No abstract

Gap junctions between neurons serve as electrical synapses, in addition to conducting metabolites and signaling molecules. During development, early-appearing gap junctions are thought to prefigure chemical synapses, which appear much later. We present evidence for this idea at a central, glutamatergic synapse and provide some mechanistic insights. Loss or reduction in the levels of the gap junction protein Gjd2b decreased the frequency of glutamatergic miniature excitatory postsynaptic currents (mEPSCs) in cerebellar Purkinje neurons (PNs) in larval zebrafish. Ultrastructural analysis in the molecular layer showed decreased synapse density. Further, mEPSCs had faster kinetics and larger amplitudes in mutant PNs, consistent with their stunted dendritic arbors. Time-lapse microscopy in wild type and mutant PNs reveals that Gjd2b puncta promote the elongation of branches and that CaMKII may be a critical mediator of this process. These results demonstrate that Gjd2b-mediated gap junctions regulate glutamatergic synapse formation and dendritic elaboration in PNs.

The ribosome is the protein synthesis machinery of cells, which provides them with essential proteins. An increase in ribosomal content and protein synthesis is evidenced in cancers, most notably in cancers with a loss of p53. However, very little is known as to how the p53 or its family influences the ribosome and translation. Interestingly, in this study, a large number of genes encoding ribosomal proteins (RP) and eukaryotic initiation factors (eIFs) that are intrinsic to ribosome assembly and translation initiation, respectively, were found to possess p53 responsive elements (REs) in their regulatory region. To understand whether p53 or its family influences the ribosome, the expression patterns of the RE-containing RP and EIF genes were examined in a p53 family target microarray database. Many RP and EIF gene expressions were found to be deregulated during the p53 or its family gene overexpression. These results indicate that ribosome assembly and its functions respond to p53 activity. The overall influence of p53 was found to be repressive on RP and EIF gene expression, which led the author to hypothesize that p53 controls the formation of ribosomes and the translation of mRNA into proteins. The study brings to light a regulatory pathway through which the p53 family influences the ribosome with great implications on the cell fate. IntroductionRibosomes are central to cellular processes because of their role in translating mRNA into proteins. The assembly of the ribosome from several ribosomal proteins (RPs) and ribosomal RNAs (rRNA) and its subsequent association with eukaryotic initiation factors (eIFs) and mRNA is a prerequisite for translation [1]. A balanced production of RPs, rRNAs and eIFs influences translation [2] [3] and determines cell fate [4] [5]. Hence, it is important to know how the transcription of ribosomal and translational genes is regulated to ensure sufficient levels of RPs and eIFs for the assembly and function of ribosomes respectively. In some cancers, the loss of p53 is correlated with an increase in ribosomal content and translation, which suggests that accelerated protein synthesis is a major contributor to oncogenesis during p53 loss [6] [7] [8] [9] [10]. Recently, an experimental knockdown of p53 in zebrafish embryos increased the ribosomal content, but the mechanism through which this is achieved is yet to be known [11]. The transcription factor p53 controls the expression of an exhaustive list of target genes, which are involved in cell cycle arrest and apoptosis, and thus acts as a tumor suppressor that regulates cell proliferation [12] [13]. On the other hand, the p53 family genes (p63 and p73) are known for their role in transcription of genes involved in development and differentiation [14]. The transcriptional targets of p53 family have responsive elements (REs), which are consensus sequences of nucleotides that are usually distributed on promoter or intronic regions. In its tetrameric form, the p53 binds to REs on target genes and influences their transcription....