Myosin light-chain expression during avian muscle development

Monoclonal antibodies to adult chicken myosin light chains were generated and used to quantitate the types of myosin light-chain (MLC) isoforms expressed during development of the pectoralis major (PM), anterior latissimus dorsi (ALD), and medial adductor (MA) muscles of the chicken. These are muscles which, in the adult, are composed predominantly of fast, slow, and a mixture of fiber types, respectively. Three distinct phases of MLC expression characterized the development of the PM and MA muscles. The first identifiable pase occurred during the period of 5-7 d of incubation in ovo. Extracts of muscles from the pectoral region (which included the presumptive PM muscle) contained only fast MLC isoforms. This period of exclusive fast light-chain synthesis was followed by a phase (8- 12 d of incubation in ovo) in which coexpression of both fast and slow MLC isoforms was apparent in both PM and MA muscles. During the period, the composition of both fast and slow MLC isoforms in the PM and MA muscles was identical. Beginning at day 12 in ovo, the ALD was also subjected to immunochemical analyses. The proportion of fast and slow MLCs in this muscle at day 12 was similar to that present in the other muscles studied. The third development phase of MLC expression began at approximately 12 d of incubation in ovo and encompassed the transition in MLC composition to the isoform patterns incubation in ovo and encompassed the transition in MLC composition to the isoform patterns typical of adult muscle. During this period, the relative proportion of slow MLC rose in both the MA and ALD and fell in the PM. By day 16, the third fast light chain, LC(3f), was apparent in extracts of both the PM and MA. These results show that there is a developmental progression in the expression of MLC in the two avian muscles studied from day 5 in ovo; first, only fast MLCs are accumulated, then both fast and slow MLC isoforms are expressed. Only during the latter third of development in ovo is the final MLC isoform pattern characteristic of a particular muscle type expressed.     

Continuous selective models

Neglecting age-structure, but taking into account matings with differential fertility in Mendelian reproduction, continuous selective models are formulated for a single locus with an arbitrary number of alleles, with or without distinguishing the sexes, and for two alleles at each of two loci in a monoecious population. In each case, without restricting the mating system, differential equations are derived for the genotypic frequencies, and the validity of the customary Malthusian-parameter differential equations for the gametic frequencies is established. Particular attention is devoted to the conditions for Hardy-Weinberg proportions under random mating. For multiple alleles at a single locus in a monoecious population, exact solutions are obtained for the following three Hardy-Weinberg models: gametic selection, no dominance, and the same selective effect for all alleles but one. The last scheme includes, as special cases, a completely dominant or recessive distinguished allele, and arbitrary selection with only two alleles. Two single-locus assortative mating patterns are analyzed for a monoecious organism using the general formalism. One of these has an arbitrary number of alleles, all the genotypes being distinguishable, while the other involves two alleles, one of which is completely dominant to the other.     

Subcellular Pathology of Human Neurodegenerative Disorders: Alzheimer-Type Dementia and Huntington''s Disease

Activities of enzyme markers of subcellular organelles have been measured in brain tissue from subjects with Alzheimer-type dementia (ATD) and Huntington's disease (HD). Significant increases in the activity of the lysosomal enzyme beta-glucuronidase were observed in both ATD temporal cortex and HD putamen. It is suggested that beta-glucuronidase activity may be a useful biochemical indicator of cellular damage in the CNS. A significant reduction in neutral alpha-glucosidase activity was observed in ATD temporal cortex and HD putamen. This change may reflect an alteration in glycoconjugate processing and may relate to the susceptibility of neurones to the degenerative processes of ATD and HD.     

Correlated reduction of velocity of shortening and the rate of energy utilization in mouse fast-twitch muscle during a continuous tetanus

Isometric tetani of slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles of the mouse were studied at 20 degrees C. The total energy cost for 3- and 9-s isometric tetani was measured as a function of length above L0 and partitioned into a filament overlap-dependent fraction and a smaller filament overlap-independent fraction. In both muscles, the rate of filament overlap-independent energy cost did not change with tetanic duration. In the EDL, but not in the soleus, the rate of filament overlap-dependent energy utilization was greater in a 3-s tetanus than in a 9-s tetanus. The force-velocity relationships were studied after 3 and 9 s of isometric tetanus. In the soleus, Vmax was 2 fiber lengths/s and was not dependent on the duration of isometric tetanus. In contrast, in the EDL, Vmas decreased from 5.9 fiber lengths/s at 3 s to 3.9 fiber lengths/s at 9 s. The velocity of unloaded shortening (Vus) was examined by the slack test method as a function of the duration of isometric tetanus duration over the range of 1-15 s. In the soleus, Vus did not change, whereas in the EDL, Vus declined progressively from 6.4 to 3.2 fiber lengths/s after an isometric tetanus of increasing duration from 1 to 15 s. These results cannot exclude the hypothesis that in a maintained tetanus there is a decrease in the intrinsic cross- bridge turnover rate in the fast-twitch EDL, but not in the slow-twitch soleus muscle.     

Properties of a Streptococcus lactis strain that ferments lactose slowly

Streptococcus lactis 7962, which ferments lactose slowly, has a lactose phosphoenolpyruvate-dependent phosphotransferase system and low phospho-beta-galactosidase activity, in addition to high beta-galactosidase activity. Lactose 6'-phosphate accumulated to a high concentration (greater than 100 mM) in cells growing on lactose. In contrast, lactic streptococci, which ferment lactose rapidly and use only the lactose-phosphotransferase system for uptake, contained high phospho-beta-galactosidase activity and low concentrations (0.9 to 1.6 mM) of lactose 6'-phosphate. It is concluded that rate-limiting phospho-beta-galactosidase activity is primarily responsible for defective lactose metabolism in S. lactis 7962.     

Serotonin Receptor Changes in Dementia of the Alzheimer Type

Serotonin receptors were assessed in post-mortem brains of control and Alzheimer-type dementia (ATD) patients using ligand binding techniques. Differential losses of serotonin S1 and S2 receptors were present in neocortex, hippocampus, and amygdala of ATD patients, whereas no significant changes were observed in basal forebrain and basal ganglia. Losses of S1 receptors were significantly age-related in the ATD group, suggesting they occurred at a later stage of the disease process. Losses of S2 receptors were considerably greater (with a reduction to 35% of control in temporal cortex) and were not age-related in ATD. Significant correlations were observed within the ATD group between S2 receptor binding and somatostatin immunoreactivity in temporal and frontal cortices. Thus the loss of S2 receptors in ATD may be a relatively early change in the disease process, and may precede the changes in ascending serotonergic neurones.