Transient down-regulation of inhibin-betaC expression following partial hepatectomy.

Inhibin-betaC is a recently described TGF-beta family member most homologous to inhibin-betaA and inhibin-betaB. By Northern analysis, inhibin-betaC mRNA was detected exclusively in the liver among a large number of adult mouse tissues surveyed. The expression of inhibin-betaC mRNA in adult liver dropped sharply and transiently following partial hepatectomy. At 6 and 12 hours following partial hepatectomy, the levels of inhibin-betaC mRNA were at least 8-fold lower than in control animals. The liver specificity of inhibin-betaC expression and its down-regulation following partial hepatectomy suggest that inhibin-betaC may function as a negative regulator of liver growth.

Oocyte-specific expression of growth/differentiation factor-9.

Growth/differentiation factor-9 (GDF-9) is a previously described member of the transforming growth factor-beta superfamily expressed specifically in the ovary in adult mice. Using in situ hybridization methods, we have localized the expression of GDF-9 messenger RNA (mRNA) exclusively to oocytes. GDF-9 mRNA was detected in oocytes at all stages of follicular development, except in primordial follicles, in both neonatal and adult ovaries. GDF-9 mRNA continued to be expressed in oocytes after ovulation, but disappeared by 1.5 days after fertilization. Based on Western analysis of ovarian extracts using antibodies raised against recombinant GDF-9 protein, GDF-9 mRNA expressed by oocytes appears to be translated. A human homolog of GDF-9 was isolated from a complementary DNA library prepared from adult ovary mRNA. The predicted human protein is 90% identical to murine GDF-9 in the mature portion of the molecule. These results are significant because no other growth factor-like molecules have been shown to be expressed specifically by oocytes and, together with results of previous studies, suggest that ovarian development and function are regulated by factors produced by both oocytes and support cells of the ovary.

Retention of a cis Golgi protein requires polar residues on one face of a predicted alpha-helix in the transmembrane domain.

The first membrane-spanning domain (m1) of the model cis Golgi protein M (formerly called E1) from the avian coronavirus infectious bronchitis virus is required for targeting to the Golgi complex. When inserted in place of the membrane-spanning domain of a plasma membrane protein (vesicular stomatitis virus G protein), the chimeric protein ("Gm1") is retained in the Golgi complex of transfected cells. To determine the precise features of the m1 domain responsible for Golgi targeting, we produced single amino acid substitutions in m1 and analyzed their effects on localization of Gm1. Expression at the plasma membrane was used as the criterion for loss of Golgi retention. Rates of oligosaccharide processing were used as a measure of rate and efficiency of transport through the Golgi complex. We identified four uncharged polar residues that are critical for Golgi retention of Gm1 (Asn465, Thr469, Thr476, and Gln480). These residues line one face of a predicted alpha-helix. Interestingly, when the m1 domain of the homologous M protein from mouse hepatitis virus is inserted into the G protein reporter, the chimeric protein is not efficiently retained in the Golgi complex, but transported to the cell surface. Although it possesses three of the four residues we identified as important in the avian m1 sequence, other residues in the membrane-spanning domain from the mouse protein must prevent efficient recognition of the polar face within the lipid bilayer of the cis Golgi.