Developmental changes in levels and forms of cholinesterases in muscles of normal and dystrophic chickens

The NMJ as a model synapse: New perspectives on formation, synaptic transmission and maintenance: Acetylcholinesterase at the neuromuscular junction

Acetylcholinesterase (AChE) is an essential enzymatic component of the neuromuscular junction where it is responsible for terminating neurotransmission by the cholinergic motor neurons. The enzyme at the neuromuscular junction (NMJ) is contributed primarily by the skeletal muscle where it is produced at higher levels in the post-synaptic region of the fibers. The major form of AChE at the NMJ is a large asymmetric form consisting of three tetramers covalently attached to a three-stranded collagen-like tail which is responsible for anchoring it to the synaptic basal lamina. Its location and expression is regulated to a large extent by the motor neurons and occurs at the transcriptional, translational and post-translational levels. While its expression can be quite rapid in tissue cultured cells, its half-life in vivo appears to be quite long, about three weeks, although more rapidly turning over pools have been described. Finally the essential nature of this enzyme is underscored by the fact that no naturally occurring null mutations of the catalytic subunit have been described in higher organisms and the few dozen humans carrying mutations in the collagen tail responsible for anchoring the enzyme at the NMJ are severely affected.

Expression and Localization of PRiMA-linked globular form acetylcholinesterase in vertebrate neuromuscular junctions

Acetylcholinesterase (AChE) is well known to process different molecular forms via the distinct interacting partners. Proline-rich membrane anchor (PRiMA)-linked tetrameric globular AChE (G4 AChE) is mainly found in the vertebrate brain; however, recent studies from our laboratory have suggested its existence at neuromuscular junctions (nmjs). Both muscle and motor neuron express AChE at the nmjs. In muscle, the expression of PRiMA-linked AChE is down-regulated during myogenic differentiation and by motor neuron innervation. As compared with muscle, spinal cord possessed higher total AChE activity and contained PRiMA-linked AChE forms. The spinal cord expression of this form increased during development. More importantly, PRiMA-linked G4 AChE identified as aggregates localized at nmjs. These findings suggest that the restricted localization of PRiMA-linked G4 AChE at the nmjs could be contributed by the pre-synaptic motor neuron and/or the post-synaptic muscle fiber.

Restricted localization of proline-rich membrane anchor (PRiMA) of globular form acetylcholinesterase at the neuromuscular junctions--contribution and expression from motor neurons

The expression and localization of the proline-rich membrane anchor (PRiMA), an anchoring protein of tetrameric globular form acetylcholinesterase (G(4) AChE), were studied at vertebrate neuromuscular junctions. Both muscle and motor neuron contributed to this synaptic expression pattern. During the development of rat muscles, the expression of PRiMA and AChE(T) and the enzymatic activity increased dramatically; however, the proportion of G(4) AChE decreased. G(4) AChE in muscle was recognized specifically by a PRiMA antibody, indicating the association of this enzyme with PRiMA. Using western blot and ELISA, both PRiMA protein and PRiMA-linked G(4) AChE were found to be present in large amounts in fast-twitch muscle (e.g. tibialis), but in relatively low abundance in slow-twitch muscle (e.g. soleus). These results indicate that the expression level of PRiMA-linked G(4) AChE depends on muscle fiber type. In parallel, the expression of PRiMA, AChE(T) and G(4) AChE also increased in the spinal cord during development. Such expression in motor neurons contributed to the synaptic localization of G(4) AChE. After denervation, the expression of PRiMA, AChE(T) and G(4) AChE decreased markedly in the spinal cord, and in fast- and slow-twitch muscles.

The activity of an endoplasmic reticulum-localized pool of acetylcholinesterase is modulated by heat shock

Primary cultures prepared from embryonic chick pectoral muscle were subjected to heat shock, and the effect on acetylcholinesterase activity in the cultures was examined. A rapid recovery in enzyme activity was observed soon after an initial heat shock-induced drop and was shown to be independent of de novo synthesis of protein, since it could occur in the presence of an inhibitor of protein synthesis. Lectin binding and sucrose gradient centrifugation studies suggested that molecular monomers and dimers found in the endoplasmic reticulum are involved in the observed recovery of acetylcholinesterase activity. Enhanced activation of a pre-existing pool of inactive enzyme was clearly not the main agent of the recovery in enzymic activity. Recovery relied principally on restoration of the activity of previously active, heat-denatured acetylcholinesterase molecules found in the endoplasmic reticulum. Possible agents involved in the recovery of enzymatic activity might be heat shock proteins acting as molecular chaperones.

Changes in the endplate accumulation of acetylcholinesterase during synapse elimination in the mouse

Focal accumulations of acetylcholinesterase (AChE; EC 3.1.1.7), cholinesterase (ChE, EC 3.1.1.8) and total cholinesterase (TChE; AChE+ChE) were examined in developing mouse diaphragm by using a modified Karnovsky/Roots staining method. The lengths of TChE and AChE reaction product accumulations reached significant peaks on postnatal day (PD) 1 (P < 0.05), decreased to a minimum on PD 9 and then increased in proportion to muscle fiber diameter (PD 9 to adult). The normalized area of accumulation (area of accumulation/fiber diameter) for AChE and TChE also decreased by 19% (P < 0.05) between PD 3 and PD 7. In contrast, ChE focal accumulation did not decrease during the period of synapse elimination, but rather increased in proportion to the postnatal growth of the muscle fiber. These results suggest that AChE is more sensitive to neurotrophic influences than ChE; particularly during late embryonic and early postnatal periods of synapse elimination.

