Multiple C4/Slp genes distinguished by expression after transfection

Sex-limited protein: in vitro and in vivo functions

Mouse complement component C4 exists in two isoforms, C4 and a protein with expression restricted to male animals called sex-limited protein (Slp). Although Slp is about 95% homologous to C4, it is generally believed to be non-functional, at least in conventional haemolytic complement assays. In a previous study, however, we showed that Slp is haemolytically active in a C1-inhibitor (C1INH)-regulated, EDTA-resistant mouse complement activation pathway. To study other possible implications of this finding, we generated constitutively expressing Slp-transgenic mice. The transgene was crossed into otherwise Slp-deficient C57Bl/6J and NZB mice. Members of the third backcross generation of C57Bl/6J mice were tested for functional Slp and classical and alternative complement pathway activities (CH50 and AP50 levels, respectively). Slp-transgenic C57Bl/6J mice showed enhanced CH50, but normal AP50 levels when compared with non-transgenic littermates. To discover a possible protective role for Slp in spontaneous systemic lupus erythematosus (SLE) in NZBxNZW (NZBxW) mice, the third backcross generation of Slp-transgenic NZB mice was mated with NZW mice and the development of SLE in the female offspring was followed. In these introductory experiments, Slp-transgenic NZBxW animals presented with a significantly extended life span. Our results imply that Slp is a mouse complement component with functions which partially resemble some of those of human C4A.

Post-transcriptional regulation of complement C4 in low C4-producing strain of mouse

The expression of the fourth component of complement (C4) of the mouse can differ 20-fold and is determined by C4-high (C4h) or C4-low (C4l) alleles. To investigate the molecular mechanisms underlying the differences in C4 expression, we compared the transcriptional activity of the C4 genes between high and low C4-producer strains of mice (B10 and FM vs B10.BR) using nuclear transcriptional and chloramphenicol acetyltransferase (CAT) assays. We also compared the level of C4-specific RNA in total and nuclear RNA of the liver. The results revealed no significant difference in transcriptional activity between C4h and C4l genes. However, the steady-state levels of C4 mRNA are ten times lower in C4l strains than in C4h strains, suggesting that the major regulation of C4 plasma levels occurs at the post-transcriptional level.

Replication program of active and inactive multigene families in mammalian cells

In a comprehensive study, the temporal replication of tissue-specific genes and flanking sequences was compared in nine cell lines exhibiting different tissue-specific functions. Some of the rules we have determined for the replication of these tissue specific genes include the following. (i) Actively transcribed genes usually replicate during the first quarter of the S phase. (ii) Some immunoglobulin genes replicate during the first half of S phase even when no transcriptional activity is detected but appear to replicate even earlier in cell lines where they are transcribed. (iii) Nontranscribed genes can replicate during any interval of S phase. (iv) Multigene families arranged in clusters of 250 kilobases or less define a temporal compartment comprising approximately one-quarter of S phase. While these rules, and others that are discussed, apply to the tissue-specific genes studied here, all tissue-specific genes may not follow this pattern. In addition, housekeeping genes did not follow some of these rules. These results provide the first molecular evidence that the coordinate timing of replication of contiguous sequences within a multigene family is a general property of the mammalian genome. The relationship between replication very early during S phase and the transcriptional activity within a chromosomal domain is discussed.

Replication program of active and inactive multigene families in mammalian cells

In a comprehensive study, the temporal replication of tissue-specific genes and flanking sequences was compared in nine cell lines exhibiting different tissue-specific functions. Some of the rules we have determined for the replication of these tissue specific genes include the following. (i) Actively transcribed genes usually replicate during the first quarter of the S phase. (ii) Some immunoglobulin genes replicate during the first half of S phase even when no transcriptional activity is detected but appear to replicate even earlier in cell lines where they are transcribed. (iii) Nontranscribed genes can replicate during any interval of S phase. (iv) Multigene families arranged in clusters of 250 kilobases or less define a temporal compartment comprising approximately one-quarter of S phase. While these rules, and others that are discussed, apply to the tissue-specific genes studied here, all tissue-specific genes may not follow this pattern. In addition, housekeeping genes did not follow some of these rules. These results provide the first molecular evidence that the coordinate timing of replication of contiguous sequences within a multigene family is a general property of the mammalian genome. The relationship between replication very early during S phase and the transcriptional activity within a chromosomal domain is discussed.

