Early embryonic development and spatiotemporal localization of mammalian primordial germ cell-associated proteins in the basal rodent Lagostomus maximus

Abstract

The gene network controlling primordial germ cell (PGC) specification in eutherian mammals has been exhaustively investigated in mice. The egg-cylinder morphology of the mouse embryo is the key event enabling inductive signals from the extra-embryonic ectoderm (ExE) to specify epiblast cells as PGCs early on. We investigated the embryonic development and the spatiotemporal localization of PGC-associated proteins in the basal Hystricognathi rodent Lagostomus maximus. L. maximus develops through a flat-disc epiblast far apart from the ExE. In the primitive streak stage, OCT4-positive cells are detected in the posterior pole of the embryo disc in the mesoderm of the proximal epiblast. In the neural plate stage, a reduced 8 to 12 OCT4-positive cell population transiently expresses FRAGILIS, STELLA and SOX17 in the posterior streak. Soon after translocation to the hindgut, pluripotent OCT4 cells start expressing VASA, and then, STELLA and FRAGILIS are turned on during migration toward the genital ridge. L. maximus shows a spatiotemporal pattern of PGC-associated markers divergent from the early PGC restriction model seen in mice. This pattern conforms to alternative models that are based on a pluripotent population in the embryonic axis, where PGCs are specified later during development.

PRDM14 Is a Unique Epigenetic Regulator Stabilizing Transcriptional Networks for Pluripotency

“…Such morphological differences in epiblasts between the embryonic disc and egg cylinder correlate with the differences in gene expression profiles and morphology of embryonic stem cells. Lagostomus maximus (plains vizcacha), which is a fossorial rodent, develops flat embryonic discs, as observed in non-rodent mammals (Leopardo and Vitullo, 2017 ). SOX17 is a critical determinant of germ cell generation in humans but not in mice, and it is not expressed in mouse PGCs.…”

On the origin of the human germline

“…Interestingly, germ cells in pig and monkey embryos, which similarly develop as bilaminar discs, also share these characteristics of the human germline Sasaki et al, 2016). Even in basal Hystricognathi rodents, Lagostomus maximus, which surprisingly develop as flat-bilaminar discs, PGCs show expression of SOX17 and absence of SOX2 expression (Leopardo and Vitullo, 2017). These observations might indicate a correspondence between embryonic structure and the associated usage of crucial transcription factors.…”

Prenatal development in Lagostomus maximus (Rodentia, Chinchillidae): A unique case among eutherian mammals of physiological embryonic death

“…The gestation time of the three analyzed females was 26–32 pfd. These data were obtained by comparison with the morphometric values (Leopardo & Vitullo, 2017). Five implantation sites were counted for each uterine horn in all females.…”

“…Likewise, space left between each implantation site allowed for easy sectioning using a scalpel. In addition, the gestation time was established from the morphometric data (Leopardo & Vitullo, 2017). All measurements were performed only on the right uterine horn.…”

“…To identify the embryonic structures, the nomenclature proposed by Roberts and Perry (1974) modified by Leopardo and Vitullo (2017) was used, which perform their measurements based on post‐fertilization days (pfd). For the microscopic description, Masson's hematoxylin–eosin and trichrome stains were used (Suvarna et al, 2018).…”