Two types of asymmetric acetylcholinesterase in chick hindlimb muscle: developmental profiles, in vivo and in cell culture, and recovery after inactivation

1. We have analyzed the behavior of two types of asymmetric molecular forms (A forms) of acetylcholinesterase (AChE) during development of chick hindlimb muscle, in vivo and in cell culture, and upon irreversible inactivation of peroneal muscle AChE with diisopropylfluorophosphate (DFP) in vivo. 2. In agreement with previous developmental studies on chick muscle, globular forms of AChE (G forms) are predominant in chick hindlimb at early embryonic ages, being gradually replaced by A forms as hatching (and, therefore, onset of locomotion) approaches. Of the two A-form types, AI appears and accumulates significantly earlier than AII, so that A/G and II/I ratios higher than 1 are attained only at about hatching time. 3. Cultures prepared from 11-day chick embryo hindlimb myoblasts express both types of A forms, with a combined activity of 27% of total AChE after 12 days in culture. AI forms appear again earlier and are much more abundant than type II asymmetric species through the life span of cultures. 4. All AChE activity in the peroneal muscle is irreversibly inactivated by injection of DFP in vivo. The recovery of A forms follows the same sequence described for normal development, with a delayed and slower recovery of AII forms as compared with AI. 5. Several hypotheses involving tail polypeptides or tissue target molecules, or posttranslational interconversion, are proposed to help explain the earlier appearance and accumulation of AI forms in chick muscle.

Cholinesterases during development of the avian nervous system

1. Long before onset of synaptogenesis in the chicken neural tube, the closely related enzymes butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) are expressed in a mutually exclusive manner. Accordingly, neuroblasts on the ventricular side of the neural tube transiently express BChE before they abruptly accumulate AChE while approaching the outer brain surface. 2. By exploiting AChE as a sensitive and early histochemical differentiation marker, we have demonstrated complex polycentric waves of differentiation spreading upon the cranial part of the chicken neural tube but a smooth rostrocaudal wave along the spinal cord. Shortly after expression of AChE, these cells extend long projecting neurites. In particular, segmented spinal motor axons originate from AChE-positive motoneurones; they navigate through a BChE-active zone within the rostral half of the sclerotomes before contacting BChE/AChE-positive myotome cells. At synaptogenetic stages, cholinesterases additionally are detectable in neurofibrillar laminae foreshadowing the establishment of cholinergic synapses. 3. In order to elucidate the functional significance of cholinesterases at early stages, we have investigated specific cholinesterase molecules and their mechanisms of action in vivo and in vitro. A developmental shift from the low molecular weight forms to the tetramers of both enzymes has been determined. In vitro, the addition of a selective BChE inhibitor leads to a reduction of AChE gene expression. Thus, in vivo and in vitro data suggest roles of cholinesterases in the regulation of cell proliferation and neurite growth. 4. Future research has to show whether neurogenetic functioning of cholinesterases can help to understand their reported alterations in neural tube defects, mental retardations, dementias and in some tumours.

Embryonic and post-natal changes in activity and molecular forms of mucosal cell butyrylcholinesterase in chicken intestine

The mucosal cells of the chicken intestine contain a cholinesterase activity essentially due to butyrylcholinesterase. The enzyme is present during embryonic and post-hatching development. The activity reaches a maximum value at day 19 in ovo and decreases prior to and after hatching up to day 4 ex ovo. Then the activity again rises reaching a second maximum at 2-3 weeks. Beyond this stage, the activity slowly decreases leveling off to the value determined in adult chicken. The enzyme exists as two globular forms (G1 and G4) soluble at low-ionic strengths. The G4 form is predominant in ovo up to day 19. From this stage and after hatching the G1 form is the main one. This change in the form proportion differentiates the mucosal cell butyrylcholinesterase from butyrylcholinesterase of other origins such as the chicken plasma enzyme which always shows a predominant G4 form.

Effects of electrical stimulation on molecular forms of butyrylcholinesterase in denervated fast and slow latissimus dorsi muscles of newly hatched chicken

The effects of denervation and direct electrical stimulation upon the activity and the molecular form distribution of butyrylcholinesterase (BuChE) were studied in fast-twitch posterior latissimus dorsi (PLD) and in slow-tonic anterior latissimus dorsi (ALD) muscles of newly hatched chicken. In PLD muscle, denervation performed at day 2 substantially reduced the rate of rapid decrease of BuChE specific activity which takes place during normal development, whereas in the case of ALD muscle little change was observed. Moreover, the asymmetric forms which were dramatically reduced in denervated PLD muscle were virtually absent in denervated ALD muscle at day 14. Denervated PLD and ALD muscles were stimulated from day 4 to day 14 of age. Two patterns of stimulation were applied, either 5-Hz frequency (slow rhythm) or 40-Hz frequency (fast rhythm). Both patterns of stimulation provided the same number of impulses per day (about 61,000). In PLD muscle, electrical stimulation almost totally prevented the postdenervation loss in asymmetric forms and led to a decrease in BuChE specific activity. In ALD muscle, electrical stimulation partially prevented the asymmetric form loss which occurs after denervation. This study emphasizes the role of evoked muscle activity in the regulation of BuChE asymmetric forms in the fast PLD muscle and the differential response of denervated slow and fast muscles to electrical stimulation.

Serum cholinesterase activity in infantile and juvenile spinal muscular atrophy

Serum acetylcholinesterase (AChE) and pseudocholinesterase (ChE) activity in infantile and juvenile spinal muscular atrophy (SMA) was determined. The total AChE activity was either normal or decreased in the childhood SMA (Type 1), the other SMA groups and disease controls (ALS, X-linked SMA). In the majority of SMA Type 1 cases (6/7 tested) an absence of the asymmetric A12 form was found. This was accompanied by changes in the other asymmetric and globular forms. The latter was, however, not specific for SMA Type 1 cases. The ChE activity was increased in the majority of SMA cases as well as disease controls. The asymmetric A12 ChE form was increased in all SMA Type 3 cases, the values of this form in SMA Type 1 was variable. A change in the ChE globular forms in SMA Type 1 and SMA Type 2 was a frequent finding. It is suggested that the absence of the asymmetric A12 AChE form in SMA Type 1 arises because of muscle cell immaturity and undeveloped muscle-nerve interactions. The reason of ChE changes is obscure.

