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Prestin is the motor protein of cochlear outer hair cells. It belongs to a distinct anion transporter family called solute carrier protein 26A, or SLC26A. Members of this family serve two fundamentally distinct functions. Although most members transport different anion substrates across a variety of epithelia, prestin (SLC26A5) is unique, functioning as a voltage-dependent motor protein. Recent evidence suggests that prestin orthologs from zebrafish and chicken are electrogenic divalent/chloride anion exchangers/transporters with no motor function. These studies appear to suggest that prestin was evolved from an anion transporter. We examined the motor and transport functions of prestin and its orthologs from four different species in the vertebrate lineage, to gain insights of how these two physiological functions became distinct. Somatic motility, voltage-dependent nonlinear capacitance (NLC), and transporter function were measured in transfected human embryonic kidney (HEK) cells using voltage-clamp and anion uptake techniques. Zebrafish and chicken prestins both exhibited weak NLC, with peaks significantly shifted in the depolarization (right) direction. This was contrasted by robust NLC with peaks left shifted in the platypus and gerbil. The platypus and gerbil prestins retained little transporter function compared with robust anion transport capacities in the zebrafish and chicken orthologs. Somatic motility was detected only in the platypus and gerbil prestins. There appears to be an inverse relationship between NLC and anion transport functions, whereas motor function appears to have emerged only in mammalian prestin. Our results suggest that motor function is an innovation of therian prestin and is concurrent with diminished transporter capabilities.

Prestin (SLC26A5) is the molecular motor responsible for cochlear amplification by mammalian cochlea outer hair cells and has the unique combined properties of energy-independent motility, voltage sensitivity, and speed of cellular shape change. The ion transporter capability, typical of SLC26A members, was exchanged for electromotility function and is a newly derived feature of the therian cochlea. A putative minimal essential motif for the electromotility motor (meEM) was identified through the amalgamation of comparative genomic, evolution, and structural diversification approaches. Comparisons were done among nonmammalian vertebrates, eutherian mammalian species, and the opossum and platypus. The opossum and platypus SLC26A5 proteins were comparable to the eutherian consensus sequence. Suggested from the point-accepted mutation analysis, the meEM motif spans all the transmembrane segments and represented residues 66–503. Within the eutherian clade, the meEM was highly conserved with a substitution frequency of only 39/7497 (0.5%) residues, compared with 5.7% in SLC26A4 and 12.8% in SLC26A6 genes. Clade-specific substitutions were not observed and there was no sequence correlation with low or high hearing frequency specialists. We were able to identify that within the highly conserved meEM motif two regions, which are unique to all therian species, appear to be the most derived features in the SLC26A5 peptide.

Until recently, breeding programs in Africa placed little emphasis on grain quality improvement. Consequently, some farmers have not adopted improved high yielding varieties because they lacked desired quality characteristics for processing and other end uses. We conducted this study to determine the effects of N application on some maize (Zea mays L.) grain quality parameters. In 1993 and 1994, five maize cultivars under four N levels (0, 30, 60, and 120 kg ha -1 ) were evaluated at Zaria (11° 11' N), northern Nigeria, on a Plinthustalf (fine-loamy isohyperthermic). Increasing N levels increased grain yield, kernel weight, and grain protein quadratically for all the cultivars. The hybrid 8644-27 had the highest grain yield and kernel weight of 5.3 Mg ha -1 and 26.62 mg kernel -1 , respectively. Average grain protein yield per unit area was not significantly different among cultivars in both years. At 30 to 60 kg N ha -1 , the cultivars 8644-27 and TZPB-SR had a greater percentage of floaters, than the other cultivars in both years, reflecting a greater proportion of floury endosperm, indicating that they would be best for traditional dry milling, where the whole grain is ground to produce flour. Also, at 30 to 60 kg N ha -1 , SPL and TZB-SR had a relatively low percentage of floaters and high test weights of over 811 kg m -3 in 1993 and 778 kg m -3 in 1994, and should give high yields of grits when processed. Thus, both cultivars have high value for industrial dry milling. Results showed that the choice of cultivar and N level may affect grain quality and they should be considered in producing maize for dry milling purposes.

