DNA repair: knockouts still mutating after first round

Recent studies have investigated whether particular DNA repair pathways are involved in the somatic hypermutation mechanism that increases antibody diversity. The primary mutation mechanism still functions in mice carrying knockouts of all repair genes examined, but mismatch repair defects affect the final outcome.     

Rotational Spectrum, Structure, and Electric Dipole Moment of Bis(difluoromethyl) Ether

The rotational spectrum of bis(difluoromethyl) ether (CF2HOCF2H) has been observed and analyzed using both a conventional Stark-modulated microwave spectrometer and a pulsed molecular beam Fabry-Perot cavity microwave (FTMW) spectrometer. The lowest energy conformer studied here has a (hydrogen) syn-anti conformation. The high sensitivity of the FTMW spectrometer permits observation and analysis of the 13C, 18O, and 2H isotopomers in natural abundance. The electric dipole moment was measured for the normal species and found to be μa = 5.020(7) x 10(-30) C. m [1.505(2) D], μb = 0.19(4) x 10(-30) C. m [0.056(11) D], μc = 0.48(2) x 10(-30) C. m [0.144(7) D], and μT = 5.047(10) x 10(-30) C. m [1.513(3) D].     

Dissolution of particulate hydroxyapatite in a macrophage organelle model

The optimum 14N pulse lengths in the 13C-14N rotational-echo adiabatic-passage double-resonance (REAPDOR) NMR experiment are determined from calculations and from experiments on samples of glycine and L-alanine. The REAPDOR experiment utilizes the adiabatic passages that 14N spins make between the 14N Zeeman energy levels during the application of a single, short 14N radiofrequency pulse. Use of a short 14N irradiation time of less than one-quarter of a rotor period ensures that the number of 14N spins that undergo more than one passage is minimized. This simplifies calculations describing 13C dipolar dephasing and provides better agreement between calculations and experiments. Recovery of the 13C-14N dipolar couplings and 14N quadrupolar coupling constants and asymmetry parameters is described.     

Perirhinal and postrhinal cortices of the rat: interconnectivity and connections with the entorhinal cortex

The cortical regions dorsally adjacent to the posterior rhinal sulcus in the rat can be divided into a rostral region, the perirhinal cortex, which shares features of the monkey perirhinal cortex, and a caudal region, the postrhinal cortex, which has connectional attributes similar to the monkey parahippocampal cortex. We examined the connectivity among the rat perirhinal (areas 35 and 36), postrhinal, and entorhinal cortices by placing anterograde and retrograde tracers in all three regions. There is a dorsal-to-ventral cascade of connections in the perirhinal and entorhinal cortices. Dorsal area 36 projects strongly to ventral area 36, and ventral area 36 projects strongly to area 35. The return projections are substantially weaker. The cascade continues with the perirhinal to entorhinal connections. Area 35 is more strongly interconnected with the entorhinal cortex, ventral area 36 somewhat less strongly, and dorsal area 36 projects only weakly to the entorhinal cortex. The postrhinal-to-perirhinal connections also follow this general pattern. The postrhinal cortex is more heavily connected with dorsal area 36 than with ventral area 36 and is more heavily connected with area 36 than with area 35. The rostral portion of the postrhinal cortex has the strongest connections with the perirhinal cortex. Like in the monkey, the perirhinal and postrhinal cortices have different patterns of projections to the entorhinal cortex. The perirhinal cortex is preferentially connected with the rostrolateral portion of the entorhinal cortex. The postrhinal cortex projects to a part of this same region but is also connected to caudal and redial portions of the entorhinal cortex. The perirhinal and postrhinal projections to the entorhinal cortex originate in layers III and V and terminate preferentially in layers II and III.     

The PPVT-R: validity as a quick screen of intelligence in a postacute rehabilitation setting for brain-injured adults

The utility of the Peabody Picture Vocabulary Test-Revised (PPVT-R) as a surrogate for the Wechsler Adult Intelligence Test-Revised (WAIS-R) was investigated in 61 brain-injured adult participants in a postacute rehabilitation setting. Idiographic comparison revealed substantial disagreement in clinical classification between the two instruments, and it is concluded that the PPVT-R is not a good surrogate for the WAIS-R for this purpose. In contrast, the PPVT-R was judged an adequate surrogate for the WAIS-R for the purpose of group comparison, as is common in biomedical research. Finally, contrary to prior report, the PPVT-R was demonstrated to measure more than simply Vocabulary. As such, in the absence of independent validation research, perhaps the most parsimonious conclusion regarding what the PPVT-R is measuring is that like each of the various subtests of the WAIS-R, the PPVT-R shares some of the variance of the construct termed intelligence, as well as demonstrates some unique variance that is likely comprised of error and, perhaps, a unique or different facet of intelligence.     

Convergence of nociceptive and non-nociceptive inputs onto spinal reflex pathways to the tibialis anterior muscle in humans

To investigate whether the familial clustering of cutaneous melanoma is consistent with Mendelian inheritance of a major autosomal gene, maximum likelihood segregation analyses were performed in a population-based sample of 1,912 families ascertained through a proband with melanoma diagnosed in Queensland between 1982 and 1990. Analyses were performed with the S.A.G.E. statistical package, using the REGTL program for a binary trait with a variable age of onset. We sought medical confirmation for all family members reported to have had melanoma, and only medically verified cases among relatives were included in the analyses. The hypothesis of codominant Mendelian inheritance gave a significantly better fit to the data than either dominant or recessive Mendelian inheritance, or environmental transmission. Overall, both Mendelian inheritance of a single major gene, and purely environmental transmission were rejected (P < 0.001). In both the single major gene and environmental models, there was strong evidence of familial dependence in melanoma occurrence (P < 0.001). These results are consistent with reported genetic heterogeneity in melanoma inheritance and suggest that other familial factors, such as pigmentation, skin type, and sun exposure habits, may play an important role in the familial clustering of melanoma.     

Neonatal mesenchyme temporal bone study: typical receding pattern versus increase in Potter's sequence

The fate of mesenchyme, which lines the fetal and newborn bony middle ear, is not well understood. The authors wished to test previous observations that a greater amount of mesenchyme was found in Potter's sequence (renal anomalies, pulmonary hypoplasia, and oligohydramnios). Using celloidin-embedded neonatal temporal bones (68 cases, 123 ears), with clinical and autopsy information, middle ear volumes were compared among diagnostic groups using analysis of variance. In 16 ears of Potter's sequence cases the volume of mesenchyme increased in proportion to the size of the middle ear. Conversely, in all other cases the volume of mesenchyme remained constant compared to increasing middle ear size. Both the volume of the bony middle ear and the volume of the air cavity increased at 15 mm3/500 g of body weight (gbw). Mesenchyme percentage decreased by 2%/500 gbw. Middle ear mesenchyme appears to recede rather than reabsorb. However, in Potter's sequence cases the volume of mesenchyme increases, raising issues of a missing renal signal that inhibits mesenchymal growth under normal circumstances.