Environmental and lunar cues are predictive of the timing of river entry and spawning-site arrival in lake sturgeon Acipenser fulvescens

The associations were quantified between daily and interannual variation in the timing of a closed population of lake sturgeon Acipenser fulvescens migration and arrival at spawning sites with stream environmental and lunar covariates. Spawning data were gathered from 1262 fish in Black Lake, Michigan 2001 to 2008 and by video monitoring 2000 to 2002. Sex-specific variation in responses to external cues was also tested. Results showed that a greater number of individuals initiated migration from lake to riverine habitats at dawn and dusk relative to other times of the day. Current and lagged effects of water temperature and river discharge, and periods in the lunar cycle were important variables in models quantifying movements into the river and timing of adult arrival at spawning sites. Different suites of covariates were predictive of A. fulverscens responses during different periods of the spawning season. The timing of initiation of migration and spawning, and the importance of covariates to the timing of these events, did not differ between sexes. Stream flow and temperature covaried with other variables including day length and the lunar cycle. Anthropogenic disruption of relationships among variables may mean that environmental cues may no longer reliably convey information for Acipenseriformes and other migratory fishes.

Functional pre- mRNA trans-splicing of coactivator CoAA and corepressor RBM4 during stem/progenitor cell differentiation

Alternative splicing yields functionally distinctive gene products, and their balance plays critical roles in cell differentiation and development. We have previously shown that tumor-associated enhancer loss in coactivator gene CoAA leads to its altered alternative splicing. Here we identified two intergenic splicing variants, a zinc finger-containing coactivator CoAZ and a non-coding transcript ncCoAZ, between CoAA and its downstream corepressor gene RBM4. During stem/progenitor cell neural differentiation, we found that the switched alternative splicing and trans-splicing between CoAA and RBM4 transcripts result in lineage-specific expression of wild type CoAA, RBM4, and their variants. Stable expression of CoAA, RBM4, or their variants prevents the switch and disrupts the embryoid body formation. In addition, CoAA and RBM4 counter-regulate the target gene Tau at exon 10, and their splicing activities are subjected to the control by each splice variant. Further phylogenetic analysis showed that mammalian CoAA and RBM4 genes share common ancestry with the Drosophila melanogaster gene Lark, which is known to regulate early development and circadian rhythms. Thus, the trans-splicing between CoAA and RBM4 transcripts may represent a required regulation preserved during evolution. Our results demonstrate that a linked splicing control of transcriptional coactivator and corepressor is involved in stem/progenitor cell differentiation. The alternative splicing imbalance of CoAA and RBM4, because of loss of their common enhancer in cancer, may deregulate stem/progenitor cell differentiation.

Downregulation of IFN-gammaR in association with loss of Fas function is linked to tumor progression

The host immune system functions as an intrinsic surveillance network in the recognition and destruction of tumor cells, and it has been demonstrated that lymphocytes and IFN-gamma are the primary tumor suppressors of the immune system. However, the immune system can concurrently select for tumor variants with reduced immunogenicity and aggressive phenotypes. We report here that tumor escape variants that have survived CTL adoptive immunotherapy exhibited decreased expression levels of both Fas and IFN-gammaR in vitro. Furthermore, examination of spontaneously arising mouse primary mammary carcinoma and lung metastases revealed that both Fas and IFN-gammaR protein levels were dramatically lower in lung metastases than in primary tumors in vivo. Functional disruption of either the Fas- or the IFN-gamma signaling pathway enhanced the colonization efficiency of preexisting metastatic tumor cells, whereas disruption of both Fas and IFN-gammaR pathways resulted in synergistic augmentation of the colonization efficiency of the preexisting metastatic tumor cells, as determined by experimental lung metastases assay. Gene expression profiling revealed that altered expression of genes involved in immediate IFN-gammaR signaling, the interferon primary response, apoptosis and tumor colonization is associated with loss of IFN-gammaR function and enhanced metastatic potential. Interestingly, disruption of IFN-gammaR function did not alter tumor cell susceptibility to CTL-mediated cytotoxicity, but is linked to enhanced infiltration of endogenous T cells in the tumor microenvironment in vivo. These findings suggest that coordinate downregulation of Fas and IFN-gammaR, 2 key components of cancer immunosurveillance system on tumor cells, leads to a more aggressive metastatic phenotype.

