Biology subjects

Horb, M.

Publications and source records attributed to Horb, M..

8 recordsLinked to original sources

bioRxiv2026

Synapse specific alterations of autophagy are a hallmark of Danon disease

Danon disease is a rare disorder caused by mutations in the LAMP2 gene, which encodes a lysosomal membrane protein key to the endolysosomal pathway and autophagy. Affected individuals show multisystemic alterations that include cardiomyopathy, skeletal muscle weakness, visual deficits and cognitive impairment. Here we establish a knockout LAMP2 line in Xenopus tropicalis that reproduces the characteristic cardiac activity, mobility impairments and vision deficits present in the disease. Damaged mitochondria were abundantly found in skeletal muscle fibers. LAMP2 mutant X. tropicalis detected light with a reduced preference for green wavelengths. Visual deficits were consistent with the finding of damaged mitochondria in the inner segment of rods but not in cones. Differences in autophagic flux were found in presynaptic terminals from photoreceptors and olfactory sensory neurons (OSNs), which establish the first synapse processing vision and olfaction, respectively. In wild-type animals autophagic shapes were observed in OSN terminals but were absent from photoreceptor ribbon synapses. In knockout LAMP2 tadpoles, autophagic organelles covered 7% of the OSN presynaptic terminal surface, a three-fold increase compared to photoreceptor terminals. These differences suggest that LAMP2 plays synapse-specific roles that could be an important determinant of the psychiatric manifestations present in Danon disease and support the use of LAMP2 X. tropicalis to shed new light on the pathological bases of this lysosomal storage disorder.

neuroscience↗

bioRxiv2025

Cell division during Xenopus gastrulation influences neuroectoderm patterning

Oriented cell division is essential for establishing the anterior-posterior body (A-P) axis in diverse species. However, in Xenopus laevis, blocking cell division during gastrulation does not impair the development of the neural tube and body elongation. Here, we demonstrate that neither neurulation nor dorsal mesoderm formation is dependent on cell division. On the other hand, neural plate elongation and A-P patterning are impacted in the absence of cell division, resulting in trunk defects and anterior defects that appear during tailbud stages. We also show that cell division is abundant around the ectoderm of the gastrulating embryo. Still, it is more intense in the dorsal ectoderm (presumptive neural plate), where there is a clear preference for A-P oriented cell divisions. Taken together, our results highlight a conserved mechanism of A-P oriented cell division that is present during neural plate elongation and patterning.

developmental biology↗

bioRxiv2024

The Xenopus respiratory system reveals common tetrapod mechanisms for growth, regeneration and healing

In recent years, we have seen a significant increase in our understanding of the mechanisms of development, regeneration, and healing of the respiratory system. However, most of these studies have been limited by their focus on mammalian systems. Here, we aimed to identify the underlying molecular mechanisms that are active during lung growth and tissue repair in amphibians, specifically Xenopus tropicalis (X. tropicalis). First, we analyzed the stem cell composition and signaling pathways that are active in epithelial and mesenchymal cells during lung growth. Then, we established a protocol for lung injury to assess the types of stem cells underlying tissue repair. In mammals, Sftpc+ (AT2) cells are alveolar stem cells that can differentiate to Krt8+ cells during lung homeostasis and post-injury repair. In this study, we identified Sftpc+ cells and Krt8+ cells, along with the activity of key developmental signaling pathways, Hippo and Wnt, during lung maturation at post-metamorphosis stages. We then established a protocol for lung injury using chemically induced injury with bleomycin, which damages the lung through oxidative stress. The results show an elevation in collagen post-injury, indicating bleomycins effect in causing lung fibrosis. X. tropicalis froglets survived 42 days post-injury, with a continuous decrease in fibrosis. To explore this effect, we analyzed the distribution of lung stem cells; Sox9 protein levels and Sftp gene expression were downregulated at the alveoli 42 days post-injury. The decrease in stem cell marker expression 42 days post-injury suggests they are differentiating as part of the healing process. Nevertheless, we could still detect them after a few weeks of healing. These results suggest that X. tropicalis has a regenerative capacity for lung tissue repair and that the same signaling pathways and stem cells are active in both amphibians and mammalian lungs during lung growth, regeneration, and healing. These findings show for the first time the physiological similarities between the anuran and the mammalian lung during growth and tissue repair processes, suggesting X. tropicalis as a potential animal model to study lung regeneration.

developmental biology↗

bioRxiv2024

ADAM interact with large protein complexes to regulate Histone modification, gene expression and splicing.

