Abstract:
The vertebrate body plan displays distinct left-right asymmetries in the position of visceral organs. This asymmetrical organization extends to the vertebrate brain that is both anatomically and functionally asymmetric. The development of left-right patterning and cerebral lateralization are thought to be regulated by evolutionary conserved genes. Here we report the evidence of the maternal effect allele mother-of-snow-white (msw) controlling the establishment of LR body asymmetries in a vertebrate embryo suggesting conserved mechanisms in the evolution and establishment of this trait. In a recent study Facchin and colleagues [1] showed that the progeny of lines of zebrafish artificially selected for the right eye preference in scrutiny a mirror had a significant increase in the frequency of reversed left-right asymmetry in the epithalamus. In the present study it is proposed that Facchin’s selection for behavioral lateralization could have lead to the isolation of a spontaneous maternal effect allele responsible for the disruption of normal left-right patterning in zebrafish neuroanatomical structures. We analyzed the genetic transmission of the msw allele and we identified three different classes of females according to the percentage of reversed brain asymmetries in their offspring. Females generating a frequency of 0-5% (class I), between 5 and 12.5% (class II) and females generating more than 12.5% (class III) of progeny with reversed asymmetries. Animals from the last group were considered as homozygous recessive females for the msw allele (HRF). We also investigated in the three classes the expression of members of signaling pathways responsible for the establishment of visceral and diencephalic left-right asymmetries and measured the size of Kupffer’s vescicle (KV). We found that HRF offspring had smaller KV and, sometimes, no vesicle at all. We could observe a correlation between the frequency of reversed parapineal and the size of KV. The msw allele has shown to be semi-dominant as class II females showed an intermediate phenotype. Our hypothesis suggests that smaller size of KV can reduce the amount of morphogens accumulated by the leftward flow, thus leading to a randomization of the expression of genes of the Nodal pathway. Moreover we evidenced significant behavioral differences between fish with opposite parapineal position subjected to various laterality tests. We could also discuss a complex but relevant influence of neuroanatomical asymmetries on zebrafish personality [2]. Now using Paired-end Mapping and next-generation sequencing techniques (SOLiD approach) we are aiming at identifying the msw allele. 1. Facchin, L., F. Argenton, and A. Bisazza, Lines of Danio rerio selected for opposite behavioural lateralization show differences in anatomical left-right asymmetries. Behavioural Brain Research, 2009. 197 (1): p. 157-165. 2. Dadda, M., et al., Early differences in epithalamic left-right asymmetry influence lateralization and personality of adult zebrafish. Behavioural Brain Research. 206 (2): p. 208-215.