The synaptonemal complexes of the nematode Caenorhabditis elegans: gametic response to retinol.

Retinol (RO) is essential for normal gene expression and progression of gametogenesis. Excessive amounts of RO in the diet results in the condition termed 'hypervitaminosis A' which severely affects gametogenesis. In the present work, the nematode Caenorhabditis elegans was grown in different concentrations of RO for up to seven generations. Decreased fecundity was positively correlated with increasing concentrations of RO with successive generations. Decreased nuclear volume was positively correlated with increasing RO concentration for each generation. Abnormal chromatin condensation was present along the bivalent and the lengths of the synaptonemal complexes (SC) were consistently longer than in the wild-type. Increasing RO concentration was also negatively correlated with the presence of SCs. The presence of disjunction regulator regions (DRR), which are decondensed regions of chromatin along the bivalent which occur in specific numbers, was negatively correlated with increasing RO concentration. By the third generation, DRRs were no longer observed in any of the organisms. This study shows that high levels of retinol in the diet affect gene expression, via changes in chromosome structure, and interferes with gamete production by inhibiting the pairing of homologous chromosomes during meiotic prophase.