Acetylcholinesterase in chick embryo latissimus dorsii muscles: effects of curarization and electrical stimulation

The accumulation of acetylcholinesterase (AChE), the changes in AChE-specific activity and in AChE molecular form distribution were studied in slow-tonic anterior latissimus dorsi (ALD) and in fast-twitch posterior latissimus dorsi (PLD) muscles of the chick embryo. From stage 36 (day 11) to stage 42 (day 17) of Hamburger and Hamilton, the AChE-specific activity decreased, while the relative proportion of asymmetric A 12 and A 8 forms increased. Repetitive injection of curare resulted at stage 42 (day 17) in a decrease in AChE-specific activity, in the accumulation of the synaptic AChE and in the expression of AChE asymmetric forms. Electrical stimulation at a relatively high frequency (40 Hz) of curarized ALD and PLD muscles resulted in a normal increase in AChE asymmetric forms, whereas a lower frequency (5 Hz) resulted in a dominance of globular forms. Both patterns of stimulation partly prevented the loss in synaptic AChE accumulations. These results suggest that in chick embryo muscles, muscle activity and its rhythms are involved in the normal evolution of AChE.

Cholinesterases from flounder muscle. Purification and characterization of glycosyl-phosphatidylinositol-anchored and collagen-tailed forms differing in substrate specificity

Flounder (Platichthys flesus) muscle contains two types of cholinesterases, that differ in molecular form and in substrate specificity. Both enzymes were purified by affinity chromatography. About 8% of cholinesterase activity could be attributed to collagen-tailed asymmetric acetylcholinesterase sedimenting at 17S, 13S and 9S, which showed catalytic properties of a true acetylcholinesterase. 92% of cholinesterase activity corresponded to an amphiphilic dimeric enzyme sedimenting at 6S in the presence of Triton X-100. Treatment with phospholipase C yielded a hydrophilic form and uncovered an epitope called the cross-reacting determinant, which is found in the hydrophilic form of a number of glycosyl-phosphatidylinositol-anchored proteins. This enzyme showed catalytic properties intermediate to those of acetylcholinesterase and butyrylcholinesterase. It hydrolyzed acetylthiocholine, propionylthiocholine, butyrylthiocholine and benzoylthiocholine. The Km and the maximal velocity decreased with the length and hydrophobicity of the acyl chain. At high substrate concentrations the enzyme was inhibited. The p(IC50) values for BW284C51 and ethopropazine were between those found for acetylcholinesterase and butylcholinesterase. For purified detergent-soluble cholinesterase a specific activity of 8000 IU/mg protein, a turnover number of 2.8 x 10(7) h-1, and 1 active site/subunit were determined.

A new membrane antigen revealed by monoclonal antibodies is associated with motoneuron axonal pathways

Chick embryonic motoneurons selectively grow out from the spinal cord as the first step of their selective axonal growth. In order to detect the molecules responsible for motoneuron outgrowth from the cord, we produced and immunohistochemically screened many monoclonal antibodies (MAbs) against cord and somite. We found that two of them, called M7412 and M7902, selectively bound to the cell surface of the anterior half of the sclerotome, where motoneurons selectively extend their axons. Immunohistochemistry and immunoblot results were identical for these antibodies and the antigen was called M7412 antigen. Although neural crest cells also migrate into the anterior half of the sclerotome, the expression of M7412 antigen by sclerotome cells was independent of the neural crest, because neural crest removal did not affect the appearance of the antigen. Furthermore, MAb M7412 bound to the mesenchymal cells along presumptive major nerve trunks in the limb and to the structures surrounding myotubes in muscles during the formation of intramuscular nerve branches. These results suggest that M7412 antigen might be a substrate for general, but not specific, growth of motoneuron axons. If this is the case, we must also infer that some molecule inhibitory for motoneuron growth is localized in the posterior half of sclerotome, because at upper cervical levels the M7412 antigen was also expressed intensely in the posterior sclerotome, whereas motoneurons still grew only into the anterior half. The M7412 antigen was transiently expressed in such various tissues as somite; muscles; blood vessels; spinal cord cells, especially motoneurons innervating the limb; and dorsal root and other peripheral ganglion cells. The M7412 antigenic molecule was extractable with NP40 from a membrane fraction of whole chick embryos and its molecular weight was estimated to be 70 kDa from immunoblot analysis. Thus, our monoclonal antibodies have revealed a new membrane-associated molecule which is likely to play a role in cell-cell interactions during development of motoneurons.

Characterization of cholinesterase molecular forms in the mucosal cells along the intestine of the chicken

The presence of a butyrylcholinesterase (BuChE, EC 3.1.1.8) in the musocal cells of the chicken intestine was demonstrated by histochemical and biochemical methods. The study of its distribution, along the intestine from duodenum to rectum, showed that the jejuno-ileum possesses the highest activity. Sucrose gradient centrifugation revealed, in all intestinal areas, two globular forms with sedimentation coefficients of 4.3 S (G1 form) and 10.8 S (G4 form). The presence of Triton X-100 in the preparations did not modify the sedimentation profiles of these two forms which can be considered as soluble BuChE. The ratio of G1/G4-forms progressively decreases along the intestine from duodenum to rectum indicating a predominance of the G4 form in the areas where the activity is low. Our results are discussed in relation to other studies of globular forms of chicken BuChE.

Posthatching changes in levels and molecular forms of acetylcholinesterase in slow and fast muscles of the chicken: effects of denervation and direct electrical stimulation

The evolution of acetylcholinesterase (AChE) activity and AChE molecular form distribution were studied in slow-tonic anterior latissimus dorsi (ALD) and in fast-twitch posterior latissimus dorsi (PLD) muscles of chickens 2-18 days of age. In ALD as well as in PLD muscles, the AChE-specific activity increased transiently from day 2 to day 4; the activity then decreased more rapidly in PLD muscle. During this period asymmetric AChE forms decreased dramatically in ALD muscle and the globular forms increased. In PLD muscle, the most striking change was the decline in A8 form between days 2 and 18 of development. Denervation performed at day 2 delayed the normal decrease in AChE-specific activity in PLD muscle, whereas little change was observed in ALD muscle. Moreover, A forms in these two muscles were virtually absent 8 days after denervation. Direct electrical stimulation depressed the rise in AChE-specific activity in denervated PLD muscle and prevented the loss of the A forms. Furthermore, the different molecular forms varied according to the stimulus pattern. In ALD muscle, electrical stimulation failed to prevent the effect of denervation. This study emphasizes the differential response of denervated slow and fast muscles to electrical stimulation and stresses the importance of the frequency of stimulation in the regulation of AChE molecular forms in PLD muscle during development.

