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A B Smit

Publications and source records attributed to A B Smit.

At least 55 records · Page 3Linked to original sources
PubMed1994

Structural characterization of a Lymnaea putative endoprotease related to human furin.

A number of peptides have been identified in the central nervous system of the freshwater snail, Lymnaea stagnalis, that function as hormones and neurotransmitters/neuromodulators. These peptides are typically proteolytically processed from larger prohormones mostly at sites composed of single or multiple basic amino acid residues. Previously we demonstrated a diversity of putative prohormone convertases that may be involved in prohormone processing in the Lymnaea brain. In the present report, we have characterized a cDNA clone encoding a putative endoprotease of 837 amino acids. The primary structure of endoprotease (Lfur2) was comparable to that of human furin and contained a putative catalytic domain, a Cys-rich domain, and a transmembrane region. The catalytic domain of Lfur2 demonstrated about 70% residue identity when compared with human furin, PACE4 and Drosophila Dfur1 and dKLIP-1. The Lfur2 gene was expressed in the central nervous system as well as various peripheral tissues of Lymnaea.

Amino Acid Sequence↗
PubMed1993

cDNA cloning of the sodium-influx-stimulating peptide in the mollusc, Lymnaea stagnalis.

We isolated and characterized a cDNA clone, encoding the prohormone of the sodium-influx-stimulating (SIS) peptide of the freshwater snail Lymnaea stagnalis. The prohormone is cleaved to generate a signal peptide of 23 amino acids and a SIS peptide of 77 amino acids. The SIS peptide as encoded by the cDNA represents a novel and complex neuropeptide, which controls the activity of sodium pumps in the integument, pericardium, ureter and nephridial gland. In situ hybridization showed that the SIS-peptide gene is expressed by the neuroendocrine, so-called Yellow Cells of the central nervous system.

Amino Acid Sequence↗
PubMed1993

The isolation of a cDNA encoding a neuropeptide prohormone from the light yellow cells of Lymnaea stagnalis.

1. The central nervous system (CNS) of the freshwater snail Lymnaea stagnalis contains several clusters of neuroendocrine cells, which synthesize neuropeptides that act as neurotransmitters, neurohormones, and/or neuromodulators, controlling a broad range of physiological processes. Using a protein chemical approach, we have previously characterized a peptide [named LYCP-A (Hoek et al., 1992], which is produced by the neuroendocrine light yellow cells (LYC), which are present as two clusters of endogenously bursting neurons in the visceral and right parietal ganglion, respectively. 2. A differential screening technique was used to isolate the cDNA that encodes the prohormone of LYCP-A. The prohormone appeared to contain three or four putative neuropeptides, one of which is LYCP-A. The organization of the identified prohormone resembles that of the histidine-rich basic peptide precursor previously identified in the R3-14 neurons of the marine snail Aplysia californica (Campanelli and Scheller, 1987). 3. In situ hybridization analysis indicates that the gene encoding the LYC prohormone is expressed in a subset of the LYC. The LYC release their peptides into the hemolymph from a neurohemal area, which is located around the CNS. In addition, the peptides are released from axonal branches in the aorta of the heart, suggesting a role in the regulation of cardiovascular functions.

Amino Acid Sequence↗
PubMed1993

Alternative splicing generates diversity of VD1/RPD2 alpha peptides in the central nervous system of Lymnaea stagnalis.

1. Two giant peptidergic neurons, VD1 and RPD2, of the visceral ganglion and right parietal ganglion of Lymnaea stagnalis, respectively, play an important role in the modulation of complex physiological and behavioral adjustments that occur as a result of changes in O2 availability. 2. By cDNA cloning, we have identified two types of VD1/RPD2 transcripts expressed in VD1 and RPD2. In addition, these transcripts are also expressed in other neurons. 3. Both transcripts encode distinct yet related VD1/RPD2 preprohormones that may be cleaved to yield distinct but overlapping sets of neuropeptides. 4. Using the polymerase chain reaction technique, we could show the existence of additional splice variants. 5. Analysis of the organization of the VD1/RPD2 gene indicates that the alpha peptide coding region is interrupted by a number of introns. 6. We concluded that the mRNA segment encoding the alpha peptide domain of the VD1/RPD2 preprohormones is alternatively spliced, thus generating different alpha peptides.

Amino Acid Sequence↗
PubMed1993

Phonologic error distributions in the Iowa-Nebraska Articulation Norms Project: consonant singletons.

