Human chimaera detectable only by investigation of her progeny

The beginning of becoming a human

According to birth certificates, the life of a child begins once their body comes out of the mother's womb. But when does their organismal life begin? Science holds a palette of answers-depending on how one defines a human life. In 1984, a commission on the regulatory framework for human embryo experimentation opted not to answer this question, instead setting a boundary, 14 days post-fertilization, beyond which any experiments were forbidden. Recently, as the reproductive technologies developed and the demand for experimentation grew stronger, this boundary may be set aside leaving the ultimate decision to local oversight committees. While science has not come closer to setting a zero point for human life, there has been significant progress in our understanding of early mammalian embryogenesis. It has become clear that the 14-day stage does in fact possess features, which make it a foundational time point for a developing human. Importantly, this stage defines the separation of soma from the germline and marks the boundary between rejuvenation and aging. We explore how different levels of life organization emerge during human development and suggest a new meaning for the 14-day stage in organismal life that is grounded in recent mechanistic advances and insights from aging studies.

Somatic deficiency causes reproductive parasitism in a fungus

Some multicellular organisms can fuse because mergers potentially provide mutual benefits. However, experimental evolution in the fungus Neurospora crassa has demonstrated that free fusion of mycelia favours cheater lineages, but the mechanism and evolutionary dynamics of this exploitation are unknown. Here we show, paradoxically, that all convergently evolved cheater lineages have similar fusion deficiencies. These mutants are unable to initiate fusion but retain access to wild-type mycelia that fuse with them. This asymmetry reduces cheater-mutant contributions to somatic substrate-bound hyphal networks, but increases representation of their nuclei in the aerial reproductive hyphae. Cheaters only benefit when relatively rare and likely impose genetic load reminiscent of germline senescence. We show that the consequences of somatic fusion can be unequally distributed among fusion partners, with the passive non-fusing partner profiting more. We discuss how our findings may relate to the extensive variation in fusion frequency of fungi found in nature.

ABO maternal-child discordance: Evidence of variable allelic expression and considerations for investigation

BACKGROUND

We report a case of apparent mother-child ABO group noninheritance. A Caucasian mother initially typed as group O and her infant group AB. Investigation ruled out preanalytical causes such as mislabeled samples and in vitro fertilization.

MATERIALS AND METHODS

Red blood cells were characterized by routine serologic testing. Genomic data were analyzed by targeted polymerase chain reaction-restriction fragment length polymorphism and Sanger sequencing. Transferase structures were modeled using PyMOL molecular visualization software.

RESULTS

Serologic testing initially demonstrated the mother was group O, father group AB, and infant group AB. Further testing of the maternal sample with anti-A,B demonstrated weak A expression. Molecular testing revealed the maternal sample had an ABO*O.01.01 allele in trans to an A allele, ABO*AW.29 (c.311T>A, p.Ile104Asn), determined by gene sequencing. The sample from the infant carried the same ABO*AW.29 allele in trans to a B allele, ABO*B.01.

CONCLUSION

ABO genotyping revealed an A transferase encoded by ABO*AW.29, with apparent variable activity. Although A antigen expression is well known to be weak in newborns, it was robust on the red blood cells (RBCs) of the AB infant and undetectable with anti-A on the mother. Variable expression of weak subgroups may reflect competition or enhancement by a codominant allele, as well as glycan chain maturation on red cells. Previous examples in group AB mothers with A_weak infants suggested that the decreased expression is primarily due to glycan immaturity. To our knowledge, this is the first reported case of the ABO*AW.29 allele presenting with weak A expression in a group A_weak mother and robust A expression in a group AB infant, suggesting the in trans allele is an important factor in determining transferase activity and may override age-related effects.

Intricacies of aetiology in intrafamilial degenerative disease

The genetic underpinnings of late-onset degenerative disease have typically been determined by screening families for the segregation of genetic variants with the disease trait in affected, but not unaffected, individuals. However, instances of intrafamilial etiological heterogeneity, where pathogenic variants in a culprit gene are not shared among all affected family members, continue to emerge and confound gene-discovery and genetic counselling efforts. Discordant intrafamilial cases lacking a mutation shared by other affected family members are described as disease phenocopies. This description often results in an over-simplified acceptance of an environmental cause of disease in the phenocopy cases, while the role of intrafamilial genetic heterogeneity, shared de novo mutations or epigenetic aberrations in such families is often ignored. On a related note, it is now evident that the same disease-associated variant can be present in individuals exhibiting clinically distinct phenotypes, thereby genetically uniting seemingly unrelated syndromes to form a spectrum of disease. Herein, we discuss the intricacies of determining complex degenerative disease aetiology and suggest alternative mechanisms of disease transmission that may account for the apparent missing heritability of disease.