Cooperative downregulation of IFN[gamma]R and Fas is functionally linked to CTL-mediated immunoselection and tumor promotion (50.3)

The host immune system functions as an intrinsic surveillance network in the recognition and destruction of tumor cells. But the immune system, at the same time can “edit” tumor cells and select for tumor variants with reduced immunogenicity through immunoselection. We report here that Fas and IFNγR were coordinately downregulated in the tumor escape variants in vitro. Examination of spontaneously arising mouse primary mammary carcinoma and lung metastases revealed that both Fas and IFNγR protein levels were also dramatically lower in lung metastases than in primary tumors in vivo. Functional disruption of either the Fas-mediated apoptosis pathway, the IFNγ signaling pathway, or both pathways together enhanced the metastatic capability of tumor cells. Gene expression profiling revealed that altered expression of genes involved in immediate IFNγR signaling, the interferon primary response, apoptosis, and tumor colonization are associated with tumor escape. Furthermore, disruption of IFNγR function did not alter tumor cell susceptibility to CTL-mediated cytotoxicity, but is linked to enhanced infiltration of endogenous T cells in the tumor microenvironment and tumor promotion in vivo. These findings suggest that coordinate downregulation of Fas and IFNγR by tumor cells, two key components of cancer immunosurveillance and immunoediting, leads to a more aggressive metastatic phenotype.

Parathyroid hormone-related protein (PTHrP) expression in ameloblastoma

OBJECTIVE

Parathyroid hormone-related protein (PTHrP) production has been demonstrated in a variety of tumor subtypes. Local production of PTHrP by metastatic tumor cells in bone has been linked to bone destruction and tumor growth. Ameloblastoma (AB) is a relatively common odontogenic epithelial neoplasm that manifests local infiltrative intraosseous growth. AB recapitulates the developing enamel epithelium, in which PTHrP recently has been demonstrated. Yet PTHrP expression in a series of ABs has not been studied to date. The purpose of this investigation is to assess the expression of PTHrP in ameloblastoma.

STUDY DESIGN

Formalin-fixed, paraffin-embedded tissue sections of ameloblastoma (n = 30; 24 conventional, 4 unicystic, and 2 arising in dentigerous cyst) were immunostained with anti-PTHrP antibody using a multistep streptavidin-peroxidase technique. Semiquantitative scoring of immunoreactivity was assessed as mild, moderate, and intense.

RESULTS

All cases (100%) demonstrated positive immunoreactivity, with mild reaction in 3 conventional ABs, 1 unicystic and 1 AB arising in dentigerous cyst, and with moderate reaction in 12 conventional ABs, 3 unicystic and 1 AB arising in dentigerous cyst. Intense immunoreactivity was seen in 9 cases of conventional AB. This difference in immunostaining was not statistically significant (Sigma2 = 4.41, df = 4, P = .358).

CONCLUSION

The results of this investigation suggest that PTHrP may play a significant role in local bone resorption, offering at least partial explanation for the tumor's infiltrative growth and destructive behavior. The uniformity of PTHrP expression by AB, as detailed in this study, may harbor significant therapeutic implications, particularly through PTHrP-blocking treatment modalities.

A charge nurse workshop based on research

The authors describe a charge nurse workshop based on a qualitative research study of charge nurse competencies and a commitment to include all levels of staff in the planning process. The workshop met the needs of nursing staff to have an interactive, educational experience that addressed leadership, human relations, and team-building skills needed for the charge nurse role and was fun. Evaluation of the workshop with lessons learned also is presented.

