Development of the Cardiac Conduction System in the Selected Groups of Reptiles as Determined by HNK‐1 Expression
Bibliographic record
Abstract
Reptilian hearts show different stages of ventricular septation from its complete absence in the basal squamates to a fully septated heart in crocodiles. We have tested the hypothesis that evolution of the specialized ventricular conduction system is linked to ventricular septation, rather than homeiothermy, as originally postulated. We studied hearts of selected reptilian species ( Pogona vitticeps – no ventricular septum, Varanus indicus – partial septum, Crocodylus siamensis – complete septum) at various stages of development to uncover any morphological evidence for specialized conduction pathways. Immunohistochemistry using smooth muscle or sarcomeric actin as myocardial markers and HNK‐1 as a marker of cardiac conduction system showed HNK‐1 expression in the myocardium of the sinus venosus, where the main cardiac pacemaker is located. There was also staining of various intensity in the extracellular matrix of cardiac cushions in all the species examined. There was an HNK‐1 positive ring‐like structure of the developing ventricular septum in the Crocodylus , and increased positivity in the Varanus , while there was no myocardial staining in the ventricle of the Pogona . In all species there was a strong staining in the cardiac nervous fibers and ganglia, and in the epicardium of the Varanus . We conclude that a primordial conduction system is present in reptilian hearts. The embryonic crocodilian hearts possess a morphological preferential conduction pathway similar to one present in the hearts of birds and mammals. Its emergence correlates with completion of ventricular septation. Support or Funding Information Supported by Ministry of Education PRVOUK P35/LF/5, institutional grant RVO: 67985823 (The Czech Academy of Sciences), and GA CR 16‐02972S.
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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 | 0.000 | 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) | 0.001 | 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 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".