Monoclonal antibodies specific for the different subunits of asymmetric acetylcholinesterase from chick muscle

The asymmetric (20S) acetylcholinesterase (AChE, EC 3.1.1.7) from 1-day-old chick muscle, purified on a column on which was immobilised a monoclonal antibody (mAb) to chick brain AChE, was used to immunise mice. Eight mAbs against the muscle enzyme were hence isolated and characterised. Five antibodies (4A8, 1C1, 10B7, 7G8, and 8H11) recognise a 110-kilodalton (kDa) subunit with AChE catalytic activity, one antibody (7D11) recognises a 72-kDa subunit with pseudocholinesterase or butyrylcholinesterase (BuChE, EC 3.1.1.8) catalytic activity, and two antibodies (6B6 and 7D7) react with the 58-kDa collagenous tail unit. Those three polypeptides can be recognised together in the 20S enzyme used, which is a hybrid AChE/BuChE oligomer. Antibodies 6B6 and 7D7 are specific for asymmetric AChE. Four of the mAbs recognising the 110-kDa subunit were reactive with it in immunoblots. Sucrose density gradient analysis of the antibody-enzyme complexes showed that the anti-110-kDa subunit mAbs cross-link multiple 20S AChE molecules to form large aggregates. In contrast, there is only a 2-3S increase in the sedimentation constant with the mAbs specific for the 72-kDa or for the 58-kDa subunit, suggesting that those subunits are more inaccessible in the structure to intermolecular cross-linking. The 4A8, 10B7, 7D11, and 7D7 mAbs showed cross-reactivity to the corresponding enzyme from quail muscle; however, none of the eight mAbs reacted with either enzyme type from mammalian muscle or from Torpedo electric organ. All eight antibodies showed immunocytochemical localisation of the AChE form at the neuromuscular junctions of chicken twitch muscles.

Identification of a 17 S asymmetric butyrylcholinesterase in chick muscle by monoclonal antibodies

A 20 S asymmetric (non-globular) form of acetylcholinesterase (AChE, E.C. 3.1.1.7) has been purified from 1-day chick muscle. This form is a hybrid molecule containing both AChE and butyrylcholinesterase (BuChE, E.C. 3.1.1.8) catalytic subunits, linked through a collagenous tail. However, the 20 S hybrid AChE/BuChE could not account for the total enzyme activities of AChE and BuChE in a high-salt/Triton X-100 extract of 1-day chick muscle. By applying AChE- and BuChE-specific monoclonal antibodies for immunoadsorption, homogeneous asymmetric AChE and BuChE forms were also identified in that extract. The homogeneous BuChE accounts for 20% of the total activity of the asymmetric BuChE present and sediments at 17 S. About 6% of the asymmetric AChE present is, likewise, in a homogeneous, instead of the hybrid, form. The 17 S asymmetric BuChE does not react with monoclonal antibodies specific for the collagenous tail of the hybrid 20 S AChE/BuChE molecule, suggesting that the collagenous subunit differs between these two forms.

An asymmetric form of muscle acetylcholinesterase contains three subunit types and two enzymic activities in one molecule

We have purified completely the principal asymmetric ("heavy") form of acetylcholinesterase (Ac-ChoEase; EC 3.1.1.7) from chick muscle (i.e., the synaptic form in the twitch muscle fibers) by using a monoclonal antibody that recognizes AcChoEase but not pseudocholinesterase (ChoEase; cholinesterase, EC 3.1.1.8). The purified protein exhibits catalytic and inhibition properties characteristic of AcChoEase and ChoEase and contains three distinct subunits of apparent sizes 110 kDa, 72 kDa, and 58 kDa in the ratio 2:2:1. The discovery of an AcChoEase/ChoEase hybrid asymmetric form has been further supported by (i) the identification of active site properties of AcChoEase in the 110-kDa subunit and of ChoEase in the 72-kDa subunit, (ii) the purification or precipitation of both activities together by, also, a ChoEase-specific monoclonal antibody, and (iii) evidence that all subunits are bound in the asymmetric forms by disulfide bonds. The 58-kDa subunit is the only one that is sensitive to digestion with purified collagenase; it carries the collagenous "tail" of the asymmetric form. A model is proposed for this form of AcChoEase.

Modes of attachment of acetylcholinesterase to the surface membrane

Acetylcholinesterase (AChE) occurs in multiple molecular forms differing in their quaternary structure and mode of anchoring to the surface membrane. Attachment is achieved by post-translational modification of the catalytic subunits. Two such mechanisms are described. One involves attachment to catalytic subunit tetramers, via disulfide bridges, of a collagen-like fibrous tail. This, in turn, interacts, primarily via ionic forces, with a heparin-like proteoglycan in the extracellular matrix. A second such modification involve the covalent attachment of a single phosphatidylinositol molecule at the carboxyl-terminus of each catalytic subunit polypeptide; the diacylglycerol moiety of the phospholipid serves to anchor the modified enzyme hydrophobically to the lipid bilayer of the plasma membrane. The detailed molecular structure of these two classes of acetylcholinesterase are discussed, as well as their biosynthesis and mode of anchoring.

Microtiter assay for acetylcholinesterase

A microtiter plate adaptation of the classical Ellman colorimetric procedure for measurement of acetylcholinesterase activity is described. This method permits use of an enzyme-linked immunosorbent assay plate reader for rapid analysis of multiple samples and is particularly suitable for analysis of acetylcholinesterase activity on sucrose gradients. The novel procedure is rapid and sensitive and does not require use of radioactive material.