A case of 46,XX/46,XX chimerism in a phenotypically normal woman

Chimerism is the presence of two genetically different cell lines within a single organism, which is rarely observed in humans. Usually, chimerism in the human body is revealed by the finding of an abnormal phenotype during a medical examination or is unexpectedly detected in routine genetic analysis. However, the incidence or underlying mechanism of chimerism remains unclear due to the lack of information on this infrequent biological event. A phenotypically normal woman with a 46,XX karyotype and atypical short tandem repeat (STR) allelic patterns observed in DNA analysis was investigated with various genetic testing methods, including STR typing based on capillary electrophoresis and massively parallel sequencing, genome-wide SNP array, and a differentially methylated parental allele assay (DMPA). The proband's parents were not available for testing to discriminate the parental allelic contribution, but the parents' alleles were recovered from testing the proband's siblings. Based on the results consistently found in multiple analyses using STR and single nucleotide polymorphism (SNP) polymorphism markers, dispermic fertilization was suggested as the underlying mechanism. The application of various molecular genetic testing methods was used to elucidate the chimerism observed in the proband in this study. In the future, the development of novel genetic markers or techniques, such as DMPA, may have potential use in the investigation of chimerism.

Histocompatibility as adaptive response to discriminatory within-organism conflict: a historical model

Multicellular tissue compatibility, or histocompatibility, restricts fusion to close kin. Histocompatibility depends on hypervariable cue genes, which often have more than 100 alleles in a population. To explain the evolution of histocompatibility, I here take a historical approach. I focus on the specific example of marine invertebrate histocompatibility. I use simple game-theoretical models to show that histocompatibility can evolve through five steps. These steps include the evolution of indiscriminate fusion, the evolution of discriminatory within-organism conflict, the evolution of minor histocompatibility, the evolution of major histocompatibility, and the evolution of major histocompatibility cue polymorphism. Allowing for gradual evolution reveals discriminatory within-organism conflict as a selective pressure for histocompatibility and associated cue polymorphism. Existing data from marine invertebrates and other organisms are consistent with this hypothesis.

When "personhood" begins in the embryo: avoiding a syllabus of errors

The following essay was delivered at the conference "Ontogeny and Human Life" at the Ponifical Athenaeum "Regina Apostolorum," November, 2007. Sponsored by the Legion of Christ, the Pontifical Academy for Life, and the John Templeton Foundation, the sessions focused on when the conceptus became a "person." My essay focused on the scientific conclusions that could aid such discussions. Moreover, after listening to the philosophical, legal, and theological discussions that ensued, I responded theologically as well. New concepts in modern embryology have made scientists revise their views concerning the autonomy of embryos and the mechanisms that generate such embryos. There are interactions between the sperm and the female reproductive tract and egg which had never been known until recently. There are also interactions between the developing organism and its environment that had been unsuspected a decade ago. Gut bacteria induce the development of the mammalian digestive system and immune system by changing the gene expression patterns in the mammalian intestine. Conversely, chemicals in our technological society can adversely affect the embryo, rendering it sterile or prone to tumors later in life. While there is no consensus among scientists as to when human life begins, both Church and science can become allies in persuading governments to regulate or ban the production and use of these fetotoxic chemicals. These new views of embryonic development change many of the stories told about human embryos and fetuses, and they have implications concerning the use of science as evidence for theological positions.

Chimera and other fertilization errors

The finding of a mixture of 46,XX and 46,XY cells in an individual has been rarely reported in literature. It usually results in individuals with ambiguous genitalia. Approximately 10% of true human hermaphrodites show this type of karyotype. However, the underlying mechanisms are poorly understood. It may be the result of mosaicism or chimerism. By definition, a chimera is produced by the fusion of two different zygotes in a single embryo, while a mosaic contains genetically different cells issued from a single zygote. Several mechanisms are involved in the production of chimera. Stricto sensu, chimerism occurs from the post-zygotic fusion of two distinct embryos leading to a tetragametic chimera. In addition, there are other entities, which are also referred to as chimera: parthenogenetic chimera and chimera resulting from fertilization of the second polar body. Furthermore, a particular type of chimera called 'androgenetic chimera' recently described in fetuses with placental mesenchymal dysplasia and in rare patients with Beckwith-Wiedemann syndrome is discussed. Strategies to study mechanisms leading to the production of chimera and mosaics are also proposed.

Mother–child exclusion due to paternal uniparental disomy 6

In a mother-child pair, false exclusions in markers on chromosome 6 have been observed. The genetic incompatibilities have been caused by paternal uniparental disomy. The consequences of such cases for investigations of parentage are discussed.

History of forensic serology and molecular genetics in the sphere of activity of the German Society for Forensic Medicine

In the field of forensic serology, essential developmental impulses have come from the sphere of activity of the German Society for Forensic Medicine. Among these are the orientating enzyme-reactive and specific tests for blood using crystallization tests, the determination of the species-specificity of the donor of the stain and the beginning of the individualization of a stain to its donor. Pioneering work has also been done in the development of blood group serology of the conventional markers. DNA analysis originated in the Anglo-Saxon region. The German Society for Forensic Medicine also contributed to its further progress and essentially influenced it e.g. by the discovery of microsatellite markers, including STRs, by the validation of numerous test methods, by optimization of these methods and by preliminary work for the use of mass spectrometry in DNA analysis.

