Evidence on hereditary occurrence of placental anastomoses in heterosexual twins in sheep

Validation of fetal microchimerism after pregnancy in the ovine using qPCR

Fetal microchimerism has been detected in maternal tissues of humans and rodents during and after pregnancy. Studies focusing on fetal DNA transfer to maternal tissues in domestic animals are limited, especially in sheep. Fetal ram DNA was observed in the maternal circulation during pregnancy, but it is not known if this chimerism persists in soft tissues after parturition. The objectives of this exploratory study were to: 1) determine if male fetal DNA is detectable in soft tissues of mature ewes after parturition and if so, determine if detection repeatability differed with lifetime offspring sex ratio and 2) determine if male fetal DNA was present in soft tissues of yearling (primiparous) ewes shortly after parturition. Eight mature (open, non-lactating) and 8 yearling (primiparous, periparturient) Rambouillet ewes were used. Mature ewes (5- to 7-yr old) had given birth to primarily 82% males (n = 4) or 71% female (n = 4) over a lifetime. Yearling ewes had birthed either a singleton male (n = 4) or female (n = 4) lambs. DNA was extracted from 10 and 11 different soft tissues from the mature and yearling ewes, respectively. Real-time PCR (qPCR) was used to identify the presence of the SRY gene in each tissue sample. Male DNA was detected in the brain and liver from one mature open ewe that had given birth to two males and six females during her lifetime. In younger ewes that gave birth to a ram lamb, male DNA was observed in the thyroid of one ewe and the pancreas and brain of a second ewe. Male DNA was detected in the ovary of one ewe that had given birth to a female lamb. Based on these data, we suggest fetal microchimerism in soft maternal tissues is possible in sheep and may remain after pregnancy has ended. The detection repeatability of male fetal DNA was not associated with sex ratio of lifetime offspring. Male DNA was observed in maternal soft tissues collected shortly after parturition. The greater detection of fetal male DNA found in younger ewes shortly after parturition may be due to not having enough time for fetal DNA clearance to occur. Future studies are warranted to further study XY chimerism in maternal tissues of the ewe and its potential role in ovine physiology.

Cytogenetic Analyses in Ewes with Congenital Abnormalities of the Genital Apparatus

Simple Summary

The disorders of sex development (DSDs) are congenital conditions characterized by inconsistency among chromosomal, gonadal, and anatomical sex development. Reproduction and prolificacy are two main parameters in the sheep industry; thus, DSDs in sheep are very detrimental. Interestingly, no DSDs-associated gene mutations have been reported in sheep so far, probably due to the fact that affected animals are not detected and studied. With the aim to deepen the knowledge about DSDs in sheep and improve diagnostic tools, screening of a sheep farm aimed to detect and study DSDs in ovine species has been started, and the actual findings relative to the first two sheep flocks analysed are reported here. In our opinion, this study demonstrates that, despite the low number of studies on ovine DSDs, if compared with other species, this problem is actually present and needs more attention.

Abstract

The Disorders of Sex Development (DSDs) are congenital conditions characterized by inconsistency among chromosomal, gonadal, and anatomical sex development. The aim of this research is to report the clinical and cytogenetic findings of four DSD cases and 13 couples of heterosexual twins in sheep. To this purpose, C- and R-banding techniques were used, and the analyses of the SRY (Sex Determining Region Y) and AMEL (Amelogenin) genes were carried out. Moreover, morphopathological analyses were performed in one case. The four DSD sheep cases were registered as females at birth, and for none of them it was possible to establish whether the subjects were born from heterosexual multiple births. Three of the four cases were diagnosed as XX/XY blood lymphocyte chimaeras, while the fourth case was diagnosed as a 54, XY SRY-positive DSD sheep. None of the heterosexual twins showed XX/XY blood chimaerism. This finding suggests that the blood chimaeric cases detected could also be due to a zygote/embryo fusion. Moreover, no gene variants involved in sheep DSD are known, the identification of which would be very useful for the sheep industry.

Blood chimerism confounds genetic relative susceptibility testing for classical scrapie in sheep

Classical scrapie disease is a transmissible spongiform encephalopathy of sheep that is enzootic in the United States. Susceptibility of sheep to classical scrapie is linked to single nucleotide polymorphisms in the prion protein gene (PRNP), forming the basis for genetic testing strategies used by national efforts to eradicate scrapie. Such efforts are occasionally hampered by inconclusive results stemming from the detection of "complex" genotypes. Naturally occurring cases of ovine chimerism are thought to account for some of these instances. In the current report, 4 naturally occurring ovine chimeras are documented through cytogenetic and molecular analyses. All 4 of these sheep had chimeric cells circulating in their blood. Blood and alternate tissue samples of ear punch and hair bulbs from one of these chimeras was submitted in batch with similar samples from control sheep for routine scrapie genetic relative susceptibility testing. A complex PRNP genotype was detected in the blood of the chimeric female but not in the alternate tissue samples or in the control sheep samples. The results demonstrate that naturally occurring blood chimerism can confound current testing efforts. The potential impacts of undetected chimeras on current scrapie eradication efforts are discussed.

