The lagena (the third otolith endorgan in vertebrates)

In this review, the structure and functions of the lagena (the third otolith organ) in an evolutionary lineage of the vertebrates are described and discussed. The lagenar macula appears first in the posterior part of the sacculus of elasmobranchs; in these animals, the lagena is considered to be involved in the balance support (orientation with respect to the gravitation force). The lagena as a separate endorgan has been described in teleost fishes; in some species, the lagena is connected with the sacculus, while in other species the interrelations of these structures can be dissimilar. The lagena supplements the functions of the sacculus; in fishes (animals with no special organ of hearing), it is involved in discrimination of sound oscillations, identification of the gravitation vector, and orientation in the course of movements within the vertical plane. In amphibians, the lagena is localized in the posterior part of the sacculus, near the auditory structures; it performs mostly vestibular and (to a much lesser extent) auditory functions. In amniotes, the lagena was first separated from the sacculus; it is localized in the cochlear canal, distally with respect to the hearing organ. Information on the functions of the lagena in amniotes is rather limited and contradictory. Central projections of this organ have been examined practically only in birds. Lagenar afferents project to the vestibular nuclei and cerebellum, while some fibers come to the auditory nuclei of the medulla. The lagena in birds can be related to their navigation abilities (birds are supposed to be capable of orienting within the magnetic field of the Earth due to the magnetic properties of the lagenar otoconia; this structure can also provide detection of movements along the vertical axis. The close proximity between the otolithic and auditory endorgans in the cochlear canal of amniotes can be indicative of the functional significance of these interrelations. This aspect, however, remains at present undiscovered. In mammals (except Monotremata), there is no lagena as an independent endorgan. Neirofiziologiya/Neurophysiology, Vol. 40, No. 2, pp. 160–178, March–April, 2008.     

The J-related segment of tim44 is essential for cell viability: a mutant Tim44 remains in the mitochondrial import site, but inefficiently recruits mtHsp70 and impairs protein translocation.

Tim44 is a protein of the mitochondrial inner membrane and serves as an adaptor protein for mtHsp70 that drives the import of preproteins in an ATP-dependent manner. In this study we have modified the interaction of Tim44 with mtHsp70 and characterized the consequences for protein translocation. By deletion of an 18-residue segment of Tim44 with limited similarity to J-proteins, the binding of Tim44 to mtHsp70 was weakened. We found that in the yeast Saccharomyces cerevisiae the deletion of this segment is lethal. To investigate the role of the 18-residue segment, we expressed Tim44Delta18 in addition to the endogenous wild-type Tim44. Tim44Delta18 is correctly targeted to mitochondria and assembles in the inner membrane import site. The coexpression of Tim44Delta18 together with wild-type Tim44, however, does not stimulate protein import, but reduces its efficiency. In particular, the promotion of unfolding of preproteins during translocation is inhibited. mtHsp70 is still able to bind to Tim44Delta18 in an ATP-regulated manner, but the efficiency of interaction is reduced. These results suggest that the J-related segment of Tim44 is needed for productive interaction with mtHsp70. The efficient cooperation of mtHsp70 with Tim44 facilitates the translocation of loosely folded preproteins and plays a crucial role in the import of preproteins which contain a tightly folded domain.     

Early mouse embryos produce and release factors with transforming growth factor activity

Summary Previous studies have shown that extracts from mouse embryos at mid and late stages of development contain factors that exhibit transforming growth factor activity. The work reported here demonstrates that cultured mouse embryos at significantly earlier stages of development produce and release factors that exhibit the characteristic property of transforming growth factors. Specifically, the data demonstrate that embryos cultured from the blastocyst stage in serum-containing medium or in serum-free medium release factors that promote the anchorage-independent growth of normal rat kidney fibroblasts. It is shown that these factors are produced and released by cells derived from the inner cell mass and by trophoblasts. The precise developmental stage when production of these factors first begins has not been determined but our findings suggest that these factors are produced by cell types associated with early postimplatation embryos. This work was supported by the Laboratory of Viral Carcinogenesis at the National Cancer Institute and by grants from the National Cancer Institute (CA-36727) and the University of Nebraska Medical Center (22-271-732). Editor's Statement This paper presents evidence that, in an in vitro assay system, early embryonic cells are capable of both synthesizing and secreting TGF-like growth factors, implicating the production of these factors in the events of early development. David W. Barnes     

