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T J Lints

Publications and source records attributed to T J Lints.

9 recordsLinked to original sources
PubMed2004

Studying the song development process: rationale and methods.

Current technology makes it possible to measure song development continuously throughout a vocal ontogeny. Here we briefly review some of the problems involved and describe experimental and analytic methods for automatic tracing of vocal changes. These techniques make it possible to characterize the specific methods the bird uses to imitate sounds: an automated song recognition procedure allows continuous song recording, followed by automated sound analysis that partition the song to syllables, extract acoustic features of each syllable, and summarize the entire song development process over time into a single database. The entire song development is then presentable in the form of images or movie clips. These Dynamic Vocal Development (DVD) maps show how each syllable type emerges, and how the bird manipulates syllable features to eventually approximate the model song. Most of the experimental and analytic methods described here have been organized into a software package, which also allows combined neural and sound recording to monitor changes in brain activity as vocal learning occurs. The software is available at http://ofer.sci.ccny.cuny.edu.

Animals↗
PubMed2004

Song development: in search of the error-signal.

Song development provides an opportunity to study the mechanisms of vocal learning dynamically at molecular, cellular and systems levels, and across time scales ranging from minutes to months. To exploit these opportunities one needs to identify appropriate units, types and time scales of vocal change in nearly real time. The previous chapter by Tchernikovski et al. in this volume described techniques that make this research strategy feasible by allowing us to observe the song learning process through a "temporal microscope" with variable degrees of resolution. In this chapter we summarize some of the new observations and raise hypotheses about the learning strategy of the bird. We focus on inferences that can be drawn from behavioral observations to the nature and complexity of the instructive signal that guides the vocal change (error-signal). We examine two effects: i) the emergence of syllable types and ii) changes in features within a syllable type. We found that different features of the same syllable change during different and sometimes disjointed developmental windows. We discuss the possibility that song imitation is achieved by correcting partial errors, and that features of those partial errors change adaptively during development, perhaps concurrently with changes in perception and in motor proficiency. Those hypotheses can be best examined by across levels investigation, starting from identifying critical moments in song development and recording of articulatory dynamics and neural patterns when only a few features of specific syllables undergo rapid changes. Such investigation could relate behavioral events to brain mechanisms that guide song learning from moment-to-moment and across extended periods.

Animals↗
PubMed1997

Cooperation of BMP7 and SHH in the induction of forebrain ventral midline cells by prechordal mesoderm.

Ventral midline cells at different rostrocaudal levels of the central nervous system exhibit distinct properties but share the ability to pattern the dorsoventral axis of the neural tube. We show here that ventral midline cells acquire distinct identities in response to the different signaling activities of underlying mesoderm. Signals from prechordal mesoderm control the differentiation of rostral diencephalic ventral midline cells, whereas notochord induces floor plate cells caudally. Sonic hedgehog (SHH) is expressed throughout axial mesoderm and is required for the induction of both rostral diencephalic ventral midline cells and floor plate. However, prechordal mesoderm also expresses BMP7 whose function is required coordinately with SHH to induce rostral diencephalic ventral midline cells. BMP7 acts directly on neural cells, modifying their response to SHH so that they differentiate into rostral diencephalic ventral midline cells rather than floor plate cells. Our results suggest a model whereby axial mesoderm both induces the differentiation of overlying neural cells and controls the rostrocaudal character of the ventral midline of the neural tube.

Animals↗
PubMed1996

Hlx homeo box gene is essential for an inductive tissue interaction that drives expansion of embryonic liver and gut.

The divergent murine homeo box gene Hlx is expressed in restricted hematopoietic cell types and, during embryogenesis, prominently in visceral mesenchyme of the developing liver, gall bladder, and gut. Targeted disruption of the gene has now established that it plays a key role in visceral organogenesis. Embryos homozygous for the mutation died around embryonic day 15 with anemia and severe hypoplasia of the liver and gut. Liver ontogeny commenced normally with formation of the liver diverticulum and differentiation of hepatocytes, but the organ failed to expand and reached only 3% of normal size. The apparent liver hypoplasia was not associated with a notable increase in apoptotic cells. Gut development also began normally, but the intestines failed to undergo extensive elongation and looping and reached only a quarter of normal length. The anemia resulted from a deficiency in the fetal form of hematopoiesis, which occurs in the liver, but no intrinsic defect in Hlx-/- hematopoietic cells was observed in vitro, and liver-derived Hlx-/- hematopoietic stem cells that were transplanted to irradiated normal mice could fully reconstitute hematopoiesis. The impaired fetal hematopoiesis therefore reflects insufficient support function provided by the minute liver. Hlx is normally expressed in visceral mesenchyme lying adjacent to the developing liver and gut epithelia affected by the mutation, but not in the epithelia themselves. Hence, Hlx regulates a mesenchymal-epithelial interaction that drives a vital growth phase in visceral organogenesis. Moreover, because mutation of Hlx blocked liver growth but not its specification, early morphogenesis, or differentiation, development of this organ appears to occur by step-wise inductive interactions under separate genetic control.

Animals↗
PubMed1996

Mesoderm-specific expression of the divergent homeobox gene Hlx during murine embryogenesis.

