A maternal dorsoventral prepattern revealed by an asymmetric distribution of ventralizing molecules before fertilization in Xenopus laevis

The establishment of the embryonic dorsoventral axis in Xenopus occurs when the radial symmetry around the egg's animal-vegetal axis is broken to give rise to the typical symmetry of Bilaterians. We have previously shown that the Notch1 protein is ventrally enriched during early embryogenesis in Xenopus laevis and zebrafish and exerts ventralizing activity through β-Catenin destabilization and the positive regulation of ventral center genes in X. laevis. These findings led us to further investigate when these asymmetries arise. In this work, we show that the asymmetrical distribution of Notch1 protein and mRNA precedes cortical rotation and even fertilization in X. laevis. Moreover, we found that in unfertilized eggs transcripts encoded by the ventralizing gene bmp4 are also asymmetrically distributed in the animal hemisphere and notch1 transcripts accumulate consistently on the same side of the eccentric maturation point. Strikingly, a Notch1 asymmetry orthogonal to the animal-vegetal axis appears during X. laevis oogenesis. Thus, we show for the first time a maternal bias in the distribution of molecules that are later involved in ventral patterning during embryonic axialization, strongly supporting the hypothesis of a dorsoventral prepattern or intrinsic bilaterality of Xenopus eggs before fertilization.

Whole transcriptome screening for novel genes involved in meiosis and fertility in Drosophila melanogaster

Reproductive success requires the development of viable oocytes and the accurate segregation of chromosomes during meiosis. Failure to segregate chromosomes properly can lead to infertility, miscarriages, or developmental disorders. A variety of factors contribute to accurate chromosome segregation and oocyte development, such as spindle assembly and sister chromatid cohesion. However, many proteins required for meiosis remain unknown. In this study, we aimed to develop a screening pipeline for identifying novel meiotic and fertility genes using the genome of Drosophila melanogaster. To accomplish this goal, genes upregulated within meiotically active tissues were identified. More than 240 genes with no known function were silenced using RNA interference (RNAi) and the effects on meiosis and fertility were assessed. We identified 94 genes that when silenced caused infertility and/or high levels of chromosomal nondisjunction. The vast majority of these genes have human and mouse homologs that are also poorly studied. Through this screening process, we identified novel genes that are crucial for meiosis and oocyte development but have not been extensively studied in human or model organisms. Understanding the function of these genes will be an important step towards the understanding of their biological significance during reproduction.

Finishing the egg

Gamete development is a fundamental process that is highly conserved from early eukaryotes to mammals. As germ cells develop, they must coordinate a dynamic series of cellular processes that support growth, cell specification, patterning, the loading of maternal factors (RNAs, proteins, and nutrients), differentiation of structures to enable fertilization and ensure embryonic survival, and other processes that make a functional oocyte. To achieve these goals, germ cells integrate a complex milieu of environmental and developmental signals to produce fertilizable eggs. Over the past 50 years, Drosophila oogenesis has risen to the forefront as a system to interrogate the sophisticated mechanisms that drive oocyte development. Studies in Drosophila have defined mechanisms in germ cells that control meiosis, protect genome integrity, facilitate mRNA trafficking, and support the maternal loading of nutrients. Work in this system has provided key insights into the mechanisms that establish egg chamber polarity and patterning as well as the mechanisms that drive ovulation and egg activation. Using the power of Drosophila genetics, the field has begun to define the molecular mechanisms that coordinate environmental stresses and nutrient availability with oocyte development. Importantly, the majority of these reproductive mechanisms are highly conserved throughout evolution, and many play critical roles in the development of somatic tissues as well. In this chapter, we summarize the recent progress in several key areas that impact egg chamber development and ovulation. First, we discuss the mechanisms that drive nutrient storage and trafficking during oocyte maturation and vitellogenesis. Second, we examine the processes that regulate follicle cell patterning and how that patterning impacts the construction of the egg shell and the establishment of embryonic polarity. Finally, we examine regulatory factors that control ovulation, egg activation, and successful fertilization.

A systematic review on the effects of acrylamide and bisphenol A on the development of Drosophila melanogaster

The current global scenario has instigated a steady upsurge of synthetic chemicals usage thereby creating a toxic environment unsuitable for animals and humans. Acrylamide and bisphenol A are some of the most common toxins found in the atmosphere due to their extensive involvement in numerous industrial processes. Acrylamide, an occupational hazard toxin has been known to cause severe nerve damage and peripheral neuronal damage in both animals and humans. General sources of acrylamide exposure are effluents from textile and paper industries, cosmetics, and thermally processed foods rich in starch. Bisphenol A (BPA) is generally found in food packaging materials, dental sealants, and plastic bottles. It is highly temperature-sensitive that can easily leach into the food products or humans on contact. The genotoxic and neurotoxic effects of acrylamide and bisphenol A have been widely researched; however, more attention should be dedicated to understanding the developmental toxicity of these chemicals. The developmental impacts of toxin exposure can be easily understood using Drosophila melanogaster as a model given considering its short life span and genetic homology to humans. In this review, we have discussed the toxic effects of acrylamide and BPA on the developmental process of Drosophila melanogaster.

Developmental and behavioural toxicity induced by acrylamide exposure and amelioration using phytochemicals in Drosophila melanogaster

Acrylamide, an environmental pollutant, is known to occur in food substances cooked at high temperatures. Studies on various models indicate acrylamide to cause several physiological conditions such as neuro- and reproductive toxicity, and carcinogenesis. In our study, exposure of Drosophila melanogaster (Oregon K strain) to acrylamide via their diet resulted in a concentration and time-dependent mortality, while the surviving flies exhibited significant locomotor deficits, most likely due to oxidative stress-induced neuronal damage. Also, Drosophila embryos exhibited signs of developmental toxicity as evidenced by the alteration in the migration of border cells and cluster cells during the developmental stages, concomitant to modulation in expression of gurken and oskar genes. Curcumin, a known antioxidant has been widely studied for its neuroprotective effects against acrylamide; however; very few studies focus on thymoquinone for its role against food toxicant. Our research focuses on the toxicity elicited by acrylamide and the ability of the antioxidants: thymoquinone, curcumin and combination of thereof, in reversing the same.