page_title: Maternal effect
section_title: In Drosophila early embryogenesis
hierarchical_section_title: Maternal effect / Maternal effects in genetics / In Drosophila early embryogenesis
caption_attribution_description: English: Ribonucleoprotein particles (GFP-Imp) in the Drosophila melanogaster egg chamber, being transported from the nurse cells to the oocyte. Scale bar indicates 10µm.
context_page_description: A maternal effect is a situation where the phenotype of an organism is determined not only by the environment it experiences and its genotype, but also by the environment and genotype of its mother. In genetics, maternal effects occur when an organism shows the phenotype expected from the genotype of the mother, irrespective of its own genotype, often due to the mother supplying messenger RNA or proteins to the egg. Maternal effects can also be caused by the maternal environment independent of genotype, sometimes controlling the size, sex, or behaviour of the offspring. These adaptive maternal effects lead to phenotypes of offspring that increase their fitness. Further, it introduces the concept of phenotypic plasticity, an important evolutionary concept. It has been proposed that maternal effects are important for the evolution of adaptive responses to environmental heterogeneity.
context_section_description: A Drosophila melanogaster oocyte develops in an egg chamber in close association with a set of cells called nurse cells. Both the oocyte and the nurse cells are descended from a single germline stem cell, however cytokinesis is incomplete in these cell divisions, and the cytoplasm of the nurse cells and the oocyte is connected by structures known as ring canals. Only the oocyte undergoes meiosis and contributes DNA to the next generation.
  Many maternal effect Drosophila mutants have been found that affect the early steps in embryogenesis such as axis determination, including bicoid, dorsal, gurken and oskar. For example, embryos from homozygous bicoid mothers fail to produce head and thorax structures.
  Once the gene that is disrupted in the bicoid mutant was identified, it was shown that bicoid mRNA is transcribed in the nurse cells and then relocalized to the oocyte. Other maternal effect mutants either affect products that are similarly produced in the nurse cells and act in the oocyte, or parts of the transportation machinery that are required for this relocalization. Since these genes are expressed in the (maternal) nurse cells and not in the oocyte or fertilised embryo, the maternal genotype determines whether they can function.
  Maternal effect genes are expresses during oogenesis by the mother (expressed prior to fertilization) and develop the anterior-posterior and dorsal ventral polarity of the egg. The anterior end of the egg becomes the head; posterior end becomes the tail. the dorsal side is on the top; the ventral side is in underneath. The products of maternal effect genes called maternal mRNAs are produced by nurse cell and follice cells and deposited in the egg cells (oocytes). At the start of development process, mRNA gradients are formed in oocytes along anterior-posterior and dorsal ventral axes.
  About thirty maternal genes are involved in pattern formation have been identified. In particular, products of four maternal effect genes are critical to the formation of anterior-posterior axis. The product of two maternal effect gene, bicoid and hunchback, regulates formation of anterior structure while another pair nanos and caudal, specifies protein that regulates formation of posterior part of embryo.
  The transcript of all four genes-bicoid, hunchback, caudal, nanos are synthesized by nurse and follicle cells and transported into the oocytes.
caption: Protein and RNA are transported in particles (white dots) from the nurse cells (maternal) to the developing oocyte in Drosophila melanogaster. Scale bar shows 10µm.
exif: {}