engleski

Sterol regulatory element binding proteins in mouse testis

Sterol regulatory element binding proteins (SREBPs) are membrane-bound transcription factors which control the metabolism of cholesterol and fatty acids in animal cells. Cleavage of SREBPs and release of the bHLH-zip domain, which enters the nucleus and binds to sterol regulatory elements (SRE), is enhanced by sterol depletion and inhibited by sterol supplementation. Previous studies suggested that SREBP-dependent pathway is responsible for regulation of cholesterol and fatty acids biosynthesis in liver and other somatic tissues, while cAMP-dependent transcriptional activator CREMt may predominate in activation of cholesterogenic gene CYP51 in male germ cells. The aim of this study was (1) to determine the expression of SREBP mRNAs in mouse germ cells and (2) to localize SREBPs proteins in mouse testis at the ultrastructural level. The expression of SREBP mRNAs was analyzed by RT-PCR method using specific fluorescent-labeled primers for SREBP-1a, -1c and SREBP-2. Amplification of the b-actin gene was used as an internal standard. RT-PCR products were analyzed by capillary electrophoresis on Abi Prism Genetic Analyzer. The cellular localization of SREBPs in mouse tissue was analyzed by immunogold electron microscopy using primary antibodies that recognize SREBP-1 and SREBP-2, and secondary antibodies bearing 10 nm gold particles, which were applied to ultrathin sections of mouse testis. The analysis of SREBP mRNA expression showed the presence of SREBP-1c and SREBP-2 transcripts in mouse testis and interstitial cells, as well as in isolated germ cells from both prepubertal and adult animals. Preliminary immuno-electron microscopy data showed the presence of SREBPs in nuclei of primary spermatocytes, in nuclei of round and elongated spermatides, and in nuclei of interstitial cells. Detection of SREBP mRNAs shows that SREBP genes are transcribed in mouse germ cells. Preliminary data indicate that the SREBP mRNA is translated and properly cleaved in spermatocytes as well as in spermatides and interstitial cells, since gold-labeled SREBP particles have been detected in nuclei of those cell types. A more detailed analysis is needed to evaluate the quantity of mature SREBP protein in different types of germ cells and its potential role in transcription of cholesterogenic genes in male germ cells.

sterol regulatory element binding proteins; mouse testis

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