Formation of a large Vasa-positive germ granule and its inheritance by germ cells in the enigmatic Chaetognaths

Development ◽  
2002 ◽  
Vol 129 (3) ◽  
pp. 661-670 ◽  
Author(s):  
Danièle Carré ◽  
Chakib Djediat ◽  
Christian Sardet
Keyword(s):  
Germ Cells ◽  
Molecular Mechanisms ◽  
Germ Plasm ◽  
Germ Line ◽  
Germinal Vesicle ◽  
Phylogenetic Position ◽  
Internal Fertilization ◽  
Cell Stage ◽  
Development And Differentiation

Chaetognaths (arrow worms) are abundant hermaphrodite marine organisms whose phylogenetic position amongst protostomes and deuterostomes is still debated. Ancient histological observations dating from a century ago described the presence in eggs of a large granule, presumed to be a germ plasm, and its probable inheritance in four primary germ cells (PGCs). Using videomicroscopy, electron microscopy and immunocytochemistry (labelling with anti-Vasa antibodies) we have followed the cycle of aggregation and dispersion of germ plasm and nuage material in eggs, embryos, PGCs and oocytes in several species of benthic (Spadella) and planctonic (Sagitta) chaetognaths. In these animals, germ cells and gametes can be observed in vivo throughout the 1-2 month life cycle.After describing internal fertilization in live animals we show that the single large (15 μm diameter) germ granule forms by a spiralling aggregation movement of small germ islands situated in the vegetal cortex at the time of first mitosis. We also demonstrate that the granule forms autonomously in unfertilized activated eggs or fertilized egg fragments. Once formed, the germ granule first associates with the cleavage furrow and is segregated into one of the first two blastomeres. The germ granule is then translocated from the cortex to the mitotic spindle during 3rd cleavage and remains in the single most-vegetal blastomere until the 32-cell stage. At the 64-cell stage the germ granule is partitioned as nuage material into two founder PGCs and further partitioned into four PGCs situated at the tip of the archenteron during gastrulation. These four PGCs migrate without dividing to reach the transverse septum, then proliferate and differentiate into oocytes and spermatocytes of two ovaries and two testes. We noted that germ plasm and nuage material were associated with mitochondria, the nucleus, the spindle and the centrosome during some stages of development and differentiation of the germ line. Finally, we demonstrate that a Vasa-like protein is present in the germ granule, in PGCs and in the electron-dense material associated with the germinal vesicle of oocytes. These features stress the conservation of cellular and molecular mechanisms involved in germ cell determination.Movies available on-line

scholarly journals CKS1 Germ Line Exclusion Is Essential for the Transition from Meiosis to Early Embryonic Development

2019 ◽  
Vol 39 (13) ◽  
Author(s):  
Zdenka Ellederova ◽  
Sonia del Rincon ◽  
Marketa Koncicka ◽  
Andrej Susor ◽  
Michal Kubelka ◽  
...  
Keyword(s):  
Cell Division ◽  
Embryonic Development ◽  
Germ Line ◽  
Germinal Vesicle ◽  
Meiotic Spindle ◽  
Anaphase Promoting Complex ◽  
Cell Stage ◽  
Germinal Vesicle Breakdown ◽  
Cks Proteins

ABSTRACT Cell division cycle (Cdc) kinase subunit (CKS) proteins bind cyclin-dependent kinases (CDKs) and play important roles in cell division control and development, though their precise molecular functions are not fully understood. Mammals express two closely related paralogs called CKS1 and CKS2, but only CKS2 is expressed in the germ line, indicating that it is solely responsible for regulating CDK functions in meiosis. Using cks2−/− knockout mice, we show that CKS2 is a crucial regulator of maturation-promoting factor (MPF; CDK1-cyclin A/B) activity in meiosis. cks2−/− oocytes display reduced and delayed MPF activity during meiotic progression, leading to defects in germinal vesicle breakdown (GVBD), anaphase-promoting complex/cyclosome (APC/C) activation, and meiotic spindle assembly. cks2−/− germ cells express significantly reduced levels of the MPF components CDK1 and cyclins A1/B1. Additionally, injection of MPF plus CKS2, but not MPF alone, restored normal GVBD in cks2−/− oocytes, demonstrating that GVBD is driven by a CKS2-dependent function of MPF. Moreover, we generated cks2cks1/cks1 knock-in mice and found that CKS1 can compensate for CKS2 in meiosis in vivo, but homozygous embryos arrested development at the 2- to 5-cell stage. Collectively, our results show that CKS2 is a crucial regulator of MPF functions in meiosis and that its paralog, CKS1, must be excluded from the germ line for proper embryonic development.

