Male-specific expression of mouse sex-limited protein requires growth hormone, not testosterone.

Abstract

Sex-limited protein (Slp), an isoform of mouse complement component C4, is expressed predominantly in liver and nearly exclusively in sexually mature males or testosterone-treated females. It is encoded by a gene (C4-Slp) whose hormonal dependence has been attributed to an androgen-responsive transcriptional enhancer introduced accidentally, alongside the C4-Slp promoter, in the guise of the 5' long terminal repeat of an ancient retrovirus. We demonstrate that the pronounced rise of C4-Slp mRNA promoted by androgens in the liver is due to nuclear factors acting at a transcriptional stage. Curiously, hypophysectomized animals of either sex fail to express the gene and are refractory to testosterone. However, gene expression at male levels is restored even more promptly by itjections of growth hormone alone. Additionally, animals carrying an ubiquitously expressed human growth hormone transgene lack C4-Slp mRNA and are insensitive to testosterone treatment. That growth hormone is sufficient to induce expression in a manner independent of androgenreceptor activity is shown by the hormonal treatment of Tfm mice. These androgen receptor-defective animals lack C4-Slp mRNA, which however can be fully induced by growth hormone ii jections. We conclude that the sexual dimorphism of C4-Slp expression employs liver nuclear mediators distinct from those directly instructed by androgens and is brought about by the intermittent rise of growth hormone, dictated by testosterone.The fourth component of complement (C4) is encoded in the mouse by two genes (C4 and C4-Slp) arranged in tandem (1) in the S region of the H-2 major histocompatibility complex and created by a recent gene duplication (2,3). Notwithstanding the 95% nucleotide (nt) identity throughout their coding (4) and noncoding regions (refs. 3, 5, and 6 and our additional unpublished data), the two genes diverge drastically in their mode of expression in that C4-Slp and not C4 is under stringent developmental and hormonal control. Soon after the discovery of this male-specific serum protein (7), it became clear that the expression of C4-Slp depends on the presence of testosterone. That is, the protein is absent from the serum of female animals or castrated males, where its expression is restored by testosterone treatment (8). As in other mammals, C4 is produced both in liver and in macrophages, but only hepatocytes synthesize Slp. Even though other hepatic genes that display sexually dimorphic regulation have been more intensively studied (9, 10), the C4/C4-Slp system is notable for its more pronounced testosterone response, the array of available regulation variants (11), and lack of the genetic and functional complexity seen in multigene families such as the androgen-inducible a2u globulin in the rat (12) and the homologous mouse major urinary protein (Mup) (13,14). The system acquires additional interest by the existence of trans-acting mutations (15, 37) that override the testosterone requirement of the C4-Slp gene.Functional analyses of the C4-Slp promote...

Transgenic Mice Showing Inflammation-Inducible Overexpression of Granulocyte Macrophage Colony-Stimulating Factor

“…Intriguingly, however, the human CRP gene is not sexually dimorphic in humans. A possible answer to this paradox lies in the fact that testosterone produces pulses of high growth hormone release in male mice (12), resulting in mean levels in serum twice those observed in females (22). Growth hormone has been shown to be able to upregulate the human CRP gene in transgenic mice (26).…”

“…Since that study, the transcription factor STAT5 has emerged as an important transducer of the pulsatile growth hormone secretion pattern seen in male rodents into sex-specific patterns of liver gene expression (11,14,24). Also, binding of STAT5 to the promoter of the murine Sex-limited protein (slp) gene, which is known to be regulated indirectly by testosterone, via its effects on growth hormone (12), results in male-specific transcription of the gene (32). In addition, Feldman et al (6) have shown that GM-CSF is involved in the activation of STAT5, thereby providing another mechanism whereby GM-CSF overexpression in male GM-CSF transgenic mice might lead to the generation of a positive feedback loop, upregulating the CRP promoter and producing more GM-CSF.…”

Sexual dimorphism of hepatic gene expression: novel biological role of KRAB zinc finger repressors revealed: Figure 1.

“…Slp is normally expressed only in adult male mice, where it responds to the positive effects of pulsatile GH stimulation (Georgatsou et al 1993). Recessive rsl mutant alleles have arisen in populations of inbred mice and result in expression of Slp in female mice at 3 wk of age .…”

Localization of the mouse gene releasing sex-limited expression of Slp.

“…In the liver, the major source of Slp, the difference in expression levels of the protein in males and females is due to nuclear factors acting at the transcriptional stage (16). Full expression of Slp in males occurs only after puberty and is dependent upon the presence of testosterone, androgen receptors, and an adult male pattern of growth hormone release (16,17).Due to an apparent tandem duplication, Slp and C4 form a small multigene family (18,19 Slp (24,25).The fascinating observation was made by Brown and Shreffler (26) that in four strains that do not contain hybrid Slp genes (FM, LG, NZB, and PL), the "sex-limitation" is removed in that females also express Slp (26). Expression of Slp was characterized in detail in the strain FM (Slpd); Slp is expressed only after 4 weeks of age in either sex and is expressed in males at higher levels than in females.…”

“…Slp was found in several independent haplotypes (Slpd, Slpu, Slps, SlpP) (13,14), and it has recently been shown to have activity in a putative complement pathway (15). In the liver, the major source of Slp, the difference in expression levels of the protein in males and females is due to nuclear factors acting at the transcriptional stage (16). Full expression of Slp in males occurs only after puberty and is dependent upon the presence of testosterone, androgen receptors, and an adult male pattern of growth hormone release (16,17).…”