Cell division
Frank J. Dye in Human Life Before Birth, 2019
We can think of each chromosome as being composed of two identical lengthwise halves called chromatids (Figure 3.4). The chromatids are held together at a constricted region called the centromere. On either side of the centromere, there protrudes an arm. If the centromere is located midway between the two ends of the chromosome, it has arms of equal length and is called a metacentric chromosome (if the centromere is not exactly at the midpoint, the resulting chromosome will be submetacentric). Conversely, if the centromere is closer to one end of the chromosome than the other, it is an acrocentric chromosome. The short and long arms of an acrocentric chromosome are referred to by the letters p (petite) and q (the next letter in the alphabet), respectively. We humans have metacentric, submetacentric, and acrocentric chromosomes (Figure 3.5).
Genetics
Manoj Ramachandran, Tom Nunn in Basic Orthopaedic Sciences, 2018
Chromosomes are composed of DNA, ribonucleic acid (RNA), polysaccharides and histone and non-histone proteins. Normally chromosomes cannot be seen under a light microscope, but during cell division they become condensed, allowing visualization at 1000× magnification. Chromosomes are thin thread-like structures that have a short p arm and a long q arm separated by a constriction known as the centromere (Figure 2.1). The chromosomes have three basic shapes depending on the centromere location. Metacentric chromosomes have p and q arms of approximately equal length, e.g. chromosome 1. Submetacentric chromosomes have p and q arms of differing lengths, e.g. chromosome 6. In acrocentric chromosomes, the centromere is near one end and, therefore, there is a very small p arm and a correspondingly longer q arm, e.g. chromosome 13.
Preimplantation Genetic Testing for Structural Rearrangements
Carlos Simón, Carmen Rubio in Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
Robertsonian translocations involve two acrocentric chromosomes (in humans, chromosomes 13, 14, 15, 21, and 22 are acrocentric chromosomes) joined at the centromere with loss of their short arms (p arm); this reduces the chromosome number to 45 (instead of 46) with no phenotypic effect (Figure 12.2a). In these translocations, chromosomes form a trivalent at the pachytene stage of meiosis (Figure 12.2b). Then the chromosomes can segregate by four modes, resulting in eight different embryo outcomes [20]. Only one mode can result in a genetically healthy ongoing pregnancy. The remaining modes of segregation lead to nullisomic or disomic gametes, generating chromosomally unbalanced embryos (monosomic or trisomic embryos) [22].
An intercomparison exercise to compare scoring criteria and develop image databank for biodosimetry in South Korea
Published in International Journal of Radiation Biology, 2021
Yang Hee Lee, Younghyun Lee, Hyo Jin Yoon, Su San Yang, Hae Mi Joo, Ji Young Kim, Seong-Jun Cho, Wol Soon Jo, Soo Kyung Jeong, Su Jung Oh, Yeong-Rok Kang, Ki Moon Seong
Variations in scoring dicentrics were often found when chromosomes with centromeres in terminal positions (D or G group) formed dicentrics, which were similarly reported in a previous study (Romm et al. 2017). Chromosomes 13, 14, 15, 21, and 22 are acrocentric chromosomes, which have short p arms and the centromere is located near one end of the chromosome. One laboratory identified dicentric chromosomes based on the specific morphology of each chromosome (Figure 2), whereas the others considered it a fragment due to less visible centromeres. All participating laboratories agreed that understanding the morphology of D and G group chromosomes would help to identify dicentrics correctly. In addition, scoring results were different when chromosomes were twisted. Some scorers confused a twisted chromosome with a dicentric chromosome. According to experienced scorers’ comments, the twisted area in a chromosome is darker than centromere, including the centromere (Figure 3), which should allow easy discrimination of dicentrics and twisted chromosomes.
CDKN2A Depletion Causes Aneuploidy and Enhances Cell Proliferation in Non-Immortalized Normal Human Cells
Published in Cancer Investigation, 2018
Zofia Hélias-Rodzewicz, Nelson Lourenco, Mariama Bakari, Claude Capron, Jean-François Emile
Analysis of metaphase spreads was performed in seven-day interval silencing experiments and revealed that the inhibition of each candidate gene induced aneuploidy. The number of abnormal metaphases was higher in candidate genes siRNA-treated cells than in the controls. These findings were similar for both cell lines (Figure 1(A,B)) (p < 0.05). For each experimental condition, at least 50 metaphases were analyzed, except for some CDCA8, CCNDBP1, and TP53BP1 experiments. For CHEK2, CCNDBP1, TP53BP1, and CDKN2A, these chromosome instability results were confirmed in 21-day experiments (Figure 1(C)). The most common chromosome alterations were losses of 1 or 2 chromosomes (Figure S4). In IMR-90 cells, the presence of aneuploidy after candidate gene silencing was validated by fluorescence in situ hybridization (FISH) with centromere probes for four different chromosomes (chromosomes 6, 12, 16, 17) (Figure 1(D), Figure S5). FISH also showed that silencing the expression of the candidate genes did not induce polyploidy (Figure 1(E)).
The association between serum sex hormone-binding globulin changes during progestin-primed ovarian stimulation and embryo outcomes: a retrospective cohort study
Published in Gynecological Endocrinology, 2022
Kai Deng, Kui Fu, Yueyue Hu, Ying Zhang, Changjun Zhang
SHBG is produced and secreted primarily by the liver, and it is positively correlated with the metabolic level [18]. Many studies have suggested that SHBG is closely related to metabolic activity. Patients with insulin resistance (IR), type 2 diabetes mellitus (T2D), fatty liver and other metabolic diseases have lower SHBG levels than normal people [19–21]. Oocyte meiosis utilizes a large amount of energy. The normal function of motor proteins and centromere-related kinases requires a high ATP supply, and their abnormal functions lead to abnormal spindle assembly, chromosome arrangement and, eventually, aneuploid oocytes [22]. The mitochondria of human embryos are all from oocytes, and the mitochondrial genetic pattern of embryos at stages 2–4 cells is disproportionate. The cleavage of embryos lacking mitochondria tends to cause cell lysis and death, and sufficient energy is key to the development of embryos [23]. Energy metabolism is crucial for oocyte maturation, fertilization and embryonic development [24]. Therefore, the increase in SHBG at the late follicular phase and on the HCG day is related to the more active cell metabolic state, which may be an important reason for the positive correlation between SHBG and oocyte/embryo quality. Hence, we reason that the SHBG elevation in the late follicular phase and on the HCG day provides adequate energy and optimizes the metabolism of fatty acids and glucose in follicles for appropriate ovarian function regulated by HNF-4α. HNF-4α upregulates downstream target gene expression of SHBG, TTR and PPL, improving the developmental competence of oocytes.