Molecular genetics of androgen-dependent and -independent expression of mouse sex-limited protein

Genes of the mouse S locus encoding C4 (the fourth component complement) and Slp (sex-limited protein) show extensive homology but are distinct in their function and regulation. In some mouse strains, such as B10.D2, Slp is androgen regulated, whereas in others, such as B10.W7R, expression of Slp is constitutive. We have previously shown that the B10.W7R strain has multiple Slp genes. In this report, we present the structure of the single C4 and four Slp genes of the B10.W7R S locus and compare the upstream flanking regions by partial sequence analysis and function in transfection assays. Of the four Slp genes, three (Slpw7.A, Slpw7.B, and Slpw7.C) have upstream and promoter regions very similar to those of C4. The fourth Slp gene (Slpw7.D) is instead virtually identical to the androgen-regulated allele (Slpd from the B10.D2 mouse) in upstream regions. In particular, far-upstream sequences from both Slpd and Slpw7.D render the bacterial chloramphenicol acetyltransferase gene hormonally responsive upon transfection into mammary carcinoma cell lines. The upstream sequences between 2 to 3 kilobases of the Slp promoter initiate transcription from multiple sites when fused proximal to the chloramphenicol acetyltransferase gene, and these transcripts are threefold more abundant in the presence of androgen. This behavior is similar for Slpd and Slpw7.D, which suggests that Slpw7.D may be androgen regulated but that this is masked in vivo by constitutive expression of the other Slp genes. Nonhomologous recombination is implicated not only in expanding the copy number of C4 and Slp genes in the B10.W7R mouse but also in creating hybrid genes with regulatory features of C4 and structural features of Slp.

DNase I-hypersensitive sites associated with expression and hormonal regulation of mouse C4 and Slp genes

There are four major regions of DNase I hypersensitivity in the 5' regions of the genes for the murine fourth component of complement (C4) and its homologous neighbor, Slp (sex-limited protein). Hypersensitivity around the start site of transcription and approximately equal to 0.5 kilobases upstream correlates qualitatively with expression of these genes. Two hypersensitive sites, at -2.3 and -2.0 kilobases, map specifically to the Slp gene and correlate with its hormonal regulation. That is, these sites are more prominent in male liver chromatin and become more apparent in chromatin from females treated with testosterone. Further, these sites are established in males to a greater extent than in females prior to expression of Slp and may reflect gene-commitment events. Comparison of chromatin from mouse strains differing in C4 and Slp alleles indicates that the four regions of hypersensitivity may be necessary but are not sufficient for high levels of expression.

Molecular genetics of androgen-dependent and -independent expression of mouse sex-limited protein

Genes of the mouse S locus encoding C4 (the fourth component complement) and Slp (sex-limited protein) show extensive homology but are distinct in their function and regulation. In some mouse strains, such as B10.D2, Slp is androgen regulated, whereas in others, such as B10.W7R, expression of Slp is constitutive. We have previously shown that the B10.W7R strain has multiple Slp genes. In this report, we present the structure of the single C4 and four Slp genes of the B10.W7R S locus and compare the upstream flanking regions by partial sequence analysis and function in transfection assays. Of the four Slp genes, three (Slpw7.A, Slpw7.B, and Slpw7.C) have upstream and promoter regions very similar to those of C4. The fourth Slp gene (Slpw7.D) is instead virtually identical to the androgen-regulated allele (Slpd from the B10.D2 mouse) in upstream regions. In particular, far-upstream sequences from both Slpd and Slpw7.D render the bacterial chloramphenicol acetyltransferase gene hormonally responsive upon transfection into mammary carcinoma cell lines. The upstream sequences between 2 to 3 kilobases of the Slp promoter initiate transcription from multiple sites when fused proximal to the chloramphenicol acetyltransferase gene, and these transcripts are threefold more abundant in the presence of androgen. This behavior is similar for Slpd and Slpw7.D, which suggests that Slpw7.D may be androgen regulated but that this is masked in vivo by constitutive expression of the other Slp genes. Nonhomologous recombination is implicated not only in expanding the copy number of C4 and Slp genes in the B10.W7R mouse but also in creating hybrid genes with regulatory features of C4 and structural features of Slp.

Sequence comparison of alleles of the fourth component of complement (C4) and sex-limited protein (Slp)

cDNA clones specific for the fourth component of complement (C4) and its androgen-regulated isotype, sex-limited protein (Slp), have been isolated from two mouse haplotypes (H-2d and H-2w7) that show differential C4 activity and differential regulation of Slp. Clones were first isolated using a cDNA probe enriched by subtractive hybridization. Subsequent screening has resulted in cDNAs spanning the entire C4d mRNA, as well as much of C4w7, Slpw7 and a short region of Slpd. The cDNAs for C4 and Slp show extensive sequence homology, but can be distinguished using oligonucleotide probes synthesized to regions of greatest sequence divergence. Sequence differences between C4 and Slp indicate structurally important features of C4 that have been altered in Slp such that Slp is unable to participate in the complement pathway. Of the few nucleotide differences between C4d and C4w7, a single base change resulting in one less glycosylation site in the C4w7 alpha chain could account for its 4-fold reduced hemolytic efficiency. Sequence comparison of multiple alleles of C4 and Slp indicates that possible gene conversion events occurred in the H-2w7 strain that has multiple Slp genes.