Biology subjects

Hammel, J. U.

Publications and source records attributed to Hammel, J. U..

8 recordsLinked to original sources

bioRxiv2025

JNK integrates immune and stress signals to balance apoptosis and proliferation in airway progenitors

Chronic inflammation disrupts epithelial regeneration, yet how immune signaling reprograms progenitor fate remains unclear. Using the Drosophila airway as a model of epithelial remodeling, we identify the c-Jun N-terminal kinase (JNK) pathway as a central integrator of immune and stress cues that balances apoptosis and compensatory proliferation in airway progenitors. Persistent activation of the innate immune IMD pathway induces simultaneous cell death and proliferation through a non-canonical route that bypasses NF-{kappa}B/Relish and instead engages JNK. Downstream, distinct transcriptional modules orchestrate these divergent fates: Foxo and AP-1 drive apoptosis, whereas the ETS factor Ets21C mediates proliferation. Genetic inhibition of JNK or its effectors restores progenitor homeostasis, while constitutive activation recapitulates inflammation-induced tissue remodeling. These responses are cell-autonomous, revealing that airway progenitors actively interpret immune and stress signals to determine their fate. Collectively, our findings uncover a modular signaling architecture that links inflammation to regeneration and highlight conserved JNK-dependent transcriptional programs as potential therapeutic targets to prevent progenitor exhaustion in chronic airway disease.

cell biology↗

bioRxiv2024

A trait-based taxonomic data base for the order Schizomida (Arachnida) with descriptions of a new fossil species from Kachin amber and the female of Surazomus palenque Villarreal, Miranda & Giupponi 2016.

Despite a global distribution throughout the tropics and sub-tropics, the order Schizomida (Arachnida) is heavily understudied and the phylogeny of the group is poorly understood. Identification keys are only available for some regions or genera but not for the entire order. (1) comprehensively reviewed the entire schizomid fauna and established a suite of characters to define all genera known at this time. This suite of characters still depicts the foundation of modern descriptions, supplemented by recently established characters, most of them documenting setation patterns on pedipalps, flagellum and chelicerae. In this paper, we present the Schizomida Trait Data Base (STDB) containing data for 25 characters based on the entire body of schizomid literature. Characters were chosen based on their use for modern taxonomic description and availability of the data. The STDB is a powerful tool that can be used by both amateurs and experienced researchers to categorise newly found specimens, both extant and fossil, down to genus level easily. Analysis using the new database gives insight into biogeographical patterns of characters. Furthermore, we are describing a new species,{dagger} Annazomus jamesi, a fossil specimen from Burmese (Kachin) amber and investigate a small collection of extant schizomids from Ecuador, which includes the previously unrecorded female of Surazomus palenque, herein described for the first time. The taxonomic assignment of both specimens is based on the STDB, highlighting the utility of the new data base approach to schizomid systematics. Arachnids, biogeography, Cretaceous, data base, fossil, new species, palaeontology, Schizomida, statistics, taxonomy

evolutionary biology↗

bioRxiv2023

Mechanical and elemental characterization of ant mandibles: consequences for bite mechanics

Chewing with the mandibles is a food processing behavior observed in most current insect lineages. Mandible morphology has an essential role in biting behavior and food processing capacity. However, the mandible cuticle can have regional differences in its mechanical properties, associated or not with the accumulation of elements that increase cuticle stiffness. The effects of such a heterogeneous distribution of cuticle material properties in the mandible responses to biting loading are still poorly explored in chewing insects. Here we measured the elemental composition and material properties of workers of an ant species, Formica cunicularia, and tested the effects of the cuticular variation in Youngs modulus (E) under bite-loading with Finite Element Analysis (FEA). We divided worker mandibles into four regions that we expect would vary in elemental composition and material properties, namely the masticatory margin, mandible blade, ventral (VMA), and dorsal (DMA) mandibular articulations with the head. Specifically, we expect the masticatory margin will show higher cuticular hardness (H) and E values, followed by the mandibular joints and the mandible blade. We also predict that such cuticle material properties variation is functionally relevant under bite-loading, changing stress patterns when compared to the mechanical responses of a mandible with a homogeneous distribution of material properties. To measure elemental composition, we used energy disperse X-ray spectroscopy, while H and E were accessed through nanoindentation tests. Mandible mechanical responses to bite-loading were tested with FEA, comparing a mandible with a homogeneous versus a heterogeneous E distribution. As expected, the mandibular regions showed distinct proportions of relevant elements, like Cu and Zn, with the masticatory margin showing the higher levels of those elements, followed by the mandibular articulations with the head and the mandible blade. The same pattern was observed regarding the values of cuticle H and E. When incorporated into FEA, this variation in E effectively changed mandible stress patterns, leading to a higher concentration of stresses in the stiffer mandibular regions, letting the softer mandible blade with relatively lower stress levels. Our results demonstrated the relevance of cuticle heterogeneity in mechanical properties to deal with bite-loading demands and suggest that the accumulation of transition metals such as Cu and Zn has a relevant correlation with such mechanical characteristics of the mandible in this ant species.

zoology↗

bioRxiv2023

Development of the branchial musculature of the Siberian sturgeon (Acipenser baerii) reveals a heterochronic shift during the evolution of acipenseriform cranial muscles