Quantitative development and molecular forms of acetyl- and butyrylcholinesterase during morphogenesis and synaptogenesis of chick brain and retina

The embryonic development of total specific activities as well as of molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) and of butyrylcholinesterase (BChE, EC 3.1.1.8) have been studied in the chick brain. A comparison of the development in different brain parts shows that cholinesterases first develop in diencephalon, then in tectum and telencephalon; cholinesterase development in retina is delayed by about 2-3 days; and the development in rhombencephalon [not studied until embryonic day 6 (E6)] and cerebellum is last. Both enzymes show complex and independent developmental patterns. During the early period (E3-E7) first BChE expresses high specific activities that decline rapidly, but in contrast AChE increases more or less constantly with a short temporal delay. Thereafter the developmental courses approach a late phase (E14-E20), during which AChE reaches very high specific activities and BChE follows at much lower but about parallel levels. By extraction of tissues from brain and retina in high salt plus 1% Triton X-100, we find that both cholinesterases are present in two major molecular forms, AChE sedimenting at 5.9S and 11.6S (corresponding to G2 and G4 globular forms) and BChE at 2.9S and 10.3S (G1 and G4, globular). During development there is a continuous increase of G4 over G2 AChE, the G4 form reaching 80% in brain but only 30% in retina. The proportion of G1 BChE in brain remains almost constant at 55%, but in retina there is a drastic shift from 65% G1 before E5 to 70% G4 form at E7.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase from the skeletal muscle of the lamprey Petromyzon marinus exists in globular and asymmetric forms

To obtain information about the evolution of acetylcholinesterase (AChE), we undertook a study of the enzyme from the skeletal muscle of the lamprey Petromyzon marinus, a primitive vertebrate. We found that the cholinesterase activity of lamprey muscle is due to AChE, not pseudocholinesterase; the enzyme was inhibited by 1,5-bis(4-allyldimethylammonium phenyl) pentane-3-one (BW284C51), but not by tetramonoisopropyl pyrophosphortetramide (iso-OMPA) or ethopropazine. Also, the enzyme had a high affinity for acetylthiocholine and was inhibited by high concentrations of substrate. A large fraction of the AChE was found to be glycoprotein, since it was precipitated by concanavalin A-agarose. Optimal extraction of AChE was obtained in a high-salt detergent-containing buffer; fractional amounts of enzyme were extracted in buffers lacking salt and/or detergent. These data suggest that globular and asymmetric forms of AChE are present. On sucrose gradients, enzyme that was extracted in high-salt detergent-containing buffer sedimented as a broad peak of activity corresponding to G4; additionally, there was usually a peak corresponding to A12. Sequential extraction of AChE in conjunction with velocity sedimentation resolved minor forms of AChE and revealed that the G1, G2, G4, A4, A8, and A12 forms of AChE could be obtained from the muscle. The identity of the forms was confirmed through high-salt precipitation and collagenase digestion. The asymmetric forms of AChE were precipitated in low ionic strength buffer, and their sedimentation coefficients were shifted to higher values by collagenase digestion.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoclonal antibodies against chicken brain acetylcholinesterase. Their use in immunopurification and immunochemistry to demonstrate allelic variants of the enzyme

Acetylcholinesterase (AChE) from 1-day chicken brain was enriched over 2000-fold by affinity chromatography using N-methylacridinium-Sepharose. This preparation was used to prepare monoclonal antibodies (mAb) directed against AChE, of which two were extensively characterised for further application. Both mAbs bound to the enzyme from the chicken with high affinity (Kd approximately 8 X 10(-10) M) and one mAb, in addition, recognised AChE from quail brain and muscle. Neither mAb cross-reacted with mammalian or fish AChE. Both mAbs recognised AChE in the endplate region of adult chicken skeletal muscle and bound with equal affinity to the three major oligomeric forms found in early ambryonic muscle. One mAb was used to immunopurify chicken brain AChE to homogeneity (over 12000-fold enrichment), with nearly complete recovery of the enzyme and without detectable proteolytic breakdown. The other mAb recognised AChE after immunoblotting and was used to screen crude brain extracts from individual chickens for allelic variations. Evidence is presented to show that two allelic forms occur, represented in SDS-PAGE by a doublet polypeptide of Mr approximately 110,000, this pattern is maintained after deglycosylation of the N-linked oligosaccharides. This variation was found throughout development and in both the brain and the muscle of individuals. We conclude that the gene encoding the catalytic subunit of chicken AChE is polymorphic with either one or two equally active alleles being expressed.

Reciprocal regulation of acetylcholinesterase and butyrylcholinesterase in mammalian skeletal muscle

Developmental regulation, from the fetal period to 11 months of age, and the influence of denervation on the appearance and disappearance of the molecular forms of acetylcholinesterase (AchE) and butyrylcholinesterase (BuchE) in rat skeletal muscle were examined. The enzyme forms were extracted from anterior tibialis in 0.01 M sodium phosphate buffer, pH 7.0, containing 1 N NaCl, 0.01 M EGTA, 1% Triton X-100, and a cocktail of antiproteases, and analyzed by velocity sedimentation on 5-20% linear sucrose gradients. Three principal forms, denoted by sedimentation coefficients of 4, 10.8, and 16 S, were observed in muscle from all age groups. The amounts of each of the molecular forms of AchE and BuchE in skeletal muscle exhibited distinct and reciprocal patterns of appearance and disappearance during pre- and postnatal development. In tissue derived from animals less than 2 weeks of age, BuchE represented the predominant component of activity in the 4 S form, was present equally with AchE in the 10.8 S form, and was subordinate to AchE in the 16 S form. Between 1 and 2 weeks of age a progressive increase in AchE activities coincident with a reduction in BuchE activities resulted in inversion in the amounts of the two enzymes present in adult muscle. Denervation of muscle caused a dramatic reduction in the presence of AchE molecular forms with no discernable influence on the presence of BuchE molecular forms. These results indicate that biosynthesis of BuchE is strictly regulated in a reciprocal manner with that of AchE, and that BuchE metabolism is independent of the state of muscle innervation. Increased synthesis of AchE and either reduced synthesis or increased degradation of BuchE can account for the reciprocal regulation of these enzymes. These characteristics of mammalian muscle contrast sharply with characteristics deduced for avian tissue (Silman et al. (1979) Nature (London) 280, 160-162). The innervation-independent metabolism of BuchE and the diverse modes of its regulation in different tissue from different species signify that BuchE function may be unrelated to cholinergic neurotransmission.

