Regulation of Reproduction by Dopamine
Nira Ben-Jonathan in Dopamine, 2020
After fertilization, the zygote undergoes several mitotic divisions and forms a solid ball, the morula, which travels down the oviduct toward the uterus (Figure 10.15). Upon reaching the 20–30 cell stage, the morula starts a process of differentiation and cavitation to form a blastocyst. The blastocyst, still surrounded by the ZP, is composed of three regions: (1) an inner cell mass, which will develop into the embryo; (2) a surrounding outer layer called the trophoblast, which will develop into the placenta; and (3) a fluid-filled cavity called the blastocoele. DA-producing pluripotent cells isolated from the inner cell mass of preimplantation monkey blastocysts provided evidence for a very early expression of DA, even before implantation [84]. Yet, what functions are fulfilled by this DA in implantation and/or in growth of the embryo, remain to be determined.
Reproductive system
David Sturgeon in Introduction to Anatomy and Physiology for Healthcare Students, 2018
Following fertilisation, the zygote undergoes a process of rapid mitotic divisions known as cleavage. The first cleavage division produces two identical cells called blastomeres that continue to divide to produce four cells, then eight cells and so on. By day 4, the zygote (or pre-embryo) has become a cluster of between 16 and 32 cells forming a ball-shaped structure known as the morula (Latin for ‘mulberry’). As the morula progresses along the fallopian tube towards the uterus, it begins to hollow out to produce a fluid-filled space called the blastocoel or blastocyst cavity. This contains a mass of cells known as a blastocyst that will eventually develop into the embryo. At about day 5, the blastocyst frees itself from the layer of cells that surround it (the zona pellucida) and floats freely in the uterus. During the following days, it presses up against the endometrium and begins the process of implantation. Enzymes break down endometrial cells and capillary walls, which allows the blastocyst to penetrate and implant into the endometrium. The blastocyst continues to secrete human chorionic gonadotropin (hCG) to ensure the corpus luteum maintains production of progesterone until the placenta can take over. Implantation is complete by about 12 days after fertilisation and, over the next few weeks, the placenta (Latin for ‘flat cake’) begins to develop.
Integrin Function in Early Vertebrate Development: Perspectives from Studies of Amphibian Embryos
Yoshikazu Takada in Integrins: The Biological Problems, 2017
Mechanistically, the process of gastrulation may be considered on several levels that include: (1) the “behavior” of the individual cells that collectively serve to “drive” morphogenesis at gastrulation, (2) the molecules mediating the shape changes and adhesive properties of these cells, and (3) the control of the timing and patterning of the cellular movements involved. Following the progression through early cleavage and blastula stages, gastrulation begins with the appearance of a slit-like invagination of bottle cells, termed the blastopore, on the dorsal side of the embryo as illustrated in Figure 1. The involuting mesoderm subsequently comes in contact with the blastocoel roof and travels along it in the direction of the animal pole. The zone of involution initiated at the dorsal lip of the blastopore spreads laterally and ventrally to enclose the endoderm, which remains visible as a yolk plug through late gastrulation. The superficial cells of the animal pole and equatorial marginal zone spread by epiboly during this process, thus covering the entire outer surface of the embryo. Inside the embryo, the endodermally derived archenteron forms as the mesoderm advances, resulting in the displacement of the blastocoel (Figure 1).
Frozen-thawed blastocyst transfer in natural cycle increase implantation rates compared artificial cycle
Published in Gynecological Endocrinology, 2019
Daniella Fernanda Cardenas Armas, Juana Peñarrubia, Anna Goday, Marta Guimerá, Ester Vidal, Dolors Manau, Francesc Fabregues
Embryo quality was assessed daily under an inverted microscope according to the number and evenness of blastomeres, rate of fragmentation, presence of multinucleation, early compactation, and cell division rate [11]. According to the morphological grading, day 3 embryos were scored on a scale of 1 (top quality) to 4 (bad quality). After fresh embryo transfer on day 3, supernumerary embryos with top or good quality (grades 1–2) were cryopreserved. Embryos graded as fairly quality (grade 3) were extendedly cultured up to day5 for possible cryopreservation at the blastocyst stage. The quality of blastocysts was assessed according to the criteria of Gardner and Schoolcraft [12] based on the degree of expansion of the blastocoele cavity and the size and the cohesiveness of the inner cell mass and the trophectoderm. Blastocysts were considered suitable for cryopreservation when the blastocoele cavity filled more than half of the volume of the embryo and the trophectoderm and inner cell mass were clearly visible.
