Sperm DNA in grasshoppers: Structural features and fertility implications

Abstract

This contribution briefly reviews the importance of grasshopper chromosomes in evolutionary studies and in achieving a comprehensive view of cytogenetics, emphasizing that meiotic chromosomes have been the traditional means for analyzing the nature of such problems. Structural changes occurring in the sperm, as a direct consequence of some chromosomal changes, have received less attention. We propose that grasshopper sperm could be a good model for the study of: 1) aspects of genome territoriality, and 2) consequences in the sperm DNA molecule, derived from a compromised meiotic process, linked with naturally forced genome hybridization. The results presented here, by using appropriate DNA probes for genome regionalization, allow the proposal of a grasshopper sperm chromosome organization. Centromere regions are distributed and concentrated at the proximal end of the sperm head where the flagellum is inserted. Also, chromosome arms are longitudinally organized from the proximal to the distal end, where the telomere of the longest autosome is the most distant genome region from the flagellum insertion. Subsequently, and because the length of the chromosome arms is different among nonhomologous chromosomes, the telomeres are distributed along the length of the sperm head. Sperm DNA quality was analyzed using the sperm chromatin-dispersion test, demonstrating that in sperm nuclei of early spermatids containing fragmented DNA, there exist large haloes of dispersed chromatin, while those nuclei remaining compact, contain an intact DNA molecule. Interestingly, and as a main difference with respect to other analyzed species, the DNA loops remain attached to a central proteic core. The aforementioned observation is clearly visible in partially elongated spermatozoa and the DNA loops forming the halo expand from this central region. This aspect of sperm chromatin organization found in grasshoppers is a new contribution to orthopterology. Further, it provides a unique insight and allows questioning the possible existence of this kind of chromatin organization in other noninsect species, where reproduction is based on gamete production.