The colonial urochordate Botryllus schlosseri: from stem cells and natural tissue transplantation to issues in evolutionary ecology

The urochordates, whose stem groups may have included the direct predecessors of the chordate line, serve as an excellent model group of organisms for a variety of scientific disciplines. One taxon, the botryllid ascidian, has emerged as the model system for studying allorecognition; this work has concentrated on the cosmopolitan species Botryllus schlosseri. Studies analyzing self-nonself recognition in this colonial marine organism point to three levels of allorecognition, each associated with different outcomes. The first level controls natural allogeneic rejections and fusions, in which blood-shared chimeras are formed. The second level leads to morphological resorption of partners within chimeras while the third allows the development of somatic and germ cell parasitic events. Recent studies on multi-chimeric entities formed in allogeneic fusions reveal evolutionary links between allorecognition, stem cell biology and ecology. Thus, the Botryllus system generates perspectives from different biological disciplines to yield a unique life history portrait.

Human natural chimerism: an acquired character or a vestige of evolution?

Analysis on five common classes of human natural chimeras (cytomictical, whole body, fetal-maternal, germ cell, and tumor chimeras) reveals that (1) they initiate only during pregnancy, (2) the most common class are chimeras which contain maternal cells, and (3) the primary mechanisms that are involved in their formation and establishment are still elusive. These classes of natural chimerism, are involved only with maladaptive phenomena such as malignancy and autoimmune diseases and without any documented benefit. A recent review has challenged the accepted dogma that the evolution of immunity is pathogen-directed and asserted that preserving individuality from littering the soma and the germline by conspecific alien cells might have been the original function of the innate immunity. Following this tenet, I propose here that human natural chimerism is a by-product of the new role evolved from primitive components of immunity to "educate" the developing embryo with the armamentarium of effector mechanisms, dedicated to purge the individual from pervasive somatic and germline variants, and is not a vestige of evolution.

Zulu XX/XX dispermic chimaera from Natal with two populations of red blood cells and patchy skin pigmentation

The chimaera is female and has two children. Her blood contains 99% group O, type AcP:BA, Pep-A:8-2 and 1% group A2B, type AcP:RA, Pep-A:1 red cells. H-, A- and B-transferase activities were demonstrated in her serum. The level of the H enzyme activity is low but is at the lower end of the normal range for group O persons. The levels of the A and B enzymes are also low but are higher than expected in a person with 1% A2B red cells in the blood. The levels of the A and B enzymes indicate that tissues other than the chimaera's haemopoietic tissue carry her genetically A2B cell line and are contributing the corresponding transferases to her plasma. Gross patchy skin pigmentation is present on the upper part of her body. The chimaera has evidently inherited two dissimilar germ nuclei from each parent.

Detection and interpretation of two different cell lines in triploid abortions

Among a series of 98 triploid abortions, there were four specimens with two cells lines. The detection of two clones was by Q-banding of chromosomes. Two of these four specimens were dizygotic twins, the third was either a mosaic or monozygotic twins with loss of a sex chromosome from one twin and the fourth was best explained as a chimaera which arose by fertilization of two female pronuclei by three sperms. These two unusual specimens had XYY sex chromosome complements which is rare among triploids. Two additional specimens were diagnosed clinically as possible twin pregnancies but only one cell line was identified from tissue culture. The frequency of twins was of the order of 1/33.

Blood group chimeras. A review

More than 70 spontaneous chimeric propositi in man are known. This review attempts to summarize the information given by 32 twin chimeras, 32 dispermic chimeras and 11 chimeras of unestablished type.

Another example of haemopoietic (twin) chimaerism in a subject unaware of being a twin

A fourth human blood group chimaera studies in Birmingham is an example of haemopoietic (twin) chimaerism in which the subject was unaware of being a twin. Chimaerism was discovered during routine antenatal serological investigation in which it was shown that the proposita has two red cell populations, one of the rhesus genotype rr, and the other R1r. Further studies showed that she has two populations of lymphocytes, one with the female karyotype, 46XX, and the other with the male karyotype, 46XY. Skin fibroblasts were all 46XX.

Origin of chi46,XX/46,XY chimerism in a human true hermaphrodite

Using chromosome heteromorphisms and blood cell types as genetic markers, we demonstrated chimerism in a chi46,XX/46,XY true hermaphrodite. The pattern of inheritance of the chromosome heteromorphisms indicates that this individual was probably conceived by the fertilization, by two different spermatozoa, of an ovum and the second meiotic division polar body derived from the ovum and subsequent fusion of the two zygotes. This conclusion is based on the identification of the same maternal chromosomes 13, 16, and 21 in both the 46,XX and 46,XY cells of the patient. In the two cell lines of the chimera, chromosomal markers showed different paternal No. 9 chromosomes and sex chromosomes, as well as the same paternal chromosome 22.