Biomedical subjects
Publications and source records attributed to A Babu.
The first cases of congenital adrenal hyperplasia III with variable clinical manifestations in female monozygotic twins are presented. Twin "A" revealed severe hypertrophy of the clitoris, labial fusion and a visible introitus. However, twin "B" manifested moderate clitoral hypertrophy, a visible introitus and no labial fusion. Neither infant had palpable gonads.
The recent advent of banding techniques has facilitated the identification of human chromosomal abnormalities in neoplasias. Utilization of a single technique for the identification of marker chromosomes has caused ambiguity because staining profiles overlap with many other chromosomal regions in the human genome. Thus, the implication of DA/DAPI technique in clinical cytogenetics has been documented by presenting a variety of cases with neoplastic syndromes.
Externally added calmodulin (CaM) restored Ca2+ regulation for the tension development by skeletal muscle fibers of hamster and rabbit desensitized by the troponin C (TnC) extraction treatment. CaM produced this action by combining with the TnC-denuded sites in the fiber. However, the binding properties differed strikingly from TnC: unlike TnC, CaM binding required the continued presence of Ca2+ and the bound portion was completely released with EGTA in the physiological milieu. The maximal uptake was 1.7 g of CaM/kg of muscle in the present study. The apparent Ca2+ sensitivity for force development with 200 micrograms/ml CaM in the solution was lower than in the native fiber or in the TnC-loaded fiber. The apparent association constant for CaM binding to the TnC-denuded sites was found as 4.9 x 10(5) M-1, and the extrapolated maximum force (Fmax) with CaM was close to PO. The intrinsic CaM level in intact muscle was also measured and was 18.6 mg/kg, amounting to about 1% of the total TnC or the CaM uptake by TnC-denuded fibers. The intrinsic CaM was not dislodged by EDTA treatment, indicating tight binding and suggesting that it exists in a separate pool from the vacated TnC sites adsorbing externally added CaM. The stringent Ca+ dependence of the CaM adsorption to TnC sites in the regulatory complex in the fiber supports the view that the evolutionary replacement of residues in the amino terminus helix portion of the "EF-hand" motif of site IV may be critical for the functional specialization by TnC.
This study describes the effects of exchanging native cardiac troponin C (CTnC) from the right ventricular muscle of Syrian hamster for purified skeletal (S) TnC from fast twitch muscles in triggering cardiac contraction. Ca2+ sensitivity of the myocardium became decreased with STnC to 62% of the original value with CTnC. Furthermore, the slope of the pCa-force curve of cardiac muscle was found to be increased with STnC. The results show that the TnC moiety, as part of the switching mechanism during activation, also regulates thin-filament cooperativity in muscle. Modifications in both the Ca2+ sensitivity and cooperativity are associated with alterations in the primary structure of TnC.
According to Starling's law of the heart, the force of contraction during the ejection of blood is a function of the end-diastolic volume. To seek the molecular explanation of this effect, a study was made of the effects of length on Ca2+ sensitivity during tension development by isolated demembranated cardiac muscle in which the cardiac form of troponin C was substituted with skeletal troponin C. The results of troponin C exchange were compared at sarcomere lengths of 1.9 and 2.4 micrometers. Enhancement of the myocardial performance at the stretched length was greatly suppressed with the skeletal troponin C compared with the cardiac troponin C. Thus the troponin C subunit of the troponin complex that regulates the activation of actin filaments has intrinsic molecular properties that influence the length-induced autoregulation of myocardial performance and may be a basis for Starling's law of the heart.
A new approach is described for reconstituting a fully desensitized skeletal muscle fiber to restore its contractility. These studies revealed a novel regulatory cofactor, 30-50,000Mr by filtration (26-55kDa by SDS PAGE). It was shown to be critical for the Ca2+-activation in the physiological milieu. The cofactor was present in skeletal and cardiac muscles as well as in brain, but not in kidney and liver. The cofactor may be a second Ca2+ switch in a dual-regulation scheme for vertebrate muscle, or could provide an essential link in the cross-bridge cycle beyond activation.
The recent addition of restriction endonucleases in obtaining selective bands in the human genome has added a new dimension to molecular genetics. However, a considerable discrepancy exists in banding patterns produced by AluI in chromosomes 19 and 20, by MboI in chromosomes 4, 5, 8, 21 and 22 and by RsaI in chromosomes 12, 21 and 22. The principal causes of these differences are highlighted.
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The heteromorphisms of C-band regions of human chromosomes are evaluated by means of restriction endonucleases AluI, DdeI, MboI, and RsaI. Every chromosome exhibits heteromorphic markers of the C-band regions except chromosome 8. Each enzyme was found to be highly characteristic in its staining profile, a result that clearly suggests the diversity of heterochromatin. The inherent C-band-region heterochromatin variability that is revealed by these enzymes provides a valuable tool in identifying markers as compared with other previously described techniques.
