Gametogenesis
Frank J. Dye in Human Life Before Birth, 2019
The cells of the body may be classified into two categories: somatic cells and germ cells. Somatic cells are not directly involved in reproduction, and include muscle cells, skin cells, and bone cells. By contrast, germ cells are directly involved in reproduction. The subset of germ cells directly involved in fertilization are called gametes or sex cells and include spermatozoa and ova (or sperm and eggs). The formation of gametes is gametogenesis and comes in two varieties: spermatogenesis in men and oogenesis in women. Gametogenesis is the only process in the body involving meiosis (all other cell divisions are mitotic) and is confined to the gonads. However, during development, the germ cells arise outside the embryonic body and subsequently migrate into the developing gonads.
Cell Biology
C.S. Sureka, C. Armpilia in Radiation Biology for Medical Physicists, 2017
Meiotic cell division takes place in the germ cells of sexually reproducing organisms. It is a unique type of cell division that takes part in the formation of germ cells (megaspores–haploid spores) in the gonads (ovaries and testes) of sexually matured people during gametogenesis. But, it is not involved in cell multiplication. During meiosis, cell division occurs twice, but the DNA replication occurs only once. So the chromosome number is reduced from the diploid (2n = 46) to the haploid (n = 23). Crossing over or exchanges of similar segments between nonsister chromatids of homologous chromosomes also occur.
Fertilization and normal embryonic and early fetal development
Hung N. Winn, Frank A. Chervenak, Roberto Romero in Clinical Maternal-Fetal Medicine Online, 2021
Fertilization is the end of the complicated process of conjunction of gametes by entering one spermatozoon into the oocyte. The gamets, ovum and sperm, contain half of the number of the chromosomes (haploid) compared with the number present in somatic cells (diploid). They obtain haploid number of chromosomes through the process of meiosis during the gametogenesis (4). The oocyte is approximately 120 mm in diameter and has a thick membrane known as zona pellucida. The spermatozoon moves using the flagellum or tail, and the total length of the spermatozoon including the tail is 60 mm. Both oocyte and spermatozoon are highly specialized sex cells. Oocytes are produced in the ovary and expelled from it during the ovulation after which fimbriae of the fallopian tube sweep the oocyte into the ampulla where it can be fertilized. Sperms are produced in seminiferous tubules of the testes and stored in epididymis and ductus deferens. Ejaculation of semen results in the deposit of million sperms in the vagina around the external uterine os. They pass through the uterus and tubes and in the ampulla they surround the secondary oocyte if it is present. When the sperm enters the oocyte, the nucleus of the mature oocyte consists of the female pronucleus and the head of the sperm separates from the tail and enlarges to become male pronucleus. Fertilization is complete when the pronuclei unite and the maternal and paternal chromosomes intermingle during metaphase of the first mitotic division of the zygote. That cell is the primordium of the human being. The inification of the pronuclei restores a haploid number of chromosomes and completes the fertilization. Therefore, fertilization is a distinct moment when the diploid cell is formed and the development of an individual human begins (3).
Higher chromosomal abnormality rate in blastocysts from a subset of patients with pericentric inversion (Inv) 1 variant
Published in Human Fertility, 2023
In general, the outcome of chromosomal structural rearrangement can be associated with the gender of carriers. However, our result showed that although the unbalanced translocation rate in embryos was twice as high for male compared to female carriers, there was no statistically significant difference between these two groups. This inconsistency may largely have stemmed from the small sample size of our study since there have been some reports on the effect of gender of the inversion carrier on meiotic segregation. Thus, Xie et al. (2019) analysed 379 blastocysts from 94 PEI carriers and found that the PGT outcome in PEI carriers was affected by their gender (Xie et al., 2019). However, the chromosome distribution in this report by Xie et al. was broad and included all 23 chromosome pairs. The meiotic segregation mechanism of this phenomenon is largely unknown, but some investigators have suggested that interference of meiotic cell division affects male and female gametogenesis in a different way.
Effect of anti-Müllerian hormone in hypothalamic Kiss-1- and GnRH-producing cell models
Published in Gynecological Endocrinology, 2021
Aki Oride, Haruhiko Kanasaki, Tuvshintugs Tumurbaatar, Zolzaya Tumurgan, Hiroe Okada, Satoru Kyo
Mammalian reproductive function is controlled by the pituitary gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which concomitantly regulate gametogenesis and steroid synthesis. Gonadotropin synthesis and secretion in pituitary gonadotrophs are mainly under the control of gonadotropin-releasing hormone (GnRH) from the hypothalamus. Furthermore, hypothalamic kisspeptin, which is encoded by the Kiss-1 gene, governs GnRH release [1,2]. Kisspeptin-producing neurons (Kiss-1 neurons) in the hypothalamus regulate GnRH neurons which are distributed in the preoptic area and anterior hypothalamus in rodents. At present, it is generally agreed that Kiss-1 neurons in the anteroventral periventricular (AVPV) region regulate the estradiol (E2)-induced GnRH/LH surge. On the other hand, Kiss-1 neurons in the arcuate nucleus (ARC) regulate the pulsatile release of GnRH, which is under the control of E2-induced negative feedback mechanisms [2]. This concept is based on work showing that E2 upregulated Kiss-1 expression in the AVPV region but repressed that in the ARC region [3,4].
Sexual dimorphism in ultradian and 24h rhythms in plasma levels of growth hormone in Indian walking catfish, Clarias batrachus
Published in Chronobiology International, 2021
Raj Naresh Gopal, Dhanananajay Kumar, Vinay Kumar Singh, Atanu Kumar Pati, Bechan Lal
In fish, GH has been further reported to influence gametogenesis (Kajimura et al. 2004), gonadal steroidogenesis (Singh et al. 1988), vitellogenesis (Björnsson et al. 1994; Mosconi et al. 2002), and oocyte maturation (Sarang and Lal 2005). A previous report (Peng and Peter 1997) revealed that GH secretion is controlled by several metabolic and reproductive hormones. These metabolites, sex steroids, thyroid hormones, and neuroendocrine secretions interact and coordinate together to regulate GH secretion and maintain its rhythmicity (Peng and Peter 1997). In catfish, in-vivo injection of sGnRH, testosterone, and morphine caused a significant increase in plasma GH secretion. Whereas, 5-hydroxy tryptophan resulted in lowered GH levels in a dose-dependent manner (Lal and Singh 2005), indicating the role of several internal metabolic factors in regulating GH plasma production. Therefore, based on the published literature, we infer that such apparent 24 h variation in plasma GH in catfish seems to have physiological roles. For instance, GH may regulate gonadal and somatic growth and may affect reproductive processes in catfish. In female catfish, GH shows different effects on somatic growth and ovarian development. The differential effect of GH was observed to depend on the season and on the time during the 24 h of its administration (Singh and Lal 2008). Similarly, in male catfish, GH caused enhanced testicular steroidogenic and spermatogenic activities. This increase further shows dependence on photoperiod and water temperature (Gopal et al. 2014).
Related Knowledge Centers
- Cell Division
- Gonad
- Ploidy
- Gamete
- Meiosis
- Precursor Cell
- Biological Life Cycle
- Gametocyte
- Alternation of Generations
- Testicle