Effects of dimethyl sulphoxide on early gametogenesis in Caenorhabditis elegans: ultrastructural aberrations and loss of synaptonemal complexes from pachytene nuclei.

In Caenorhabditis elegans, loss of viability and fertility was observed after treatment with dimethyl sulphoxide (DMSO). The decrease in life span is associated with senescent morphology of meiotic prophase nuclei, such that nuclei from young and old specimens cannot be differentiated. Aging in oocytes at the pachytene stage of meiotic prophase is characterized by nucleo-cytoplasmic aberrations, increased density of the nucleoplasm and cytoplasm and decrease in numbers of mitochondria (Goldstein and Curis, 1987). Increasing concentrations of DMSO result in decrease in fertility and increased production of abnormal gametes. At DMSO concentrations higher than 5.0%, synaptonemal comlexes (SC) are absent from the nuclei, thus, effective pairing and segregation of homologous chromosomes is not possible. The absence of SCs may be the result of: (1) a premeiotic colchicine-like effect which influences pairing of chromosomes; (2) changes in the structure of the DNA due to DMSO binding that results in changes in expression of the DNA; and (3) changes in temporal DNA synthesis in response to DMSO. Since the SC is essential for regulating pairing and subsequent separation of bivalents, the lack of an SC explains the loss of fertility, due to the production of unbalanced gametes, observed in DMSO treated specimens.