manner and induced crystal cell rupture dependent on Notch signaling. Moreover, additive PpV prevented the rupture of crystal cells in lymph glands upon a needle injury, suggesting the involvement of PpV in wound healing. Altogether, our results indicated that PpV plays a dual role in lymph glands, preventing crystal cell proliferation to limit the cell number, as well as inhibiting crystal cell rupture to maintain their survival.