The positional effect of presumptive primordial germ cells (pPGCs) on their differentiation into PGCs in Xenopus

Development ◽  
1988 ◽  
Vol 102 (3) ◽  
pp. 527-535
Author(s):  
K. Ikenishi ◽  
Y. Tsuzaki
Keyword(s):  
Germ Cells ◽  
Germ Plasm ◽  
Germ Line ◽  
Anterior Part ◽  
Primordial Germ Cells ◽  
Positional Effect ◽  
In Series

To determine whether the location of ‘germ plasm’-bearing cells [presumptive primordial germ cells (pPGCs)] is crucial for their differentiation into PGCs in Xenopus, [3H]thymidine-labelled pPGCs were implanted into the anterior or posterior halves of the endoderm in unlabelled host neurulae. Labelled PGCs in the genital ridges of experimental tadpoles were investigated by autoradiography. When the labelled pPGCs were implanted into posterior halves of the endoderm where host pPGCs are situated, 65 and 77% of the experimental tadpoles (designated as p-tadpoles) had the labelled PGCs in series I and II, respectively. When implanted into the anterior halves, 20 and 27% of the experimental tadpoles (a- tadpoles) had the labelled PGCs in series I and II, respectively. In p-tadpoles, the average numbers of labelled PGCs per tadpole were 8á7 in series I and 10 in series II, whereas they were 2á0 in a-tadpoles of both series. Both the proportion and the average number in p-tadpoles of both series were significantly different from those in a-tadpoles. In both series, labelled PGCs in p-tadpoles were found to be distributed throughout the genital ridges while those in a-tadpoles were localized only in the anterior part of the ridges. These facts indicate that the location of pPGCs in the endoderm affects their successful migration into the genital ridges, and that not only the presence of the germ plasm but also the proper location in endoderm are prerequisites to PGC differentiation of the germ line cells.

scholarly journals Potential for Virus Endogenization in Humans through Testicular Germ Cell Infection: the Case of HIV

2020 ◽  
Vol 94 (24) ◽  
Author(s):  
Dominique Mahé ◽  
Giulia Matusali ◽  
Claire Deleage ◽  
Raquel L. L. S. Alvarenga ◽  
Anne-Pascale Satie ◽  
...  
Keyword(s):  
Germ Cells ◽  
Germ Line ◽  
Landscape Analysis ◽  
Testicular Germ Cell ◽  
Early Protein ◽  
Immunodeficiency Virus ◽  
Molecular Landscape ◽  
Hiv 1

