Biology subjects

Hausen, H.

Publications and source records attributed to Hausen, H..

4 recordsLinked to original sources

bioRxiv2026

Annelid eye evolution revealed by developmental, ultrastructural, and connectome analyses of cerebral eyes in Malacoceros fuliginosus

Eye evolution has long attracted interest, yet how multiple cerebral eyes within a lineage originate and diversify remains unclear. Annelids display exceptional diversity in eye number and structure, but the homology and function of distinct eye pairs are poorly understood. Here we investigate the cerebral eyes of the sedentary annelid Malacoceros fuliginosus using an integrated developmental, molecular, ultrastructural, and connectomic approach. We show that both the early-developing ventral and later-developing dorsal eyes are simple, few-celled, inverted rhabdomeric eyes that express transcription factors with conserved roles in animal eye development. Two r-opsin paralogs and distinct neurotransmitters are differentially expressed in different photoreceptor cells of the eyes. Ultrastructural reconstructions across larval development reveal differences in cellular composition and growth dynamics, while axonal tracing shows that photoreceptors from ventral and dorsal eyes project to overlapping regions of the larval brain. The overall organization and projections resemble those described in the errant annelid Platynereis dumerilii. Together, these data support the hypothesis that an ancestral cerebral eye duplicated early in annelid evolution, giving rise to multiple eye pairs with stage-specific functions.

evolutionary biology↗

bioRxiv2025

Ectopic head regeneration after nervous system ablation in a sea anemone

Some animals are able to regenerate all missing cell types and large body parts after bisection, a phenomenon called whole-body regeneration. Many of these animals regenerate the correct tissues and structures with remarkable fidelity according to the original polarity of the body, reflecting positional information present in the remaining tissue. Understanding the cellular and molecular basis of this positional information is a central question in regeneration biology. In planarians and acoels, muscle cells have been shown to carry such positional information, but where this information originates and whether this function is conserved in other highly regenerative animals, is not well understood. Here we use the cnidarian Nematostella vectensis to address the role of the nervous system in whole-body regeneration. We generated a transgenic line for conditional ablation of neurons and first showed that Nematostella can repeatedly regenerate its nervous system. Bisection experiments following nervous system ablation showed that all head fragments regenerate a second head instead of a foot, whereas foot fragments correctly regenerate the missing head. We further found that regenerating head fragments of nervous system-ablated animals increase the expression of Wnt signaling genes that in wildtype animals are only upregulated in regenerating foot fragments. These molecular changes and the initiation of ectopic head regeneration precede the re-appearance of neurons, suggesting that the nervous system does not directly control whether a head or foot will be regenerated. Instead, we propose a model in which the nervous system provides positional information to the tissue of the body column, and that this information allows foot regeneration by suppressing a default program for head regeneration.

developmental biology↗

bioRxiv2022

Comparative analysis defines a broader FMRFamide-gated sodium channel family and determinants of neuropeptide sensitivity

FMRFamide and similar neuropeptides are important physiological modulators in most invertebrates, but the molecular basis of FMRFamide activity at its receptors is unknown. We therefore sought to identify the molecular determinants of FMRFamide potency in one of its native targets, the excitatory FMRFamide-gated sodium channel (FaNaC) from gastropod mollusks. Using molecular phylogenetics and electrophysiological measurement of function, we identified a broad FaNaC family that includes mollusk and annelid channels gated by FMRFamide, FVRIamides, and/or Wamides (or myoinhibitory peptides). A comparative analysis of this broader FaNaC family and other channels from the overarching DEG/ENaC superfamily, incorporating mutagenesis and experimental dissection of function, identified a pocket of amino acid residues that determines activation of FaNaCs by neuropeptides. Although this pocket has diverged in distantly related DEG/ENaC channels that are activated by other ligands, such as mammalian acid-sensing ion channels, we show that it nonetheless contains residues that determine enhancement of those channels by similar peptides. This study thus identifies amino acid residues that determine FMRFamide activity at FaNaCs and illuminates evolution of ligand recognition in one branch of the DEG/ENaC superfamily of ion channels.

biochemistry↗

bioRxiv2020

3D-printed Planktonic Observational Setup and Analysis Pipeline TrackmateTaxis

Planktonic organisms are a cornerstone of marine ecosystems. They vary significantly in size and have a repertoire of behaviors to aid them to survive and navigate their three-dimensional environment. One of the most important cues is light. A variety of setups were used to study the swimming behavior of specific organisms, but broader and comparative investigations need more versatile solutions. With the help of 3D printing, we designed and constructed a modular and flexible behavioral observation setup that enables recordings of animals down to 50m or up to a few centimeters. A video analysis pipeline using ImageJ and python allows a quick, automated, and robust tracking solution, capable of processing many videos automatically. A modular light path allows the addition of filters or use of pulse width modulation to equalize photon emission of LEDs or additional LEDs to mix different wavelengths. Optionally, a spectrometer can be installed to enable live monitoring of a stimulus. We tested the setup with two phototactic marine planktonic larvae. First, we investigated the spectral sensitivity of the 7-day old larvae of the polychaete Malacoceros fuliginosus and second, the behavior of the 200m spherical bryozoan coronated larvae of Tricellaria inopinata to ultraviolet light coming from the bottom of the vessel. The setup and pipeline were able to record and analyze hundreds of animals simultaneously. We present an inexpensive, modular, and flexible setup to study planktonic behavior of a variety of sizes.

animal behavior and cognition↗