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Aneuploidy in Human Oocytes and Preimplantation Embryos
Published in Carlos Simón, Carmen Rubio, Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
Oocytes and spermatocytes halve their chromosome numbers by a specialized division known as “meiosis.” Although the chromosome content in sperm and activated oocytes are the same, their development to mature gametes is highly dimorphic. Primordial germ cells migrate to the genital ridges during fetal development and the gonadal environment determines whether the cells induce meiosis (oocyte) or remain arrested until puberty (males) (20). Mouse studies have shown that fetal oocytes initiate meiosis and differentiation due to the presence of retinoic acid in the fetal ovary (67,68). The fetal oocytes replicate their DNA forming sister chromatids that are cohesed together. During meiotic prophase I, the homologous chromosomes align and recombine (69), which forms the bivalent chromosome structure (Figure 8.6). The oocytes then enter a prolonged arrest (dictyate) until menarche, when a single follicle matures and the egg completes the first meiotic division. Oocyte numbers within the ovary are depleted from fetal development until the onset of menopause. Only 450 of the 5–7 million fetal oocytes complete the first meiotic division, and even fewer go on to segregate sister chromatids after fertilization, which induces the completion of the second meiotic division (70).
Regulation of Reproduction by Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
The specific roles of genetics vs. hormones in sexual differentiation of the brain is covered in Section 10.2 and Figure 10.1. Here the focus is on the development and differentiation of the male and female internal and external genitalia. Whether possessing an XX or and XY karyotype, every human embryo goes initially through an ambisexual stage with the potential to acquire either masculine or feminine characteristics. As illustrated in Figure 10.17A, a 4- to 6-week-old human embryo has indifferent gonads, a pair of Wolffian ducts capable of forming male internal genitalia, a pair of Müllerian ducts serving as the anlage of the internal female genitalia, and bipotential structures of the external genitalia (Figure 10.17B). Depending on the genetic program, the inner medullary tissue of the indifferent gonad will become the testicular components (in response to SRY), while the outer cortical tissue will develop into an ovary in the absence of SRY. Accordingly, the primordial germ cells will become spermatogonia or oogonia.
Testicular stem cells, spermatogenesis and infertility
Published in Rajender Singh, Molecular Signaling in Spermatogenesis and Male Infertility, 2019
Deepa Bhartiya, Sandhya Anand, Hiren Patel, Ankita Kaushik, Sreepoorna Pramodh
Understanding testicular stem cells biology is of utmost importance, since it regulates the daily production of sperm by a process termed spermatogenesis. In this chapter, we describe the journey of sperm production that begins early on during development with the migration of primordial germ cells (PGCs). With recent advances in technologies available, like lineage tracing, germ cell transplantation, germ cell ablation, etc., reproductive biologists are now well equipped to unfold the mysteries behind the true nature and biology of testicular stem cells. Any adverse effect on spermatogenesis would result in reduced sperm count, infertility and sometimes could even lead to cancer. This basic understanding of testicular stem cells is also required to comprehend the deleterious effects of oncotherapy on the testes and whether the non-functional testis could be coaxed to enter a regeneration pathway to produce sperm that will help improve the quality of life of cancer survivors.
Pediatric Primary Yolk Sac Tumour of the Kidney: Recommendations for Pretreatment Diagnosis
Published in Fetal and Pediatric Pathology, 2023
Shilpi Thakur, Aanchal Kakkar, Manisha Jana, Prasenjit Das, Sandeep P. Agarwala, Venkateswaran K. Iyer
Germ cell tumors (GCTs) arise from differentiation of primordial germ cells. They most frequently occur in the gonads, but can arise at extra-gonadal sites, either in midline or non-midline locations. Extra-gonadal GCTs account for 1–2.5% of all GCTs, most commonly occur in the mediastinum and retroperitoneum, and have been reported at other unusual locations such as nasal sinuses, prostate, vagina and stomach [6]. Yolk sac tumor (YST) is a malignant GCT resembling extraembryonic structures including yolk sac, allantois, and extraembryonic mesenchyme [7, 8]. GCTs arising in unusual extragonadal locations are often unsuspected clinically, and due to their wide morphological spectrum, may resemble more common primary malignancies occurring in that organ. In core biopsies, all morphological features may not be evident, further enhancing the difficulty and resulting in erroneous diagnosis. We present an intrarenal YST initially misdiagnosed as Wilms tumor on core biopsy, which on resection was a YST, to emphasize that not all pediatric renal tumors are nephroblastoma. A pre-operative alpha-fetoprotein may have helped avoid this misdiagnosis.
Spectrum and tissue distribution of RB1 pathogenic alleles in mosaic retinoblastoma patients
Published in Ophthalmic Genetics, 2022
Yan Zhang, Wen-Bin Wei, Junyang Zhao, Xiaolin Xu, Fufeng Wang
The correlation between mosaicism level and heritability risk is important. Following primordial germ cell (PGC) differentiation embryonic cells are restricted to either somatic or germ tissues. Variant alleles occurring before this developmental period can be present in both types of tissues (8). The abundance of mutant somatic cells may reflect the timing of variant allele occurrence and potentially predict the risk for a variant allele to be transmitted to the offspring. Rushow et al. reported eight mosaics with RB1 variant alleles at levels ranging from 5% to 25% who were followed until child-bearing age. Three had children or a fetus who carried their RB1 variant alleles. The lowest level of mosaicism among those three parents was 7.5%. However, another patient with RB1 variant allele (c.763C>T) was detected to have 7.5% mutant DNA in blood but no variant allele in his sperm (7). Due to the interplay of multiple factors mosaicism levels are not necessarily proportional to heritability risk. It is important to note that in pure germline mosaicism the variant alleles may be transmitted to offspring but not detectable in blood. A sufficient number of adults who are mosaic for RB1 variant alleles is necessary in order to correlate the percentage of mosaicism with the probability of having affected offspring or positive mosaicism in sperm (i.e. germline mosaicism). However, there appears to be no clear-cut demarcation to distinguish between somatic and germline mosaicism.
Aluminum reproductive toxicity: a summary and interpretation of scientific reports
Published in Critical Reviews in Toxicology, 2020
The development of an oocyte begins as a primordial germ cell. Early in embryonic development these cells migrate into the future site of the ovaries, undergo meiotic cell division, and multiply, resulting in primary oocytes (primordial follicle) within the ovary. Their development is arrested until puberty, when follicle stimulating hormone (FSH) produced by the pituitary gland stimulates some to begin to mature, developing through follicle stages (primary, secondary, and if fertilized tertiary (Graafian) follicles), in the process of folliculogenesis. Most die (atresia) during these stages. During the resumption of cell division, the oocyte’s nucleus (germinal vesicle) breaks down and the first polar body (that forms concomitantly during oocyte division) is extruded. Follicle cells secrete and release estrogen that feeds back to the pituitary gland to decrease FSH release and increase luteinizing hormone (LH) release. This causes the follicle to rupture, resulting in release of the egg (ovulation), that migrates into the fallopian tubes where it can be fertilized by sperm. The ruptured follicle forms a corpus luteum, a transitory endocrine organ that secretes estrogen and progesterone. The latter feeds back to the pituitary gland to decrease LH release. The fertilized oocyte forms a mature egg cell (ovum). When the oocyte and sperm chromosomes combine, it becomes a zygote, which divides as it migrates into the uterus, creating the pregnant (gravid) state.