Low frequency chronic electrical stimulation of normal and dystrophic chicken muscle

The fast-twitch posterior latissimus dorsi muscle of normal and genetically dystrophic chickens was subjected to continuous indirect electrical stimulation at 10 Hz for periods of 4-8 weeks. To sustain this in vivo nerve stimulation an internally implantable miniature stimulator device was designed. This regime of stimulation caused complete fatigue of the normal muscle within 5 min of its initiation. The dystrophic muscles maintained a very small degree of contractile activity during this initial phase. Tangible twitching of the muscle returned in 5 week birds between 3 and 5 days and in 10 week birds between 11 and 16 days after implantation. After 4 weeks of stimulation, no significant change was measured in the time-to-peak of the isometric twitch response, nor in the half-relaxation time. The resistance to fatigue was significantly increased in the stimulated muscles when tested with a series of tetani at 40 Hz. The mean fibre area was decreased, in all muscles stimulated for longer than 3 weeks, in comparison to their contralateral controls, except where fibre splitting in dystrophic birds abnormally reduced the control value. The majority fibre type of the muscle was changed from type IIB to IIA. The histochemical reactions for both NADH-linked oxidation and phosphorylase were distinctly increased in the stimulated muscles. In normal muscle, stimulation increased somewhat the number of nuclei per unit area and changed their intracellular distribution, so that a greater proportion was found adjacent to the sarcolemma. The normal posterior latissimus dorsi muscle responded to chronic stimulation with increases of 3-6-fold in its acetylcholinesterase (AChE) activity. The maximum change in AChE occurred after 2 weeks stimulation; a steady level, 3 times that of the control unstimulated muscle, persisted at later times. Chronic stimulation suppressed the over-production of AChE that is characteristic of dystrophic chicken fast-twitch muscle, to attain a level comparable to the AChE activity in a stimulated normal muscle. Stimulation exerted a strong normalizing influence on dystrophic muscle, as assessed morphologically. The characteristic fibre rounding, fibre hypertrophy and myonuclear proliferation were reduced. This influence was most marked where the stimulation was initiated before the major pathological changes had occurred, but was also significant when commenced in strongly affected birds of 10-11 weeks.

Skeletal muscle acetylcholinesterase molecular forms in amyotrophic lateral sclerosis

Acetylcholinesterase (AChE) molecular forms in muscle biopsies from control and amyotrophic lateral sclerosis (ALS) patients were extracted under low (G: globular forms) and high (A: asymmetric forms) ionic strength conditions and were evaluated by velocity sedimentation analysis. Total AChE activity in endplate-containing ALS muscle sections was reduced by an average of 65% of control muscle levels. This decrement resulted from an almost complete disappearance of 9.5S (G4) and 8.0S (A4) AChE and significant decreases in the 3.8S (G1), 12.1S (A8), and 15.8S (A12) forms (66%, 9%, and 25% of control, respectively). In most of the ALS biopsies examined, ultrastructural-cytochemical analysis revealed large reductions in AChE reaction product of both synaptic infoldings (extracellular) and sarcoplasmic reticulum (intracellular) of the muscles' motor endplate regions. These data are compatible with the view that alterations observed in AChE forms from ALS muscles are related to disturbances in the normal "trophic" interactions between nerve and muscle.

Aggregating factor from Torpedo electric organ induces patches containing acetylcholine receptors, acetylcholinesterase, and butyrylcholinesterase on cultured myotubes

A factor in extracts of the electric organ of Torpedo californica causes the formation of clusters of acetylcholine receptors (AChRs) and aggregates of acetylcholinesterase (AChE) on myotubes in culture. In vivo, AChRs and AChE accumulate at the same locations on myofibers, as components of the postsynaptic apparatus at neuromuscular junctions. The aim of this study was to compare the distribution of AChRs, AChE, and butyrylcholinesterase (BuChE), a third component of the postsynaptic apparatus, on control and extract-treated myotubes. Electric organ extracts induced the formation of patches that contained high concentrations of all three molecules. The extract-induced aggregation of AChRs, AChE, and BuChE occurred in defined medium, and these components accumulated in patches simultaneously. Three lines of evidence indicate that a single factor in the extracts induced the aggregation of all three components: the dose dependence for the formation of patches of AChRs was the same as that for patches of AChE and BuChE; the AChE- and BuChE-aggregating activities co-purified with the AChR-aggregating activity; and all three aggregating activities were immunoprecipitated at the same titer by a monoclonal antibody against the AChR-aggregating factor. We have shown previously that this monoclonal antibody binds to molecules concentrated in the synaptic cleft at neuromuscular junctions. Taken together, these results suggest that during development and regeneration of myofibers in vivo, the accumulation at synaptic sites of at least three components of the postsynaptic apparatus, AChRs, AChE, and BuChE, are all triggered by the same molecule, a molecule similar if not identical to the electric organ aggregating factor.

