The Period protein homolog LIN-42 regulates germline development in C. elegans

Clock gene homologs lin-42 and kin-20 regulate circadian rhythms in C. elegans

Circadian rhythms are endogenous oscillations in nearly all organisms, from prokaryotes to humans, allowing them to adapt to cyclical environments for close to 24 h. Circadian rhythms are regulated by a central clock, based on a transcription-translation feedback loop. One important protein in the central loop in metazoan clocks is PERIOD, which is regulated in part by Casein kinase 1ε/δ (CK1ε/δ) phosphorylation. In the nematode Caenorhabditis elegans, period and casein kinase 1ε/δ are conserved as lin-42 and kin-20, respectively. Here, we studied the involvement of lin-42 and kin-20 in the circadian rhythms of the adult nematode using a bioluminescence-based circadian transcriptional reporter. We show that mutations of lin-42 and kin-20 generate a significantly longer endogenous period, suggesting a role for both genes in the nematode circadian clock, as in other organisms. These phenotypes can be partially rescued by overexpression of either gene under their native promoter. Both proteins are expressed in neurons and epidermal seam cells, as well as in other cells. Depletion of LIN-42 and KIN-20, specifically in neuronal cells after development, was sufficient to lengthen the period of oscillating sur-5 expression. Therefore, we conclude that LIN-42 and KIN-20 are critical regulators of the adult nematode circadian clock through neuronal cells.

Regulation of the circadian clock in C. elegans by clock gene homologs kin-20 and lin-42

Circadian rhythms are endogenous oscillations present in nearly all organisms from prokaryotes to humans, allowing them to adapt to cyclical environments close to 24 hours. Circadian rhythms are regulated by a central clock, which is based on a transcription-translation feedback loop. One important protein in the central loop in metazoan clocks is PERIOD, which is regulated in part by Casein kinase 1 ε/δ (CK1 ε/δ ) phosphorylation. In the nematode Caenorhabditis elegans , period and casein kinase 1ε/δ are conserved as lin-42 and kin-20 , respectively. Here we studied the involvement of lin-42 and kin-20 in circadian rhythms of the adult nematode using a bioluminescence-based circadian transcriptional reporter. We show that mutations of lin-42 and kin-20 generate a significantly longer endogenous period, suggesting a role for both genes in the nematode circadian clock, as in other organisms. These phenotypes can be partially rescued by overexpression of either gene under their native promoter. Both proteins are expressed in neurons and seam cells, a population of epidermal stem cells in C. elegans that undergo multiple divisions during development. Depletion of LIN-42 and KIN-20 specifically in neuronal cells after development was sufficient to lengthen the period of oscillating sur-5 expression. Therefore, we conclude that LIN-42 and KIN-20 are critical regulators of the adult nematode circadian clock through neuronal cells.

The ATXN2 Orthologs CID3 and CID4, Act Redundantly to In-Fluence Developmental Pathways throughout the Life Cycle of Arabidopsis thaliana

RNA-binding proteins (RBPs) are key elements involved in post-transcriptional regulation. Ataxin-2 (ATXN2) is an evolutionarily conserved RBP protein, whose function has been studied in several model organisms, from Saccharomyces cerevisiae to the Homo sapiens. ATXN2 interacts with poly(A) binding proteins (PABP) and binds to specific sequences at the 3'UTR of target mRNAs to stabilize them. CTC-Interacting Domain3 (CID3) and CID4 are two ATXN2 orthologs present in plant genomes whose function is unknown. In the present study, phenotypical and transcriptome profiling were used to examine the role of CID3 and CID4 in Arabidopsis thaliana. We found that they act redundantly to influence pathways throughout the life cycle. cid3cid4 double mutant showed a delay in flowering time and a reduced rosette size. Transcriptome profiling revealed that key factors that promote floral transition and floral meristem identity were downregulated in cid3cid4 whereas the flowering repressor FLOWERING LOCUS C (FLC) was upregulated. Expression of key factors in the photoperiodic regulation of flowering and circadian clock pathways, were also altered in cid3cid4, as well as the expression of several transcription factors and miRNAs encoding genes involved in leaf growth dynamics. These findings reveal that ATXN2 orthologs may have a role in developmental pathways throughout the life cycle of plants.

Prospects of circadian clock in joint cartilage development

Altering the food intake, exercise, and sleep patterns have a great influence on the homeostasis of the biological clock. This leads to accelerated aging of the articular cartilage, susceptibility to arthropathy and other aspects. Deficiency or overexpression of certain circadian clock-related genes accelerates the cartilage deterioration and leads to phenotypic variation in different joints. The process of joint cartilage development includes the formation of joint site, interzone, joint cavitation, epiphyseal ossification center, and cartilage maturation. The mechanism by which, biological clock regulates the cell-cycle, growth, metabolism, and other biological processes of chondrocytes is poorly understood. Here, we summarized the interaction between biological clock proteins and developmental pathways in chondrogenesis and provided the evidence from other tissues that further predicts the molecular patterns of these protein-protein networks in activation, proliferation, and differentiation. The purpose of this review is to gain deeper understanding of the evolution of cartilage and its irreversibility seen in damage and aging.