Chromatoid body assembling and nucleolar cycle: Two important physiological events for the spermatogenesis in vertebrates

Abstract

This study aimed to find physiological, morphological, and/or structural relationship between two important physiological events that take place during vertebrate spermatogenesis: the nucleolar cycle and chromatoid body (CB) assembly. Both process were analyzed by cytogenetics and ultrastructural analysis, which were carried out in adult male of four vertebrate species: Tilapia rendalli (Teleostei, Ciclidae), Dendropsophus minutus (Amphibia, Anura), Phrynops geoffroanus (Reptilia, Testudines), and Oryctolagus cuniculus (Mammalia, Lagomorpha). We also determined the number of nucleoli contained in spermatogonia and earlier/round spermatids, besides of performing measurements of the ratio between nuclear and nucleolar areas of spermatogonia and earlier/round spermatids. We found minor differences in some aspects of both nucleolar cycle and chromatoid body assembly, such as nucleolar architecture, timing of nucleolar disruption at first meiosis division, timing of CB assembly in the cytoplasm of germ cells, CB association to other structures, and its positioning in the cytoplasm of earlier/round spermatids. In general, there was no alteration regarding the number of organized nucleoli in the nucleus of cells undergoing through meiotic division. All species had generally one single organized nucleolus in both germ cell types, with an exception to O. cuniculus, which showed a higher number of germ cells with 2, 3, or 4 organized nucleoli. There was an increase in the nuclear and nucleolar area ratio mean between diploid spermatogonia and haploid earlier/round spermatids in all species, mainly in T. rendalli and P. geoffroanus. This increase is probably related to the decrease in the nucleolar size after germ cells undergo the meiotic division. Many factors could contribute to the reduction of nucleolar area after meiosis, one of them being the probable migration of the nucleolar fragments to the cytoplasm of germ cells in prophase I, where they may play a role in CB assembling, as previously proposed. Former detection of nucleolar proteins in the chemical composition of the CB is a strong evidence supporting this idea. If nucleolar proteins would play a role in the CB physiology acting in the RNA processing or if they would be translocated to the CB, because they are targeted for degradation in late steps of the spermatogenesis process, are further questions that still need to be investigated. However, the evidences showed in this study point for the existence of a physiological, morphological, and/or structural link between the CB assembly and the nucleolar cycle in the spermatogenesis process of vertebrates. © 2013 Nova Science Publishers, Inc. All rights reserved.