Identification and expression of the achaete-scute complex in the silkworm, Bombyx mori.

Recently, the study of achaete-scute (AS-C) homologues has contributed enormously to understanding of gene duplication and function evolution, particularly in Diptera. We identified four AS-C homologue genes in the silkworm, Bombyx mori, referred to as BmASH, BmASH2, BmASH3, and Bmase. The complex displayed tandem array structure in the genome. Analysis of spatial expression profiles showed that they all were expressed in obviously higher levels in wing disc than in other tissues, suggesting that they might play important roles in the development of the wing. Furthermore, we found that their expression profiles in the wing discs were mostly correlated with the development of the scales, especially the BmASH gene. RNA interference results further indicated that BmASH was necessary for scale formation in silkworm wing.

Molecular cloning and characterization of a chitosanase from the chitosanolytic bacterium Burkholderia gladioli strain CHB101.

A chitosanase was purified from the culture fluid of the chitino- and chitosanolytic bacterium Burkholderia gladioli strain CHB101. The purified enzyme (chitosanase A) had a molecular mass of 28 kDa, and catalyzed the endo-type cleavage of chitosans having a low degree of acetylation (0-30%). The enzyme hydrolyzed glucosamine oligomers larger than a pentamer, but did not exhibit any activity toward N-acetylglucosamine oligomers and colloidal chitin. The gene coding for chitosanase A (csnA) was isolated and its nucleotide sequence determined. B. gladioli csnA has an ORF encoding a polypeptide of 355 amino acid residues. Analysis of the N-terminal amino acid sequence of the purified chitosanase A and comparison with that deduced from the csnA ORF suggests post-translational processing of a putative signal peptide and a possible substrate-binding domain. The deduced amino acid sequence corresponding to the mature protein showed 80% similarity to the sequences reported from Bacillus circulans strain MH-K1 and Bacillus ehimensis strain EAG1, which belong to family 46 glycosyl hydrolases.

Psychometric functions for gap detection in noise measured from young and aged subjects.

Psychometric functions for gap detection of temporal gaps in wideband noise were measured in a "yes/no" paradigm from normal-hearing young and aged subjects with closely matched audiograms. The effects of noise-burst duration, gap location, and uncertainty of gap location were tested. A typical psychometric function obtained in this study featured a steep slope, which was independent of most experimental conditions as well as age. However, gap thresholds were generally improved with increasing duration of the noise burst for both young and aged subjects. Gap location and uncertainty had no significant effects on the thresholds for the young subjects. For the aged subjects, whenever the gap was sufficiently away from the onset or offset of the noise burst, detectability was robust despite uncertainty about the gap location. Significant differences between young and aged subjects could be observed only when the gap was very close to the signal onset and offset.

Estimating parameters for psychometric functions using the four-point sampling method.

Although a psychometric function describing a subject's responses to some physical stimuli is of considerable value, characterizing such functions is time consuming and, hence, is not carried out routinely in psychophysical experiments. A principal reason for the lack of efficiency in characterizing a psychometric function is the use of sampling methods that either converge on a single point on the psychometric function, such as the PEST method, or which distribute observations uniformly over a wide range, such as the constant stimuli method. As an alternative, a multimodal four-point sampling method has been proposed [C. F. Lam, J. H. Mills, and J. R. Dubno, J. Acoust. Soc. Am. 99, 3689-3693 (1996)]. A psychometric function is then fitted to the four points (each with several trials) to estimate the threshold and slope parameters of the psychometric function. Adaptive methods, such as the up-down methods [H. Levitt, J. Acoust. Soc. Am. 49, 467-477 (1971)], can be used to provide good initial estimates of the threshold and spread parameters of a psychometric function described by a logistic function. In ongoing studies of age-related changes in auditory masking and discrimination, this new four-point sampling method has been applied to determine psychometric functions for absolute thresholds as a function of duration, thresholds in simultaneous and forward masking, frequency discrimination, and intensity discrimination in both young and aged human subjects. Results indicate that a reduction in data collection time of about 50% with no increase in variance can be achieved. This increase in efficiency applies to simple detection tasks by normal hearing subjects as well as to complex discrimination tasks by older subjects with hearing loss.

Effects of aging on the fine structure of the 2f1-f2 acoustic distortion product.