The errors on consonant singletons made by children in the Iowa-Nebraska Articulation Norms Project (Smit, Hand, Freilinger, Bernthal, & Bird, 1990) were tabulated by age range and frequency. The prominent error types can usually be described as phonological processes, but there are other common errors as well, especially distortions of liquids and fricatives. Moreover, some of the relevant phonological processes appear to be restricted in the range of consonants or word-positions to which they apply. A metric based on frequency of use is proposed for determining that an error type is or is not atypical. Changes in frequency of error types over the age range are examined to determine if certain atypical error types are likely to be developmental, that is, likely to self-correct as the child matures. Finally, the clinical applications of these data for evaluation and intervention are explored.

Age Factors↗
PubMed1993

Phonologic error distributions in the Iowa-Nebraska Articulation Norms Project: word-initial consonant clusters.

The errors on word-initial consonant clusters made by children in the Iowa-Nebraska Articulation Norms Project (Smit, Hand, Freilinger, Bernthal, & Bird, 1990) were tabulated by age range and frequency. The error data show considerable support for Greenlee's (1974) stages in the acquisition of clusters: the youngest children show cluster reduction, somewhat older children show cluster preservation but with errors on one or more of the cluster elements, and the oldest children generally show correct production. These stages extended to three-element clusters as well. Typical cluster reduction errors were (a) reduction to the obstruent in obstruent-plus-approximant clusters and (b) reduction to the second element in /s/-clusters. When clusters were preserved, but one member was in error, the error was typically the same as for the singleton consonant. Cluster errors are discussed in terms of theories of phonologic development, including open genetic programs and feature geometry. These data are expected to be useful in evaluation and treatment of disorders of phonology.

Articulation Disorders↗
PubMed1993

Evolutionary conservation of the insulin gene structure in invertebrates: cloning of the gene encoding molluscan insulin-related peptide III from Lymnaea stagnalis.

Although insulins and structurally related peptides are found in vertebrates as well as in invertebrates, it is not clear whether the genes encoding these hormones have emerged from a single ancestral (insulin)-type of gene or, alternatively, have arisen independently through convergent evolution from different types of gene. To investigate this issue, we cloned the gene encoding the molluscan insulin-related peptide III (MIP III) from the freshwater snail, Lymnaea stagnalis. The predicted MIP III preprohormone had the overall organization of preproinsulin, with a signal peptide and A and B chains, connected by two putative C peptides. Although MIP III was found to share key features with vertebrate insulins, it also had unique structural characteristics in common with the previously identified MIPs I and II, thus forming a distinct class of MIP peptides within the insulin superfamily. MIP III is synthesized in neurones in the brain. It is encoded by a gene with the overall organization of the vertebrate insulin genes, with three exons and two introns, of which the second intron interrupts the coding region of the C peptides. Our data therefore demonstrate that in the Archaemetazoa, the common ancestor of the vertebrates and invertebrates, a primordial peptide with a two-chain insulin configuration encoded by a primordial insulin-type gene must have been present.

Amino Acid Sequence↗
PubMed1992

Molluscan putative prohormone convertases: structural diversity in the central nervous system of Lymnaea stagnalis.

In the cerebral ganglia of the central nervous system of the freshwater snail Lymnaea stagnalis many neuropeptides are proteolytically processed from larger prohormones at sites marked by both single and multiple basic amino acids. In the present study we identified cloned cDNA and PCR products corresponding to three putative endoproteases that may be involved in prohormone processing. The cDNA encodes a protein of 653 residues with an overall sequence identity of 60%, 41%, 35%, 40%, and 27% with the recently characterized endoproteases PC2, PC1/3, PC4, furin and Kex2, respectively. The Lymnaea preproconvertase has approximately 80% homology with the catalytic domain, and approximately 40% and approximately 50% with the N- and C-terminal part, respectively, of the vertebrate PC2. Two cloned PCR products, Lfur 1 and Lfur 2, show highest sequence identity to furin. Expression of the LPC2 gene is exclusively in the central nervous system, where two LPC2 transcripts of 3.0 and 4.8 kb were detected.

Amino Acid Sequence↗
PubMed1992

The Light Green Cells of Lymnaea: a neuroendocrine model system for stimulus-induced expression of multiple peptide genes in a single cell type.