The studies on intact fibers of the frog and fast-twitch skinned fibers of the Syrian hamster suggest the presence of intermediate low-force (weak) and high-force (strong) attachments in the cross-bridge cycle. Our results suggest that the weak and strong attachments may be separately regulated by independent calcium switches. The switch for weak bridges operates by calcium or decreasing ionic strength, such that in low ionic strength in skinned fibers the bridges form even in the virtual absence of TnC and calcium. The weak to strong transition appears to require Ca in both low and high ionic strengths. The Ca action effecting this transition may be mediated also by TnC and/or may involve the myosin moiety. Thus, the possibility is raised that Ca may act at two separate steps in the cross-bridge mechanism under physiological conditions.
The present study describes experiments on the myocardial trabeculae from the right ventricle of Syrian hamsters whose troponin C (TnC) moiety was exchanged with heterologous TnC from fast skeletal muscle of the rabbit. These experiments were designed to help define the role of the various classes of Ca2+-binding sites on TnC in setting the characteristic sensitivities for activations of cardiac and skeletal muscles. Thin trabeculae were skinned and about 75% of their troponin C extracted by chemical treatment. Tension development on activations by Ca2+ and Sr2+ was found to be nearly fully blocked in such TnC extracted preparations. Troponin C contents and the ability to develop tension on activations by Ca2+ and Sr2+ was permanently restored after incubation with 2-6 mg/ml purified TnC from either rabbit fast-twitch skeletal muscle (STnC) or the heart (CTnC, cardiac troponin C). The native (skinned) cardiac muscle is characteristically about 5 times more sensitive to activation by Sr2+ than fast muscle, but the STnC-loaded trabeculae gave response like fast muscle. Attempts were also made to exchange the TnC in psoas (fast-twitch muscle) fibers, but unlike cardiac muscle tension response of the maximally extracted psoas fibers could be restored only with homologous STnC. CTnC was effective in partially extracted fibers, even though the uptake of CTnC was complete in the maximally extracted fibers. The results in this study establish that troponin C subunit is the key in setting the characteristic sensitivity for tension control in the myocardium above that in the skeletal muscle. Since a major difference between skeletal and cardiac TnCs is that one of the trigger sites (site I, residues 28-40 from the N terminus) is modified in CTnC and has reduced affinity for Ca2+ binding, the possibility is raised that this site has a modulatory effect on activation in different tissues and limits the effectiveness of CTnC in skeletal fibers.
The pericentric chromatin of chromosome 18 was found to be far more heterogeneous for restriction endonuclease AluI (5'...AG decrease CT...3') than previously thought. The extent of such heterogeneity was characterized using 50 normal Caucasians and 5 cases of trisomy 18 or Edwards' Syndrome. The AluI-resistant chromatin can arbitrarily be classified into at least five sizes by comparison with the length of the short arm (p) of chromosome 18. They are: negative (1), small (2), medium (3), large (4) and very large (5) with incidences of 11.30%, 19.13%, 29.57%, 29.57% and 10.43%, respectively. In addition the location of the chromatin can be classified into four types depending upon the position relative to the primary constriction. For example: Type I (absent); Type II (present on p arm only); Type III (present on q arm only); Type IV (present on centromere and extending into both p and q arms). The incidences of types I, II, III, and IV were 11.30%, 62.61%, 0.87%, and 25.22%, respectively. Based on limited data, AluI-resistant chromatin was found to be predominantly "large" and "very large" in Edwards' Syndrome samples. In addition, no case with negative Alu-resistant chromatin was noted. Therefore, it is tempting to speculate that the amount of chromatin present on the centromere might play a role in non-disjunction in Edwards' Syndrome cases. Although the variation observed in the present study is continuous, the proposed classification has some important implications for future investigations.
The most recent addition to the various selective staining methods is the technique using restriction endonucleases to digest the metaphase chromosomes and subsequent staining by Giemsa (endonuclease/Giemsa technique). One of the endonucleases, AluI, which induces a characteristic modified C-band pattern is evaluated for its application in cancer cytogenetics using malignant lymphoid cells. The pattern obtained by AluI/Giemsa has been routinely useful in identifying some of the unusual markers that are difficult by routine banding. The centromeric regions are found to be far more heterogeneous by AluI resulting in frequent heteromorphic markers on several chromosomes. This has provided additional information to detect the donor cells in grafts after bone marrow transplantation.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
The incidence of supernumerary or accessory human chromosomes in clinically normal and abnormal cases lead to a variety of questions. Thus genetic counselling in such cases is often a difficult task.
To characterize the tension control in vertebrate striated muscle fibers, and to obtain insights into the cross-bridge mechanisms, Ca2+ activation on troponin C (TnC)-extracted skinned fibers was studied in standard (180 mM, physiological) and low (20-41 mM) ionic strength solutions. By tension measurement, TnC-extracted fibers had nearly lost their Ca2+ sensitivity in the standard ionic strength solutions, but surprisingly the fiber still exhibited significant tension on activation with Ca2+ in low ionic strength. Also, the presence of weak bridges (zero-force bridges) was inferred by stiffness measurements in Ca2+-free low ionic strength solution, and were found even after TnC extraction. The possibility is discussed that dual regulation by Ca2+ is present in the vertebrate muscle. One mechanism activates the thin filaments. The second may directly control the kinetic step for the transition between the weak and strong bridges, in the cross-bridge cycle in the fiber, and in this way may act as an additional Ca2+ switch.