Biology subjects

Hong, R. L.

Publications and source records attributed to Hong, R. L..

8 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↗

bioRxiv2024

Automated Cell Lineage Reconstruction using Label-Free 4D Microscopy

Here we describe embGAN, a deep learning pipeline that addresses the challenge of automated cell detection and tracking in label-free 3D time lapse imaging. embGAN requires no manual data annotation for training, learns robust detections that exhibits a high degree of scale invariance and generalizes well to images acquired in multiple labs on multiple instruments.

developmental biology↗

bioRxiv2021

Influence of environmental temperature on mouth-form plasticity in Pristionchus pacificus acts through daf-11-dependent cGMP signaling

Mouth-form plasticity in the nematode Pristionchus pacificus has become a powerful system to identify the genetic and molecular mechanisms associated with phenotypic (developmental) plasticity. In particular, the identification of developmental switch genes that can sense environmental stimuli and reprogram developmental processes has confirmed long-standing evolutionary theory. Together with the associated gene regulatory networks, these developmental switch genes have been important to show that plasticity is consistent with the Modern Synthesis of evolution. However, how these genes are involved in the direct sensing of the environment, or if the switch genes act downstream of another, primary environmental sensing mechanism, remains currently unknown. Here, we study the influence of environmental temperature on mouth-form plasticity. Using forward and reverse genetic technology including CRISPR/Cas9, we show that mutations in the guanylyl cyclase Ppa-daf-11, the Ppa-daf-25/AnkMy2 and the cyclic nucleotide-gated channel Ppa-tax-2 eliminate the response to elevated temperatures. Together, our study indicates that DAF-11, DAF-25 and TAX-2 have been co-opted for environmental sensing during mouth-form plasticity regulation in P. pacificus. This work suggests that developmental switch genes integrate environmental signals including perception by cGMP signaling.

genetics↗

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↗

bioRxiv2017

A Species-Specific Nematocide that Results in Terminal Embryogenesis

Nematode-insect interactions are ubiquitous, complex, and constantly changing as the host and nematode coevolve. The entomophilic nematode Pristionchus pacificus is found on a myriad of beetle species worldwide, though the molecular dynamics of this relationship are largely unknown. To better understand how host cues affect P. pacificus embryogenesis, we characterized the threshold of sensitivity to the pheromone (Z)-7-tetradecen-2-one (ZTDO) by determining the minimum exposure duration and developmental window that results in P. pacificus embryonic lethality. We found early-stage embryos exposed to volatile ZTDO for as few as four hours all display terminal embryogenesis, characterized by punctuated development up to 48 hours later, with abnormal morphology and limited lumen formation. To determine if the pheromone arrests pre-hatching development by suffocating or permeabilizing the eggshells, we raised embryos under anoxic condition as well as examined eggshell permeability using the lipophilic dye FM4-64. We found that asphyxiating the embryos arrested embryogenesis in a reversible manner but did not phenocopy the effects of ZTDO exposure, whereas the ZTDO-induced disruption of embryogenesis did correlate with increased eggshell permeability. The effects of ZTDO are also highly specific, as other lipid insect compounds do not produce any detectable embryocidal effect. The high specificity and unusual teratogenic effect of ZTDO may be important in mediating the host-nematode relationship by regulating P. pacificus development.\n\nSummary StatementInsect-associated nematodes coordinate their development using host cues to \"walk the line\" between mutualism and pathogenesis. A host pheromone causes terminal embryogenesis by permeablizing the nematode eggshell.

developmental biology↗