Biology subjects

Melchert, A.

Publications and source records attributed to Melchert, A..

2 recordsLinked to original sources

bioRxiv2020

iPSC culture expansion selects against putatively actionable mutations in the mitochondrial genome

While human induced pluripotent stem cells (iPSCs) offer fascinating prospects for research and clinics, evaluating their genomic stability before applications is of utmost importance. During reprogramming, clonal hiPSC lines derived from the same parental cell population were observed to harbor different mitochondrial DNA (mtDNA) variants and variant heteroplasmy levels. It is unknown to date to which extent this unequal segregation of heteroplasmies between cells arises from mosaicism in the parental cell population, selection on mutated mtDNA molecules on the cellular or organelle level, genetic drift during reduction of mtDNA during reprogramming (genetic bottleneck), or de novo mutations. We analyzed mtDNA variants in 26 clonal iPSC lines by mtDNA sequencing. We did not observe a strong bottleneck or any selection for cells with specific mtDNA variants (clonal eliteness) during reprogramming. iPSC culture expansion, however, selects against putatively actionable mutations in the mitochondrial genome that may affect mitochondrial function and cell metabolism. In contrast, heteroplasmy levels of neutral variants remained stable or increased within clonal iPSC lines during culture expansion. Interestingly, the mtDNA copy number per cell got transiently reduced during targeted differentiation of iPSCs into cardiomyocytes, but mtDNA heteroplasmy levels were not affected. Altogether, our results point towards a scenario in which intra-cellular selection on mtDNA during culture expansion, but not during reprogramming or differentiation, pivotally shapes the mutational landscape of the mitochondrial genome in iPSCs. Other mechanisms such as inter-cellular selection, genetic bottleneck, and genetic drift exert minor impact.

genomics↗

bioRxiv2019

Cardiovascular parameters in capitive blue-fronted amazon parrots (Amazona aestiva, Linnaeus, 1758) with varying body condition scores

This study aims at determining the echocardiographic, radiographic and tomographic parameters of blue-fronted Amazon parrots (Amazona aestiva) with varying body condition scores. Thirty-five birds grown in captivity were included in the study and allocated into groups according to their respective body condition scores: Lean, Ideal and Obese. The echocardiographic evaluation revealed that obese parrots presented lower right ventricle dimensions in diastole than lean parrots. The fractional shortening was considerably lower in obese parrots than in parrots with lean and ideal body condition scores, but without statistical significance. The flow rate and the aortic pressure gradient were lower in the lean group than in the ideal group. No differences were observed between the groups when comparing the radiographic and tomographic measurements. Therefore, as is the case in mammals, we can conclude that alterations in the nutritional state of blue-fronted amazon parrots lead to cardiovascular dysfunctions detected only through an echocardiographic evaluation, which represents an important diagnostic tool for these animals. Computed tomography scans allowed a better identification of the structures of the cardiovascular system without the overlaying structures of the celomatic cavity observed in radiographic images. However, radiographic examinations should still be considered the standard screening examination to identify cardiac alterations such as increased or reduced organ dimensions. Standardizing the technique and describing the measurements obtained in this study may serve as a basis for further research.

physiology↗