Biology subjects

Klemm, U.

Publications and source records attributed to Klemm, U..

5 recordsLinked to original sources

bioRxiv2026

Mutagenesis study of a Bacteriophytochrome - insights for the development of labels for optical imaging.

Bacteriophytochromes (BphPs) find increasing interest as near-infrared (NIR) labels for imaging. Applications range from whole animal imaging to cell-to super-resolution microscopy. Here we present a comprehensive study of a BphP from Rhizobium etli (ReBphP) allowing mutant-based insights into BphP photophysics. This is complemented by QM/MM-optimized deep-learning structure predictions of ReBphP and variants in their photoswitched states, rationalizing the effects of variants. Pertaining to imaging, based on our study we identify a bright and far red-shifted BphP for imaging in mammalian cells as well as a fluorescent photoswitching BphP. Utilizing the latter, we introduce photoswitching fluorescence background suppression for in vivo whole animal fluorescence imaging achieving higher contrast over background than possible utilizing non-switching labels.

biochemistry↗

bioRxiv2023

MicroRNA-221/222-expression in HSC and MPP safeguards their quiescence and multipotency by downregulating stress-independent and dependent expression of IEG and of several myelo/granulopoiesis-enhancing target genes.

The microRNA cluster-221/222 is expressed in hematopoietic stem cells (HSC) and multipotent progenitors (MPP). To study its function in hematopoiesis, we generated mice, in which this cluster is selectively deleted by Vav-cre in HSC and, thus, in all hematopoietic cells. Fluorescence-activated cell sorting analyses of the lineage-negative HSC and MPP compartments in bone marrow at unperturbed, steady state hematopoiesis detect strong activation of HSC to MPP, as well as increased granulocytes in the periphery, induced by miR-221/222-deficiency. Short-term social stress on mice also activates HSC to MPP, but the time of stress is too short to detect further increases in granulocyte numbers. Single cell deep mRNA sequencing identifies Fos as direct, and Jun as well as six other immediate early genes (IEG) as indirect targets of miR-221/222 at unperturbed hematopoiesis. Three of these IEG - Klf6, Nr4a1 and Zfp36 - have previously been found to influence myelo/granulopoiesis. Short stress induces higher levels of the same, and an even larger number of IEGs, now also in MPP, indicating, that stress and miR-221/222 both activate HSC to MPP by IEG upregulation in perturbed hematopoiesis. Furthermore, combined stress and miR-221/222-deficiency rapidly increase numbers of myelo/granulocyte progenitors (MEP, GMP) in bone marrow. Additional indirect miR-221/222-targets become detectable in MPP, of which H3f3b has previously been found to influence myelopoiesis. In serial transplantations, miR-221/222-deficient HSC retain their capacity to home to, and become resident in bone marrow, but they loose their lymphopoietic capacities, thus their multipotency. Our results suggest, that miR-221/222-expression in HSC and MPP safeguards their quiescence and multipotency by downregulating the expression of IEG and of myelo/granulopoiesis-enhancing target genes. Since miR-221/222 is also expressed in human HSC and MPP, its expression should improve clinical settings of human bone marrow transplantations.

immunology↗

bioRxiv2020

Functional multispectral optoacoustic tomography imaging of hepatic steatosis development in mice

The increasing worldwide prevalence of obesity, fatty liver diseases, as well as the emerging understanding of the importance of lipids in multi-faceted aspects of various other diseases is generating significant interest in lipid research. Lipid visualization in particular can play a critical role in understanding functional relations in lipid metabolism. In this study, we investigate the potential of multispectral optoacoustic tomography (MSOT) as a novel modality to non-invasively visualize lipids in laboratory mice. Using an obesity-induced non-alcoholic fatty liver disease (NAFLD) mouse model, we examined whether MSOT could detect and differentiate different grades of hepatic steatosis and monitor the accumulation of lipids in the liver quantitatively over time, without the use of contrast agents, i.e. in label free mode. Moreover, we demonstrate the efficacy of using the real-time clearance kinetics of indocyanine green (ICG) in the liver as a biomarker to evaluate the organs function and assess the severity of NAFLD. This study demonstrates MSOT as an efficient imaging tool for lipid visualization in preclinical studies, particularly for the assessment of NAFLD.

bioengineering↗

bioRxiv2020

Multiplexed whole animal imaging with reversibly switchable optoacoustic proteins

We describe two photochromic proteins for cell-specific in vivo optoacoustic (OA) imaging with signal unmixing in the temporal domain. We show highly sensitive, multiplexed visualization of T lymphocytes, bacteria and tumors in the mouse body and brain. We developed machine learning-based software that allows commercial imaging systems to be used for temporal unmixed OA imaging, enabling its routine use in life sciences.

biochemistry↗

bioRxiv2018

Transition of Wnt signaling microenvironment delineates the squamo-columnar junction and emergence of squamous metaplasia of the cervix

The transition zones (TZ) between squamous and columnar epithelium constitute hotspots for the emergence of cancers. Carcinogenesis at these sites is often preceded by the development of metaplasia, where one epithelial type invades the neighboring one. It remains unclear how these niches are restrained at the boundary between the two epithelial types and what factors contribute to metaplasia. Here we show that the cervical squamo-columnar junction derives from two distinct stem cell lineages that meet at the TZ. In contrast to the prevailing notion, our analysis of cervical tissue showed that the TZ is devoid of any locally restricted, specialized stem cell population, which has been implicated as precursor of both cervical squamous cell carcinoma and adenocarcinoma. Instead, we reveal that these cancers originate from two separate stem cell lineages. We show that the switch in the underlying Wnt signaling milieu of the stroma is a key determinant of proliferation or quiescence of epithelial stem cell lineages at the TZ. Strikingly, while the columnar lineage of the endocervix is driven by Wnt signaling, the maintenance of squamous stratified epithelium of the ectocervix and emergence of squamous metaplasia requires inhibition of Wnt signaling via expression of Dickkopf2 (Dkk2) in the underlying stroma. Moreover, Notch signaling is required for squamous cell stratification. Thus, our results indicate that homeostasis at the TZ is not maintained by a transition from one epithelial type to another but rather results from alternative signals from the stromal compartment driving the differential proliferation of the respective cell lineages at the squamo-columnar junction.

cancer biology↗