# Longitudinal imaging of stem cell coordination and cross-regulation in the testis niche

> **NIH NIH R01** · DREXEL UNIVERSITY · 2021 · $57,510

## Abstract

Proper function of the Drosophila testis and consistent production of sperm requires exquisite
coordination between two resident stem cell populations—the germline stem cells (GSCs) and
the somatic Cyst Stem Cells. Germ cell differentiation requires that every one GSC daughter (a
gonialblast, or Gb) is completed encased or encysted by precisely two daughters of the Cyst
Stem Cell lineage. The testis niche coordinates production of daughter cells from these two
stem cell populations by imposing a cytokinetic delay on the GSCs and requiring cell contact
with encysting cells in order for abscission, the final step of cytokinesis, to be triggered.
Interestingly, there is significant variability in the length of the cytokinetic pause (30 to 75% of
the cell cycle). For the system to achieve robustness with a three-cell unit consistently formed,
the variability in pause length suggests that the pause, encystment and trigger must be capable
of each compensating for changes in timing of the other steps. This predicts substantial cross-
talk between the two stem cell lineages to monitor proliferation rates, stem cell numbers and
cytokinesis timing. Prior studies revealed only a small degree of coordination in proliferation in
the niche. In fact, our analysis showed a lack of any significant mitotic synchrony between
GSCs and their flanking CySCs and no evidence that CySCs flanking the same GSC were
mitotically coordinated. Thus, we hypothesize that it is not mitosis, but modified GSC cytokinesis
combined with cross-talk and monitoring of daughter cell numbers between the two stem cell
populations, that generates a robust system to coordinate daughter cell release from the niche.
Our feedback model predicts that defects in cytokinesis timing would affect proliferation while
changes in proliferation or stem cell number would affect cytokinesis timing. Here, we will
directly assess the degree of coordination between Gb encystment and abscission by
simultaneous imaging of both stem cell populations. We will then determine the degree of co-
regulation and cross talk between the two stem cell lineages to identify the underlying
mechanisms that ensure a robust outcome

## Key facts

- **NIH application ID:** 10336198
- **Project number:** 3R01GM138705-02S1
- **Recipient organization:** DREXEL UNIVERSITY
- **Principal Investigator:** Kari Lenhart
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $57,510
- **Award type:** 3
- **Project period:** 2020-08-01 → 2025-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10336198

## Citation

> US National Institutes of Health, RePORTER application 10336198, Longitudinal imaging of stem cell coordination and cross-regulation in the testis niche (3R01GM138705-02S1). Retrieved via AI Analytics 2026-05-31 from https://api.ai-analytics.org/grant/nih/10336198. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*