RESUMEN
Hox genes encode evolutionarily conserved transcription factors that specify regional identities along the anterior-posterior (A-P) axis. Although some Hox genes are known to regulate the differentiation of certain neurons, to what extent Hox genes are involved in the terminal specification of the entire nervous system is unclear. Here, we systematically mapped the expression of all six Hox genes in C. elegans nervous system and found Hox expression in 97 (32%) of the 302 neurons in adult hermaphrodites. Our results are generally consistent with previous high-throughput expression mapping and single-cell transcriptomic studies. Detailed analysis of the fate markers for these neurons revealed that Hox genes regulate the differentiation of 29 (25%) of the 118 classes of C. elegans neurons. Hox genes not only regulate the specification of terminal neuronal fates through multiple mechanisms but also control subtype diversification along the A-P axis. The widespread involvement of Hox genes in neuronal differentiation indicates their roles in establishing complex nervous systems.
Asunto(s)
Proteínas de Caenorhabditis elegans , Caenorhabditis elegans , Animales , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/metabolismo , Genes Homeobox/genética , Proteínas de Homeodominio/genética , Proteínas de Homeodominio/metabolismo , Neuronas/metabolismoRESUMEN
Molecular chaperones often work collaboratively with the ubiquitylation-proteasome system (UPS) to facilitate the degradation of misfolded proteins, which typically safeguards cellular differentiation and protects cells from stress. In this study, however, we report that the Hsp70/Hsp90 chaperone machinery and an F-box protein, MEC-15, have opposing effects on neuronal differentiation, and that the chaperones negatively regulate neuronal morphogenesis and functions. Using the touch receptor neurons (TRNs) of Caenorhabditis elegans, we find that mec-15(-) mutants display defects in microtubule formation, neurite growth, synaptic development and neuronal functions, and that these defects can be rescued by the loss of Hsp70/Hsp90 chaperones and co-chaperones. MEC-15 probably functions in a Skp-, Cullin- and F-box- containing complex to degrade DLK-1, which is an Hsp90 client protein stabilized by the chaperones. The abundance of DLK-1, and likely other Hsp90 substrates, is fine-tuned by the antagonism between MEC-15 and the chaperones; this antagonism regulates TRN development, as well as synaptic functions of GABAergic motor neurons. Therefore, a balance between the UPS and the chaperones tightly controls neuronal differentiation.
Asunto(s)
Proteínas de Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/metabolismo , Proteínas F-Box/metabolismo , Proteínas HSP90 de Choque Térmico/metabolismo , Microtúbulos/metabolismo , Neuritas/fisiología , Animales , Proteínas de Caenorhabditis elegans/antagonistas & inhibidores , Proteínas de Caenorhabditis elegans/genética , Proteínas F-Box/antagonistas & inhibidores , Proteínas F-Box/genética , Neuronas GABAérgicas/metabolismo , Proteínas HSP90 de Choque Térmico/antagonistas & inhibidores , Proteínas HSP90 de Choque Térmico/genética , Proteínas de Choque Térmico/metabolismo , Quinasas Quinasa Quinasa PAM/metabolismo , Chaperonas Moleculares/antagonistas & inhibidores , Chaperonas Moleculares/genética , Chaperonas Moleculares/metabolismo , Mutagénesis , Neuronas Aferentes/metabolismo , Fosforilación , Complejo de la Endopetidasa Proteasomal/metabolismo , Estabilidad Proteica , Interferencia de ARN , ARN Bicatenario , Ubiquitina/metabolismo , UbiquitinaciónRESUMEN
Mutations in tubulins affect microtubule (MT) dynamics and functions during neuronal differentiation and their genetic interaction provides insights into the regulation of MT functions. We previously used Caenorhabditis elegans touch receptor neurons to analyze the cellular impact of tubulin mutations and reported the phenotypes of 67 tubulin missense mutations, categorized into three classes: loss-of-function (lf), antimorphic (anti), and neomorphic (neo) alleles. In this study, we isolated 54 additional tubulin alleles through suppressor screens in sensitized backgrounds that caused excessive neurite growth. These alleles included 32 missense mutations not analyzed before, bringing the total number of mutations in our collection to 99. Phenotypic characterization of these newly isolated mutations identified three new types of alleles: partial lf and weak neo alleles of mec-7/ß-tubulin that had subtle effects and strong anti alleles of mec-12/α-tubulin. We also discovered complex genetic interactions among the tubulin mutations, including the suppression of neo mutations by intragenic lf and anti alleles, additive and synthetic effects between mec-7 neo alleles, and unexpected epistasis, in which weaker neo alleles masked the effects of stronger neo alleles in inducing ectopic neurite growth. We also observed balancing between neo and anti alleles, whose respective MT-hyperstablizing and -destabilizing effects neutralized each other.