Jejunal self-filling blind loops with subsequent small bowel bacterial overgrowth (SBBO) induce hepatobiliary injury in genetically susceptible Lewis rats. Lesions consist of portal tract inflammation, bile duct proliferation, and destruction. To determine the pathogenesis of SBBO-induced hepatobiliary injury, we treated Lewis rats with SBBO by using several agents with different mechanisms of activity. Buffer treatment, ursodeoxycholic acid, prednisone, methotrexate, and cyclosporin A failed to prevent SBBO-induced injury as demonstrated by increased plasma aspartate aminotransferase (AST) and elevated histology scores. However, hepatic injury was prevented by mutanolysin, a muralytic enzyme whose only known activity is to split the beta 1-4 N-acetylmuramyl-N-acetylglucosamine linkage of peptidoglycan-polysaccharide (PG-PS), a bacterial cell wall polymer with potent inflammatory and immunoregulatory properties. Mutanolysin therapy started on the day blind loops were surgically created and continued for 8 wk significantly diminished AST (101 +/- 37 U/liter) and liver histology scores (2.2 +/- 2.7) compared to buffer-treated rats (228 +/- 146 U/liter, P < 0.05, 8.2 +/- 1.9, P < 0.001 respectively). Mutanolysin treatment started during the early phase of hepatic injury, 16-21 d after surgery, decreased AST in 7 of 11 rats from 142 +/- 80 to 103 +/- 24 U/liter contrasted to increased AST in 9 of 11 buffer-treated rats from 108 +/- 52 to 247 +/- 142 U/liter, P < 0.05. Mutanolysin did not change total bacterial numbers within the loop, eliminate Bacteroides sp., have in vitro antibiotic effects, or diminish mucosal PG-PS transport. However, mutanolysin treatment prevented elevation of plasma anti-PG antibodies and tumor necrosis factor-alpha (TNF alpha) levels which occurred in buffer treated rats with SBBO and decreased TNF alpha production in isolated Kupffer cells stimulated in vitro with PG-PS. Based on the preventive and therapeutic activity of this highly specific muralytic enzyme, we conclude that systemic uptake of PG-PS derived from endogenous enteric bacteria contributes to hepatobiliary injury induced by SBBO in susceptible rat strains.

Hybrids adapted to West and Central Africa were developed by the International Institute of Tropical Agriculture (IITA) in the 1980s, which enabled the establishment of several private seed companies in Nigeria. Despite the superior agronomic performance of hybrids, farmers still prefer their traditional cultivars in some areas because they possess desired storage and processing characteristics for local maize dishes. A study was conducted to evaluate physical, chemical, and water absorption characteristics of eleven tropical maize hybrids developed at IITA as indicators of their suitability for common end-uses in the region. Significant differences were observed among hybrids for all the parameters investigated but none of the hybrids excelled in all quality characteristics. Hybrid 8644-31 had relatively high test weight, thousand kernel weight, hardness index, percent protein, ash, and crude fibre. However, it was low in starch content, total sugars, and water absorption index of grain. Protein, ash, crude fibre, starch, amylose, and amylopectin values for all the hybrids fell within the normal range for maize. Values for total sugars ranged from 3.04 to 5.69% and fat content ranged from 3.35 to 9.80%. Nearly all the hybrids had fat content values which were higher than those reported elsewhere for normal maize. The presence of genetic variation among the hybrids suggests that potential exist for improvement of grain quality to suit specific processing and food use requirements through selection and breeding. Breeding programmes in developing countries should target hybrid development to meet the requirements of producers, processors, and consumers. Key Words: Chemical characteristics, hybrid maize, physical properties, West Africa Resume Des hybrides adaptes aux conditions de l'Afrique centrale et occidentale ont ete mis au point par l'Institut international d'agriculture tropicale (IITA) au cours des annees 80, ce qui a permis l'etablissement de plusieurs societes privees de production semenciere au Nigeria. Malgre la performance agronomique superieure des hybrides, les agriculteurs preferent encore leurs cultivars traditionnels dans certaines localites parce qu'ils sont dotes des caracteristiques de stockage et de transformation recherchees pour les mets locaux. Une etude a ete menee pour evaluer les caracteristiques physiques, chimiques et d'absorption d'eau de 11 hybrides de mais tropical mis au point par l'IITA, en tant qu'indicateurs de leur conformite a des utilisations finales courantes dans la region. Pour tous les parametres etudies, des differences significatives ont ete observees parmi les hybrides. Aucun des hybrides n'etait dote de toutes les caracteristiques de qualite. Pour l'hybride 8644-31, le poids test, le poids de mille grains, l'indice de durete, la teneur en proteine, en cendre et en fibre brut etaient relativement eleves. Cependant, la teneur en amidon, sucres totaux et l'indice d'absorption d'eau des grains etaient faibles. La teneur en proteine, cendre, fibre brut, amidon, amylose et amylopectine pour tous les hybrides se situait dans la gamme normale relative au mais. Pour les sucres totaux, la gamme etait de 3,04 a 5,69%. La teneur en matiere grasse etait de l'ordre de 3,35 a 9,80% et presque tous les hybrides avaient une teneur plus elevee que celle du mais normal indiquee ailleurs. La variation genetique observee parmi les hybrides suggere qu'il existe un potentiel d'amelioration de la qualite des grains afin de les adapter aux besoins de transformation specifiques et d'utilisation alimentaire grâce a la selection et a l'amelioration. Les programmes d'amelioration des pays en developpement devraient se concentrer sur la mise au point des hybrides en vue de satisfaire les besoins des producteurs, des transformateurs et des consommateurs. Mots Cles: Caracteristiques chimiques, mais hybride, proprietes physiques, West Africa (African Crop Science Journal 8(4) 2000: 419-428)