Self-cleaving peptides for expression of multiple genes in Dictyostelium discoideum

Development of a 2A peptide-based multigene expression system and its application for enhanced production of ganoderic acids in Ganoderma lucidum

Ganoderma has received much attention for its medicinal value, but the manipulation of multiple genes remains a challenge, hindering the genetic engineering of this species for the development of cell factories. Here, we first showed that the presence of an intron is necessary for the efficient expression of the endogenous cDNA of carboxin-resistant gene (cbx) in G. lucidum. Then, the self-cleaving function of 2 A peptide was investigated in G. lucidum by linking cbx cDNA to the codon-optimized hygromycin B-resistant gene (ophph) using the 2A-peptide sequence. The results showed that cbx cDNA and ophph can be successfully expressed in G. lucidum in a bicistronic manner from a single transcript. Moreover, the expression of both genes was not affected by the order within the 2 A cassette. In addition, simultaneous expression of cbx cDNA, ophph, and codon-optimized yellow fluorescent protein gene (opyfp) was conducted for the first time in G. lucidum using the 2 A peptide-based approach. The developed method was successfully applied to express both cDNA of the 3-hydroxy-3-methylglutaryl coenzyme A reductase (hmgr) and squalene epoxidase gene (se) for enhanced production of ganoderic acids (GAs) in G. lucidum. The engineered strain produced the maximum content of GA-Mk, GA-T, GA-S, and GA-Me were 26.56±3.53,39.58±3.75, 16.54±2.16, and 19.1±1.87 μg/100 mg dry weight, respectively. These values were 3.85-, 4.74-, 3.65-, and 3.23-fold higher than those produced by the control strain. The developed method will be useful for the manipulation of complex metabolic or regulatory pathways involving multiple genes in Ganoderma.

Single-cell discovery of m6A RNA modifications in the hippocampus

N 6-Methyladenosine (m6A) is a prevalent and highly regulated RNA modification essential for RNA metabolism and normal brain function. It is particularly important in the hippocampus, where m6A is implicated in neurogenesis and learning. Although extensively studied, its presence in specific cell types remains poorly understood. We investigated m6A in the hippocampus at a single-cell resolution, revealing a comprehensive landscape of m6A modifications within individual cells. Through our analysis, we uncovered transcripts exhibiting a dense m6A profile, notably linked to neurological disorders such as Alzheimer's disease. Our findings suggest a pivotal role of m6A-containing transcripts, particularly in the context of CAMK2A neurons. Overall, this work provides new insights into the molecular mechanisms underlying hippocampal physiology and lays the foundation for future studies investigating the dynamic nature of m6A RNA methylation in the healthy and diseased brain.

A versatile 2A peptide-based strategy for ectopic expression and endogenous gene tagging in Trypanosoma cruzi

Nearly all expression vectors currently available for Trypanosoma cruzi were conceived to produce a single primary transcript containing the genes of interest along with those that confer antibiotic resistance. However, since each messenger RNA (mRNA) matures separately, drug selection will only guarantee the expression of those derived from the selectable marker. Therefore, commonly a considerable fraction of the cells recovered after selection with these expression vectors, although resistant do not express the protein of interest. Consequently, in order to counteract this disadvantage, we developed vectors with an alternative arrangement in which the gene of interest and antibiotic resistance are fused sharing the same mRNA. To test this configuration, we included the coding sequence for the green fluorescent protein (mEGFP) linked to the one conferring neomycin resistance (Neo). Additionally, to allow for the production of two independent proteins the sequence for a Thosea asigna virus self-cleaving 2A peptide (T2A) was inserted in-between. Cells obtained with these vectors displayed higher mEGFP expression levels with more homogeneous transgenic parasite populations than those transfected with more conventional independent mRNA-based alternatives. Moreover, as determined by Western blot, 2A mediated fusion protein dissociation occurred with high efficiency in all parasite stages. In addition, these vectors could easily be transformed into endogenous tagging constructs that allowed the insertion, by ends-in homologous recombination, of a hemagglutinin tag (HA) fused to the actin gene. The use of 2A self-cleaving peptides in the context of single mRNA vectors represents an interesting strategy capable of improving ectopic transgene expression in T. cruzi as well as providing a simple alternative to more sophisticated methods, such as the one based on CRISPR/Cas9, for the endogenous labeling of genes.

Proliferation history and transcription factor levels drive direct conversion

The sparse and stochastic nature of reprogramming has obscured our understanding of how transcription factors drive cells to new identities. To overcome this limit, we developed a compact, portable reprogramming system that increases direct conversion of fibroblasts to motor neurons by two orders of magnitude. We show that subpopulations with different reprogramming potentials are distinguishable by proliferation history. By controlling for proliferation history and titrating each transcription factor, we find that conversion correlates with levels of the pioneer transcription factor Ngn2, whereas conversion shows a biphasic response to Lhx3. Increasing the proliferation rate of adult human fibroblasts generates morphologically mature, induced motor neurons at high rates. Using compact, optimized, polycistronic cassettes, we generate motor neurons that graft with the murine central nervous system, demonstrating the potential for in vivo therapies.