The fine structures of 2f1-f2 acoustic distortion products (ADP) were measured in four groups of human subjects: (1) young with normal hearing, (2) aged with normal or near-normal hearing, (3) aged subjects with more severe hearing loss above 2000 Hz, and (4) young with hearing similar to those of the normal- or near-normal-hearing aged group. The purpose of this study was to investigate how ADP fine structure changes with age and hearing loss. Results show that the fine structure is observable whenever the ADP is measurable, and its sharpness, defined as the peak-to-peak frequency distance, is independent of age hearing loss, and longitudinal amplitude change. There is a large variance in ADP peak amplitudes in aged subjects with or without hearing loss as compared to young normal hearing subjects, the aged group generally having lower peak amplitudes than those of the young group. According to an ANOVA analysis with absolute threshold as covariate, the null hypothesis stating that there is no aging effect on the ADP peak responses cannot be ruled out, a conclusion similar to that made by Stover and Norton [J. Acoust. Soc. Am. 94, 2670-2681 (1993)]. On the other hand, threshold changes cannot explain all the differences in ADP amplitude. It is clear that the relationship between ADP amplitudes and behavioral thresholds can differ between young and aged populations. At primary levels of 50 dB SPL, almost normal ADP magnitudes are often found in aged subjects even when associated with a 35-dB hearing loss, whereas for young subjects ADPs typically were not measurable when associated with the pure-tone thresholds of 20 dB HL or higher. This dichotomy may be explained by the different etiologies of cochlear pathologies predominant in the two groups.

Modeling the fine structure of the 2f1-f2 acoustic distortion product. I. Model development.

The fine structure of the 2f1-f2 acoustic distortion product (ADP) as a function of frequency has been measured in human subjects and shows a series of sharp peaks and valleys (rippling) with peak-to-valley level differences of up to 15-20 dB. In order to delineate the cause of the ADP rippling pattern, a computer model was developed to simulate the behavior of the ADP, specifically the ADP fine structure. The ADP model includes the middle ear and cochlea. The middle ear was treated as a simple signal delivery system in both the forward and reverse directions. The ADP was assumed to be generated within the cochlea by nonlinear elements taken to be the outer hair cells (OHCs), and an array of ADP generators was used to simulate the OHCs along the basilar membrane (BM). The magnitude and phase of the output of each of the ADP generators were functions of the local responses of the two primary traveling waves. The traveling waves were calculated from a passive transmission line model of the BM using the WKB approximation, coupled to a second-order resonance to mimic the contribution from active OHC feedback. The system output of ADP in dB was proportional to the weighted vectorial sum of all the components, arriving at the stapes. Parameters such as lateral coupling and feedback gain were examined.

Modeling the fine structure of the 2f1-f2 acoustic distortion product. II. Model evaluation.

In a previous article, a vector sum model was developed that successfully reproduces the ADP rippling pattern when a nonuniformity is introduced in the active damping factor, a parameter that is inversely related to the energy gain contribution of the outer hair cells [OHCs, Sun et al., J. Acoust. Soc. Am. 96, 2166-2174 (1994)]. Here, the mean of the damping factor is increased nonlinearly with input level, mimicking the saturation of the active feedback of the OHCs. The passive damping factor in the transmission line model was also nonlinearly increased with input level to reproduce the frequency shift of the peak of the traveling wave observed in experimental data. The resulting model simulates an ADP that is compatible with data from human subjects wherein the ADP fine structure does not saturate with level. Moreover, the model suggests that the shifting of the ADP pattern with level is a direct result of the peak shift of the traveling wave, thus implicating the nonlinear damping factors as the underlying basis of this phenomenon. The input/output (I/O) functions of the simulated ADP emissions at specific frequencies were also examined. The resulting functions show a variety of shapes, depending on the pattern of ADP fine structure around the I/O frequency, and the way the fine structure shifts as primary levels increase. These I/O functions are also similar to those observed in human subjects, even with regard to overall slopes which approximate one. Thus the model illustrates how cubic distortion generators coupled with damping on linearities can yield I/O function slopes on the order of one, rather than the expected three.(ABSTRACT TRUNCATED AT 250 WORDS)

Fine structure of the 2f1-f2 acoustic distortion product: changes with primary level.

The fine frequency structure of the 2f1-f2 acoustic distortion product (ADP fine structure) was examined in ten human subjects with normal hearing. Primary frequencies (f1 and f2) were incremented in steps of 1/32 octave with an f2/f1 ratio of 1.2. The primary levels were kept equal to each other and varied from 45 to 65 dB SPL in 2.5-dB steps. The results show that the ADP fine structure is characterized by a series of peaks and valleys across frequency, with a peak-to-peak frequency spacing of about 3/32 octave and a peak-to-valley amplitude ratio of up to 20 dB. At frequencies below 4000 Hz, as primary level increases, the sharpness of the ADP fine structure is not significantly reduced and the pattern gradually shifts to lower frequencies. At frequencies above 4000 Hz, a flattening of the pattern is sometimes observed at high levels. A consequence of the underlying process responsible for the fine structure is that ADP input/output (I/O) functions can be highly variable in shape. Dramatic shape changes can occur for ADP I/O functions obtained with primary frequency changes of as little as 1/32nd of an octave. The outward cause of I/O function variability is the behavior of the ADP fine structure with level; i.e., it remains robust at high levels and systematically shifts to lower frequencies with level. As a result, ADP peaks can shift to valleys with increasing level and vice versa. Thus, small shifts in primary frequency can result in significant changes in the shape of the ADP I/O function in humans.