Cranial neural crest (CNC) cells are key stem cells that contribute to most of the facial structures in vertebrates. ADAM (A Disintegrin And Metalloprotease) proteins are essential for the induction and migration of the CNC. We have shown that Adam13 associates with the transcription factor Arid3a to regulate gene expression. Here we show that Adam13 modulates Histone modifications in the CNC. We show that Arid3a binding to the tfap2 promoter depends on the presence of Adam13. This association promotes the expression of one tfap2 variant expressed in the CNC that uniquely activates the expression of gene critical for CNC migration. We show that both Adam13 and human ADAM9 associate with proteins involved in histone modification and RNA splicing, a function critically affected by the loss of Adam13. We propose that ADAMs may act as extracellular sensors to modulate chromatin availability, leading to changes in gene expression and splicing.

developmental biology↗

bioRxiv2024

Sf3b4 mutation in Xenopus tropicalis causes RNA splicing defects followed by massive gene dysregulation that disrupt cranial neural crest development

Nager syndrome is a rare craniofacial and limb disorder characterized by midface retrusion, micrognathia, absent thumbs, and radial hypoplasia. This disorder results from haploinsufficiency of SF3B4 (splicing factor 3b, subunit 4) a component of the pre-mRNA spliceosomal machinery. The spliceosome is a complex of RNA and proteins that function together to remove introns and join exons from transcribed pre-mRNA. While the spliceosome is present and functions in all cells of the body, most spliceosomopathies - including Nager syndrome - are cell/tissue-specific in their pathology. In Nager syndrome patients, it is the neural crest (NC)-derived craniofacial skeletal structures that are primarily affected. To understand the pathomechanism underlying this condition, we generated a Xenopus tropicalis sf3b4 mutant line using the CRISPR/Cas9 gene editing technology. Here we describe the sf3b4 mutant phenotype at neurula, tail bud, and tadpole stages, and performed temporal RNA-sequencing analysis to characterize the splicing events and transcriptional changes underlying this phenotype. Our data show that while loss of one copy of sf3b4 is largely inconsequential in Xenopus tropicalis, homozygous deletion of sf3b4 causes major splicing defects and massive gene dysregulation, which disrupt cranial NC cell migration and survival, thereby pointing at an essential role of Sf3b4 in craniofacial development.

developmental biology↗

bioRxiv2024

Do organisms need an impact factor? Citations of key biological resources including model organisms reveal usage patterns and impact.

Research resources like transgenic animals and antibodies are the workhorses of biomedicine, enabling investigators to relatively easily study specific disease conditions. As key biological resources, transgenic animals and antibodies are often validated, maintained, and distributed from university based stock centers. As these centers heavily rely largely on grant funding, it is critical that they are cited by investigators so that usage can be tracked. However, unlike systems for tracking the impact of papers, the conventions and systems for tracking key resource usage and impact lag behind. Previous studies have shown that about 50% of the resources are not findable, making the studies they are supporting irreproducible, but also makes tracking resources difficult. The RRID project is filling this gap by working with journals and resource providers to improve citation practices and to track the usage of these key resources. Here, we reviewed 10 years of citation practices for five university based stock centers, characterizing each reference into two broad categories: findable (authors could use the RRID, stock number, or full name) and not findable (authors could use a nickname or a common name that is not unique to the resource). The data revealed that when stock centers asked their communities to cite resources by RRID, in addition to helping stock centers more easily track resource usage by increasing the number of RRID papers, authors shifted from citing resources predominantly by nickname ([~]50% of the time) to citing them by one of the findable categories ([~]85%) in a matter of several years. In the case of one stock center, the MMRRC, the improvement in findability is also associated with improvements in the adherence to NIH rigor criteria, as determined by a significant increase in the Rigor and Transparency Index for studies using MMRRC mice. From this data, it was not possible to determine whether outreach to authors or changes to stock center websites drove better citation practices, but findability of research resources and rigor adherence was improved.

bioinformatics↗

bioRxiv2022

Age associated DNA methylation changes in Xenopus frogs

Age-associated changes in DNA methylation have been widely established and characterized in mammals but not yet extended to other species. We present clear evidence that the aquatic vertebrate species Xenopus tropicalis displays clear patterns of age-associated changes in DNA methylation. This observation allows us to leverage the unique resources available for Xenopus to study how DNA methylation relates to other hallmarks of aging. We have generated whole genome bisulfite sequencing (WGBS) profiles in nine samples representing young, mature and old adults and characterize the gene- and chromosome-scale changes. Moreover, we selected a few thousands CpG sites to expand the findings in a larger cohort of individuals through targeted DNA methylation analysis to produce a cost effective epigenetic clock assay.

systems biology↗

bioRxiv2021

Generation of a new six1-null line in Xenopus tropicalis for study of development and congenital disease

The vertebrate Six (Sine oculis homeobox) family of homeodomain transcription factors play critical roles in the development of several organs. Six1 plays a central role in cranial placode development, including the precursor tissues of the inner ear, as well as other cranial sensory organs and the kidney. In humans, mutations in SIX1 underlie some cases of branchio-oto-renal syndrome (BOR), which is characterized by moderate to severe hearing loss. We utilized CRISPR/Cas9 technology to establish a six1 mutant line in Xenopus tropicalis that is available to the research community. We demonstrate that at larval stages, the six1-null animals show severe disruptions in gene expression of putative Six1 target genes in the otic vesicle, cranial ganglia, branchial arch and neural tube. At tadpole stages, six1-null animals display dysmorphic Meckels, ceratohyal and otic capsule cartilage morphology. This mutant line will be of value for the study of the development of several organs as well as congenital syndromes that involve these tissues.

developmental biology↗