Sequential production of gametes during meiosis in trypanosomes

Meiosis is a core feature of eukaryotes that occurs in all major groups, including the early diverging excavates. In this group, meiosis and production of haploid gametes have been described in the pathogenic protist, Trypanosoma brucei, and mating occurs in the salivary glands of the insect vector, the tsetse fly. Here, we searched for intermediate meiotic stages among trypanosomes from tsetse salivary glands. Many different cell types were recovered, including trypanosomes in Meiosis I and gametes. Significantly, we found trypanosomes containing three nuclei with a 1:2:1 ratio of DNA contents. Some of these cells were undergoing cytokinesis, yielding a mononucleate gamete and a binucleate cell with a nuclear DNA content ratio of 1:2. This cell subsequently produced three more gametes in two further rounds of division. Expression of the cell fusion protein HAP2 (GCS1) was not confined to gametes, but also extended to meiotic intermediates. We propose a model whereby the two nuclei resulting from Meiosis I undergo asynchronous Meiosis II divisions with sequential production of haploid gametes.

BOARD INVITED REVIEW: Post-transfer consequences of in vitro-produced embryos in cattle

In vitro embryo production (IVP) in cattle has gained worldwide interest in recent years, but the efficiency of using IVP embryos for calf production is far from optimal. This review will examine the pregnancy retention rates of IVP embryos and explore causes for pregnancy failures. Based on work completed over the past 25 yr, only 27% of cattle receiving IVP embryos will produce a live calf. Approximately 60% of these pregnancies fail during the first 6 wk of gestation. When compared with embryos generated by superovulation, pregnancy rates are 10% to 40% lower for cattle carrying IVP embryos, exemplifying that IVP embryos are consistently less competent than in vivo-generated embryos. Several abnormalities have been observed in the morphology of IVP conceptuses. After transfer, IVP embryos are less likely to undergo conceptus elongation, have reduced embryonic disk diameter, and have compromised yolk sac development. Marginal binucleate cell development, cotyledon development, and placental vascularization have also been documented, and these abnormalities are associated with altered fetal growth trajectories. Additionally, in vitro culture conditions increase the risk of large offspring syndrome. Further work is needed to decipher how the embryo culture environment alters post-transfer embryo development and survival. The risk of these neonatal disorders has been reduced by the use of serum-free synthetic oviductal fluid media formations and culture in low oxygen tension. However, alterations are still evident in IVP oocyte and embryo transcript abundances, timing of embryonic cleavage events and blastulation, incidence of aneuploidy, and embryonic methylation status. The inclusion of oviductal and uterine-derived embryokines in culture media is being examined as one way to improve the competency of IVP embryos. To conclude, the evidence presented herein clearly shows that bovine IVP systems still must be refined to make it an economical technology in cattle production systems. However, the current shortcomings do not negate its current value for certain embryo production needs and for investigating early embryonic development in cattle.

MICRONUCLEI - AS A BIOMARKER OF GENOTOXICITY IN AUTOMOBILE MECHANICS OF WESTERN MAHARASHTRA

Objective: The aim of this study was to assess the potential cytogenetic damage associated with occupational exposure to polycyclic aromatic hydrocarbons (PAHs) among automobile mechanics (AMs) using micronuclei (MNs) and other nuclear abnormalities (NAs) such as binucleate cell (BN), karyorrhexis (KR), and karyolysis (KL) as biomarkers of genotoxicity.Methods: The study was conducted on 60 AMs between age group of 20–40 years who were working in automobile garages for more than 1 year from western Maharashtra, and 60 healthy males with same socioeconomic status were chosen as controls. AMs were divided into three groups based on their duration of exposure, i.e. 1–5 years, 6–10 years, and more than 11 years. The exfoliated buccal cells were obtained and fixed with methanol for 10 min. Then, air-dried and stained it with Giemsa stain. Statistical analysis was done using unpaired t-test for two groups and one-way ANOVA for multiple groups of exposures.Results: The mean values of MN, BN, KR, and KL in AMs (8.20, 13.57, 16.70, and 22.10, respectively) are significantly increased as compared to controls (5.10, 8.82, 12.30, and 16.12, respectively). As the year of exposure increased, the mean values of MN and other NAs were significantly increased in AMs (p<0.05).Conclusion: MN and other NAs reflect genetic changes and events associated with carcinogenesis. Therefore, the results of this study indicate that AMs exposed to PAHs are under risk of significant cytogenetic damage. Therefore, it is important to provide and to create better awareness of occupational hazards among these workers to promote occupational safety.

The Complex Containing Drosophila Myb and RB/E2F2 Regulates Cytokinesis in a Histone H2Av-Dependent Manner

In Drosophila , mutation of the oncogene Myb reduced the expression of mitotic genes, such as polo and ial , and caused multiple mitotic defects, including disrupted chromosome condensation and abnormal spindles. We now show that binucleate cells, the hallmark phenotype of cytokinesis failure, accumulate in Myb -null ovarian follicle cell and wing disc epithelia. Myb functions as an activator in the generally repressive D rosophila R BF, E 2F2, and M yb (dREAM)/Myb-MuvB complex. Absence of the dREAM subunit Mip130 or E2F2 suppressed the Myb -null cytokinesis defect. Therefore, we used Myb -null binucleate cells as a quantitative phenotypic readout of transcriptional repression by the dREAM complex. In the absence of Myb, the complex was sensitive to the dose of the subunits E2F2, Mip120, Caf1, and Lin-52 but not Mip130 or Mip40. Surprisingly, reduction of the dose of His2Av / H2A . z also suppressed the Myb -null binucleate cell phenotype, suggesting a novel role for this variant histone in transcriptional repression by the dREAM complex.