The solubilization of platelet membrane-bound acetylcholinesterase and aryl acylamidase by exogenous or endogenous phosphatidylinositol specific phospholipase C

Phosphatidylinositol specific phospholipase C from Staphylococcus aureus could solubilize acetylcholinesterase up to 55% from sheep platelets in the presence of ethylenediaminetetra acetic acid (EDTA). The endogenous phosphatidylinositol specific phospholipase C of platelets activated by deoxycholate (at 3-5 mM) could also solubilize the enzyme to a similar extent. The solubilized enzyme could be further purified to apparent homogeneity by affinity chromatography without the use of any detergents. It is suggested that phosphatidylinositol specific phospholipase C will be a useful tool in the solubilization of acetylcholinesterase from mammalian sources and its purification free of detergents. The present study also demonstrates the parallel behaviour of acetylcholinesterase and aryl acylamidase in platelets confirming their identity.

Solubilization of membrane-bound acetylcholinesterase by a phosphatidylinositol-specific phospholipase C

Phosphatidylinositol-specific phospholipase C (PIPLC) quantitatively solubilizes acetylcholinesterase (AChE) from purified synaptic plasma membranes and intact synaptosomes of Torpedo ocellata electric organ. The solubilized AChE migrates as a single peak of sedimentation coefficient 7.0S upon sucrose gradient centrifugation, corresponding to a subunit dimer. The catalytic subunit polypeptide of AChE is the only polypeptide detectably solubilized by PIPLC. This selective removal of AChE does not affect the amount of acetylcholine released from intact synaptosomes upon K+ depolarization. PIPLC also quantitatively solubilizes AChE from the surface of intact bovine and rat erythrocytes, but only partially solubilizes AChE from human and mouse erythrocytes. The AChE released from rat and human erythrocytes by PIPLC migrates as a approximately 7S species on sucrose gradients, corresponding to a catalytic subunit dimer. PIPLC does not solubilize particulate AChE from any of the brain regions examined of four mammalian species. Several other phospholipases tested, including a nonspecific phospholipase C from Clostridium welchii, fail to solubilize AChE from Torpedo synaptic plasma membranes, rat erythrocytes, or rat striatum.

Physicochemical behaviour and structural characteristics of membrane-bound acetylcholinesterase from Torpedo electric organ. Effect of phosphatidylinositol-specific phospholipase C

Quantitative solubilization of the phospholipid-associated form of acetylcholinesterase (AChE) from Torpedo electric organ can be achieved in the absence of detergent by treatment with phosphatidylinositol-specific phospholipase C (PIPLC) from Staphylococcus aureus [Futerman, Low & Silman (1983) Neurosci. Lett. 40, 85-89]. The sedimentation coefficient on sucrose gradients of AChE solubilized in detergents (DSAChE) varies with the detergent employed. However, the coefficient of AChE directly solubilized by PIPLC is not changed by detergents. Furthermore, PIPLC can abolish the detergent-sensitivity of the sedimentation coefficient of DSAChE purified by affinity chromatography, suggesting that one or more molecules of phosphatidylinositol (PI) are co-solubilized with DSAChE and remain attached throughout purification. DSAChE binds to phospholipid liposomes, whereas PIPLC-solubilized AChE and DSAChE treated with PIPLC do not bind even to liposomes containing PI. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis shows that PIPLC-solubilized AChE, like unmodified DSAChE, is a catalytic subunit dimer; electrophoresis in the presence of reducing agent reveals no detectable difference in the Mr of the catalytic subunit of unmodified DSAChE, of AChE solubilized by PIPLC and of AChE solubilized by Proteinase K. The results presented suggest that DSAChE is anchored to the plasma membrane by one or more PI molecules which are tightly attached to a short amino acid sequence at one end of the catalytic subunit polypeptide.

Polymorphism of pseudocholinesterase in Torpedo marmorata tissues: comparative study of the catalytic and molecular properties of this enzyme with acetylcholinesterase

We report the existence, in Torpedo marmorata tissues, of a cholinesterase species (sensitive to 10(-5) M eserine) that differs from acetylcholinesterase (AChE, EC 3.1.1.7) in several respects: (a) The enzyme hydrolyzes butyrylthiocholine (BuSCh) at about 30% of the rate at which it hydrolyzes acetylthiocholine (AcSCh), whereas Torpedo AChE does not show any activity on BuSCh. (b) It is not inhibited by 10(-5) M BW 284C51, but rapidly inactivated by 10(-8) M diisopropylfluorophosphonate. (c) It does not exhibit inhibition by excess substrate up to 5 X 10(-3) M AcSCh. (d) It does not cross-react with anti-AChE antibodies raised against purified Torpedo AChE. This enzyme is obviously homologous to the "nonspecific" or pseudocholinesterase (pseudo-ChE, EC 3.1.1.8) that exists in other species, although it is closer to "true" AChE than classic pseudo-ChE in several respects. Thus, it shows the highest Vmax with acetyl-, and not propionyl- or butyrylthiocholine, and it is not specifically sensitive to ethopropazine. Pseudo-ChE is apparently absent from the electric organs, but represents the only cholinesterase species in the heart ventricle. Pseudo-ChE and AChE coexist in the spinal cord and in blood plasma, where they contribute to AcSCh hydrolysis in comparable proportions. Pseudo-ChE exists in several molecular forms, including collagen-tailed forms, which can be considered as homologous to those of AChE. In the heart the major component of pseudo-ChE appears to be a soluble monomeric form (G1). This form is inactivated by Triton X-100 within days.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of activities and forms of cholinesterases in human primary brain tumors

The activities and molecular forms of cholinesterases were studied in a collection of primary brain tumors consisting of primarily gliomas and meningiomas, together with samples of forebrain taken postmortem from patients suffering from diseases unrelated to the nervous system. Both types of tumors, as well as normal forebrain, contained substantial amounts of cholinesterase activity and some gliomas contained exceptionally high levels. In both normal forebrain and meningiomas, acetylcholinesterase (acetylcholine hydrolase; EC 3.1.1.7) accounted for almost all the cholinesterase activity, but in almost all gliomas elevated pseudocholinesterase (acylcholine acylhydrolase; EC 3.1.1.8) could be detected. The cholinesterase activity of both normal forebrain and gliomas migrated on sucrose gradients as a major component of 10-11 S together with a minor component of 4-5 S. In meningiomas a light (4.5 S) form was the principal component.

