Morphological gradients in the starling basilar papilla

The starling cochlea was studied with TEM at four locations along the basilar papilla to investigate gradients in morphological features over the papilla's length and width. Hair cell shape changes continuously from neural to abneural and from basal to apical. Unlike the situation in mammals, there are no distinct populations of hair cells; the previously described types (tall hair cells and short hair cells) are merely extremes in a continuum. Contacts between THC are a normal feature. Except at the base of the papilla, SHC have very large cuticular plates, suggesting a micromechanical function for these cells. In contrast to the THC, the SHC normally completely lack afferent innervation; this indicates that their function is restricted to within the basilar papilla itself. © 1992 Wiley-Liss, Inc.     

Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications

Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of individuals representing 54 species of frogs, two species of salamanders, a caecilian, and a lungfish. Eight of these sites were present in all species examined, and two were found in all but one species. Alignment of these conserved restriction sites revealed, among anuran 28S rRNA genes, five regions of major length variation that correspond to four of 12 previously identified divergent domains of this gene. One of the divergent domains (DD8) consists of two regions of length variation separated by a short segment that is conserved at least throughout tetrapods. Most of the insertions, deletions, and restriction-site variations identified in the 28S gene will require sequence-level analysis for a detailed reconstruction of their history. However, an insertion in DD9 that is coextensive with frogs in the suborder Neobatrachia, a BstEII site that is limited to representatives of two leptodactylid subfamilies, and a deletion in DD10 that is found only in three ranoid genera are probably synapomorphies.      

Factor interactions with the simian virus 40 early pre-mRNA influence branch site selection and alternative splicing.

To study the interaction of splicing factors with the simian virus 40 early-region pre-RNA, which can be alternatively spliced to produce large T and small t mRNAs, we used an in vitro RNase protection assay that defines the 5' boundaries of factor-RNA interactions. Protection products reflecting factor interactions with the large T and small t 5' splice sites and with the multiple lariat branch site region were characterized. All protection products were detected very early in the splicing reaction, before the appearance of spliced RNAs. However, protection of the large T 5' splice site was detected well before small t 5' splice site and branch site protection products, which appeared simultaneously. Oligonucleotide-targeted degradation of small nuclear RNAs (snRNAs) revealed that protection of the branch site region, which occurred at multiple sites, required intact U2 snRNA and was enhanced by U1 snRNA, while protection of the large T and small t 5' splice sites required both U1 and U2 snRNAs. Analysis of several pre-RNAs containing mutations in the branch site region suggests that factor interactions involving the multiple copies of the branch site consensus determine the selection of branch points, which is an important factor in the selection of alternative splicing pathways.     

Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells

Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction.     

Influence of food intake but independence of body weight on puberty in female sheep

The effect of maintaining female sheep at a body weight intermediate between the normal weight for puberty (30-35 kg) and 20 kg (puberty suppressed) on the onset of oestrous cycles was studied. In addition, the influence of ad-libitum food intake or insulin infusion was studied in animals previously maintained at 20 kg. Coopworth ewe lambs (10 weeks old) were allocated to one of 6 treatments: (A) ad-libitum fed (n = 6), (B) ad-libitum fed to 28 kg then maintained at that weight (n = 6), (C) ad-libitum fed to 24 kg then maintained at that weight (n = 6), (D) maintained at 20 kg until Week 29 and then fed ad libitum (n = 6), (E) maintained at 20 kg and infused with 0.1 U insulin/kg/24 h for 2 weeks from 29-31 weeks of age (n = 5), (F) maintained at 20 kg (n = 6). The lambs were penned indoors under natural photo-period, which was decreasing virtually throughout the study, and fed a pelleted concentrate diet which was recorded daily. They were blood sampled twice a week, and plasma was analysed for progesterone. Puberty was defined as the date when plasma concentrations of progesterone first exceeded 1 ng/ml. In addition, ewes in Groups D, E and F were blood sampled every 10 min for 8 h on Days 0 and +12 of the insulin infusion or access to ad-libitum feeding and the plasma was analysed for luteinizing hormone (LH).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative Zone Electrophoresis of Enzymes of Pseudomonas solanacearum and Pseudomonas cepacia

The technique of starch-gel electrophoresis with specific staining for a series of enzymes was used to compare 21 Pseudomonas strains representing both P. cepacia and P. solanacearum. These experiments produced no evidence for close similarity of the two species. Twelve strains of P. solanacearum were compared by means of data obtained from nine different enzymes, and the data indicate that these strains belong in two biotypes. Except for the assignment of two strains, these groups are the same as the two major groups previously derived from nutritional properties and from deoxyribonucleic acid hybridization experiments. Eleven enzymes were available for comparisons of the P. cepacia strains. Eight of these strains form a homogeneous group, but the last strain, number 249, differs considerably from the other representatives of the species.