ABSTRACT Viruses have colonized the germ line of our ancestors on several occasions during evolution, leading to the integration in the human genome of viral sequences from over 30 retroviral groups and a few nonretroviruses. Among the recently emerged viruses infecting humans, several target the testis (e.g., human immunodeficiency virus [HIV], Zika virus, and Ebola virus). Here, we aimed to investigate whether human testicular germ cells (TGCs) can support integration by HIV, a contemporary retrovirus that started to spread in the human population during the last century. We report that albeit alternative receptors enabled HIV-1 binding to TGCs, HIV virions failed to infect TGCs in vitro. Nevertheless, exposure of TGCs to infected lymphocytes, naturally present in the testis from HIV+ men, led to HIV-1 entry, integration, and early protein expression. Similarly, cell-associated infection or bypassing viral entry led to HIV-1 integration in a spermatogonial cell line. Using DNAscope, HIV-1 and simian immunodeficiency virus (SIV) DNA were detected within a few TGCs in the testis from one infected patient, one rhesus macaque, and one African green monkey in vivo. Molecular landscape analysis revealed that early TGCs were enriched in HIV early cofactors up to integration and had overall low antiviral defenses compared with testicular macrophages and Sertoli cells. In conclusion, our study reveals that TGCs can support the entry and integration of HIV upon cell-associated infection. This could represent a way for this contemporary virus to integrate into our germ line and become endogenous in the future, as happened during human evolution for a number of viruses. IMPORTANCE Viruses have colonized the host germ line on many occasions during evolution to eventually become endogenous. Here, we aimed at investigating whether human testicular germ cells (TGCs) can support such viral invasion by studying HIV interactions with TGCs in vitro. Our results indicate that isolated primary TGCs express alternative HIV-1 receptors, allowing virion binding but not entry. However, HIV-1 entered and integrated into TGCs upon cell-associated infection and produced low levels of viral proteins. In vivo, HIV-1 and SIV DNA was detected in a few TGCs. Molecular landscape analysis showed that TGCs have overall weak antiviral defenses. Altogether, our results indicate that human TGCs can support HIV-1 early replication, including integration, suggesting potential for endogenization in future generations.

scholarly journals Multicellularity makes somatic differentiation evolutionarily stable

2016 ◽  
Vol 113 (30) ◽  
pp. 8362-8367 ◽  
Author(s):  
Mary E. Wahl ◽  
Andrew W. Murray
Keyword(s):  
Germ Cells ◽  
Germ Line ◽  
Somatic Cells ◽  
Potential Benefits ◽  
Fitness Benefits ◽  
Reproductive Division Of Labor ◽  
Multicellular Organisms ◽  
Reproductive Division ◽  
Evolutionarily Stable

Many multicellular organisms produce two cell lineages: germ cells, whose descendants produce the next generation, and somatic cells, which support, protect, and disperse the germ cells. This germ-soma demarcation has evolved independently in dozens of multicellular taxa but is absent in unicellular species. A common explanation holds that in these organisms, inefficient intercellular nutrient exchange compels the fitness cost of producing nonreproductive somatic cells to outweigh any potential benefits. We propose instead that the absence of unicellular, soma-producing populations reflects their susceptibility to invasion by nondifferentiating mutants that ultimately eradicate the soma-producing lineage. We argue that multicellularity can prevent the victory of such mutants by giving germ cells preferential access to the benefits conferred by somatic cells. The absence of natural unicellular, soma-producing species previously prevented these hypotheses from being directly tested in vivo: to overcome this obstacle, we engineered strains of the budding yeast Saccharomyces cerevisiae that differ only in the presence or absence of multicellularity and somatic differentiation, permitting direct comparisons between organisms with different lifestyles. Our strains implement the essential features of irreversible conversion from germ line to soma, reproductive division of labor, and clonal multicellularity while maintaining sufficient generality to permit broad extension of our conclusions. Our somatic cells can provide fitness benefits that exceed the reproductive costs of their production, even in unicellular strains. We find that nondifferentiating mutants overtake unicellular populations but are outcompeted by multicellular, soma-producing strains, suggesting that multicellularity confers evolutionary stability to somatic differentiation.

scholarly journals Potential for virus endogenization in humans through testicular germ cell infection: the case of HIV

2020 ◽  
Author(s):  
Dominique Mahé ◽  
Giulia Matusali ◽  
Claire Deleage ◽  
Raquel L. L. S. Alvarenga ◽  
Anne-Pascale Satie ◽  
...  
Keyword(s):  
Germ Cells ◽  
Germ Line ◽  
Landscape Analysis ◽  
Testicular Germ Cell ◽  
Early Protein ◽  
The Future ◽  
Molecular Landscape ◽  
Hiv 1

