Characterization of Mahogunin Ring Finger‐1 expression in mice

Abstract

Mutations in mouse Mahogunin Ring Finger-1 (Mgrn1) were first recognized for their effect on agouti-mediated pigment-type switching. Mgrn1 null mutants are completely black and develop spongiform degeneration of the brain. Mgrn1 hypomorphs have dark fur but do not develop neurodegeneration. We characterized a new Mgrn1 hypomorphic allele caused by a gene-trap insertion. Mice homozygous for this mutation are slightly darker than non-mutant animals. They show reduced overall expression of Mgrn1 and two of the four normal Mgrn1 isoforms are replaced by beta-GEO fusion proteins that differ from the normal proteins at their carboxy termini. To investigate the role of different Mgrn1 isoforms in pigment-type switching, we used quantitative relative reverse transcriptase polymerase chain reaction to examine their expression in the skin of Mgrn1 mutant and control mice. Most Mgrn1 mutants produce little or no normal Mgrn1 in the skin. Mgrn1 null mutant mice overexpressing isoform I or III, which are normally absent or weakly expressed in adult skin, had normal agouti-banded hairs. Our results indicate that reduced levels of MGRN1 cause the pigmentation phenotypes of Mgrn1 mutant mice and that there are no significant differences in the function of the four MGRN1 isoforms in pigment-type switching.

Mice with mutations in Mahogunin ring finger‐1 (Mgrn1) exhibit abnormal patterning of the left–right axis

“…Axes: D, dorsal; V, ventral; L, left; R, right. (Bagher et al, 2006), to visualize the MGRN1-␤-GEO fusion protein they produce. X-gal staining and in situ hybridization gave comparable results.…”

“…Attempts to make this allele congenic on the C3H/HeJ or 129S1/ SvImJ backgrounds were unsuccessful as embryonic lethality approached 100% by the fifth backcross generations. C3H/HeJ-Mgrn1 md-2J mice (Sweet and Davisson, 1995) have an ϳ8-kb IAP insertion in exon 13 that results in the production of aberrant Mgrn1 RNA transcripts (Phan et al, 2002;Bagher et al, 2006). Mice were obtained from a cryopreserved stock at the Jackson Laboratory and subsequently maintained by intercrossing siblings.…”

“…C3H/HeJ and 129S1/SvImJ control mice were originally obtained from the Jackson Laboratory and maintained in-house by brother-sister inbreeding. Mgrn1 Gt(pGT1Lxf)XC712Wcs (abbreviated to Mgrn1 XC712 ) mutant mice were generated from a mouse embryonic stem cell (ESC) line generated by BayGenomics that carries a gene-trap insertion in intron 17 of the Mgrn1 locus, trapping two of the four normal RNA isoforms (Bagher et al, 2006). The gene-trap vector is composed of a strong splice acceptor sequence upstream of a ␤-geo reporter gene (␤-galactosidase fused to neomycin phosphotransferase) followed by a polyadenylation signal (Stryke et al, 2003).…”

“…Mice homozygous for a null allele, Mgrn1 md-nc , produce no detectable mRNA transcript, have black fur, and exhibit reduced embryonic viability (Phillips, 1963(Phillips, , 1971He et al, 2003). Mice homozygous for a hypomorphic allele, Mgrn1 md-2J , produce reduced amounts of aberrant mRNA transcript, have dark fur, and also exhibit reduced embryonic viability (Phan et al, 2002;Bagher et al, 2006). We observed complete situs inversus in a small number (Ͻ1%) of adult Mgrn1 md-nc mutant mice, which led to the hypothesis that reduced viability in Mgrn1 mutants was due to congenital heart defects resulting from abnormal LR patterning.…”

Mahogunin Ring Finger-1 (MGRN1) E3 Ubiquitin Ligase Inhibits Signaling from Melanocortin Receptor by Competition with Gαs

“…We show that human melanoma cells express 4 alternative splicing forms of MGRN1 similar to mouse cells (26). All the isoforms inhibit MC1R functional coupling to the cAMP cascade without decreasing MC1R plasma membrane density or intracellular stability.…”