Anxiolytic effects of kava extract and kavalactones in the chick social separation-stress paradigm

RATIONALE

Piper methysticum extract (kava kava) possesses numerous therapeutic properties, but it is unknown which of its principle constituents (kavalactones) subserve such effects.

OBJECTIVES

This experiment sought to characterize the putative anxiolytic properties of P. methysticum extract and its six principle kavalactones in the chick social separation-stress paradigm.

METHODS

Eight-day-old chicks received intraperitoneal injections of either vehicle, chlordiazepoxide (5.0 mg/ml per kg), P. methysticum extract (containing 30% kavalactones), kavain, dihydrokavain, methysticin, dihydromethysticin, yangonin, or desmethoxyyangonin (30 mg/ml per kg for kava compounds) 30 min prior to being tested in the presence of two conspecifics or in isolation for a 3-min observation period. Latency to adopt a ventral recumbent posture to index sedation, number of vocalizations to index separation distress, and a composite pain score (in response to 50 microliters 0.10% formalin injection into the plantar surface of the foot) to index stress-induced analgesia served as dependent measures.

RESULTS

Both chlordiazepoxide and P. methysticum extract attenuated separation-induced distress vocalizations and stress-induced analgesia. Dihydrokavain attenuated separation-induced distress vocalizations.

CONCLUSIONS

These findings suggest that the anxiolytic effects of P. methysticum extract may be mediated, in part, by dihydrokavain.

Early development of the neural plate, neural crest and facial region of marsupials

Marsupial mammals have a distinctive reproductive strategy. The young are born after an exceptionally short period of organogenesis and are consequently extremely altricial. Yet because they must be functionally independent in an essentially embryonic condition, the marsupial neonate exhibits a unique suite of adaptations. In particular, certain bones of the facial region, most cranial musculature and a few additional structures are accelerated in their development. In contrast, central nervous system structures, especially the forebrain, are markedly premature at birth, resembling an embryonic d 11 or 12 mouse. This review examines the developmental processes that are modified to produce these evolutionary changes. The focus is on the early development of the neural plate, neural crest and facial region in the marsupial, Monodelphis domestica, compared with patterns reported for rodents. Neural crest begins differentiation and migration at the neural plate stage, which results in large accumulations of neural crest in the facial region at an early stage of development. The early accumulation of neural crest provides the material for the accelerated development of oral and facial structures. The first arch region is massive in the early embryo, and the development of the olfactory placode and frontonasal region is advanced relative to the forebrain region. The development of the forebrain is delayed in marsupials relative to the hindbrain or facial region. These observations illustrate how development may be modified to produce evolutionary changes that distinguish taxa. Further, they suggest that development is not necessarily highly conserved, but instead may be quite plastic.

Morphology and mechanics of tongue movement in the African pig-nosed frog Hemisus marmoratum: a muscular hydrostatic model

The goal of this study was to investigate morphological adaptations associated with hydrostatic elongation of the tongue during feeding in the African pig-nosed frog Hemisus marmoratum. Whereas previous studies had suggested that the tongue of H. marmoratum elongates hydraulically, the anatomical observations reported here favour a muscular hydrostatic mechanism of tongue elongation. H. marmoratum possesses a previously undescribed compartment of the m. genioglossus (m. genioglossus dorsoventralis), which is intrinsic to the tongue and whose muscle fibres are oriented perpendicular to the long axis of the tongue. On the basis of the arrangement and orientation of muscle fibres in the m. genioglossus and m. hyoglossus, we propose a muscular hydrostatic model of tongue movement in which contraction of the m. genioglossus dorsoventralis, together with unfolding of the intrinsic musculature of the tongue, results in a doubling in tongue length. Electron micrographs of sarcomeres from resting and elongated tongues show that no special adaptations of the sarcomeres are necessary to accommodate the observed doubling in tongue length during feeding. Rather, the sarcomeres of the m. genioglossus longitudinalis are strikingly similar to those of anuran limb muscles. The ability to elongate the tongue hydrostatically, conferred by the presence of the m. genioglossus dorsoventralis, is associated with the appearance of several novel aspects of feeding behaviour in H. marmoratum. These include the ability to protract the tongue slowly, thereby increasing capture success, and the ability to aim the tongue in azimuth and elevation relative to the head. Compared with other frogs, the muscular hydrostatic system of H. marmoratum allows more precise, localized and diverse tongue movements. This may explain why the m. genioglossus of H. marmoratum is composed of a larger number of motor units than that of other frogs.

