Biology subjects

Thoma, H.

Publications and source records attributed to Thoma, H..

3 recordsLinked to original sources

bioRxiv2026

Nanoscale imaging resolves canonical topology and intracellular dynamics of SUN5/SPAG4L during mammalian spermiogenesis

SUN5 is a testis-specific SUN domain protein essential for connecting the sperm tail to the nucleus. However, until now, its precise localization, intracellular dynamics, and membrane topology during spermiogenesis have remained controversial. To address these discrepancies, we applied ultrastructure expansion microscopy (U-ExM) to systematically track SUN5 redistribution throughout spermiogenesis. This approach enabled a detailed reconstruction of SUN5 localization across developmental stages and revealed previously undescribed enrichment at the perinuclear ring (PNR) and the microtubule manchette, suggesting secondary functions at the PNR or a potential role in intra-manchette transport (IMT). Complementary immunogold labelling using the Tokuyasu method, together with biochemical assays, demonstrated that SUN5 adopts a membrane localization and topology consistent with that of classical SUN domain proteins. Quantitative measurements of the nuclear envelope architecture at the head-to-tail coupling apparatus (HTCA) further enabled us to present a refined structural model of SUN5 positioning at the head-tail junction. Overall, our findings resolve previous discrepancies in the field and provide a coherent framework for understanding SUN5 organization and its role in mammalian spermiogenesis. Summary StatementIn the presented study, we analyzed the dynamic redistribution of SUN5 during mammalian spermiogenesis and resolved its topology in developing spermatids to gain insights concerning the proteins molecular function in head-tail coupling.

cell biology↗

bioRxiv2022

Sun4 is a type II transmembrane protein of the spermatid inner nuclear membrane that forms heteromeric assemblies with Sun3 and interacts with Lamin B3

SUN domain proteins are conserved proteins of the nuclear envelope and key components of the LINC complexes (linkers of the nucleoskeleton and the cytoskeleton). Previous studies have demonstrated that the testis-specific SUN domain protein Sun4 is a vital player in spermatogenesis, critically involved in the directed shaping of the spermatid nucleus. Its molecular properties relating to this crucial function, however, have remained largely unknown. Previous studies presented quite controversial data for the general organization and orientation of Sun4 within the spermatid nuclear envelope. In the present study, we have re-evaluated this issue in detail and present new robust data on the Sun4 topology and its interactions at the nucleo-cytoplasmic junction. We identified Sun4 as an integral protein of the inner nuclear membrane, sharing a classical SUN domain protein topology. Similar to other SUN domain proteins, the C-terminal SUN domain of Sun4 locates to the perinuclear space and the N-terminus is directed to the nucleoplasm, where it interacts with the spermiogenesis specific Lamin B3. We found that Sun4 in its natural environment forms heteromeric assemblies with Sun3 and, beyond this, it is crucially involved in the regulation of Sun3 expression. Together, our results contribute to a better understanding of the specific function of Sun4 at the spermatid nucleo-cytoplasmic junction and the entire process of sperm-head formation. Summary statementIn our current study, we have analyzed in detail the biochemical and dynamic properties of the testis-specific SUN domain protein Sun4 and we provide novel insights into its interaction behavior at the spermatid nucleo-cytoplasmic junction.

cell biology↗

bioRxiv2020

Parallel monitoring of mRNA abundance, localisation and compactness with correlative single molecule FISH on LR White embedded samples

Single mRNA molecules are frequently detected by single molecule fluorescence in situ hybridisation (smFISH) using branched DNA technology. While providing strong and background-reduced signals, the method is inefficient in detecting mRNAs within dense structures, in monitoring mRNA compactness and in quantifying abundant mRNAs. To overcome these limitations, we have hybridised slices of high pressure frozen, LR White embedded cells (LR White smFISH). mRNA detection is physically restricted to the surface of the resin. This enables single molecule detection of RNAs with accuracy comparable to RNA sequencing, irrespective of their abundance, while at the same time providing spatial information on RNA localisation that can be complemented with immunofluorescence and electron microscopy, as well as electron tomography. Moreover, LR White embedding restricts the number of available probe pair recognition sites for each mRNA to a small subset. As a consequence, differences in signal intensities between RNA populations reflect differences in RNA tertiary structures, and we show that the method can be employed to probe for mRNA compactness. We apply LR White smFISH to answer some outstanding questions related to trans-splicing, RNA granules and mitochondrial RNA editing, using trypanosomes and their versatile RNA biology as a model system.

cell biology↗