Heterochronic shifts are regarded one of the major evolutionary changes acting on developmental modules and underlying the origin of morphological disparity. Conserved characters, rarely subject to heterochronic shifts during the curse of evolution, in contrast could indicate underlying developmental or functional constraints. Here we use the development of the cranial musculature Siberian sturgeon (Acipenser baerii) as a model to investigate the role of heterochrony during the evolution of the craniofacial system of Actinopterygii. Using histology, fluorescent antibody staining and fast propagation-based phase contrast imaging in combination with 3D-reconstruction we describe the development of the branchial and hypobranchial musculature. We show that the development of the first branchial arch is accelerated compared to other basal-branching actinopterygians leading to a more synchronous development with the hyoid arch. A pattern that could relate to the derived migratory behaviour of the neural crest cells in sturgeons. In contrast, the developmental timing of the more posterior branchial musculature, including the cucullaris muscle in the Siberian sturgeon, appears to be highly conserved compared to other Actinopterygii and even Osteognathostomata. This could indicate the presence of functional or developmental constraints underlying the evolution of the muscles at the head/trunk interface.

zoology↗

bioRxiv2021

Gaining Insight into the Deformation of Achilles Tendon Entheses in Mice

Understanding the biomechanics of tendon entheses is fundamental for surgical repair and tissue engineering, but also relevant in biomimetics and palaeontology. 3D imaging is becoming increasingly important in the examination of soft tissue deformation. But entheses are particularly difficult objects for micro-computed tomography because they exhibit extreme differences in X-ray attenuation. In this article, the ex vivo examination of Achilles tendon entheses from mice using a combination of tensile tests and synchrotron radiation-based micro-computed tomography is reported. Two groups of specimens with different water content are compared with regard to strains and volume changes in the more proximal free tendon and the distal tendon that wraps around the Tuber calcanei. Tomograms of relaxed and deformed entheses are recorded with propagation-based phase contrast. The tissue structure is rendered in sufficient detail to enable manual tracking of patterns along the tendon, as well as 3D optical flow analysis in a suitable pair of tomograms. High water content is found to increase strain and to change the strain distribution among proximal and distal tendon. In both groups, the volume changes are higher in the distal than in the proximal tendon. These results support the existence of a compliant zone near the insertion. They also show that the humidity of the specimen environment has to be controlled. Necessary steps to extend the automatic tracking of tissue displacements to all force steps are discussed.

zoology↗

bioRxiv2020

Becoming symbiotic - the symbiont acquisition and the early development of bathymodiolin mussels

Symbiotic associations between animals and microorganisms are widespread and have a profound impact on the ecology, behaviour, physiology, and evolution of the host. Research on deep-sea mussels of the genus Bathymodiolus has revealed how chemosynthetic symbionts sustain their host with energy, allowing them to survive in the nutrient-poor environment of the deep ocean. However, to date, we know little about the initial symbiont colonization and how this is integrated into the early development of these mussels. Here we analysed the early developmental life stages of B. azoricus, "B". childressi and B. puteoserpentis and the changes that occur once the mussels are colonized by symbionts. We combined synchrotron-radiation based {micro}CT, correlative light and electron microscopy and fluorescence in situ hybridization to show that the symbiont colonization started when the animal settled on the sea floor and began its metamorphosis into an adult animal. Furthermore, we observed aposymbiotic life stages with a fully developed digestive system which was streamlined after symbiont acquisition. This suggests that bathymodiolin mussels change their nutritional strategy from initial filter-feeding to relying on the energy provided by their symbionts. After [~]35 years of research on bathymodiolin mussels, we are beginning to answer fundamental ecological questions concerning their life cycle and the establishment of symbiosis.

zoology↗

bioRxiv2020

Parallel evolution of direct development in frogs - Skin and thyroid gland development in African Squeaker Frogs (Anura: Arthroleptidae: Arthroleptis)

Cases of parallel evolution offer the possibility to identify adaptive traits and to uncover developmental constraints on the evolutionary trajectories of these traits. The independent evolution of direct development, from the ancestral biphasic life history in frogs is such a case of parallel evolution. In frogs, aquatic larvae (tadpoles) differ profoundly from their adult forms and exhibit a stunning diversity regarding their habitats, morphology and feeding behaviors. The transition from the tadpole to the adult is a climactic, thyroid hormone (TH)-dependent process of profound and fast morphological rearrangement called metamorphosis. One of the organ systems that experiences the most comprehensive metamorphic rearrangements is the skin. Direct-developing frogs lack a free-swimming tadpole and hatch from terrestrial eggs as fully formed froglets. In the few species examined, development is characterized by the condensed and transient formation of some tadpole-specific features and the early formation of adult-specific features during a "cryptic" metamorphosis. In this study we show that skin in direct-developing African squeaker frogs (Arthroleptis) is also repatterned from a tadpole-like to an adult-like histology during a cryptic metamorphosis. This repatterning correlates with an increase of thyroid gland activity. A comparison with data from the Puerto Rican coqui (Eleutherodactylus coqui) reveals that direct development might have evolved in parallel in these frogs by a comparable heterochronic shift of thyroid gland activity. This suggests that the development of many adult-features is still constrained by the ancestral dependency on thyroid hormone signaling.

developmental biology↗

bioRxiv2019

Profiling cellular diversity in sponges informs animal cell type and nervous system evolution

The evolutionary origin of metazoan cell types such as neurons, muscles, digestive, and immune cells, remains unsolved. Using whole-body single-cell RNA sequencing in a sponge, an animal without nervous system and musculature, we identify 18 distinct cell types comprising four major families. This includes nitric-oxide sensitive contractile cells, digestive cells active in macropinocytosis, and a family of amoeboid-neuroid cells involved in innate immunity. We uncover presynaptic genes in an amoeboid-neuroid cell type, and postsynaptic genes in digestive choanocytes, suggesting asymmetric and targeted communication. Corroborating this, long neurite-like extensions from neuroid cells directly contact and enwrap choanocyte microvillar collars. Our data indicate a link between neuroid and immune functions in sponges, and suggest that a primordial neuro-immune system cleared intruders and controlled ciliary beating for feeding.

developmental biology↗