Divya Nair

Regulation of the earliest erythroid progenitors is not well understood, yet it is relevant to some types of anemia that are refractory to treatment with erythropoietin (Epo). Recent work shows that early erythroid (burst-forming unit–erythroid [BFU-e] and colony-forming unit–erythroid [CFU-e]) progenitors form a developmental continuum characterized by gradual increase in the proportion of cells in S phase of the cycle. Here, we proposed 2 distinct hypotheses to explain this finding, either the presence of quiescent progenitors or the gradual shortening of G1 and the cycle with differentiation. Using a mouse expressing a timer-protein transgene that reports cell cycle duration, we determined that, in vivo, early erythroid progenitors undergo orderly gradual shortening of the cycle as they mature and approach terminal differentiation. There was no evidence of quiescent BFU-e or CFU-e progenitors in tissue. We found that BFU-e and CFU-e progenitors are highly responsive to hypoxic stress and to its Epo and glucocorticoid mediators. Epo and hypoxia accelerated the pattern of gradual cell cycle shortening throughout early erythropoiesis, whereas, conversely, dexamethasone prolonged the cycle specifically in proerythroblasts. Furthermore, Epo and hypoxia generated rapid increase in early progenitor cell size and dynamic changes in cell surface marker expression. Our data suggest that high Epo or hypoxic stress promote rapid increase in the rate of growth in biomass across the entire erythroid trajectory including in the earliest BFU-e progenitors, and indicates that stress progenitors are of the same type and lineage as those sustaining basal erythropoiesis.

An endophytic bacterial strain from a marine green alga, Ulva lactuca, was isolated and identified by 16S rRNA gene sequencing method. The bacterial isolate was found to secrete two major families of cyclic depsilipopeptides, surfactins, and fengycins. Sequencing of the isolated lipopeptides was carried out using the MSⁿ data obtained from an electrospray ionization (ESI) ion trap mass spectrometer coupled to an HPLC system. The assigned sequences were confirmed by a chemical derivatization approach involving esterification followed by mass spectrometric analysis. Distinction of leucine residues from isoleucine was established through a combined electron transfer dissociation-collision-induced dissociation (ETD-CID) method. The fengycins described in this study were found to cause significant delay of growth of two plants, Vigna radiata (mung bean) and Oryza sativa (rice). To the best of our knowledge, this is the first study describing identification and characterization of cyclic peptides from an endophytic Bacillus sp. isolated from marine algae.