Author/Editor		Fon-Tacer, Klementina; Kalanj-Bognar, Svjetlana; Waterman, Michael R; Rozman, Damjana
Title		Lanosterol metabolism and sterol regulatory element binding protein (SREBP) expression in male germ cell maturation
Type		članek
Source		J Steroid Biochem Mol Biol
Vol. and No.		Letnik 85
Publication year		2003
Volume		str. 429-38
Language		eng
Abstract		Expression of genes involved in cholesterol biosynthesis in male germ cells is insensitive to the negative cholesterol feedback regulation, in contrast to cholesterol level-sensitive/sterol regulatory element binding protein (SREBP)-dependent gene regulation in somatic cells. The role of sterol regulatory element binding proteins in spermatogenic cells was an enigma until recently, when a soluble, 55 kDa cholesterol-insensitive form of SREBP2 (SREBP2gc) was discovered [Mol. Cell. Endocrinol. 22 (2002) 8478], being translated from a germ cell-specific SREBP2 mRNA. Our RT-PCR results also show that SREBP2 as well as SREBPIc mRNAs are detectable in prepubertal and postpubertal male germ cells while SREBP 1 a is not detected. Surprisingly, three SREBP2 immunoreactive proteins (72, 63 and 55 kDa), that are not present in mouse liver nuclei, reside in testis nuclei of prepubertal and adult mice. The 55 kDa protein is likely SREBP2gc, the other two isoforms are novel. HPLC measurements in liver and testes of fasted prepubertal and postpubertal mice showed no significant difference in cholesterol level. However, FF-MAS and lanosterol/testis-meiosis activating sterol (T-MAS) intermediates that are detectable mainly in testes, increase in fasted postpubertal mice which coincides well with the elevated level of 68 kDa SREBP2. Similar to SREBP2gc, the two novel SREBP2 immunoreactive proteins seem to be insensitive to the level of cholesterol.
Descriptors		LANOSTEROL GENE EXPRESSION REGULATION DNA-BINDING PROTEINS TESTIS TRANSCRIPTION FACTORS MICE, INBRED CBA LIVER SPERMATOGENESIS SEX MATURATION POLYMERASE CHAIN REACTION RNA, MESSENGER