During spermiogenesis, the elongating rat spermatid chromatin undergoes a gradual process of condensation which is initiated in the round spermatids at "step 7" of cytodifferentation in stage VII and extending to elongated spermatids at "step 19" of cytodifferentiation in stage VIII. The mechanism of chromatin condensation in the elongating spermatids is an elaborate process that encompasses several biochemical and biological aspects culminating in the deposition of protamine in DNA grooves. The protamination of sperm chromatin involves expression and storage of proteins involved in condensation, removal and degradation of nuclear histones and their replacement by transition proteins and protamine 1, transcriptional silencing and DNA repair, reduction of nuclear volume, repackaging of protaminated chromatin in torroids and development of a characteristic head shape and perforatorium. A study was undertaken in my laboratory to delineate the role of follicle stimulating hormone (FSH) and testosterone in the condensation of nuclear chromatin in the elongating spermatids of sexually competent species of rat. Towards this end, sexually competent male Holtzmann rats were treated with 20 mg/Kg/d per os (oral supplementum) of cyproterone acetate and 3 mg/Kg/d i.p (intra peritoneal) of fluphenazine decanoate to induce a functional deficiency in either testosterone or FSH. In both rat models, membrane-impermeable CMA3 fluorescent dye uptake assay for GC-rich prospective sites of DNA protamination, was indicative of insufficiency of protamine 1 in spermatozoa taken from caput epididymides of treated rats whereas a fluorescent TUNEL assay indicated the presence of nicked chromatin strands only in protamine-deficient spermatozoa derived from caput epididymides of fluphenazine-treated rats with functional deficiency of FSH. Western blotting of acid-soluble sperm basic proteins had confirmed the near absence of protamine 1 in treated rat spermatozoa in both models. Electron Microscopic evaluation too revealed fine ultrastructural changes in the nuclear membrane of cyproterone acetate as well as fluphenazine decanoate treated spermatozoa derived from caput epididymides. Electrophoretic analysis of caput sperm nuclear basic proteins substantiated the observations at cellular level and revealed a pattern of abnormal persistence of acid-soluble nuclear basic proteins in both rat models, the levels being more prominent in fluphenazine treated rats. Our studies suggest that adequate levels of both FSH and testosterone could be essential during the stages of spermatidal condensation and led us to hypothesize the existence of an endocrine-regulated molecular mechanism for histone to protamine transition and maintenance of chromatin integrity during chromatin condensation in the testis during spermiogenesis.

Cell-based bioassays have been suggested for screening of hormones and drug bioactivities. They are a plausible alternative to animal based methods. The technique used is called receptor/reporter system. Receptor/reporter system was initially developed as a research technique to understand gene function. Often reporter constructs containing viral promoters were used because they could be expressed with very 'high' magnitude in a variety of cell types in the laboratory. On the other hand mammalian genes are expressed in a cell/tissue specific manner, which makes them (i.e. cells/tissues) specialized for specific function in vivo. Therefore, if the receptor/reporter system is to be used as a cell-based screen for testing of hormones and drugs for human therapy then the choice of cell line as well as the promoter in the reporter module is of prime importance so as to get a realistic measure of the bioactivities of 'test' compounds. We evaluated two conventionally used viral promoters and a natural mammalian promoter, regulated by steroid hormone progesterone, in a cell-based receptor/reporter system. The promoters were spliced into vectors expressing enzyme CAT (chloramphenicol acetyl transferase), which served as a reporter of their magnitudes and consistencies in controlling gene expressions. They were introduced into breast cell lines T47D and MCF-7, which served as a cell-based source of progesterone receptors. The yardstick of their reliability was highest magnitude as well as consistency in CAT expression on induction by sequential doses of progesterone. All the promoters responded to induction by progesterone doses ranging from 10-12 to 10-6 molar by expressing CAT enzyme, albeit with varying magnitudes and consistencies. The natural mammalian promoter showed the most coherence in magnitude as well as dose dependent expression profile in both the cell lines. Our study casts doubts on use of viral promoters in a cell-based bioassay for measuring bioactivities of drugs and hormones for human therapy and suggests caution regardingtranslation in toto, of a research technique as a cell-based bioassay for drug screening.

BackgroundThe putative regulatory role of the male reproductive hormones in the molecular mechanism underlying chromatin condensation remains poorly understood. In the past decade, we developed two adult male rat models wherein functional deficits of testosterone or FSH, produced after treatments with 20 mg/Kg/d of cyproterone acetate (CPA) per os, for a period of 15 days or 3 mg/Kg/d of fluphenazine decanoate (FD) subcutaneously, for a period of 60 days, respectively, affected the rate of sperm chromatin decondensation in vitro. These rat models have been used in the current study in order to delineate the putative roles of testosterone and FSH in the molecular mechanism underlying remodelling of sperm chromatin.ResultsWe report that deficits of both testosterone and FSH affected the turnover of polyubiquitylated histones and led to their accumulation in the testis. Functional deficits of testosterone reduced expression of MIWI, the 5-methyl cap binding RNA-binding protein (PIWIlike murine homologue of the Drosophila protein PIWI/P-element induced wimpy testis) containing a PAZ/Piwi-Argonaut-Zwille domain and levels of histone deacetylase1 (HDAC1), ubiquitin ligating enzyme (URE-B1/E3), 20S proteasome α1 concomitant with reduced expression of ubiquitin activating enzyme (ube1), conjugating enzyme (ube2d2), chromodomain Y like protein (cdyl), bromodomain testis specific protein (brdt), hdac6 (histone deacetylase6), androgen-dependent homeobox placentae embryonic protein (pem/RhoX5), histones h2b and th3 (testis-specific h3). Functional deficits of FSH reduced the expression of cdyl and brdt genes in the testis, affected turnover of ubiquitylated histones, stalled the physiological DNA repair mechanism and culminated in spermiation of DNA damaged sperm.ConclusionsWe aver that deficits of both testosterone and FSH differentially affected the process of sperm chromatin remodelling through subtle changes in the ‘chromatin condensation transcriptome and proteome’, thereby stalling the replacement of ‘dynamic’ histones with ‘inert’ protamines, and altering the epigenetic state of condensed sperm chromatin. The inappropriately condensed chromatin affected the sperm chromatin cytoarchitecture, evident from subtle ultrastructural changes in the nuclei of immature caput epididymal sperm of CPA- or FD-treated rats, incubated in vitro with dithiothreitol.

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