We review recent experiments showing that the cerebral neuroendocrine Light Green Cells (LGCs) of the freshwater snail, Lymnaea stagnalis, express a family of distinct though related molluscan insulin-related peptide (MIP) genes. The LGCs are involved in the regulation of a wide range of interrelated life processes associated with growth, (energy) metabolism and reproduction. We consider the mechanism of generation of diversity among MIPs, and present evidence that conditions with distinct effects on growth, metabolism and reproduction also can induce distinct patterns of expression of the MIP and schistosomin genes. The stimulus-dependent expression of multiple neuropeptide genes enormously increases the adaptive potential of a peptidergic neuron. We suggest that this contributes significantly to the information-handling capacity of the brain.

Amino Acid Sequence↗
PubMed1992

Evolution of the vasopressin/oxytocin superfamily: characterization of a cDNA encoding a vasopressin-related precursor, preproconopressin, from the mollusc Lymnaea stagnalis.

Although the nonapeptide hormones vasopressin, oxytocin, and related peptides from vertebrates and some nonapeptides from invertebrates share similarities in amino acid sequence, their evolutionary relationships are not clear. To investigate this issue, we cloned a cDNA encoding a vasopressin-related peptide, Lys-conopressin, produced in the central nervous system of the gastropod mollusc Lymnaea stagnalis. The predicted preproconopressin has the overall architecture of vertebrate preprovasopressin, with a signal peptide, Lys-conopressin, that is flanked at the C terminus by an amidation signal and a pair of basic residues, followed by a neurophysin domain. The Lymnaea neurophysin and the vertebrate neurophysins share high sequence identity, which includes the conservation of all 14 cysteine residues. In addition, the Lymnaea neurophysin possesses unique structural characteristics. It contains a putative N-linked glycosylation site at a position in the vertebrate neurophysins where a strictly conserved tyrosine residue, which plays an essential role in binding of the nonapeptide hormones, is found. The C-terminal copeptin homologous extension of the Lymnaea neurophysin has low sequence identity with the vertebrate counterparts and is probably not cleaved from the prohormone, as are the mammalian copeptins. The conopressin gene is expressed in only a few neurons in both pedal ganglia of the central nervous system. The conopressin transcript is present in two sizes, due to alternative use of polyadenylylation signals. The data presented here demonstrate that the typical organization of the prohormones of the vasopressin/oxytocin superfamily must have been present in the common ancestors of vertebrates and invertebrates.

Amino Acid Sequence↗
PubMed1992

Characterization of a cDNA clone encoding molluscan insulin-related peptide V of Lymnaea stagnalis.

A cDNA clone encoding molluscan insulin-related peptide V (MIP V) was isolated from a cDNA library of the central nervous system (CNS) of the freshwater snail, Lymnaea stagnalis, using a heterologous screening with a previously identified MIP II cDNA. The MIP V cDNA encodes a preprohormone resembling the organization of preproinsulin, with a putative signal sequence, and an A and B chain, however, in this case connected by two distinct C peptide, C alpha and C beta, instead of one single C peptide. This phenomenon, which is shared by the MIP II precursor, represents a new development in the prohormone organization of peptides belonging to the insulin superfamily. The A and B chains of MIPs V, I and II, differ remarkably in primary structure; in contrast, the C alpha peptide domains are almost identical. MIP V has only limited sequence similarity with insulins and related peptides. Both MIP V and I exhibit structural features, which make them a unique class of the insulin superfamily. The MIP I, II and V genes are expressed in a single type of neuron: the growth controlling neuroendocrine light green cells of the Lymnaea CNS.

Amino Acid Sequence↗
PubMed1992

Characterization of a cDNA clone encoding multiple copies of the neuropeptide APGWamide in the mollusk Lymnaea stagnalis.

Male mating behavior of the simultaneous hermaphrodite freshwater snail Lymnaea stagnalis is controlled by a neuronal network that consists of various types of peptidergic neurons, as well as serotonergic cells. In the present article, we describe the isolation and characterization of a cDNA clone that encodes a multipeptide preprohormone expressed in the anterior lobe of the right cerebral ganglion, in a group of neurons that principally innervate the penial complex. The preprohormone is 219 amino acids in length and contains 10 copies of the peptide Ala-Pro-Gly-Trp-Gly. Posttranslational processing of the prohormone may lead to the generation of the amidated neuropeptide Ala-Pro-Gly-Trp-amide (APGWamide), an amidated C-terminal anterior lobe peptide, and four connecting peptide sequences, C1-C4. We show by in situ and filter hybridizations that neurons of the right anterior lobe comprise the major site of expression of the APGWamide gene. Expression of the APGWamide gene is detected in the CNS of both adult animals and noncopulating juveniles. Peptides derived from the APGWamide prohormone are probably involved in the control of a part of the male mating behavior and have both central and peripheral targets.