AbstractViruses have colonized the germ line of our ancestors at several occasions during evolution, leading to the integration in the human genome of viral sequences from over 30 retroviral groups and a few non-retroviruses. Among the recently emerged viruses infecting humans, several target the testis (eg HIV, Zika and Ebola viruses). Here we aimed to investigate whether human testicular germ cells (TGCs) can support integration by HIV, a contemporary retrovirus that started to spread in the human population during the last century. We report that albeit alternative receptors enabled HIV-1 binding to TGCs, HIV virions failed to infect TGCs in vitro. Nevertheless, exposure of TGCs to infected lymphocytes, naturally present in the testis from HIV+ men, led to HIV-1 entry, integration and early protein expression. Similarly, cell-associated infection or bypassing viral entry led to HIV-1 integration in a spermatogonial cell line. Using DNAscope, HIV-1 and SIV DNA were detected within a few TGCs in the testis from one infected patient, one rhesus macaque and one African Green monkey in vivo. Molecular landscape analysis revealed that early TGCs were enriched in HIV early co-factors up to integration and had overall low antiviral defenses when compared with testicular macrophages and Sertoli cells. In conclusion, our study reveals that TGCs can support the entry and integration of HIV upon cell-associated infection. This could represent a way for this contemporary virus to integrate our germline and become endogenous in the future, as happened during human evolution for a number of viruses.ImportanceViruses have colonized the host germ line at many occasions during evolution to eventually become endogenous. Here we aimed at investigating whether human testicular germ cells (TGCs) can support such viral invasion by studying HIV interactions with TGCs in vitro. Our results indicate that isolated primary TGCs express alternative HIV-1 receptors allowing virions binding but not entry. However, HIV-1 entered and integrated in TGCs upon cell-associated infection, and produced low level of viral proteins. In vivo, HIV-1 and SIV DNA was detected in a few TGCs. Molecular landscape analysis showed that TGCs have overall weak antiviral defenses. Altogether, our results indicate that human TGCs can support HIV-1 early replication including integration, suggesting potential for endogenization in the future generations.

scholarly journals Germline competent mesoderm: the substrate for vertebrate germline and somatic stem cells?

Biology Open ◽  
2021 ◽  
Vol 10 (10) ◽  
Author(s):  
Aaron M. Savage ◽  
Ramiro Alberio ◽  
Andrew D. Johnson
Keyword(s):  
Stem Cells ◽  
Stem Cell ◽  
Germ Cells ◽  
Molecular Mechanisms ◽  
Germ Plasm ◽  
Cell Types ◽  
Model Organisms ◽  
Developmental Potential ◽  
Tissue Specific ◽  
Tissue Specific Stem Cells

ABSTRACT In vitro production of tissue-specific stem cells [e.g. haematopoietic stem cells (HSCs)] is a key goal of regenerative medicine. However, recent efforts to produce fully functional tissue-specific stem cells have fallen short. One possible cause of shortcomings may be that model organisms used to characterize basic vertebrate embryology (Xenopus, zebrafish, chick) may employ molecular mechanisms for stem cell specification that are not conserved in humans, a prominent example being the specification of primordial germ cells (PGCs). Germ plasm irreversibly specifies PGCs in many models; however, it is not conserved in humans, which produce PGCs from tissue termed germline-competent mesoderm (GLCM). GLCM is not conserved in organisms containing germ plasm, or even in mice, but understanding its developmental potential could unlock successful production of other stem cell types. GLCM was first discovered in embryos from the axolotl and its conservation has since been demonstrated in pigs, which develop from a flat-disc embryo like humans. Together these findings suggest that GLCM is a conserved basal trait of vertebrate embryos. Moreover, the immortal nature of germ cells suggests that immortality is retained during GLCM specification; here we suggest that the demonstrated pluripotency of GLCM accounts for retention of immortality in somatic stem cell types as well. This article has an associated Future Leaders to Watch interview with the author of the paper.

scholarly journals Efficient GFP-labeling and analysis of spermatogenic cells using the IRG transgene and flow cytometry

2018 ◽  
Author(s):  
Leah L. Zagore ◽  
Cydni C. Akesson ◽  
Donny D. Licatalosi
Keyword(s):  
Flow Cytometry ◽  
Germ Cells ◽  
Molecular Mechanisms ◽  
Control Cell ◽  
Cell Types ◽  
Cell Development ◽  
Specific Gene ◽  
Haploid Male ◽  
Human Reproductive ◽  
Development And Differentiation

