O5: Nuclear phenotype in the ventricular myocytes of the Greenland shark (Somniosus microcephalus)

Aged cardiac myocytes present defective nuclear morphology associated with loss of
peripheral heterochromatin, as well as overall heterochromatin content, and, recently,
enlarged nucleoli were shown to be a signature of ageing and shorter lifespan. Such
characteristics can also be observed in Hutchinson-Gilford progeria syndrome (a premature
ageing disorder).
With a maximum lifespan of ≥272 years, assessing the nuclear phenotype across Greenland
shark (Somniosus microcephalus) individuals of various ages provides a unique opportunity
to determine whether these hallmarks of ageing occur in that extremely long-lived vertebrate
species as in the case of normal ageing.
Here, we applied a semi-automated 3D segmentation method (relying on deep learning) to
reconstruct three distinct regions (nucleolus, heterochromatin, euchromatin) of ventricular
nuclei (n = 54) across six Greenland shark specimens of ages ranging ~100-210 years-old.
We found that nucleolar size was not only comparatively small (relative to human, the mouse
and the fruitfly), but also tended to decrease in older individuals.
Euchromatin volume was tightly correlated to nuclear size whereas heterochromatin was
not; as such, heterochromatin content did not statistically differ across the six Greenland
shark individuals.
All 54 ventricular nuclei displayed the typical corkscrew shape in association with
heterochromatin localized along the nuclear periphery.
Altogether these data suggest that the Greenland shark may be able to sustain low ribosome
biogenesis and activity throughout its lifespan in conjunction with heterochromatin
maintenance. The consequence of which may relate to slow cellular metabolism.