Have gene knockouts caused evolutionary reversals in the mammalian first arch?

Many recent gene knockout experiments cause anatomical changes to the jaw region of mice that several investigators claim are evolutionary reversals. Here we evaluate these mutant phenotypes and the assertions of atavism. We argue that following the knockout of Hoxa-2, Dlx-2, MHox, Otx2, and RAR genes, ectopic cartilages arise as secondary consequences of disruptions in normal processes of cell specification, migration, or differentiation. These disruptions cause an excess of mesenchyme to accumulate in a region through which skeletal progenitor cells usually migrate, and at a site of condensation that is normally present in mammals but that is too small to chondrify. We find little evidence that these genes, when disrupted, cause a reversion to any primitive condition and although changes in their expression may have played a role in the evolution of the mammalian jaw, their function during morphogenesis is not sufficiently understood to confirm such hypotheses.

Extreme bilateral molar rotation in Monodelphis domestica (Marsupialia: Didelphidae)

Rotation of a tooth around an axis perpendicular to the occlusal plane through angles approaching 180 degrees is a rare anomaly found in the mammalian dentition. A specimen of Monodelphis domestica was found to show such extreme rotation of both lower last molars, with consequent disruption of normal occlusion and wear. A review of the literature discovered 41 other reported cases of extreme rotation, from four different orders of mammals. The distribution of extreme rotation within the dentition can be summarized as follows. It is found only in isolated teeth or in contralateral pairs of teeth. Bilateral rotation is far more common than would be expected based on the chance of the independent occurrence of two rotations. Extreme rotation has a significantly higher frequency in upper rather than lower teeth, in premolars rather than other teeth, and on the left- rather than the right--hand side. The incidence of extreme rotation across mammals was estimated to be approx. 1 in 5850.

Characterization of human SHC p66 cDNA and its processed pseudogene mapping to Xq12-q13.1

SHC is an adapter protein in the Ras-MAPkinase pathway that is involved in the regulation of cell growth and differentiation. The p46 and p52 isoforms are thought to be produced by the use of two alternative translation initiation sites in a 3.4-kb transcript from the SHCA gene, which maps to chromosome 1q21. The p66 isoform could be encoded by a different 3.8- or 2.8-kb transcript of the same gene or alternatively by a SHC-related gene. To characterize other putative genes coding for SHC-like proteins, primers from the 3' UTR of the SHCA gene were used to screen a yeast artificial chromosome (YAC) library by polymerase chain reaction (PCR). Two YAC clones, 20D11B and 36D1D, were isolated and used as probes for fluorescence in situ hybridization analysis. Both these probes hybridized to chromosome Xq12-q13.1. This novel SHC-related sequence was characterized by direct sequencing of vectorette library PCR products produced from clone 20D11B. A transcript of 3.2 kb that was 85% identical to the mouse Shc cDNA encoding the p66 isoform was identified. Sequence analysis demonstrated the presence of multiple stop codons identifying this isoform of SHC as a processed pseudogene. Using primers designed on the basis of the nucleotide sequence of the pseudogene, we have now amplified and sequenced a human cDNA that encodes the SHC p66 protein. Thus, we have characterized the human SHC p66 isoform cDNA and identified a processed SHC pseudogene that maps to chromosome Xq12-q13.1.

