Intrafollicular spontaneous parthenogenetic development of dromedary camel oocytes

Uterotubal junction of the bovine (Bos taurus) versus the dromedary camel (Camelus dromedarius): Histology and histomorphometry

This study aims to conduct a comparative analysis of the uterotubal junction in two distinct mammalian species, the bovine (Bos taurus) and the dromedary camel (Camelus dromedarius), focusing on histological and histomorphometric parameters. Uterotubal junction (UTJ) was dissected from 8 cows and 12 camels with dominant follicles, and processed for H&E staining for histology, and histomorphometry examination. The results showed that the camel uterotubal junction papillae (UTJP) existed only in camels and was completely absent in cattle. Histologically, the cow UTJ appears with a star-shaped lumen, and the mucosa is lined by a simple columnar epithelium with ciliated and non-ciliated cells. Superficial (SG) and deep glands (DG) were abundant in the submucosa. Camel UTJP is a conical structure, it has a pale yellowish colour, 0.5 ± 0.2 cm height, and 0.3 ± 0.1 cm width, and it has a distinct sphincter at the tip towards the uterine lumen. In the camel UTJP, the lumen is wider, and the mucosa showed large multiple folds lined with ciliated and non-ciliated cells in a pseudostratified columnar epithelium. The submucosa showed no mucosal glands. Lumen area, lumen epithelial height, luminal epithelial density, the thickness of the muscular layer, number of folds, fold height, epithelial height, fold area and epithelial perimeter were higher in camel UTJP (p < .001) than cow UTJ, while the total endosalpinx area and glandular epithelial density were lower in camel UTJP (p < .001) than in cow UTJ. In conclusion, this study elucidates potential variations in the uterotubal junction between bovines and dromedary camels, providing valuable insights into their reproductive adaptations. The epithelial lining, absence of glands and the thick layer of tunica muscularis might indicate that camel UTJP could play a mechanical role in selecting spermatozoa and assisting the hatching of blastocysts during their passage into the uterus.

Oocyte Spontaneous Activation: An Overlooked Cellular Event That Impairs Female Fertility in Mammals

In mammals, including humans, mature oocytes are ovulated into the oviduct for fertilization. Normally, these oocytes are arrested at metaphase of the second meiosis (MII), and this arrest can be maintained for a certain period, which is essential for fertilization in vivo and oocyte manipulations in vitro, such as assisted reproduction in clinics and nuclear/spindle transfer in laboratories. However, in some species and under certain circumstances, exit from MII occurs spontaneously without any obvious stimulation or morphological signs, which is so-called oocyte spontaneous activation (OSA). This mini-review summarizes two types of OSA. In the first type (e.g., most rat strains), oocytes can maintain MII arrest in vivo, but once removed out, oocytes undergo OSA with sister chromatids separated and eventually scattered in the cytoplasm. Because the stimulation is minimal (oocyte collection itself), this OSA is incomplete and cannot force oocytes into interphase. Notably, once re-activated by sperm or chemicals, those scattered chromatids will form multiple pronuclei (MPN), which may recapitulate certain MPN and aneuploidy cases observed in fertility clinics. The second type of OSA occurs in ovarian oocytes (e.g., certain mouse strains and dromedary camel). Without ovulation or fertilization, these OSA-oocytes can initiate intrafollicular development, but these parthenotes cannot develop to term due to aberrant genomic imprinting. Instead, they either degrade or give rise to ovarian teratomas, which have also been reported in female patients. Last but not the least, genetic models displaying OSA phenotypes and the lessons we can learn from animal OSA for human reproduction are also discussed.

Meiotic Instability Generates a Pathological Condition in Mammalian Ovum

Maintenance of metaphase-II (M-II) arrest in ovum is required to present itself as a right gamete for successful fertilization in mammals. Surprisingly, instability of meiotic cell cycle results in spontaneous exit from M-II arrest, chromosomal scattering and incomplete extrusion of second polar body (PB-II) without forming pronuclei so called abortive spontaneous ovum activation (SOA). It remains unclear what causes meiotic instability in freshly ovulated ovum that results in abortive SOA. We propose the involvement of various signal molecules such as reactive oxygen species (ROS), cyclic 3',5' adenosine monophosphate (cAMP) and calcium (Ca²⁺) in the induction of meiotic instability and thereby abortive SOA. These signal molecules through their downstream pathways modulate phosphorylation status and activity of cyclin dependent kinase (cdk1) as well as cyclin B1 level. Changes in phosphorylation status of cdk1 and its activity, dissociation and degradation of cyclin B1 destabilize maturation promoting factor (MPF). The premature MPF destabilization and defects in other cell cycle regulators possibly cause meiotic instability in ovum soon after ovulation. The meiotic instability results in a pathological condition of abortive SOA and deteriorates ovum quality. These ova are unfit for fertilization and limit reproductive outcome in several mammalian species including human. Therefore, global attention is required to identify the underlying causes in greater details in order to address the problem of meiotic instability in ova of several mammalian species icluding human. Moreover, these activated ova may be used to create parthenogenetic embryonic stem cell lines in vitro for the use in regenerative medicine.Graphical abstract.

Kinetics of meiotic maturation in oocytes from unstimulated ovaries and duration of pronucleus presence and preimplantation development

OBJECTIVE

To evaluate the meaning of meiotic maturation kinetics and duration of pronucleus presence (DPP) for parthenogenetic activation outcome.

DESIGN

Retrospective study.

SETTING

University hospital.

PATIENT(S)

Eight patients with endometrioid adenocarcinoma and 65 patients who underwent in vitro fertilization (IVF) with intracytoplasmic sperm injection (ICSI).

INTERVENTION(S)

After collection of oocytes from nonstimulated ovaries of patients with endometrioid adenocarcinoma, in vitro maturation (IVM) and parthenogenetic activation performed with time-lapse imaging; after ICSI, embryos similarly incubated with time-lapse imaging.

MAIN OUTCOME MEASURE(S)

Timing of the release of the first polar body (fPB), DPP, and developmental stage with IVM and parthenogenetic activation; after ICSI, assessment of DPP and preimplantation developmental stage.

RESULT(S)

With IVM, 55.2% of oocytes matured; 53.1% of fPBs were released within 24 hours, and 46.9% of fPBs were released after 24 hours. Regarding developmental stage, oocytes that released fPB later during IVM tended to develop more than oocytes that released the fPB within 24 hours. For embryos from parthenogenetic activation the DPP was statistically significantly shorter than the DPP of embryos from ICSI. With ICSI, the DPP was statistically significantly shorter in embryos that developed to ≥8 cells than embryos whose final development included ≤7 cells. The development rate in parthenogenetic activation was statistically significantly lower than that in ICSI.

CONCLUSION(S)

Embryo development is negatively affected by DPP that is too short or too long. When the DPP was short with parthenogenetic activation, embryo development did not proceed, indicating that DPP is an important determinant of parthenogenetic activation outcomes as with the timing of fPB release.