Biology subjects

Masoudi, N.

Publications and source records attributed to Masoudi, N..

3 recordsLinked to original sources

bioRxiv2022

Restricted effects of the sole C. elegans Daughterless/E homolog, HLH-2, on nervous system development

Are there common mechanisms of neurogenesis used throughout an entire nervous system? Making use of the well-defined and relatively small size of the nervous system of the nematode C. elegans, we explored to what extent canonical proneural class I/II bHLH complexes are responsible for neurogenesis throughout the entire C. elegans nervous system. Distinct, lineage-specific proneural "class II" bHLH factors are generally thought to operate via interaction with a common, "class I" bHLH subunit, encoded by Daugtherless in flies, the E (E2A, E2-2, HEB) proteins in vertebrates, and hlh-2 in C. elegans. To eliminate function of all proneuronal class I/II bHLH complexes, we therefore genetically removed maternal and zygotic hlh-2 gene activity. We observed broad effects on neurogenesis, but still detected normal neurogenesis in many distinct neuron-producing lineages of the central and peripheral nervous system. Moreover, we find that hlh-2 selectively affects some aspects of neuron differentiation while leaving others unaffected. While our studies confirm the function of proneuronal class I/II bHLH complexes in many different lineages throughout a nervous system, we conclude that their function is not universal, but rather restricted by lineage, cell type and components of differentiation programs affected.

neuroscience↗

bioRxiv2021

Visualizing the organization and differentiation of the male-specific nervous system of C. elegans

Sex differences in the brain are prevalent throughout the animal kingdom and particularly well appreciated in the nematode C. elegans. While 294 neurons are shared between the two sexes, the nervous system of the male contains an additional 93 malespecific neurons, most of which have received very little attention so far. To make these neurons amenable for future study, we describe here how a multicolor, multipromoter reporter transgene, NeuroPAL, is capable of visualizing the distinct identities of all male specific neurons. We used this tool to visualize and characterize a number of features of the male-specific nervous system. We provide several proofs of concept for using NeuroPAL to identify the sites of expression of gfp-tagged reporter genes. We demonstrate the usage of NeuroPAL for cellular fate analysis by analyzing the effect of removal of developmental patterning genes, including a HOX cluster gene (egl-5), a miRNA (lin-4) and a proneural gene (lin-32/Ato), on neuronal identity acquisition within the male-specific nervous system. We use NeuroPAL and its intrinsic cohort of more than 40 distinct differentiation markers to show that, even though male-specific neurons are generated throughout all four larval stages, they execute their terminal differentiation program in a coordinated manner in the fourth larval stage that is concomitant with male tale retraction. This wave of differentiation couples neuronal maturation programs with the appearance of sexual organs. We call this wave "just-in-time" differentiation by its analogy to the mechanism of "just-in-time" transcription of metabolic pathway genes.

neuroscience↗

bioRxiv2021

Piecemeal regulation of convergent neuronal lineages by bHLH transcription factors in C. elegans

Classic cell lineage studies in the nematode Caenorhabditis elegans as well as recent lineage tracing in vertebrates have shown that cells of the same type can be generated by distinct cellular lineages that originate in different parts of the developing embryo ("lineage convergence"). Several C. elegans neuron classes composed of left/right or radially symmetric class members display such lineage convergence, in that individual neurons of the same class derive from distinct, non-bilaterally symmetric lineages. We show here that the C. elegans Atonal homolog lin-32/Ato, a bHLH transcription factor, is differentially expressed in neuronal lineages that give rise to left/right or radially symmetric class members. Loss of lin-32/Ato results in the selective loss of the expression of panneuronal markers and terminal selector-type transcription factors that confer neuron class-specific features. We discovered that another bHLH transcription factor, the Achaete Scute-homolog hlh-14 is expressed in mirror image pattern to lin-32/Ato in a subset of the left/right symmetric neuron pairs and is required to induce neuronal identity and terminal selector expression on the contralateral side of the animal. These findings demonstrate that distinct lineage histories converge via distinct bHLH factors on the level of induction of terminal selector identity determinants, which thus serve as integrators of distinct lineage histories. We also describe neuron-to-neuron identity transformations in lin-32/Ato mutants, which we propose to also be the result of misregulation of terminal selector gene expression.

developmental biology↗