Biology subjects

Grullon, G.

Publications and source records attributed to Grullon, G..

3 recordsLinked to original sources

bioRxiv2025

Joint disruption of Ret and Ednrb transcription drives cell fate reversal in the Enteric Nervous System in Hirschsprung disease

Despite extensive genetic heterogeneity, 72% of pathogenic alleles for Hirschsprung disease (HSCR) arise from coding and regulatory variants in genes of the RET and EDNRB gene regulatory network (GRN) in the enteric nervous system (ENS). Reduced signaling of these two receptors below a threshold in enteric neural crest-derived cells (ENCDCs) leads to a molecular tipping point at which otherwise lesser cellular defects result in aganglionosis. To elucidate the mechanisms leading to enteric neuronal loss from these genetic defects, we generated four strains of mice carrying reduced function alleles at Ret or Ednrb or both, along with their wildtype alleles. ENS tissue- and single-cell gene expression profiling of the developing and postnatal gastrointestinal tract in five mouse models, with various combinations of mutant alleles, revealed 3 major insights: (i) Ret and Ednrb deficiency, rather than complete loss, is sufficient to induce HSCR, (ii) Ret and Ednrb demonstrate strong trans interactions, and (3) disruption of this interaction leads to cellular fate changes to compensate for neuronal loss. This study of targeted mouse models of a multifactorial disorder reveals how increasing dosage of genetic defects within a GRN leads to quantifiably increasing dysregulation from genotype to gene expression to cellular identity to function. Importantly, our studies establish that aganglionosis results only with severely reduced gene expression at both receptor genes and their consequent disruption of normal and compensatory cell fate trajectories.

genetics↗

bioRxiv2025

Synergistic effects of Ret coding and enhancer loss-of-function alleles cause progressive loss of inhibitory motor neurons in the enteric nervous system

Hirschsprung disease (HSCR) is a congenital enteric neuropathy caused by disrupted development of enteric neural crest-derived cells (ENCDCs). Although pathogenic coding variants in RET account for many cases, the largest genetic contribution to HSCR risk arises from a common non-coding variant (rs2435357) within a SOX10-bound RET enhancer (MCS+9.7) that reduces RET gene expression in vivo and triggers expression changes in other ENS genes in the human fetal gut. However, the ENS cell types affected by this enhancer and the mechanisms by which these transcriptional changes lead to HSCR remain unknown. Here, we investigated the role of this enhancer by generating mice carrying a deletion of the orthologous Ret mcs+9.7 enhancer ({Delta}mcs+9.7). Single-cell RNA sequencing of E14.5 embryonic gut demonstrated that enhancer deletion reduced Ret expression by 8% without altering ENS cell composition. However, reduced Ret expression was restricted to differentiating neurons and inhibitory motor neuron lineages, revealing cell type-specific enhancer activity. To determine the functional consequences of further reducing Ret dosage, we generated compound heterozygous mice carrying both the enhancer deletion and a Ret coding null allele (+/{Delta}mcs+9.7;+/CFP). These mice exhibited additive reductions in Ret expression, altered Sox10 expression, dysregulation of cell-cycle and neuronal differentiation programs, and selective depletion of developing inhibitory motor neuron lineages. These findings establish a cell type-specific role for the mcs+9.7 enhancer in modulating Ret dosage and reveal how subtle enhancer perturbations alter neural subtype specification without overt hypoganglionosis, suggesting that HSCR arises from a cascade of cellular defects triggered by >50% loss of Ret function.

genetics↗

bioRxiv2024

Neuron Derived Cytokine Interleukin-34 Controls Developmental Microglia Function

Neuron-microglia interactions dictate the development of neuronal circuits in the brain. However, the factors that regulate these processes across development are largely unknown. Here, we find that IL34, a neuron-derived cytokine, is upregulated in early development and maintains neuroprotective, mature microglia in the anterior cingulate cortex (ACC) of mice. We show that IL34 is upregulated in the second week of postnatal life and is expressed primarily in excitatory neurons. Excitatory-neuron specific knock-out of IL34 reduced microglia number and TMEM119 expression and increased aberrant microglial phagocytosis of excitatory thalamocortical synapses in the ACC. Acute, low dose blocking of IL34 at postnatal day 15 similarly decreased TMEM119 and inappropriately increased microglial phagocytosis of synapses. Viral overexpression of IL34 induced TMEM119 expression and prevented appropriate microglial phagocytosis of synapses. These findings establish IL34 as a key regulator of neuron-microglia crosstalk in postnatal brain development, controlling both microglial maturation and synapse engulfment.

neuroscience↗