Cerebral palsy: a comprehensive review

Cerebral palsy is a broad range of static, nonprogressive motor disabilities that present from birth or early childhood as a result of injury to neuromotor components of the central nervous system. Motor performance is normally coordinated via communication between the cerebral cortex, thalamus, basal ganglia, brain stem, cerebellum, spinal cord, and communicating sensori-motor pathways. This complex network lends itself to injury at many different levels. Etiologies are numerous and can occur during the prenatal, perinatal, and postnatal periods. The severity of the neurologic deficit and the clinical manifestations are varied depending on the time, location and nature of the original injury. In order to approach cerebral palsy systematically, the primary health care practitioner must be prepared to recognize neuromotor deficits, diagnose and classify the type of disorder, and implement a methodical treatment plan. The purpose of this article is to review the etiology, pathophysiology, diagnostic classification (Swedish system), clinical manifestations, and therapeutic management of cerebral palsy and prepare the advanced practice nurse to care for the individual and family.

Use of electronic networking for the enhancement of mental health services

In the Behavioral Informatics Tomorrow column of our November/December, 1994, issue, we presented an introduction to the basic concepts and techniques of electronic communication via the Internet, as well some resources for behavioral healthcare professionals who already utilize electronic bulletin board services (BBS). Now we offer this more detailed article for those interested in utilizing archies, gophers, browsers and chats to gain access to the rapidly growing body of behavioral healthcare informational resources residing in Cyberspace. The authors present dozens of mental health BBs, conferences and networks--with instructions on how to get there.

Development of craniofacial musculature in Monodelphis domestica (Marsupialia, Didelphidae)

Development of craniofacial muscles of Monodelphis domestica (Marsupialia, Didelphidae) is described. In a period of 4-6 days all craniofacial muscles in M. domestica progress from myoblast condensation, to striated myofibers that are aligned in the direction of adult muscles and possess multiple, lateral nuclei. This process begins 1 to 2 days before birth and continues during the first few days after birth. Compared to other aspects of cranial development, muscle development in M. domestica is rapid. This rapid and more or less simultaneous emergence of craniofacial muscles differs from the previously described pattern of development of the cranial skeleton in marsupials, which displays a mosaic of acceleration and deceleration of regions and individual elements. Unlike the skeletal system, craniofacial muscles show no evidence of regional specialization during development. M. domestica resembles eutherian mammals in the relatively rapid and more or less simultaneous differentiation of all craniofacial muscles. It differs from eutherian taxa in that most stages of myogenesis occur postnatally, following the onset of function. The timing of the development of muscular and skeletal structures is compared and it is concluded that the relatively early development of muscle is not reflected by any particular acceleration of the differentiation or growth of skeletal structures. Finally, the difficulties in accounting for complex internal arrangements of muscles such as the tongue, given current models of myogenesis are summarized.

Are neuromotor systems conserved in evolution?

Hypotheses that neuromotor systems are conserved during evolution are examined. Focus is on the fundamental assumption underlying such hypotheses, that neuromotor patterns are homologous. The criteria for testing hypotheses of homology are briefly reviewed and applied to several cases in which neuromotor conservatism has been proposed. It is concluded that few studies of neuromotor conservatism are complete enough to convincingly corroborate a hypothesis of homology. Particular problems include an absence of specific definitions of the parameters designating the conserved neuromotor pattern and the lack of sufficiently broad and detailed phylogenetic tests. The hypothesis that terrestrially feeding vertebrates exhibit a conservative feeding program, which has acted as a constraint in evolution, receives particular attention and it is concluded that existing data do not support this hypothesis.

