Blocking the Bromodomains Function Contributes to Disturbances in Alga Chara vulgaris Spermatids Differentiation

Abstract

Bromodomain containing (BRD) proteins play an essential role in many cellular processes. The aim of this study was to estimate activity of bromodomains during alga Chara vulgaris spermatids differentiation. The effect of a bromodomain inhibitor, JQ1 (100 μM), on the distribution of individual stages of spermatids and their ultrastructure was studied. The material was Feulgen stained and analysed in an electron microscope. JQ1 caused shortening of the early stages of spermiogenesis and a reverse reaction at the later stages. Additionally, in the same antheridium, spermatids at distant developmental stages were present. On the ultrastructural level, chromatin fibril system disorders and significantly distended endoplasmic reticulum (ER) cisternae already at the early stages were observed. Many autolytic vacuoles were also visible. The ultrastructural disturbances intensified after prolonged treatment with JQ1. The obtained data show that JQ1 treatment led to changes in the spermatid number and disturbances in chromatin condensation and to cytoplasm reduction. The current studies show some similarities between C. vulgaris and mammals spermiogenesis. Taken together, these results suggest that JQ1 interferes with the spermatid differentiation on many interdependent levels and seems to induce ER stress, which leads to spermatid degeneration. Studies on the role of bromodomains in algae spermiogenesis have not been conducted so far.

Differentiation Disorders of Chara vulgaris Spermatids following Treatment with Propyzamide

“…Ultrastructural changes induced by propyzamide concerned, e.g., the ER system and manchette, and resembled the defense mechanism against the harmful effects of propyzamide. The disturbances in the ER system caused as a result of ER stress were also observed in different cell types and also in C. vulgaris following treatment with bromodomain inhibitor JQ1 [59,68,69]. In the internodal cells of Nitella (Characean) following dinitroaniline treatment, the cortical ER changed its orientation while increasing the size of the mesh [70].…”

“…During the analysis performed on the spermiogenesis process, it should also be noted that, although these processes occurring in mammals and Chara present numerous similarities [3,4,55,56,59], sperm develops in different cell systems. In the literature, there remains little information showing the extent to which tubulin function disturbances caused by different inhibitors can affect cells during the process of spermatogenesis [5,18,19,58,60,61].…”

“…On the basis of the previous studies conducted on C. vulgaris spermatids, it is well known that the inhibition of the activity of the 26S proteasomes, DNA topoisomerase II, and bromodomains, which are necessary for the correct exchange of histones into protamines, causes disturbances in the structure of chromatin; however, the nucleus shape and microtubular manchette were not altered [3,55,59]. Only in the case of treatment with JQ1, following Feulgen staining, some nuclei at stage X were thinner than that of the control sample, presenting an altered surface [59].…”

“…On the basis of the previous studies conducted on C. vulgaris spermatids, it is well known that the inhibition of the activity of the 26S proteasomes, DNA topoisomerase II, and bromodomains, which are necessary for the correct exchange of histones into protamines, causes disturbances in the structure of chromatin; however, the nucleus shape and microtubular manchette were not altered [3,55,59]. Only in the case of treatment with JQ1, following Feulgen staining, some nuclei at stage X were thinner than that of the control sample, presenting an altered surface [59]. It seems likely that the observed changes in the chromatin structure in the present study were the effect of a disturbance in IMT related to the different arrangement or loss of microtubules in the manchette and the fragmentation of the nuclear envelope, which plays an important role in the process of nucleus-cytoplasm transport.…”

A brief history of the Feulgen reaction

“…Indeed, in 2020, the application of Feulgen staining was described for imaging of ovaries and developing embryo sacs in maize (Kalinowska et al 2020 ). During the same year, Wojtczak applied the Feulgen reaction to study the spermatid differentiation of the alga Chara vulgaris , highlighting important similarities with mammal spermiogenesis (Wojtczak 2020 ).…”