Asymmetric Distribution of pl10 and bruno2, New Members of a Conserved Core of Early Germline Determinants in Cephalochordates

Abstract

Molecular fingerprinting of conserved germline and somatic "stemness" markers in different taxa have been key in defining the mechanism of germline specification ("preformation" or "epigenesis"), as well as expression domains of somatic progenitors. The distribution of molecular markers for primordial germ cells (PGCs), including vasa, nanos, and piwil1, as well as Vasa antibody staining, support a determinative mechanism of germline specification in the cephalochordate Branchiostoma lanceolatum, similarly to other amphioxus species. pl10 and bruno2, but not bruno4/6, are also expressed in a pattern consistent with these other germline genes, adding to our repertoire of PGC markers in lancelets. Expression of nanos, vasa, and the remaining markers (musashi, pufA, pufB, pumilio, and piwil2) may define populations of putative somatic progenitors in the tailbud, the amphioxus posterior growth zone, or zones of proliferative activity. Finally, we also identify a novel expression domain for musashi, a classic neural stem cell marker, during notochord development in amphioxus. These results are discussed in the context of germline determination in other taxa, stem cell regulation, and regenerative capacity in adult amphioxus.

Diversification and Germ-Line Determination Revisited: Linking Developmental Mechanism with Species Richness

“…Of mechanistic importance, evidence suggests that all species of cephalochordate studied employ a determinative mode of PGC specification (Wu et al, 2011;Zhang et al, 2013;Dailey et al, 2016), indicating that the acquisition of determinative specification does not by necessity lead to enhanced speciation. Rather, as we have discussed elsewhere (Crother et al, 2007;Johnson et al, 2011), data such as these suggest that the acquisition of determinative PGC specification may facilitate speciation.…”

Amphioxus regeneration: evolutionary and biomedical implications

“…In neurula stages, these PGCs are nestled posteriorly in endoderm of the tailbud (Fig. 3D, E), and remain as a cluster near the anus in premouth larval stages in all species examined (Wu et al, 2011;Zhang et al, 2013;Dailey et al, 2016).…”

“…Although cephalochordates are generally reported as using an inductive mode, recent data in four amphioxus species (all Branchiostoma) suggest rather an inherited mechanism for primordial germ cell (PGC) formation (Wu et al, 2011;Zhang et al, 2013;Dailey et al, 2016). At the two-cell stage, a number of highly conserved germline transcripts including nanos (Fig.…”

“…Both transcripts and protein of one of the key germline determinants in the PGCs, vasa, localise to this domain, as do nanos and piwil1 and piwil2 (Wu et al, 2011;Zhang et al, 2013;Dailey et al, 2016). Vasa plays a general role in regulating translation in the soma (Poon et al, 2016) and nanos2 has recently been shown to transiently repress translation in PGCs via inhibition of eIF1a in sea urchins (Ouhlen et al, 2017).…”

Early development of amphioxus links evolutionary events with vertebrates

“…Amphioxus oocyte dynamics including the nuage and the localization of maternal factors are still poorly characterized, but some maternal mRNAs in eggs have been reported. Some germ line marker mRNAs such as vasa, nanos, piwi1, pl10, bruno2, and tdrd (tudor-domain containing) are localized near the vegetal pole, and others such as pumilio, mago-nashi, and mex3 are near the animal poles with some ubiquitously distributed mRNAs (Wu et al, 2011;Zhang et al, 2013;Yue et al, 2015;Dailey et al, 2016). Seemingly corresponding to these bipolar distributions of the germ line markers, mRNAs related to Wnt/b-Catenin signaling are not localized to the vegetal side, from which gastrulation starts (Qian et al, 2013;Wang et al, 2016).…”