Cranial osteogenesis in Monodelphis domestica (Didelphidae) and Macropus eugenii (Macropodidae)

The pattern of onset and general rate of cranial ossification are compared in two marsupials, Monodelphis domestica (Didelphidae) and Macropus eugenii (Macropodidae). In both species a similar suite of bones is present at birth, specifically those surrounding the oral cavity and the exoccipital, and in both postnatal events follow a similar course. The facial skeleton matures more rapidly than the neurocranium, which is characterized by an extended period of ossification. Most dermal bones begin ossification before most endochondral bones. Endochondral bones of the neurocranium are particularly extended in both the period of onset of ossification and the rate of ossification. These data confirm suggestions that morphology at birth is conservative in marsupials and we hypothesize that the pattern of cranial osteogenesis is related to two distinct demands. Bones that are accelerated in marsupials are correlated with a number of functional adaptations including head movements during migration, attachment to the teat, and suckling. However, the very slow osteogenesis of the neurocranium is probably correlated with the very extended period of neurogenesis. Marsupials appear to be derived relative to both monotreme and placental mammals in the precocious ossification of the bones surrounding the oral cavity, but share with monotremes an extended period of neurocranial osteogenesis.

Nonspecificity of the Anda A60-tb ELISA test for serodiagnosis of mycobacterial disease

The conventional methods for the laboratory diagnosis of tuberculosis and other mycobacterial diseases are time consuming and beyond the scope of most of the small and medium-sized hospital facilities. Therefore, there has been considerable interest in the development of a serological method for the detection of antibodies against mycobacteria. We recently evaluated a commercially available ELISA test (Anda Biologicals, Strasbourg, France) that measures antibody levels to A60 antigen, a membrane glycoprotein that is found in most mycobacteria. Of the 123 patients with positive pulmonary cultures for Mycobacterium tuberculosis, 82% had detectable antibodies against the kit antigen. Of the 68 patients with extrapulmonary tuberculosis, 59% yielded positive results. Specimens from 2 of the 12 patients that grew Mycobacterium avium-intracellulare complex, and one each with Mycobacterium fortuitum and Mycobacterium chelonei, were considered significant on the basis of medical history and repeated isolation of the bacterium from clinical specimens, and these patients yielded positive serology. Of the healthy, normal PPD positive and PPD negative controls, 24% gave false positive results.

Electromyography of the fin musculature of the cuttlefish Sepia officinalis

The musculature of the fins of the cuttlefish Sepia officinalis (Mollusca, Cephalopoda) was studied with electromyography to test predictions of the functional role of the various muscle masses. Previous research had shown the fins to consist of a tightly packed, three-dimensional array of muscle with distinct zones of anaerobic glycolytic and oxidative muscle fibres. In addition, a network of crossed oblique connective tissue fibres was observed within the musculature. In a previous paper a model of the function of the muscle and connective tissue was presented. In the present paper, we present recordings of electrical activity from the various muscle bundles in the fin, in conjunction with the output from an electronic movement-monitoring device, and correlate muscle activity with both the phase and the intensity of the fin-beat cycle. The results obtained here support the hypothesis that the oxidative muscle fibres produce gentle fin movements and are consistent with the hypothesis that the network of crossed oblique connective tissue fibres provides skeletal support. The results also support predictions that the anaerobic glycolytic muscle fibres both produce vigorous fin movements and provide support for that movement. This study provides a critical test of models of the role of the tightly packed, three-dimensional array of muscle found in muscular hydrostats such as the arms and tentacles of cephalopods and tongues of mammals and lizards.

Histological demonstration of muscle spindles in the tongue of the rat

The presence and distribution of neuromuscular spindles in the lingual musculature of the laboratory rat is described. The findings counter the commonly held belief that neuromuscular spindles are not found in the tongue musculature of non-primate mammals. The hypothesis that fundamentally different neural systems control lingual movements in primate and non-primate mammals therefore cannot be supported. The differences in the distribution of spindles in primate and non-primate mammals may be related to the patterns of lingual movements and the distribution of muscle fibre types.

