Transcriptome sequencing and histology reveal dosage compensation in the liver of triploid pre-smolt Atlantic salmon

Triploid Atlantic salmon (Salmo salar L.) is seen as one of the best solutions to solve key issues in the salmon farming industry, such as the impact of escapees on wild stocks and pre-harvest sexual maturation. However, the effects of triploidy on salmon smoltification are poorly understood at the molecular level, even though smoltification is a very sensitive period that has a major influence on survival rate and performance of farmed salmon. In this study, we have compared the liver transcriptomes of diploid and triploid Atlantic salmon at three ontogeny stages: fry, parr and smolt. In diploid fish, a total of 2,655 genes were differentially expressed between fry and parr, whereas 506 genes had significantly different transcript levels between parr and smolts. In triploids, 1,507 and 974 genes were differentially expressed between fry and parr, and between parr and smolts, respectively. Most of these genes were down-regulated and 34 genes were differentially expressed between ploidies at the same stage. In both ploidy groups, the top differentially expressed genes with ontogeny stage belonged to common functional categories that can be related to smoltification. Nucleotide and energy metabolism were significantly down-regulated in fry when compared to parr, while immune system processes were significantly down-regulated in parr when compared to smolts. The close resemblance of enriched biological processes and pathways between ploidy groups suggests that triploidy is regulated by genome dosage compensation in Atlantic salmon. Histological analysis revealed that areas of vacuolization (steatosis) were present only in fry and parr stages, in contrast to a compact cellular histology with glycogen granules after smoltification. There was no significant difference in vacuolization between ploidy groups at the fry stage but the liver of diploid parr had a 33.5% higher vacuolization area compared to their triploid counterparts. Taken together, our data provide novel insights into the changes that occur at the molecular and histological level in the liver of both diploid and triploid Atlantic salmon prior to and during smoltification.

Karyometry of pseudostratified, metaplastic and dysplastic nasal epithelium by morphometry and stereology. 1. A general model for automated image analysis of epithelia

Nuclear enlargement, usually due to the existence of abnormally high DNA (ploidy) values, is one of the alterations most often encountered in pathological epithelia, especially in cancerous and precancerous states. Direct DNA measurements on microscopic sections are impossible, and karyometric studies must take the difficult stereologic problem of spheroid sectioning into account. A mathematical model is proposed to describe an aggregate of separate parallel anisotropic prolate spheroids of variable size and eccentricity. This model appears suitable for the study of epithelial nuclei. After a tentative estimation of the biopsy angle, the application of the model to nuclear profile measurements produces the stereologic data of the mean spheroid nucleus: major and minor axes (and their ratio), volume, surface area (and the V/S ratio), and numerical density. Considerable time may be saved by the use of an image analyser with a specific algorithm. Most of the steps are entirely automated, but the user retains the interactive choice of the nuclei to be studied, for instance by separating the different epithelial layers. The profile data are computer-filed and several programs can yield the stereologic estimations and plots of nuclear profile areas. Poolings of cases of similar histologic staging and nearly the same sectioning angle can be used for the profile area plots. The model has been applied to pseudostratified and altered nasal mucosa of nickel workers. The stereologic estimates, mainly the nuclear volume, correlate well with histologic gradings. The nuclear profile area plots are considered useful for an assessment of the nuclear polyploidism. The complete model should be applicable to many other types of functionally or pathologically altered epithelia, particularly for cancer and precancer screenings, when the use of sectioned material is a prerequisite.