Janischewskyidae n. fam. and the duplicature of Palaeozoic ostracodes

A duplicature with a very broad inner calcified lamella is revealed in representatives of the genus Janischewskya Batalina 1926. The presence of this structure necessitates the elimination of Janischewskya from the family Hollinidae. A new family of unknown ordinal disposition – Janischewskyidae – is erected. At present, a duplicature is ascertained in four groups of Palaeozoic ostracodes – Podocopina, Parapodocopina, Selebratina-Coryellina , Janischewskyidae. □stracoda, Janischewskyidae, inner calcified la-mella, Carboniferous.
     

Mouse blastocyst immunosurgery with commercial antiserum to mouse erythrocytes

Summary Immunosurgery is a useful technique for the isolation of inner cell masses from murine blastocysts. Conventionally, rabbit antisera made ad hoc against murine splenic or fetal cells or fibroblasts have been used as antibody sources. We investigated the feasibility of using commercially available rabbit antiserum to murine erythrocytes (anti-RBC) and compared it with rabbit antiserum generated ad hoc to murine L-cells (anti-L-cell). Our results indicate that anti-RBC is at least as effective as anti-L-cell serum for the immunosurgical isolation of inner cell masses, which became either miniblastocysts (later forming outgrowths) or embryoid bodies (undergoing ectoderm-endodermlike differentiation within 48 h). Because anti-RBC is commercially available, the technical modification described herein increases the accessibility of the immunosurgical protocol for the isolation of murine inner cell masses.     

细菌吸附及转运芳香族化合物的研究进展

芳香族化合物是一类具有苯环结构的有机物,它们结构稳定,不易分解,并可通过食物链进行生物富集和生物放大,对生态环境及人类健康造成极大危害。细菌具有超强的分解代谢能力,能降解多环芳烃(polycyclic aromatic hydrocarbons, PAHs)等多种难降解芳香族污染物。吸附和转运是细菌进行芳香族化合物细胞内代谢的前提。虽然芳香族化合物的细菌降解已取得较为显著的研究进展,但吸附和转运机理仍不甚清楚。本文讨论了细菌对芳香族化合物的吸附有积极作用的细胞表面疏水性、生物被膜形成和细菌趋化性等影响因素,总结了FadL家族、TonB依赖性受体蛋白、OmpW家族等外膜转运系统和主要协同转运蛋白超家族(major facilitator superfamily, MFS)转运体、ATP结合盒(ATP-binding cassette, ABC)转运蛋白等内膜转运系统对该类化合物跨膜运输作用,并对跨膜转运机制进行了讨论和阐述,旨在为芳香族污染物的防控和治理提供一定理论参考。     

Import of a new chloroplast inner envelope protein is greatly stimulated by potassium phosphate

A cDNA clone encoding a major chloroplast inner envelope membrane protein of 96 kDa (IEP96) was isolated and characterized. The protein is synthesized as a larger-molecular-weight precursor (pIEP96) which contains a cleavable N-terminal transit sequence of 50 amino acids. The transit peptide exhibits typical stromal targeting information. It is cleaved in vitro by the stromal processing peptidase, though the mature protein is clearly localized in the inner envelope membrane. Translocation of pIEP96 into chloroplasts is greatly stimulated in the presence of 80 mM potassium phosphate which results in an import efficiency of about 90%. This effect is specific for potassium and phosphate, but cannot be ascribed to a membrane potential across the inner envelope membrane. Protein sequence analysis reveals five stretches of repeats of 26 amino acids in length. The N-terminal 300 amino acids are 45% identical (76% similarity) to the 35 kDa -subunit of acetyl-CoA carboxyl-transferase from Escherichia coli. The C-terminal 500 amino acids share significant similarity (69%) with USOI, a component of the cytoskeleton in yeast.Abbreviations P_i phosphate - IEP inner envelope membrane protein - pIEP precursor form of IEP - SSU small subunit of ribulose-1,5-bisphosphate carboxylase oxygenase - IEP96_pep peptide specific antiserum to IEP96 - IEP96_pol polyspecific antiserum to IEP96     

