ERD2, a yeast gene required for the receptor-mediated retrieval of luminal ER proteins from the secretory pathway

Resident proteins of the ER lumen carry a specific tetrapeptide signal (KDEL or HDEL) that prevents their secretion. We have previously described the isolation of yeast mutants that fail to retain such resident proteins within the cell. Here we describe ERD2, a gene required for retention. It encodes a 26 kd integral membrane protein whose abundance determines the efficiency and capacity of the retention system. Reduced expression of ERD2 leads to secretion of proteins bearing the HDEL signal, whereas overexpression of ERD2 improves retention both in wild-type cells and in other mutants. These results are consistent with other evidence that ERD2 encodes the HDEL receptor (see accompanying paper). The gene is also required, perhaps indirectly, for normal protein transport through the Golgi, and hence for growth. We discuss possible roles for ERD2 in the secretory pathway.     

Monoclonal antibodies to the murine zona pellucida protein with sperm receptor activity: effects on fertilization and early development

During development and maturation, mammalian oocytes are surrounded by the zona pellucida which in the mouse is comprised of three sulfated glycoproteins, ZP-1, ZP-2, and ZP-3. Previously, monoclonal antibodies to ZP-2 have been isolated. The isolation and characterization of monoclonal antibodies specific for ZP-3, the zona protein with sperm receptor activity are now reported. Following passive immunization, these monoclonal antibodies localize to the intraovarian zonae pellucidae and their presence precludes both in vivo and in vitro fertilization of subsequently ovulated eggs. Monoclonal antibodies specific for either ZP-2 or ZP-3 also completely block in vitro fertilization at relatively low concentration ranging from 0.4 to 75 micrograms/ml. The contraceptive effect requires the presence of the zona and appears to inhibit the penetration of the zona pellucida by sperm rather than by blocking the sperm binding site. Neither antibody interferes with in vitro development from the two-cell to the blastocyst stage or with subsequent hatching from the enveloping zona pellucida.     

Cell-free translation of mitochondrial nicotinamide nucleotide transhydrogenase

Mammalian nicotinamide nucleotide transhydrogenase is translated as a 5000 daltons larger molecular weight precursor in a cell-free system programmed with rat liver polysomes. The mature rat liver enzyme had the same molecular weight as the purified beef heart enzyme, 115 000 daltons. The precursor was not processed in vitro by liver mitochondria or by a rat liver mitochondrial matrix fraction, nor did it appear to bind to mitochondria. In contrast, pre-FeS protein of the cytochrome bc₁ complex was processed in the same samples by both mitochondria and matrix, suggesting an important difference in the processing mechanisms or in the efficiency of processing of the two precursors.     

The Conversion of Nitrite to Nitrogen Oxide(s) by the Constitutive NAD(P)H-Nitrate Reductase Enzyme from Soybean

A two-step purification protocol was used in an attempt to separate the constitutive NAD(P)H-nitrate reductase [NAD(P)H-NR, pH 6.5; EC 1.6.6.2] activity from the nitric oxide and nitrogen dioxide (NO_(x)) evolution activity extracted from soybean (Glycine max [L.] Merr.) leaflets. Both of these activities were eluted with NADPH from Blue Sepharose columns loaded with extracts from either wild-type or LNR-5 and LNR-6 (lack constitutive NADH-NR [pH 6.5]) mutant soybean plants regardless of nutrient growth conditions. Fast protein liquid chromatography-anion exchange (Mono Q column) chromatography following Blue Sepharose affinity chromatography was also unable to separate the two activities. These data provide strong evidence that the constitutive NAD(P)H-NR (pH 6.5) in soybean is the enzyme responsible for NO_(x) formation. The Blue Sepharose-purified soybean enzyme has a pH optimum of 6.75, an apparent K_m for nitrite of 0.49 millimolar, and an apparent K_m for NADPH and NADH of 7.2 and 7.4 micromolar, respectively, for the NO_(x) evolution activity. In addition to NAD(P)H, reduced flavin mononucleotide (FMNH₂) and reduced methyl viologen (MV) can serve as electron donors for NO_(x) evolution activity. The NADPH-, FMNH₂-, and reduced MV-NO_(x) evolution activities were all inhibited by cyanide. The NADPH activity was also inhibited by p-hydroxymer-curibenzoate, whereas, the FMNH₂ and MV activities were relatively insensitive to inhibition. These data indicate that the terminal molybdenum-containing portion of the enzyme is involved in the reduction of nitrite to NO_(x). NADPH eluted both NR and NO_(x) evolution activities from Blue Sepharose columns loaded with extracts of either nitrate- or zero N-grown winged bean (Psophocarpus tetragonolobus [L.]), whereas NADH did not elute either type of activity. Winged bean appears to contain only one type of NR enzyme that is similar to the constitutive NAD(P)H-NR (pH 6.5) enzyme of soybean.     