Influence of post-thaw culture duration on pregnancy outcomes in frozen blastocyst transfer cycles
Published in Systems Biology in Reproductive Medicine, 2023
Hui Ji, Shanren Cao, Hui Ding, Li Dong, Chun Zhao, Junqiang Zhang, Jing Lu, Xiuling Li, Xiufeng Ling
The selection criteria for thawed embryos before transfer must be carefully planned and rigorous to maximize the pregnancy outcomes. Normally, embryos are transferred after a short culture duration, that is, after thawing for 1–6 h (Ahlstrom et al. 2013; Ferreux et al. 2018; Tubbing et al. 2018). In contrast, some fertility centers use a long post-thaw culture interval (16–24 h) (Kang et al. 2013; Haas et al. 2016; Yang et al. 2016). One advantage of having the different protocols is the flexibility of laboratory workflow; embryos can be thawed in the afternoon one day before transfer on a working day or in the morning of a transfer day during weekends and holidays (Fang et al. 2016). Moreover, the uterine cavity is an optimal incubator, and in vitro embryo culture conditions cannot replicate the fallopian tube and uterine environments in vivo. As such, some blastocysts fail to develop in vitro but can show high implantation rates in vivo (Haas et al. 2018). Therefore, a short post-thaw culture protocol is more feasible. However, several publications have suggested that a short culture period might be insufficient to evaluate the developmental potential of blastocysts and that a long culture period could increase the degree of blastocoel expansion and provide more valuable information required for the selection of embryos (Guerif et al. 2003; Du et al. 2016; Minasi et al. 2016; Herbemont et al. 2018).
The age-related required number of zygotes estimated from prior clinical studies of preimplantation genetic testing for aneuploidy (PGT-A)
Published in Systems Biology in Reproductive Medicine, 2023
Tasuku Mariya, Takeshi Sugimoto, Takema Kato, Toshiaki Endo, Hiroki Kurahashi
Table 2 summarizes the prior studies used for our current calculations. Since the reported finding of Gardner and colleagues that transferring blastocyst stage embryos can improve the pregnancy rate (Gardner et al. 1998), many studies have further investigated this phenomenon. However, few subsequent reports have confirmed the development rate of zygotes to blastocysts by age group. The investigation by Kato et al. (2012) was relatively large-scale with detailed age grouping but was a single-center study using a minimal ovarian stimulation method. Warshaviak et al. (2019) described the development rate from a zygote to the 8-cell stage in two age groups. Although the relatively older report by Janny and Menezo (1996) satisfied the inclusion criteria for our current analyses, we used the most recent large-scale report by Sainte-Rose et al. (2021) to estimate the rate of zygotes that will develop a useful blastocyst. Useful blastocysts were defined morphologically, based on the expansion of the blastocoel cavity (B1–B6) and the number and cohesiveness of the inner cell mass (ICM) and trophectoderm (TE) cells (Gardner et al. 1998). Sainte-Rose et al. grouped blastocysts morphologically as ‘good’ (B3–B6, AA/AB/BA/BB) or ‘average’ (B3–B6, AC/CA/BC/CB) with regard to useful blastocysts in their investigation (Sainte-Rose et al. 2021).
Related Knowledge Centers
- Gastrulation
- Inner Cell Mass
- Trophoblast
- Cellular Differentiation
- Blastocyst
- Blastulation
- Animal Embryonic Development
- Cleavage
- Zygote
- Fertilisation