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Browsing by Subject "Vertebrate development"

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    Temporal and Spatial Requirement of the Nodal induced head mesendoderm in neurulation AND An inexpensive, efficient method for regular egg collection from a zebrafish in a recirculating system
    (2013-07) Gonsar, Ngawang Youdon
    Chapter 2 Zebrafish in our laboratory are usually bred by removing the fish from the recirculating aquatic system and placing them into 1-2 L spawning tanks. These spawning tanks consist of a bottom reservoir, a lid, and an insert that fits in closely into the bottom reservoir. When the fish breed, the eggs fall through holes of the insert and into the reservoir, thus preventing them from being cannibalized. Because fish in these spawning tanks are not fed and do not get fresh water, they are bred only once a week. During a period where we had high demand for embryos, we instead tried breeding the fish for multiple consecutive days on the recirculating system. Fish were placed into the spawning insert as usual, but the insert was placed into the home tank instead of into the bottom reservoir. We found that there was no significant difference in the number of fertilized eggs produced between the spawning tank and home tank breeding methods. Further, the fish in the home tanks regularly produced fertile embryos over a 28-day time course, with the highest number of eggs per pair produced by the tank with only one pair of adult fish. This method is time-saving as fish bred in home tanks only require to be set up once. It is also an effective way to collect embryos over long periods from the same pair or group of fish and to more easily obtain embryos from stocks with low spawning frequency. Chapter 3 The neural tube is the precursor to the brain and spinal cord. Failure of neural tube closure in humans is one of the most common causes of birth defects. Zebrafish with a decrease in Nodal signaling have a phenotype that is analogous to the fatal human birth defect anencephaly, which is caused by an open anterior neural tube. Previous work in our laboratory has found that Nodal signaling acts through the induction of the head mesendoderm and anterior mesoderm, which underlie the anterior neural tube. Using a pharmacological approach, we determined that Nodal signaling is required up to the late blastula stage of 4.3 hpf for a closed neural tube. This falls within the developmental period when Nodal signaling is most active in mesendoderm and mesoderm induction, supporting the model that Nodal acts through the induction of these tissues. We also found there was a strong correlation between the presence of multiple anterior mesendodermal and mesoderm tissues and neural tube closure. However, no individual tissue was required for neural tube closure. Our finding identifies a specific time window of when Nodal is required for the process of neurulation. This time occurs before the neuroectoderm starts to form, suggesting that Nodal and anterior mesendoderm/mesoderm act very early in the process of neurulation. Further, the finding that multiple mesendodermal/mesodermal tissues are involved suggests that wide region of tissue helps promote closure of the adjacent neural tube.