Biology subjects

Carstensen, H. R.

Publications and source records attributed to Carstensen, H. R..

5 recordsLinked to original sources

bioRxiv2025

Identity and functions of monoaminergic neurons in the predatory nematode Pristionchus pacificus reveal nervous system conservation and divergence

Changes in neurotransmitter usage in homologous neurons may drive evolutionary adaptations in neural circuits across animal phylogeny. The predatory nematode Pristionchus pacificus can be used as a model system to examine nervous system evolution by comparing neurotransmitter expression with that of C. elegans and other nematodes. Here we characterize P. pacificus neurotransmitter expression and function in specific neurons, focusing on its complete set of monoaminergic neurons. We discover patterns of conservation as well as novelties. We examine the roles of monoamines in specific behaviors using neurotransmitter synthesis and vesicular transporter mutants, finding possible differences in the control of host-finding and dispersal behavior.

neuroscience↗

bioRxiv2025

The rewiring of a terminal selector regulatory cascade generates convergent neuronal laterality

Neuronal identity is established and maintained by "terminal-selector" transcription factors, yet how these networks evolve remains unclear. We examined the specification of the chemosensory ASE and thermosensory AFD neurons in the nematode Pristionchus pacificus, a species that expresses the terminal-selector, Ppa-CHE-1, in both sensory neurons. To determine if the ASE neurons exhibits left-right laterality, we used HCR-FISH and transgenic reporters to discover 8 ASE left-right-specific and 3 AFD-specific receptor-type guanylyl-cyclases. Late embryos exhibit a multipotential state in which AFD precursors transiently co-express ASEL, ASER and AFD markers. A forward genetic screen for defects in ASER asymmetry identified a Ppa-DIE-1 homolog, whereas the maintenance of AFD neuronal identity requires another terminal-selector, Ppa-TTX-1, and CNG channels, Ppa-TAX-2/TAX-4. Defects in miRNA-processing convert ASEL to ASER fate while mutations in conserved regions in the 3' UTR of the cog-1 homolog reveal multiple miRNA binding sites that toggle between left/right ASE versus AFD identities. Together, these results demonstrate that P. pacificus deploys a convergent, likely miRNA-mediated regulatory repertoire to generate left/right neuronal asymmetry and highlight changes in the Ppa-cog-1 3 UTR as a key locus for rewiring selector networks.

developmental biology↗

bioRxiv2024

Evolution of lateralized gustation in nematodes

Animals with small nervous systems have a limited number of sensory neurons that must encode information from a changing environment. This problem is particularly exacerbated in nematodes that populate a wide variety of distinct ecological niches but only have a few sensory neurons available to encode multiple modalities. How does sensory diversity prevail within this constraint in neuron number? To identify the genetic basis for patterning different nervous systems, we demonstrate that sensory neurons in Pristionchus pacificus respond to various salt sensory cues in a manner that is partially distinct from that of the distantly related nematode Caenorhabditis elegans. By visualizing neuronal activity patterns, we show that contrary to previous expectations based on its genome sequence, the salt responses of P. pacificus are encoded in a left/right asymmetric manner in the bilateral ASE neuron pair. Our study illustrates patterns of evolutionary stability and change in the gustatory system of nematodes. Animals with small nervous systems have evolved left and right asymmetry in their neurons to process various salts at different concentrations.

neuroscience↗

bioRxiv2020

The Regulation of Developmental Diapause is Coordinated with Molting and Olfaction

Developmental and behavioral plasticity allow animals to prioritize alternative genetic programs during fluctuating environments. Behavioral remodeling may be acute in animals that interact with host organisms, since reproductive adults and the developmentally arrested larvae often have different ethological needs for chemical stimuli. To understand the genes that coordinate development and behavior, we used the nematode model Pristionchus pacificus to characterize mutants that inappropriately enter developmental diapause to become dauer larvae (Daf-c). We found several key olfactory differences between P. pacificus and C. elegans Daf-c dauers. In addition, the two P. pacificus Daf-c alleles disrupt steroid synthesis required for proper regulation of the conserved canonical steroid hormone receptor DAF-12, whose dauer-constitutive and cuticle exsheathment phenotypes can be rescued by the feeding of {Delta}7-dafachronic acid. One allele, csu60, has a deletion in the sole HydroxySteroid Dehydrogenase (HSD) in P. pacificus. Both hsd-2(csu60) adults and dauers show enhanced attraction to a beetle pheromone, possibly due to the heterochronic activation of dauer-specific neuronal development in the adults. Surprisingly, this enhanced odor attraction acts independently of daf-12, revealing unexpected targets of steroid hormones regulating ecdysis and olfaction in P. pacificus. Author SummaryThe remarkable evolutionary success of nematodes can be attributed to their dispersal ability as stress-resistant dauer larvae and the equivalent parasitic infective larvae. The decision to enter dauer development is regulated by a conserved steroid hormone receptor that receives multiple external and internal cues, though the extent in which these cues also coordinate other physiological and behavioral processes is not well understood in divergent species. We used the insect-associated nematode Pristionchus pacificus to genetically dissect two mutants that form dauers inappropriately, and found that one mutation in a steroidogenic enzyme, Ppa-hsd-2, is predicted to abolish the biosynthesis of the hormones needed to negatively regulate dauer entry when food is available. Unexpectedly, Ppa-HSD-2 is also required to properly complete the dauer larval molt, known as exsheathment, as well as to confer differences in adult versus dauer larvae chemotaxis behavior towards a host pheromone. Given that dauers are the host-seeking stage of parasitic nematodes, hormonal disruption represents a tenable target for biological control.

developmental biology↗

bioRxiv2019

Evolution of neuronal anatomy and circuitry in two highly divergent nematode species

The nematodes C. elegans and P. pacificus populate diverse habitats and display distinct patterns of behavior. To understand how their nervous systems have diverged, we undertook a detailed examination of the neuroanatomy of the chemosensory system of P. pacificus. Using independent features such as cell body position, axon projections and lipophilic dye uptake, we have assigned homologies between the amphid neurons, their first-layer interneurons, and several internal receptor neurons of P. pacificus and C. elegans. We found that neuronal number and soma position are highly conserved. However, the morphological elaborations of several amphid cilia are different between them, most notably in the absence of winged cilia morphology in P. pacificus. We established a synaptic wiring diagram of amphid sensory neurons and amphid interneurons in P. pacificus and found striking patterns of conservation and divergence in connectivity relative to C. elegans, but very little changes in relative neighborhood of neuronal processes.\n\nImpact StatementThe substrate for evolutionary divergence does not lie in changes in neuronal cell number or targeting, but rather in sensory perception and synaptic partner choice within invariant, prepatterned neuronal processes.

neuroscience↗