Biology subjects

Coppenrath, K.

Publications and source records attributed to Coppenrath, K..

6 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↗

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↗

bioRxiv2023

Photoreceptor disc incisures form as an adaptive mechanism ensuring the completion of disc enclosure

The first steps of vision take place within a stack of tightly packed disc-shaped membranes, or "discs", located in the outer segment compartment of photoreceptor cells. In rod photoreceptors, discs are enclosed inside the outer segment and contain deep indentations in their rims called "incisures". The presence of incisures has been documented in a variety of species, yet their role remains elusive. In this study, we combined traditional electron microscopy with three-dimensional electron tomography to demonstrate that incisures are formed only after discs become completely enclosed. We also observed that, at the earliest stage of their formation, discs are not round as typically depicted but rather are highly irregular in shape and resemble expanding lamellipodia. Using genetically manipulated mice and frogs and measuring outer segment protein abundances by quantitative mass spectrometry, we further found that incisure size is determined by the molar ratio between peripherin-2, a disc rim protein critical for the process of disc enclosure, and rhodopsin, the major structural component of disc membranes. While a high perpherin-2 to rhodopsin ratio causes an increase in incisure size and structural complexity, a low ratio precludes incisure formation. Based on these data, we propose a model whereby normal rods express a modest excess of peripherin-2 over the amount required for complete disc enclosure in order to ensure that this important step of disc formation is accomplished. Once the disc is enclosed, the excess peripherin-2 incorporates into the rim to form an incisure.

cell biology↗

bioRxiv2022

Maternal Wnt11b regulates cortical rotation during Xenopus axis formation: analysis of maternal-effect wnt11b mutants

Asymmetric signalling centres in the early embryo are essential for axis formation in vertebrates. These regions, namely the dorsal morula, yolk syncytial layer, and distal hypoblast/anterior visceral endoderm (in amphibians, teleosts and mammals, respectively), require the localised stabilisation of nuclear Beta-catenin (Ctnnb1), implying that localised Wnt/Beta-catenin signalling activity is critical in their establishment. However, it is becoming increasingly apparent that the stabilisation of Beta-catenin in this context may be initiated independently of secreted Wnt growth factor activity. In Xenopus, dorsal Beta-catenin stabilisation is initiated by a requisite microtubule-mediated symmetry-breaking event in the fertilised egg: "cortical rotation". Vegetally-localised wnt11b mRNA has been implicated upstream of Beta-catenin in this context, as has the dorsal enrichment of Wnt ligand-independent activators of Beta-catenin, but the extent that each of these processes contribute to axis formation in this paradigm remains unclear. Here we describe a maternal effect mutation in Xenopus laevis wnt11b.L, generated by CRISPR mutagenesis. We demonstrate a maternal requirement for timely and complete gastrulation morphogenesis and a zygotic requirement for proper left-right asymmetry. We also show that a subset of maternal wnt11b mutants have axis and dorsal gene expression defects, but that Wnt11b likely does not act through the Wnt coreceptor Lrp6 or through Dishevelled, which we additionally show (using exogenous constructs) do not exhibit patterns of activity consistent with roles in early Beta-catenin stabilisation. Instead, we find that microtubule assembly and cortical rotation are reduced in wnt11b mutant eggs, leading to less organised and directed vegetal microtubule arrays. In conclusion, we propose that Wnt11b signals to the cytoskeleton in the egg or early zygote to enable robust cortical rotation, and thus acts in the distribution of putative dorsal determinants rather than as a component or effector of the determinants themselves.

developmental 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↗