Amino Acid Sequence↗
PubMed1991

Characterization of a cDNA clone encoding molluscan insulin-related peptide II of Lymnaea stagnalis.

A cDNA clone encoding molluscan insulin-related peptide (MIP) II was isolated from a cDNA library of the central nervous system (CNS) of the freshwater snail, Lymnaea stagnalis, using a heterologous screening with a previously identified MIP cDNA (renamed MIP-I cDNA). The MIP-II cDNA encodes a preprohormone resembling the organization of preproinsulin, with a putative signal sequence, and A and B chains; however, in this case connected by two distinct C peptides, C alpha and C beta, instead of a single C peptide, a phenomenon which represents a new development in the prohormone organization of peptides belonging to the insulin superfamily. The A and B chains of MIP II and I differ remarkably in primary structure; in contrast, the C alpha peptide domains are fully identical. MIP II has only limited sequence similarity with insulins and related peptides. Both MIP II and I exhibit structural features, which make them a unique class of the insulin superfamily. The MIP I and II genes are expressed in a single type of neuron: the growth-controlling neuroendocrine light green cells of the Lymnaea CNS.

Amino Acid Sequence↗
PubMed1991

3'-end fluorochromized and haptenized oligonucleotides as in situ hybridization probes for multiple, simultaneous RNA detection.

We have used fluorescein-, digoxigenin- and biotin-(di)deoxyXTPs and terminal deoxynucleotidyl transferase for small scale labeling of synthetic oligonucleotide probes and here we show the applicability of such probes for the in situ detection of multiple RNA sequences. The enzymatic 3'-end-labeling methods proved to be good alternatives for the chemical fluorochrome and hapten labeling of 5'-end alkylamino-derivatized oligonucleotides. By combining 3'-end fluorescein-, biotin-, and digoxigenin-labeled oligonucleotides, double and triple hybridizations are feasible. For example, we demonstrated simultaneously mRNAs coding for caudodorsal cell hormone, a molluscan insulin-related peptide, and 28 S ribosomal RNA in cryostat sections of the cerebral ganglia of the pond snail Lymnaea stagnalis.

Animals↗
PubMed1990

The Iowa Articulation Norms Project and its Nebraska replication.

The purpose of the Iowa Articulation Norms Project and its Nebraska replication was to provide normative information about speech sound acquisition in these two states. An assessment instrument consisting of photographs and a checklist form for narrow phonetic transcription was administered by school-based speech-language pathologists to stratified samples of children in the age range 3-9 years. The resulting data were not influenced by the demographic variables of population density (rural/urban), SES (based on parental education), or state of residence (Iowa/Nebraska); however, sex of the child exerted a significant influence in some of the preschool age groups. The criteria used to determine acceptability of a production appeared to influence outcomes for some speech sounds. Acquisition curves were plotted for individual phoneme targets or groups of targets. These curves were used to develop recommended ages of acquisition for the tested speech sounds, with recommendations based generally on a 90% level of acquisition. Special considerations were required for the phonemes /ng s z/.

Age Factors↗
PubMed1990

Simultaneous detection of different mRNA sequences coding for neuropeptide hormones by double in situ hybridization using FITC- and biotin-labeled oligonucleotides.

Oligonucleotides labeled with FITC or biotin were applied for detection of specific mRNAs in microscopic preparations by in situ hybridization. The oligonucleotides were labeled with one FITC or biotin molecule at the 5' end or with a tail of biotin molecules at the 3' end. The target sequences were mRNAs coding for an ovulation hormone (CDCH) in the caudodorsal cells (CDC) of the pond snail Lymnaea stagnalis and a molluscan insulin-like peptide (MIP) in the light green cells (LGC) of the same organism. The hybridized oligonucleotides were detected either directly after the hybridization procedure by fluorescence microscopy or indirectly after an immunocytochemical procedure to visualize the biotin or FITC moiety. The results indicate that the detectability of the mRNA sequences is at least partially dependent on the accessibility of the target sequences for the immunocytochemical detection systems. The positive hybridization results obtained with oligonucleotides containing different labels enabled us to perform double hybridization experiments for simultaneous detection of CDCH and MIP mRNAs in one tissue section. Using FITC- and biotin-labeled oligonucleotides, we also demonstrated simultaneously different sequences on the same mRNA molecule.

Animals↗