Roles for the integrin VLA-4 and its counter receptor VCAM-1 in myogenesis.

Mammalian myogenesis is biphasic: primary myoblasts fuse to form primary myotubes, then secondary myoblasts align along the primary myotubes and form secondary myotubes, which comprise most of adult muscle. We provide evidence that an integrin (VLA-4) and its counter receptor (VCAM-1) have a role in secondary myogenesis. Both receptors are synthesized by cultured muscle cells: VLA-4 is induced as myotubes form, whereas VCAM-1 is present on myoblasts and myotubes. In vivo, both molecules are expressed at sites of secondary myogenesis, VLA-4 on primary and secondary myotubes, and VCAM-1 on secondary myoblasts and on regions of secondary myotubes apposed to primary myotubes. These patterns suggest that VLA-4-VCAM-1 interactions influence alignment of secondary myoblasts along primary myotubes and/or the fusion of secondary myoblasts. In support of the latter possibility, antibodies to VLA-4 or VCAM-1 inhibit myotube formation in culture.     

Maternal High‐Fat Diet Effects on Adaptations to Metabolic Challenges in Male and Female Juvenile Nonhuman Primates

Objective

This study aimed to determine whether maternal high‐fat diet (HFD) consumption in nonhuman primates alters the ability of offspring to adapt metabolically to nutrient and caloric challenges.

Methods

Offspring from Japanese macaque dams fed either a control (CTR) diet or HFD were weaned onto a CTR diet creating two groups: maternal HFD (mHFD, n = 18) and maternal CTR (mCTR) diet (n = 12). Male and female offspring were exposed to a 5‐day 30% calorie restriction and to a 35‐day HFD challenge (HFDC), at 16 and 24 months of age, respectively. Caloric intake, body weight, and energy expenditure were measured.

Results

Offspring from both groups showed similar body weight, food intake, and metabolic adaptations to a 5‐day calorie restriction. mHFD offspring demonstrated increased food intake and early weight gain in response to a 35‐day HFDC; however, group differences in weight dissipated during the challenge. Unlike mCTR animals, the mHFD group had a significant increase in fasting insulin after acute HFD exposure.

Conclusions

The current findings indicate that offspring exposed to an mHFD show metabolic adaptations to calorie restriction that are largely similar to those of offspring exposed to a mCTR diet but show delayed adaptation upon exposure to an acute HFDC.

     

Ultrastructure of the spermatozoid of Lycopodium obscurum (Lycopodiaceae)

Ultrastructural observations reveal that the spermatozoid of Lycopodium obscurum is crescent shaped and contains two posteriorly directed flagella that are inserted at the front of the cell. The nucleus is broad and elongated with a narrow posterior projection or nuclear diverticulum. Spline microtubules (MTs) number 180 at their maximum and provide the framework for the cell. These MTs extend from the anterior of the locomotory apparatus and along the outermost surface of the nucleus, with a central shank of 14–17 MTs encircling the cell for at least one-third gyre beyond the nucleus. The two basal bodies are slightly staggered and positioned at the front of the cell over a highly elongated multilayered structure (MLS). The MLS extends laterally around the cell anterior and curves posteriorly over the nucleus. One large anterior mitochondrion is situated subjacent to the MLS, while numerous small mitochondria are scattered near or among the lobes of the single plastid. The plastid rests on the inner nuclear surface and contains numerous large starch grains. This cell differs from that of L. cernuum, the only other species of Lycopodium examined to date, in that it is more elongated and has an anterior-posterior orientation of the nucleus, basal bodies, MLS, and spline. Comparisons with coiled gametes of bryophytes and Selaginella suggest that some degree of coiling and cell streamlining may be ancestral in archegoniate spermatozoids.