Two distinct populations of prestalk cells within the tip of the migratory Dictyostelium slug with differing fates at culmination

Abstract

The ecmA gene of Dictyostelium encodes an extracellular matrix protein and is selectively expressed in prestalk cells. We show that its promoter contains discrete elements that direct expression in different subpopulations of prestalk cells. Prestalk(pst)A cells occupy the front half of the prestalk region. Expression in pstA cells requires DNA sequences close to the cap site of the gene and a separate, upstream region that acts in combination with the gene proximal sequences. PstO cells are situated in the rear half of the prestalk region and at least two separate and redundant promoter regions direct expression within them. All constructs that are expressed in pstO cells are also expressed in anterior-like cells (ALCs); cells that resemble prestalk cells but which are scattered throughout the prespore region. This observation suggests that pstO cells and ALCs may be very similar in their properties. If development occurs under conditions in which a migratory slug is not formed, there is an ordered movement of cells into the stalk tube. PstA cells enter the stalk tube first, followed by a proportion of the pstO cells. The remainder of the pstO cells contribute to the upper cup, an ALC-derived subpopulation of prestalk cells which is located at the apex of the spore head. After prolonged slug migration, a discrete pstO zone appears not to be maintained and, at culmination, pstO cells are found scattered throughout the stalk.

Novel RNAseq-Informed Cell-type Markers and Their Regulation Alter Paradigms of Dictyostelium Developmental Control

“… Initial studies of the genes are indicated by locus tag superscripts: * studied here; # ( Kin et al, 2018 ); %:( Chen et al, 2017 ); $: ( Ceccarelli et al, 1991 ); £:( Early et al, 1993 ); &:( Jermyn and Williams, 1991 ). For StaE basal disc expression was initially not reported ( Kin et al, 2018 ), but was detected in replicate experiments ( Supplementary Figure S3 ).…”

“…Out of the 29 novel RNAseq informed cell-type markers that were validated here and previously ( Kin et al, 2018 ) ( Table 1 ), we selected 18 genes that showed expression patterns representative for the whole set to study regulation by added stimuli. This subset was supplemented with ecmA and ecmB expressed from their full promoters ( Jermyn and Williams, 1991 ) and from the pstO and pstA regions for ecmA ( Early et al, 1993 ) and the ST-region for ecmB ( Ceccarelli et al, 1991 ), and with the c-di-GMP responsive stalk gene staC and unresponsive gene staD , that were both detected in an RNAseq study of a dgcA knock-out ( Chen et al, 2017 ). Pools of Ax2 cells, freshly transformed with gene fusions of lacZ to the promoters of all markers were developed on non-nutrient agar to a stage just before the gene in question started to be expressed.…”

“…As discussed above, for staD this was likely due to limited stalk specificity. PstA and pstO are previously characterized fragments of the ecmA promoter that are respectively expressed in the front and back of the slug prestalk region ( Early et al, 1993 ). Their regulation does not add up to that of the DIF-1 and c-di-GMP activated full ecmA promoter, indicating that results obtained with these markers should be interpreted with caution.…”

“…The full ecmA promoter directs expression in the slug prestalk cells and ALCs, and in the stalk, lower cup and basal disc of the fruiting body ( Jermyn and Williams, 1991 ). The cap-site proximal pstA region of the ecmA promoter directs expression in the front half of the prestalk region and the stalk, while the more distal pstO sequence directs expression in ALCs and the upper cup ( Early et al, 1993 ). In the slug, the full ecmB promoter directs expression in the core of the tip and in a subpopulation of ALCs, the pstB cells, while in the fruiting body the ecmB promoter is active in the stalk, basal disc and upper and lower cups ( Jermyn and Williams, 1991 ).…”

Oxygen-dependent regulation of E3(SCF)ubiquitin ligases and a Skp1-associated JmjD6 homolog in development of the social amoeba Dictyostelium

“…B , schematic illustration of the starvation-induced developmental cycle of Dictyostelium discoideum . Prestalk cells and anterior-like cells are labeled blue ( 83 ). The life cycle is renewed when spores from a fruiting body germinate to become feeding amoebae.…”