Differences in membrane unsaturated fatty acids and electron spin resonance in different types of myeloid leukemia cells

The fatty acid composition and some physical properties of intact cells and isolated plasma membranes of two types of mouse myeloid leukemia cell clone grown in culture have been examined. One clone type, MGI⁺D⁺, can be induced by the macrophage and granulocyte-inducing protein (MGI) to differentiate into mature macrophages and granulocytes. The other clone type, MGI⁺D^?, could not be induced to differentiate into mature cells. A two-fold increase in the ratio of saturated fatty acid to unsaturated fatty acid was found in the MGI⁺D^? compared to the MGI⁺D⁺ clones. The MGI⁺D^? clones produced an unusual polyunsaturated C_20:5 fatty acid at 28°C, whereas the MGI⁺D⁺ clones did not grow at this temperature. The cells and their isolated plasma membranes were studied by electron spin resonance. The motion of the 5-nitroxide stearate spin label was found to be higher in the intact cells and in the membranes of MGI⁺D^? clones than of the MGI⁺D⁺ clones. The cells of MGI⁺D⁺ clones showed a similar freedom of motion to normal myeloblasts from the bone marrow. The results indicate that myeloid leukemia cells which differ in their competence to be induced to differentiate into mature cells have different physical properties of their plasma membranes and that this is correlated with their fatty acid acyl chain composition.     

Effect of cholesterol and dipalmitoyl phosphatidylcholine enrichment on the kinetics of Na−Li exchange of human erythrocytes

Summary The effects of cholesterol loading and depletion and of a 10% replacement of native phosphatidylcholine by dipalmitoyl phosphatidylcholine (di 16:0-PC) on kinetic properties of human red cell Na–Li exchange have been studied.Compared to control erythrocytes (cholesterol/phospholipid ratio (C/P=0.8–0.9)),V _max of phloretin-sensitive Li uptake and of Li efflux stimulated by extracellular Na (Na _o ) were reduced by 15–30% in cholesterol-loaded red cells (C/P=1.05–1.33). The apparentK _m values for external Li (Li _o ) and for internal Li (Li _i ) were decreased by about one-third in these cells. Cholesterol depletion (C/P=0.7) exerted opposite effects on the kinetics of Na _o -dependent Li efflux. On augmentingC/P from 0.66 to 1.0,V _max of Na _o -dependent Li efflux was reduced by about 30%; increasingC/P above 1.0 caused no further lowering ofV _max. Li leakage rates monotonically decreased over the whole range ofC/P ratios examined (0.66–1.3). This indicates that Na–Li exchange and Li leak are differentially affected by cholesterol.Incorporation of di 16:0-PC (replacement of 3% of total red cell phospholipids) caused similar kinetic alterations of Na–Li exchange as a rise in membrane cholesterol by 20–50%. Notably, selective incorporation of di 16:0-PC into the outer monolayer increased both intra- and extracellular Li binding affinities of Na–Li exchange and lowered its maximum velocity. Thus, both di 16:0-PC enrichment and cholesterol loading exerted an uncompetitive type of transport inhibition. The results are in agreement with the hypothesis that the kinetic alterations of red cell Na–Li exchange seen in a subgroup of essential hypertensive patients could be due to subtle changes in the molecular species composition of individual phospholipids.     

Inner mitochondrial membrane anion channel is present in brown adipocytes but is not identical with the uncoupling protein

Summary Vesicles of inner mitochondrial membrane, mitoplasts, from rat brown adipose tissue were prepared by osmotic swelling and studied using the patch-clamp technique. Current events of a 107.8±8.7 pS (n=16, 21°C) channel were recorded in the mitoplast-attached mode. This channel was selective for anions and its kinetics resembled those of channels previously found in liver and heart mitochondria of mouse and ox. In whole-mitoplast mode each of five purine nucleotides (20 m) blocked the channel. This is the first demonstration of pharmacological blockade of this type of channel. Although a similar anion channel in mouse and ox mitochondria was suggested to be the uncoupling protein (UCP) associated with nonshivering thermogenesis, we present several arguments against this possibility. Thus we describe a high-conductance, purine-nucleotide-binding, anion selective mitochondrial channel, that is not the UCP.