Cytogenetic screening of livestock populations in Europe: an overview

Clinical animal cytogenetics development began in the 1960's, almost at the same time as human cytogenetics. However, the development of the two disciplines has been very different during the last four decades. Clinical animal cytogenetics reached its 'Golden Age' at the end of the 1980's. The majority of the laboratories, as well as the main screening programs in farm animal species, presented in this review, were implemented during that period, under the guidance of some historical leaders, the first of whom was Ingemar Gustavsson. Over the past 40 years, hundreds of scientific publications reporting original chromosomal abnormalities generally associated with clinical disorders (mainly fertility impairment) have been published. Since the 1980's, the number of scientists involved in clinical animal cytogenetics has drastically decreased for different reasons and the activities in that field are now concentrated in only a few laboratories (10 to 15, mainly in Europe), some of which have become highly specialized. Currently between 8,000 and 10,000 chromosomal analyses are carried out each year worldwide, mainly in cattle, pigs, and horses. About half of these analyses are performed in one French laboratory. Accurate estimates of the prevalence of chromosomal abnormalities in some populations are now available. For instance, one phenotypically normal pig in 200 controlled in France carries a structural chromosomal rearrangement. The frequency of the widespread 1;29 Robertsonian translocation in cattle has greatly decreased in most countries, but remains rather high in certain breeds (up to 20-25% in large beef cattle populations, even higher in some local breeds). The continuation, and in some instances the development of the chromosomal screening programs in farm animal populations allowed the implementation of new and original scientific projects, aimed at exploring some basic questions in the fields of chromosome and/or cell biology, thanks to easier access to interesting biological materials (germ cells, gametes, embryos ...).

Sex chromosome chimerism and the freemartin syndrome in Rideau Arcott sheep

In cattle, nearly all heifers born co-twin to a male are freemartins, XX/XY chimeras that exhibit a characteristic masculinized phenotype. However, in sheep, while litters containing males and females are common, freemartins are relatively rare. The primary aim of this study was to determine the frequency and features of XX/XY chimerism in female Rideau Arcott sheep. Also, breeding records were used to investigate the effect of litter size and sex ratios, as well as the genetic basis of the condition. Finally, the migration and transcriptional competence of cells of the opposite sex in the XX/XY female and male chimeras was explored. Genomic DNA (gDNA) from peripheral blood cells of ewes was screened by PCR for the male-specific SRY gene. Of 230 lambs screened, 10 were identified as chimeras. Litter size and sex ratio showed no statistically significant effect on the frequency of chimerism. PCR and FISH analysis confirmed the presence of opposite sex cells in female and male chimeras, and in the case of ewes, their migration to tissues other than blood. Transcriptional activity of SRY and AMH was detected in gonads of ewes, whereas XIST expression was detected in white blood cells of chimeric rams. It was concluded that the frequency of sex chromosome chimerism in Rideau Arcott sheep is estimated at 4.35%, with no significant effect of litter size and sex ratio. Moreover, as it was shown that opposite sex cells can migrate to tissues other than blood and be transcriptionally active in chimeric sheep, we speculate on the role they can play in these animals.

The mitochondrial genome in embryo technologies

The mammalian mitochondrial genome encodes for 37 genes which are involved in a broad range of cellular functions. The mitochondrial DNA (mtDNA) molecule is commonly assumed to be inherited through oocyte cytoplasm in a clonal manner, and apparently species-specific mechanisms have evolved to eliminate the contribution of sperm mitochondria after natural fertilization. However, recent evidence for paternal mtDNA inheritance in embryos and offspring questions the general validity of this model, particularly in the context of assisted reproduction and embryo biotechnology. In addition to normal mt DNA haplotype variation, oocytes and spermatozoa show remarkable differences in mtDNA content and may be affected by inherited or acquired mtDNA aberrations. All these parameters have been correlated with gamete quality and reproductive success rates. Nuclear transfer (NT) technology provides experimental models for studying interactions between nuclear and mitochondrial genomes. Recent studies demonstrated (i) a significant effect of mtDNA haplotype or other maternal cytoplasmic factors on the efficiency of NT; (ii) phenotypic differences between transmitochondrial clones pointing to functionally relevant nuclear-cytoplasmic interactions; and (iii) neutral or non-neutral selection of mtDNA haplotypes in heteroplasmic conditions. Mitochondria form a dynamic reticulum, enabling complementation of mitochondrial components and possibly mixing of different mtDNA populations in heteroplasmic individuals. Future directions of research on mtDNA in the context of reproductive biotechnology range from the elimination of adverse effects of artificial heteroplasmy, e.g. created by ooplasm transfer, to engineering of optimized constellations of nuclear and cytoplasmic genes for the production of superior livestock.

What is a marmoset?

Callitrichid primates typically give birth to twin offspring that are somatic chimeras of cells derived from two products of conception. Each individual is thus the phenotype of two sibling genotypes, one of which may be more closely related to the germ line of the individual's parents than to the individual's own germ line. Chimerism could therefore help to explain the evolution of alloparental care and social suppression of reproduction in callitrichids. Placental chimerism may also have important implications for understanding kin interactions within the womb: on one side of the coin, the intimate juxtaposition of genotypes provides unique opportunities for antagonistic interactions between embryos; on the other side, chimerism could facilitate cooperation between sibling genotypes.