The Effects Of Aneuploidy On Posterior Development In Danio Rerio

Aneuploidy is the state of having more or fewer sets of chromosomes than what naturally occurs in the organism. In cases of aneuploidy, the altered number of chromosomes is associated with proportional changes in cell volume. To address this question, the zebrafish is an ideal model. Their external fertilization allows us to observe development from the one-cell stage. Protocols were developed for generating haploid and tetraploid embryos. This allowed a comparison of embryonic development between normal diploid embryos versus haploid and tetraploid embryos with half or double the normal number of chromosomes, respectively. The altered chromosome number was confirmed using karyotyping. Analysis of the gross morphology of the embryos at 24 hours post fertilization found haploid and tetraploid embryos to have shortened and malformed posterior bodies. Next, in situ hybridization was performed to determine whether gene expression was affected in the somites (blocks of developing muscle) or somite boundaries. Expression of myod1 was disrupted in haploid and tetraploid embryos, indicating defects in normal muscle development. Similarly, expression of xirp2a showed disruptions to the somite boundaries. These results support the hypothesis that aneuploidy affects posterior development by causing defects in somite development. These findings are supported by the growing interest in mechanical forces in development.