AbstractSpermatogenesis is a highly ordered developmental program that produces haploid male germ cells. The study of male germ cell development in the mouse has provided unique perspectives into the molecular mechanisms that control cell development and differentiation in mammals, including tissue-specific gene regulatory programs. An intrinsic challenge in spermatogenesis research is the heterogeneity of germ and somatic cell types present in the testis. Techniques to separate and isolate distinct mouse spermatogenic cell types have great potential to shed light on molecular mechanisms controlling mammalian cell development, while also providing new insights into cellular events important for human reproductive health. Here, we detail a versatile strategy that combines Cre-lox technology to fluorescently label germ cells, with flow cytometry to discriminate and isolate germ cells in different stages of development for cellular and molecular analyses.

Mice with AML1 (Runx1) Haploinsufficiency Have Significant Platelet Abnormalities That Accurately Mimic Those Seen in Human Patients with Germ Line Inactivating Mutations in AML1.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1595-1595
Author(s):  
Weili Sun ◽  
Shirley Steward ◽  
Tamara Pestina ◽  
Carl W. Jackson ◽  
James R. Downing
Keyword(s):  
Acute Leukemia ◽  
Platelet Function ◽  
Molecular Mechanisms ◽  
Germ Line ◽  
Genetic Alterations ◽  
Loss Of Function ◽  
Hematopoietic Stem ◽  
Transcriptional Targets ◽  
Platelet Disorder

Abstract The AML1/CBFβ transcription complex, a critical regulator of the formation of definitive hematopoietic stem cells (HSC), is one of the most frequent targets of genetic alterations in acute leukemia. In addition to somatic alterations of AML1 and CBFβ in acute leukemia, germ-line loss-of-function mutations of AML1 are the underlying cause of an autosomal dominant familial platelet disorder with a predisposition to acute myeloid leukemia (FPD/AML). Importantly, a subset of the mutations identified in families with FPD/AML result in AML1 null allele, suggesting that AML1 haploinsufficiency is the underlying molecular abnormality. To explore the functional consequences of AML1 halpoinsufficiency on megakaryocyte development and platelet function, we analyzed the hematopoietic system of AML1+/- mice. Loss of a single AML1 allele resulted in a 15% reduction in the number of circulating platelets and a significant impairment in platelet function including a decrease in dense granule content and an impaired ability to aggregate in response to collagen stimulation. Further analysis indentified a left shift in the DNA ploidy of megakaryocytes and a reduction in GPV expression, consistent with impaired megakaryocyte maturation. In addition, electron microscopy indicated a reduction in platelet demarcation channels within the cytoplasm of megakaryocytes. Importantly, however, we did not observe a reduction in the total number of megakaryoctyes or a decrease in megakaryocyte colony forming units. These data suggest that the haploinsufficiency of AML1+/− does not alter the initial formation of megakaryocytes, but instead impairs the ability of these cells to efficiently mature and produce functional platelets. To explore the underlying mechanism responsible for the observed impairment in megakaryocyte maturation, we analyzed the pattern of expression of several putative AML1 transcriptional targets. Although AML1 binding sites have been identified within the promoter of c-mpl, the gene encoding the receptor for thrombopoietin (TPO), we did not observe any difference in c-mpl expression levels or in circulating TPO concentration between AML1+/− and +/+ mice. In addition, in vivo TPO stimulation induced a similar magnitude of megakaryocyte maturation and platelet production in both AML1+/+ and +/− mice. By contrast, analysis of members of the protein kinase C (PKC) family of gene, several which have been identified as transcriptional targets of AML1, revealed a reduction in PKCδ levels in platelets from AML1+/− mice. Taken together, our data suggest that AML1 haploinsufficiency leads to abnormalities in platelet that are identical to those observed in patients with FPD/AML. Thus, these mice should prove useful for exploring the molecular mechanisms through which AML regulates the normal maturation of megakaryocytes. Our early analysis suggests altered PKCδ signaling is a possible contributing factor to the observed phenotypic abnormalities.

