Biology subjects

Rossi, A. M.

Publications and source records attributed to Rossi, A. M..

3 recordsLinked to original sources

bioRxiv2023

The fission yeast cytokinetic ring component Fic1 promotes septum formation

In Schizosaccharomyces pombe septum formation is coordinated with cytokinetic ring constriction but the mechanisms linking these events are unclear. In this study, we explored the role of the cytokinetic ring component Fic1, first identified by its interaction with the F-BAR protein Cdc15, in septum formation. We found that the fic1 phospho-ablating mutant, fic1-2A, is a gain-of-function allele that suppresses myo2-E1, the temperature-sensitive allele of the essential type-II myosin, myo2. This suppression is achieved by the promotion of septum formation and required Fic1s interaction with the F-BAR proteins Cdc15 and Imp2. Additionally, we found that Fic1 interacts with Cyk3 and that this interaction was likewise required for Fic1s role in septum formation. Fic1, Cdc15, Imp2, and Cyk3 are the orthologs of the Saccharomyces cerevisiae ingression progression complex, which stimulates the chitin synthase Chs2 to promote primary septum formation. However, our findings indicate that Fic1 promotes septum formation and cell abscission independently of the S. pombe Chs2 ortholog. Thus, while similar complexes exist in the two yeasts that each promote septation, they appear to have different downstream effectors. Summary StatementThe S. pombe cytokinetic ring protein Fic1 promotes septum formation in a manner dependent on interactions with the cytokinetic ring components Cdc15, Imp2, and Cyk3.

cell biology↗

bioRxiv2021

A comprehensive series of temporal transcription factors in the fly visual system

The brain consists of thousands of different neuronal types that are generated through multiple divisions of neuronal stem cells. These stem cells have the capacity to generate different neuronal types at different stages of their development. In Drosophila, this temporal patterning is driven by the successive expression of temporal transcription factors (tTFs). While a number of tTFs are known in different animals and across various parts of the nervous system, these have been mostly identified by informed guesses and antibody availability. We used single-cell mRNA sequencing to identify the complete series of tTFs that specify most Drosophila medulla neurons in the optic lobe. We tested the genetic interactions among these tTFs. While we verify the general principle that tTFs regulate the progression of the series by activating the next tTFs in the series and repressing the previous ones, we also identify more complex regulations. Two of the tTFs, Eyeless and Dichaete, act as hubs integrating the input of several upstream tTFs before allowing the series to progress and in turn regulating the expression of several downstream tTFs. Moreover, we show that tTFs not only specify neuronal identity by controlling the expression of cell type-specific genes. Finally, we describe the very first steps of neuronal differentiation and find that terminal differentiation genes, such as neurotransmitter-related genes, are present as transcripts, but not as proteins, in immature larval neurons days before they are being used in functioning neurons; we show that these mechanisms are conserved in humans. Our results offer a comprehensive description of a temporal series of tTFs in a neuronal system, offering mechanistic insights into the regulation of the progression of the series and the regulation of neuronal diversity. This represents a proof-of-principle for the use of single-cell mRNA sequencing for the comparison of temporal patterning across phyla that can lead to an understanding of how the human brain develops and how it has evolved.

developmental biology↗

bioRxiv2019

Extrinsic cues cooperate with intrinsic temporal factors to increase neuronal diversity

Temporal patterning of neural progenitors leads to the sequential production of diverse neuronal types. To better understand how extrinsic cues interact with intrinsic temporal programs to contribute to temporal patterning, we studied the Drosophila mushroom body neural progenitors (neuroblasts). Each of these four neuroblasts divides ~250 times to sequentially produce only three main neuronal types over the course of ~9 days of development: {gamma}, followed by {beta}, and finally {beta} neurons. The intrinsic temporal clock is composed of two RNA-binding proteins, IGF-II mRNA binding protein (Imp) and Syncrip (Syp), that are expressed in opposing temporal gradients. Activin signaling affects the production of {beta} neurons but whether and how this extrinsic cue interacts with the intrinsic temporal program was not known. We show that the Activin ligand Myoglianin produced from glia regulates the levels of the intrinsic temporal factor Imp in mushroom body neuroblasts. In neuroblasts mutant for the Activin signaling receptor baboon, Imp levels are higher than normal during the {beta} temporal window, leading to the specific loss of the {beta} neurons. The intrinsic temporal clock still progresses but with a delay, skipping the {beta} window without affecting the total number of neurons produced: The number of {gamma} neurons increases, {beta} disappear and the number of {beta} neurons decreases. Our results illustrate that an extrinsic cue modifies an intrinsic temporal program to increase neuronal diversity.

developmental biology↗