Localization of Lipid Exchange Machinery to TBC‐ER Contact Sites
Bibliographic record
Abstract
The production of sperm cells in the mammalian testis is complex, and requires a well‐organized restructuring of the epithelium to which late spermatids are attached before their subsequent release at the completion of spermatogenesis. Disassembly of large adhesion like junction complexes called ‘ectoplasmic specializations’ (ESs) is necessary for late spermatids to detach from Sertoli cells. Endocytic structures proposed to disassemble ESs are called ‘tubulobulbar complexes’ (TBCs). TBCs share some similarities with clathrin‐mediated endocytosis (CME) in that they have a clathrin coated pit and a dendritic actin network that likely drives invagination. Unlike CME however, the actin network is not as temporary, and forms a long extended neck that progresses into an actin free portion that forms a swollen bulb, while the structure is still continuous with the Sertoli cell plasma membrane. Using antibody localization techniques, we have previously established the identity of the TBC bulb as an early endosome. Interestingly, the bulbs of TBCs form extensive ER contacts, the function of which is unclear. Recent expansions in our understanding of ER contacts have revealed that they serve at least three important functions with respect to ER‐endosome contacts: (1) positioning and scission of endosomes (2) calcium exchange and (3) lipid transfer. We have previously localized calcium exchange machinery to the TBC‐ER contact site, but never before have lipid transfer machinery been localized here, or to any structures related to the apical processes of Sertoli cells. If lipid transfer occurs at TBC‐ER contacts, then protein machinery known to be involved in these processes should be localized to these sites. Here we use immunofluorescence and STED super resolution imaging to localize known lipid exchange machinery to the ER of Sertoli cell apical processes. Oxysterol binding protein‐related protein 9 (ORP9) was localized to the TBC‐ER contacts and a known ORP interactor and anchor, VAMP‐associated protein A (VAPA), was localized ubiquitously throughout the ER of the apical process, including the TBC‐ER contact. This data is consistent with the hypothesis that lipid exchange is one of the key functions of TBC‐ER contacts. Support or Funding Information Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant awarded to AWV; Alexander Graham Bell Scholarship (NSCERC) awarded to AA This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.003 |
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 source (direct Gemma or distilled Codex), 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".