scholarly journals Causes and evolutionary consequences of primordial germ-cell specification mode in metazoans

2017 ◽  
Vol 114 (23) ◽  
pp. 5784-5791 ◽  
Author(s):  
Carrie A. Whittle ◽  
Cassandra G. Extavour
Keyword(s):  
Germ Cells ◽  
Gene Networks ◽  
Evolutionary Biology ◽  
Large Scale ◽  
Germ Plasm ◽  
Germ Line ◽  
Primordial Germ Cell ◽  
Sequence Evolution ◽  
Animal Evolution ◽  
Germ Cell Specification

In animals, primordial germ cells (PGCs) give rise to the germ lines, the cell lineages that produce sperm and eggs. PGCs form in embryogenesis, typically by one of two modes: a likely ancestral mode wherein germ cells are induced during embryogenesis by cell–cell signaling (induction) or a derived mechanism whereby germ cells are specified by using germ plasm—that is, maternally specified germ-line determinants (inheritance). The causes of the shift to germ plasm for PGC specification in some animal clades remain largely unknown, but its repeated convergent evolution raises the question of whether it may result from or confer an innate selective advantage. It has been hypothesized that the acquisition of germ plasm confers enhanced evolvability, resulting from the release of selective constraint on somatic gene networks in embryogenesis, thus leading to acceleration of an organism’s protein-sequence evolution, particularly for genes expressed at early developmental stages, and resulting in high speciation rates in germ plasm-containing lineages (denoted herein as the “PGC-specification hypothesis”). Although that hypothesis, if supported, could have major implications for animal evolution, our recent large-scale coding-sequence analyses from vertebrates and invertebrates provided important examples of genera that do not support the hypothesis of liberated constraint under germ plasm. Here, we consider reasons why germ plasm might be neither a direct target of selection nor causally linked to accelerated animal evolution. We explore alternate scenarios that could explain the repeated evolution of germ plasm and propose potential consequences of the inheritance and induction modes to animal evolutionary biology.

scholarly journals Bone Marrow Microenvironmental Changes Underlie Reduced RAG-mediated Recombination and B Cell Generation in Aged Mice

2004 ◽  
Vol 200 (4) ◽  
pp. 411-423 ◽  
Author(s):  
Joseph E. Labrie ◽  
Alex P. Sah ◽  
David M. Allman ◽  
Michael P. Cancro ◽  
Rachel M. Gerstein
Keyword(s):  
Bone Marrow ◽  
B Cells ◽  
B Cell ◽  
Molecular Mechanisms ◽  
Extrinsic Factors ◽  
Cell Stage ◽  
Aged Mice ◽  
Microenvironmental Factors ◽  
Bone Marrow Chimeras

During aging, adaptive immunity is severely compromised, due in part to decreased production of B lymphocytes and loss of immunoglobulin (Ig) diversity. However, the molecular mechanisms that underlie age-associated diminished B cell production remain unclear. Using in vivo labeling, we find that this reduction in marrow pre–B cells reflects increased attrition during passage from the pro–B to pre–B cell pool. Analyses of reciprocal bone marrow chimeras reveal that the magnitude and production rates of pre–B cells are controlled primarily by microenvironmental factors, rather than intrinsic events. To understand changes in pro–B cells that could diminish production of pre–B cells, we evaluated rag2 expression and V(D)J recombinase activity in pro–B cells at the single cell level. The percentage of pro–B cells that express rag2 is reduced in aged mice and is correlated with both a loss of V(D)J recombinase activity in pro–B cells and reduced numbers of pre–B cells. Reciprocal bone marrow chimeras revealed that the aged microenvironment also determines rag2 expression and recombinase activity in pro–B cells. Together, these observations suggest that extrinsic factors in the bone marrow that decline with age are largely responsible for less efficient V(D)J recombination in pro–B cells and diminished progression to the pre–B cell stage.

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