A quiet space during rush hour: Quiescence in primordial germ cells

Somatic cell conversion to a germ cell lineage: A violation or a revelation?

The germline is unique and immortal (or at least its genome is). It is able to perform unique jobs (meiosis) and is selected for genetic changes. Part of being this special also means that entry into the germline club is restricted and cells of the soma are always left out. However, the recent evidence from multiple animals now suggests that somatic cells may join the club and become germline cells in an animal when the original germline is removed. This "violation" may have garnered acceptance by the observation that iPScells, originating experimentally from somatic cells of an adult, can form reproductively successful eggs and sperm, all in vitro. Each of the genes and their functions used to induce pluripotentiality are found normally in the cell and the in vitro conditions to direct germline commitment replicate conditions in vivo. Here, we discuss evidence from three different animals: an ascidian, a segmented worm, and a sea urchin; and that the cells of a somatic cell lineage can convert into the germline in vivo. We discuss the consequences of such transitions and provide thoughts as how this process may have equal precision to the original germline formation of an embryo.

Epigenetic Regulation during Primordial Germ Cell Development and Differentiation

Germline development varies significantly across metazoans. However, mammalian primordial germ cell (PGC) development has key conserved landmarks, including a critical period of epigenetic reprogramming that precedes sex-specific differentiation and gametogenesis. Epigenetic alterations in the germline are of unique importance due to their potential to impact the next generation. Therefore, regulation of, and by, the non-coding genome is of utmost importance during these epigenomic events. Here, we detail the key chromatin changes that occur during mammalian PGC development and how these interact with the expression of non-coding RNAs alongside broader epitranscriptomic changes. We identify gaps in our current knowledge, in particular regarding epigenetic regulation in the human germline, and we highlight important areas of future research.

The Treasury of Wharton's Jelly

Background

Postnatal umbilical cord tissue contains valuable mesenchymal progenitor cells of various differentiation stages. While mesenchymal stem cells are plastic-adherent and tend to differentiate into myofibroblastic phenotypes, some round cells detach, float above the adherent cells, and build up cell aggregates, or form spheroids spontaneously. Very small luminescent cells are always involved as single cells or within collective forms and resemble the common well-known very small embryonic-like cells (VSELs). In this study, we investigated these VSELs-like cells in terms of their pluripotency phenotype and tri-lineage differentiation potential.

Methods

VSELs-like cells were isolated from cell-culture supernatants by a process that combines filtering, up concentration, and centrifugation. To determine their pluripotency character, we measured the expression of Nanog, Sox-2, Oct-4, SSEA-1, CXCR4, SSEA-4 on gene and protein level. In addition, the cultured cells derived from UC tissue were examined regarding their potential to differentiate into three germ layers.

Result

The VSELs-like cells express all of the pluripotency-associated markers we investigated and are able to differentiate into meso- endo- and ectodermal precursor cells.

Conclusions

Umbilical cord tissue hosts highly potent VSELs-like stem cells.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12015-021-10217-8.

Limitations of cross- and multigenerational plasticity for marine invertebrates faced with global climate change

Although cross generation (CGP) and multigenerational (MGP) plasticity have been identified as mechanisms of acclimation to global change, the weight of evidence indicates that parental conditioning over generations is not a panacea to rescue stress sensitivity in offspring. For many species, there were no benefits of parental conditioning. Even when improved performance was observed, this waned over time within a generation or across generations and fitness declined. CGP and MGP studies identified resilient species with stress tolerant genotypes in wild populations and selected family lines. Several bivalves possess favourable stress tolerance and phenotypically plastic traits potentially associated with genetic adaptation to life in habitats where they routinely experience temperature and/or acidification stress. These traits will be important to help 'climate proof' shellfish ventures. Species that are naturally stress tolerant and those that naturally experience a broad range of environmental conditions are good candidates to provide insights into the physiological and molecular mechanisms involved in CGP and MGP. It is challenging to conduct ecologically relevant global change experiments over the long times commensurate with the pace of changing climate. As a result, many studies present stressors in a shock-type exposure at rates much faster than projected scenarios. With more gradual stressor introduction over longer experimental durations and in context with conditions species are currently acclimatized and/or adapted to, the outcomes for sensitive species might differ. We highlight the importance to understand primordial germ cell development and the timing of gametogenesis with respect to stressor exposure. Although multigenerational exposure to global change stressors currently appears limited as a universal tool to rescue species in the face of changing climate, natural proxies of future conditions (upwelling zones, CO₂ vents, naturally warm habitats) show that phenotypic adjustment and/or beneficial genetic selection is possible for some species, indicating complex plasticity-adaptation interactions.

Transcriptomic and functional analysis of the oosome, a unique form of germ plasm in the wasp Nasonia vitripennis

BACKGROUND

The oosome is the germline determinant in the wasp Nasonia vitripennis and is homologous to the polar granules of Drosophila. Despite a common evolutionary origin and developmental role, the oosome is morphologically quite distinct from polar granules. It is a solid sphere that migrates within the cytoplasm before budding out and forming pole cells.

RESULTS

To gain an understanding of both the molecular basis of oosome development and the conserved essential features of germ plasm, we quantified and compared transcript levels between embryo fragments that contained the oosome and those that did not. The identity of the differentially localized transcripts indicated that Nasonia uses a distinct set of molecules to carry out conserved germ plasm functions. In addition, functional testing of a sample of localized transcripts revealed potentially novel mechanisms of ribonucleoprotein assembly and pole cell cellularization in the wasp.

CONCLUSIONS

Our results demonstrate that the composition of germ plasm varies significantly within Holometabola, as very few mRNAs share localization to the oosome and polar granules. Some of this variability appears to be related to the unique properties of the oosome relative to the polar granules in Drosophila, and some may be related to differences in pole formation between species. This work will serve as the basis for further investigation into the patterns of germline determinant evolution among insects, the molecular basis of the unique properties of the oosome, and the incorporation of novel components into developmental networks.