Molecular forms of acetylcholinesterase in synaptic and extrasynaptic regions of avian tonic muscle

Molecular forms of acetylcholinesterase and pseudocholinesterase were analyzed directly in the micro-dissected individual endplates of a slow-tonic chicken muscle. The major form in the endplate is the L2(6.5 S) form, while the collagen-tailed H2c (20 S) form, normally considered to be the synaptic form, is a very minor component, in contrast to its predominance at the chicken fast-twitch fibre endplate. The same is true for pseudocholinesterase at these endplates. Outside the tonic fibre endplates the same forms occur as at the endplates, but at a very much lower concentration. The enzyme at the tonic fibre endplate cannot be attached to the basal lamina by a collagen tail, but appears to have a hydrophobic attachment. Acetylcholinesterase is functional at tonic fibre endplates, but the absence of the collagen-tailed form may account for the lower efficiency of the enzymic removal of acetylcholine there.

Degeneration and regeneration of neuromuscular junctions in chicken iris muscle after crush of the ciliary nerves: a study of ultrastructural changes and of cholinergic enzymes

Degeneration of neuromuscular junctions in the iris muscle was observed to have occurred 4 days after ciliary nerve crush. By day 10 reinnervation had commenced and by day 30 the maturation of neuromuscular junctions was nearly complete. The loss and recovery of acetylcholinesterase activity in the iris muscle paralleled the denervation-reinnervation process, with recovery being completed by day 30, whereas the loss in the activity of choline acetyltransferase had not yet completely recovered at this time. The acetylcholinesterase activity localized cytochemically at synaptic sites followed the same trend as the total activity in the iris muscle, whereas acetylcholinesterase localized at myo-muscular junctions showed only slight changes. The acetylcholinesterase molecular forms displayed changes in their relative proportions, which could be related to the time course of the denervation-reinnervation process and to the cytochemical localization of the activity.

Involvement of fast and slow twitch muscle fibres in avian muscular dystrophy

The extent of differential fibre type involvement in chicken muscular dystrophy can be assessed quantitatively by the statistical parameters of fibre area, nuclei content and nuclei distribution in the individual fibre types. Two muscles, the posterior latissimus dorsi (PLD) and the serratus metapatagialis (SMP), were found to have similar overall fibre type composition, although the latter contains two subtypes of type I fibres, one of which has not previously been recognised in avian muscle. In both muscles, type IIB fibres are most affected by the progressive pathology. Nuclear proliferation is one of the histopathological features which can be measured, and in the PLD, the mean number of total nuclei in type IIB fibre cross-sections (Nt) is increased from 2.23 in normal chickens to 3.70 in dystrophic chickens, by 60 days. The corresponding values for Nt in type IIB muscle fibres of the SMP at 50 days are 1.74 and 5.10. Likewise, statistical analyses of the distribution of the fibre areas and their variability demonstrate that the incidence of abnormality in chicken dystrophy is greatest in type IIB fibres in both these muscles. Although type I fibres in the PLD are resistant to dystrophic change, it is noteworthy that in the SMP the type I fibres, also, are severely affected from an early stage, by these quantitative criteria. On the other hand, all fibres in a tonic muscle, the metapatagialis latissimus dorsi, are unaffected, as is true of all other tonic muscles previously studied. It is concluded that any twitch fibre type can, in principle, be affected by the actions of the gene concerned, and that this expression can be greatly modified in individual muscles by various physiological features, for example their natural pattern of use or relative disuse.

Structural change in muscles of the dystrophic chicken. II. Progression of the histopathology in the pectoralis muscle

Dystrophic (D) and normal (N) chicken pectoral muscle was analysed for histopathological differences from the embryo (day 20) through to the mature adult stage. A variety of indices of structural changes were used, to express the progression quantitatively. At the embryonic stage, fibroblast numbers (but not satellite cell numbers) are increased in D. D shows fibre hypertrophy discernible from about 4 days after hatching. Other abnormalities of fibre size and shape appear in D from about 2 weeks onwards. Nuclei numbers and location change characteristically in D, compared to N, from about 4 days, and these differences subsequently become very prominent. Fibre splitting and phagocytosis become significant in D from about 2 weeks onwards and increase noticeably thereafter. The later stages in D, with gross loss of muscle fibres, are also described, in the pectoral and posterior latissimus dorsi muscles. The analyses show that some of the structural changes in D precede the discernible difference in fibre type composition which develops between D and N. The changes in the muscle used provide a basis for assessing the effects of drug treatments at various stages, including the early post-hatch period.

Thermal inactivation of the molecular forms of acetylcholinesterase and butyrylcholinesterase

To compare acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) and butyrylcholinesterase (acylcholine acylhydrolase, EC 3.1.1.8), we utilized the physical parameter of thermolability. In serum or muscle extracts from mouse and rat, butyrylcholinesterase was inactivated as a unimodal function of temperature. Inactivation began at 51 degrees C and was complete at 54-57 degrees C (depending upon time of incubation). Acetylcholinesterase was inactivated in two stages. A 60% decrease in activity from 42 to 48 degrees C was followed by a plateau. The second stage of inactivation began at 51 degrees C and was complete at 57-60 degrees C (depending upon time of incubation). Sucrose density gradients revealed that the partial loss of acetylcholinesterase activity at 48 degrees C was due to inactivation of the monomeric 4 S enzyme, which was the most thermolabile molecular form in each tissue examined. When heated after isolation on density gradients, most of the forms of acetylcholinesterase and butyrylcholinesterase lost activity as a single exponential function of time. The monomers of both enzymes were inactivated fastest. Inactivation of the larger froms was slower and required higher temperatures. Tetrameric 10 S acetylcholinesterase was unique in following a time course that could only be fitted by a double exponential equation (i.e., when this form was heated to 55 degrees C, almost 60% of the activity showed a short half-life while the remainder showed a long half-life). This behavior did not reflect differences in the thermolability of soluble and membrane-derived tetramers.