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Mullerian inhibiting substance (MIS) in the adult rat ovary can be detected by immunohistochemistry in the granulosa cells of growing preantral follicles and in the cumulus oophorus and periluminal granulosa cells of antral follicles in estrus, metestrus, diestrus, and proestrus. Neither the corpus luteum nor atreitic follicles stained for MIS. During proestrus, dramatic changes occurred in the large preovulatory antral follicles, which early in the day manifest intense MIS-specific staining in the granulosa cells located close to the oocyte, however, at 2300 h, just before ovulation when the germinal vesicle was extruded to indicate resumed meiotic division, MIS staining waned. When the morphology of the late preovulatory stage was created experimentally in 26-day-old immature ovaries by stimulating 48 h earlier with hCG, the intense staining of the granulosa cells surrounding the oocytes from untreated ovaries was lost in the cumulus cells of such hCG-treated animals. This temporal pattern of MIS staining and the prior demonstration that MIS could inhibit in vitro meiosis of oocytes from untreated immature rats suggest that this regressor, well characterized in the fetal testis, might function in the ovary as a regulator of oocyte maturation and follicular development during the adult reproductive cycle.

The Clarke-Carbon clone bank of hybrid plasmid Escherichia coli DNA has been screened for plasmids able to complement an E. coli strain deficient for the production of beta-cystathionase. Clone 4-14 had the ability to complement a deletion mutation at this locus and expressed higher levels of beta-cystathionase than the wild-type strain. The transfer of the plasmid carried by this clone to a strain that constitutively expresses all the enzymes of the methionine biosynthetic pathway results in 100-fold overproduction of beta-cystathionase as compared to wild-type levels. With use of this strain, an efficient three-step purification scheme is described that gives 90% pure enzyme in 54% yield with a specific activity of 215 IU/mg. This enzyme is characterized as to molecular weight (280 000), number of subunits (six), pyridoxal phosphate binding (5.7 mol of pyridoxal phosphate bound/mol of protein, Km of 0.005 mM), amino acid composition, substrate specificity, and kinetic properties.

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The ontogeny of Müllerian Inhibiting Substance (MIS) production was studied in the immature developing rat ovary using immunohistochemistry and bioassay. In a graded organ culture assay, in which regression of the Müllerian duct of the 14 1/2-day rat fetus was used as a measure of bioactivity, MIS could not be detected in ovarian fragments from fetal rats. After birth, however, MIS bioactivity first became detectable at 4 days of age. Fragments from ovaries of rats 7 days of age and older contained moderate levels of MIS activity which remained detectable throughout the prepubertal period, although extreme individual variability was characteristic. A rabbit polyclonal antibody against human recombinant MIS was used to localize MIS in rat ovarian tissue. Avidin-biotin enhanced immunoperoxidase staining could not detect MIS in the 15-day fetal or 1 day postnatal ovary, where no follicular growth was noticed. In ovaries from rats 1 week or older, where follicular growth was apparent, MIS could be localized specifically and exclusively in the cytoplasm of granulosa cells. MIS was found more in the innermost layers of granulosa cells than in the peripheral layers in preantral follicles. In antral follicles, MIS was found predominantly in the cumulus oophorus cells and periantral cells. In these developing ovaries, MIS could not be found in follicles with features of atresia.

Male neonates develop respiratory distress syndrome (RDS) with a greater incidence and mortality than do female neonates; the cause of this male disadvantage remains obscure. Male fetuses are exposed to higher levels of androgens and Müllerian inhibiting substance (MIS). Androgens have been shown to inhibit fetal lung maturation, and recent evidence in vitro indicates that MIS, a Sertoli cell-derived glycoprotein made early in ontogeny of the testis, may also inhibit lung development. To study whether this fetal regressor might inhibit maturation of the fetal lung in vivo, we injected human recombinant MIS (rMIS) into fetal rats, measured serum levels of rMIS using an enzyme-linked immunosorbent assay, and analyzed fetal lung tissue histologically and for protein, glycogen, DNA, and disaturated phosphatidylcholine content. Peak serum levels of recombinant MIS were measured at 6 h, with an apparent elimination half-life of 3 h, and without leakage into adjacent littermates injected with vehicle alone. Female fetal rat lung tissue exposed to recombinant MIS (10(-9) M, 10(-8) M) revealed depressed disaturated phosphatidylcholine content both 48 and 72 h after injection compared with female vehicle-injected littermates. Male lungs of the same gestational age appeared inhibited at a higher (10(-8) M) rMIS dose. These inhibitory effects observed in vivo confirm those previously seen in vitro and suggest that MIS, as well as androgens, may play a causative or important ancillary role in the sexual dimorphism that characterizes the neonatal respiratory distress syndrome.

Analysis of the ontogeny and localization of the amino (N)-terminal and carboxy (C)-terminal cleavage products of Müllerian Inhibiting Substance (MIS) and their modulation by hormones of the hypothalamic-pituitary gonadal axis by immunohistochemistry and Northern analysis led to the discovery of a novel mode of posttranslational regulation of this differentiating agent. Antibody to both holo- and C-terminal MIS identically stained the cytosol of testicular Sertoli cells from 21-day fetal rats, whereas staining of antibody to N-terminal MIS localized to the basement membrane of seminiferous tubules. In addition, when studied longitudinally, basement membrane staining for N-terminal MIS persisted; cytosolic staining for C-terminal MIS was no longer detectable in post-natal testes, but marked basement membrane staining for the N-terminal fragment could still be observed in the testes of untreated 7-day postnatal animals. When 19-day fetuses were injected with FSH, testes collected 2 days later showed less immunohistochemical staining for holo-, N-, and C-terminal MIS, and less MIS messenger RNA. This suggested that FSH downregulates MIS transcription, as had been shown previously in neonatal testes treated with FSH. Testes collected at 21 days from fetuses treated at day 19 in utero with human CG or testosterone, also showed less staining for holo-MIS, but, surprisingly, increased staining for the N- and C-terminal fragments. These changes in MIS protein were accompanied by no or minimal changes in MIS messenger RNA levels, indicating that human CG and testosterone do not affect transcription, but may regulate the cleavage and/or dissociation of MIS. This study describes a form of post-translational regulation of MIS and shows that both transcription and processing of MIS may be differentially modulated by gonadotropins and sex steroids.