We have determined the expression pattern of the divergent homeobox gene Hlx during post-implantation mouse development, utilizing in situ hybridization. Expression was mesoderm-specific and occurred in a complex tissue distribution. Transcripts were first detected at 9.5 days post coitum (p.c.) in splanchnic mesoderm of the midgut and hindgut region, then during organogenesis, prominently in mesenchyme of the developing liver, gall bladder, and intestines, as well as their mesenteric tissues. In the foregut, lung mesenchyme became positive from 10.5 days p.c. Hlx transcripts were also detected in a subset of skeletal myogenic cells: those within branchial arches from 9.5 days p.c. and within limb buds from 12 days p.c. Hlx was not expressed in myogenic cells which are derived from the myotome and populate the trunk. However, from 10 days p.c., expression was seen in a region of the sclerotome immediately adjacent to the myotome and corresponding to precursors of the ribs and vertebral neural arches. In the anterior-posterior aspect of the developing sclerotome, Hlx expression was out of register with original segmental boundaries (intersomitic fissures), a pattern consistent with a classical hypothesis that the developing vertebral column undergoes resegmentation. Hlx expression was also observed in vibrissae, pericardium, snout mesenchyme, and meningeal epithelium. Overall, expression of Hlx in only a subset of individual lineage progenitors and at know sites of inductive tissue interactions, suggests that the gene regulates local patterning or growth through cell:cell signalling at those embryonic sites.

Animals↗
PubMed1995

Functional expression of the tachykinin NK1 receptor by floor plate cells in the embryonic rat spinal cord and brainstem.

1. The floor plate is a ventral mid-line structure that plays a pivotal role in the organization of the developing vertebrate central nervous system. Previous studies have demonstrated that the floor plate may provide signals that induce neuronal differentiation and guide axons; however, it is not known whether the floor plate can itself respond to signals that derive from surrounding tissue. 2. The peptide substance P is one of the first transmitters to be expressed in the developing spinal cord. To determine whether the floor plate may respond to substance P we have examined the expression of the principal substance P receptor (the tachykinin NK1 receptor) by floor plate cells of the rat embryonic spinal cord using immunocytochemistry, in situ hybridization and fura-2 calcium imaging. 3. Immunocytochemistry demonstrated selective expression of the NK1 receptor by cells at the ventral mid-line of the spinal cord. Double immunofluorescence labelling with the specific floor plate marker FP3 indicated that NK1 receptor expression is confined to cells in the lateral region of the floor plate. 4. In order to confirm the specificity of the NK1 receptor immunoreactivity we performed in situ hybridization histochemistry using antisense cRNA probes directed against the NK1 receptor. In situ hybridization demonstrated selective expression of NK1 receptor mRNA by floor plate cells. 5. The ontogeny of NK1 receptor protein and mRNA expression in the floor plate was defined. NK1 receptor expression occurred in a rostrocaudal progression that begins at embryonic day 10-11 (E10-E11) and is complete by E12-E14. The restriction of NK1 receptor expression to the lateral part of the floor plate was conserved throughout embryonic development. 6. NK1 receptor signalling was assessed by monitoring substance P-evoked changes in the intracellular concentration of calcium ions ([Ca2+]i) of acutely dissociated cells from the floor plate region. Application of substance P (5 nM) elevated [Ca2+]i in 10% of cells examined. 7. Selective neurokinin agonists were used to identify the receptor subtype involved in the substance P-evoked elevation of [Ca2+]i. Acetyl-[Arg6,Sar9,Met(O2)11]-substance P(6-11) (5 nM) and [Sar9,Met(O2)11]-substance P (5 nM), two highly selective NK1 receptor agonists, both elevated [Ca2+]i in floor plate cells that responded to substance P. [beta-Ala8]-neurokinin A(4-10) (50 nM) and senktide (50 nM), selective agonists respectively of NK2 and NK3 receptors, had no effect on [Ca2+]i.

Amino Acid Sequence↗
PubMed1994

XNkx-2.5, a Xenopus gene related to Nkx-2.5 and tinman: evidence for a conserved role in cardiac development.

We have isolated a Xenopus homeodomain sequence, XNkx-2.5, which shows significant similarity to mouse Nkx-2.5 and to the Drosophila tinman gene product. In Drosophila, tinman is required for formation of the heart and visceral mesoderm structures. In situ hybridization studies show that XNkx-2.5 is expressed in the heart region during early Xenopus development and later is also expressed in gut tissue. The observed similarity of sequences and expression patterns suggests that the regulatory mechanisms underlying heart formation may be conserved between distant species.

Amino Acid Sequence↗
PubMed1993

Nkx-2.5: a novel murine homeobox gene expressed in early heart progenitor cells and their myogenic descendants.

We have isolated two murine homeobox genes, Nkx-2.5 and Nkx-2.6, that are new members of a sp sub-family of homeobox genes related to Drosophila NK2, NK3 and NK4/msh-2. In this paper, we focus on the Nkx-2.5 gene and its expression pattern during post-implantation development. Nkx-2.5 transcripts are first detected at early headfold stages in myocardiogenic progenitor cells. Expression preceeds the onset of myogenic differentiation, and continues in cardiomyocytes of embryonic, foetal and adult hearts. Transcripts are also detected in future pharyngeal endoderm, the tissue believed to produce the heart inducer. Expression in endoderm is only found laterally, where it is in direct apposition to promyocardium, suggesting an interaction between the two tissues. After foregut closure, Nkx-2.5 expression in endoderm is limited to the pharyngeal floor, dorsal to the developing heart tube. The thyroid primordium, a derivative of the pharyngeal floor, continues to express Nkx-2.5 after transcript levels diminish in the rest of the pharynx. Nkx-2.5 transcripts are also detected in lingual muscle, spleen and stomach. The expression data implicate Nkx-2.5 in commitment to and/or differentiation of the myocardial lineage. The data further demonstrate that cardiogenic progenitors can be distinguished at a molecular level by late gastrulation. Nkx-2.5 expression will therefore be a valuable marker in the analysis of mesoderm development and an early entry point for dissection of the molecular basis of myogenesis in the heart.

Amino Acid Sequence↗