Biology subjects

Hammer, P.

Publications and source records attributed to Hammer, P..

4 recordsLinked to original sources

bioRxiv2026

The Role of Secondary Chordae Tendineae in Mitral Valve Mechanics: A Benchtop Study

PurposeSecondary chordae tendineae (CT) are frequently disregarded during mitral valve (MV) repair. However, their contribution to MV biomechanics remains poorly understood. We hypothesized that secondary CT play an important role in maintaining leaflet geometry during valve closure. MethodsEleven explanted porcine MVs were micro-CT scanned in a systolic configuration under three conditions: (1) physiological baseline with all secondary CT intact, (2) transection of the A2 strut CT, and (3) transection of all secondary CT. Billowing height (BH), coaptation height (CH) along the parasternal long-axis view, and coaptation area (CA) were quantified and compared between conditions. An increase in BH[≥] 2 mm from baseline was defined as pathological. ResultsTransection of the A2 strut CT increased BH by 3.1 mm, exceeding the pathological billowing threshold by 1.1 mm (padj = 0.003). CH decreased by 0.6 mm (padj = 0.003), whereas CA showed no significant change compared with baseline. Subsequent transection of all secondary CT further increased BH to 4.8 mm relative to baseline, corresponding to 2.8 mm above the billowing threshold (padj = 0.003). CH did not differ significantly, while CA decreased by 0.35 cm2 compared with baseline (padj = 0.029). All values represent medians. ConclusionSecondary CT play a critical role in stabilizing MV leaflet geometry. Their transection resulted in increased leaflet billowing and reduced coaptation metrics associated with unfavorable MV repair outcomes. Preservation or reconstruction of secondary CT may therefore be an important consideration in MV repair strategies.

bioengineering↗

bioRxiv2026

Testing Reversibility of Endosymbiotic Gene Transfer between Chloroplast and Nucleus

Most proteins targeted to the organelles of endosymbiotic origin are encoded in the nuclear genome, placing them under the regulatory dominance of the nucleus. For photosynthetic eukaryotes, nuclear-encoded chloroplast proteins arise via two routes: First, genes of cyanobacterial origin were relocated to the nucleus through endosymbiotic gene transfer (EGT). Second, proteins of eukaryotic origin emerged to support chloroplast function and structure. These proteins are reimported into the chloroplast via an import machinery. Reversing the transfer of such genes from the nucleus to the chloroplast genome may offer insights into chloroplast regulation and evolution. In this study, we established a highly efficient and accessible electroporation protocol for chloroplast transformation in the green alga Chlamydomonas reinhardtii, and used it to reverse-transfer two nuclear-encoded genes encoding proteins arising via the two routes described above: the cyanobacteria-derived chloroplast division protein FtsZ1 and the Rubisco-linker EPYC1 of eukaryotic origin. Regardless of origin, both chloroplast-encoded FtsZ1 and EPYC1 showed proper localization and functionality comparable to their nuclear-encoded counterparts. Together, our study provides a robust protocol for chloroplast transformation, a platform for investigating the evolutionary drivers of EGT, and a foundation for advancing chloroplast bioengineering. SIGNIFICANCE STATEMENTO_LIEndosymbiotic gene transfer has resulted in the mass migration of genes from the chloroplast genome to the nuclear genome. Reversing the gene transfer could reveal the evolutionary significance of genome partitioning. C_LIO_LIUsing the green alga Chlamydomonas reinhardtii, this study developed an efficient, electroporation-based protocol for chloroplast transformation. Relocating the genes encoding two chloroplast-targeted proteins, FTSZ1 and EPYC1, to the chloroplast genome showed that the proteins maintained normal localization and function. C_LIO_LIThe established transformation protocol facilitates systematic testing of reverse gene transfer to elucidate the potential evolutionary advantages of genome partitioning and opens new avenues for chloroplast bioengineering. C_LI

cell biology↗

bioRxiv2023

Estimation of effective population size and effective number of breeders in an abundant and heavily exploited marine teleost

Obtaining reliable estimates of the effective number of breeders N(b) and generational effective population size (Ne) for fishery-important species is challenging because they are often iteroparous and highly abundant, which can lead to bias and imprecision. However, recent advances in understanding of these parameters, as well as the development of bias correction methods, have improved the capacity to generate reliable estimates. We utilized samples of both single-cohort young of the year and mixed-age adults from two geographically and genetically isolated stocks of the Australasian snapper (Chrysophrys auratus) to investigate the feasibility of generating reliable Nb and Ne estimates for a fishery species. Snapper is an abundant, iteroparous broadcast spawning teleost that is heavily exploited by recreational and commercial fisheries. Employing neutral genome-wide SNPs and the linkage-disequilibrium method, we determined that the most reliable Nb and Ne estimates could be derived by genotyping at least 200 individuals from a single cohort. Although our estimates made from the mixed-age adult samples were generally lower and less precise than those based on a single cohort, they still proved useful for understanding relative differences in genetic effective size between stocks. The correction formulas applied to adjust for biases due to physical linkage of loci and age structure resulted in substantial upwards modifications of our estimates, demonstrating the importance of applying these bias corrections. Our findings provide important guidelines for estimatingNb and Ne for iteroparous species with large populations. This work also highlights the utility of samples originally collected for stock structure and stock assessment work for investigating genetic effective size in fishery-important species.

genomics↗

bioRxiv2023

Bioregional boundaries and genomically-delineated stocks in snapper (Chrysophrys auratus) from southeastern Australia

Marine species often exhibit genetic discontinuities concordant with biogeographic boundaries, frequently occurring due to changes in ocean circulation, bathymetry, coastline topography and temperature. Here we used 10,916 single nucleotide polymorphisms (SNPs) to assess the concordance between population genomic differentiation and coastal biogeography in the fishery important snapper (Chrysophrys auratus) across southeastern Australia. Additionally, we investigated whether spatial scales of assessment and management of snapper align with evidence from population genomics. Across 488 snapper samples from 11 localities between the west coast of South Australia and the south coast of New South Wales, we detected genomic structure concordant with the regions three biogeographic provinces. We also detected fine-scale genetic structuring relating to spatial variation in spawning and recruitment dynamics, as well as temporal stability in the genomic signal associated with two important spawning grounds. The current management boundaries in the region coincided with either the genetic breaks at bioregional boundaries or with localscale variation. Our study highlights the value of population genomic surveys in species with high dispersal potential for uncovering stock boundaries and demographic variation related to spawning and recruitment. It also illustrates the importance of marine biogeography in shaping population structure in commercial species with high dispersal potential.

genomics↗