Germ Cell Segregation from the <i>Drosophila</i> Soma Is Controlled by an Inhibitory Threshold Set by the Arf-GEF Steppke
Bibliographic record
Abstract
Germline cells segregate from the soma to maintain their totipotency, but the cellular mechanisms of this segregation are unclear. The Drosophila melanogaster embryo forms a posterior group of primordial germline cells (PGCs) by their division from the syncytial soma. Extended plasma membrane furrows enclose the PGCs in response to the germ plasm protein Germ cell-less (Gcl) and Rho1-actomyosin activity. Recently, we found that loss of the Arf-GEF Steppke (Step) leads to similar Rho1-dependent plasma membrane extensions but from pseudocleavage furrows of the soma. Here, we report that the loss of step also leads to premature formation of a large cell group at the anterior pole of the embryo . These anterior cells lacked germ plasm, but budded and formed at the same time as posterior PGCs, and then divided asynchronously as PGCs also do. With genetic analyses we found that Step normally activates Arf small G proteins and antagonizes Rho1-actomyosin pathways to inhibit anterior cell formation. A uniform distribution of step mRNA around the one-cell embryo cortex suggested that Step restricts cell formation through a global control mechanism. Thus, we examined the effect of Step on PGC formation at the posterior pole. Reducing Gcl or Rho1 levels decreased PGC numbers, but additional step RNAi restored their numbers. Reciprocally, GFP-Step overexpression induced dosage- and Arf-GEF-dependent loss of PGCs, an effect worsened by reducing Gcl or actomyosin pathway activity. We propose that a global distribution of Step normally sets an inhibitory threshold for Rho1 activity to restrict early cell formation to the posterior.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".