Form and function of the tongue in agamid lizards with comments on its phylogenetic significance

The morphology of the tongue of agamid lizards is reviewed and discussed in the context of its functional and phylogenetic significance. It is shown that in several features, including the development of the central musculature of the tongue into a ring muscle and the presence of a genioglossus internus muscle in adults, the tongue in most agamids is derived relative to that in other squamates. In some features, such as the vertical connective tissue septa, agamids share primitive features with Sphenodon. Some conditions found in agamids are also found in anoline iguanids. Two genera, Uromastyx and Leiolepis, differ significantly from other agamids in intrinsic tongue musculature. The functional significance of the unique tongue morphology is that agamids utilize a different mechanism of tongue protrusion from that of other lizards. This mechanism involves the production of force against the lingual process, leading to an anterior slide of the tongue, and is detailed in this paper. Finally, I discuss the mechanical basis for the transformation series of tongue protrusion mechanisms from agamids to chamaeleonids. It is suggested that the mechanism of tongue protrusion in chamaeleonids is not unique, but is a highly derived state of the condition found in agamids.

Morphology and function of the tongue and hyoid apparatus in Varanus (Varanidae, Lacertilia)

The morphology and function of the tongue and hyoid apparatus in Varanus were examined by anatomical and experimental techniques. Morphological features unique to Varanus include a highly protrusible tongue that has lost a roughened dorsal surface, an exceptionally strong and mobile hyobranchial apparatus, a well-defined joint between the ceratohyal and anterior process, and a series of distinct muscles inserting at the anterior hyobranchial region. Varanus is also unusual among lizards in a number of feeding behaviors; it ingests prey entirely by inertial feeding, as the tongue does not participate in food transport. Further specializations include an increased reliance on hyobranchial movements in drinking and pharyngeal packing and compression. The long, narrow tongue is most likely related to the mechanics of tongue protrusion; the increased amount, strength, and complexity of hyobranchial movement is related to the fact that the hyobranchium in Varanus replaces the tongue in many functions. Previous hypotheses for the origin of these adaptations are discussed, and the difficulties of attributing these specializations to any specific scenario of adaptation or constraint are emphasized.

Strain gauge measurement of mesokinetic movement in the lizard Varanus exanthematicus

Single-element strain gauges were placed across the mesokinetic joint of the skull of the savanna monitor lizard, Varanus exanthematicus Bosc, in order to document the extent and timing of mesokinetic movement. In addition, rosette strain gauges were placed on various points of the palato-maxillary segment. Strain recordings and simultaneous cineradiographic films or videotapes were taken during normal feeding activities, including the strike, prey manipulation, ingestion and pharyngeal compression. Tensile strain, indicating lowering (retraction) of the palato-maxillary segment, was observed during all stages of feeding. Compressive strain, indicating lifting (protraction) of the palato-maxillary segment, generally appeared briefly in the strike and during pharyngeal compression. Maximum tensile strains were always larger than maximum compressive strains within each sequence. The highest levels of tensile strain occurred during prey manipulation periods, which were characterized by isometric biting. Strain on the palato-maxillary segment revealed a pattern of timing similar to the one at the mesokinetic joint, although strain levels were at least an order of magnitude lower. These data directly contradict conventional models of the function of the kinetic skull in lizards. We conclude that the kinetic apparatus in lizards is not a mechanism for actively moving the palato-maxillary unit and is therefore not a mechanism for increasing gape or actively controlling upper jaw movements.

Structural components and characteristics of Reichert's membrane, an extra-embryonic basement membrane

This paper presents an analysis of mouse and rat Reichert's membrane, a thick basement membrane formed between the trophoblast and parietal endoderm cells of early mammalian embryos. When analyzed by polyacrylamide gel electrophoresis. Reichert's membranes from rat and mouse conceptuses appear simple and consist primarily of collagen and 4 noncollagenous glycoproteins of approximate Mr = 415,000, 245,000, 170,000, and 50,000. The proteins at 415,000 and 245,000 are similar in molecular weight to laminin and are immunoprecipitated by anti-laminin antiserum. The protein at 170,000 is co-precipitated with laminin and represents a novel form of a laminin-like protein, whereas the protein at 50,000 is unrelated to laminin. Using metabolic labeling experiments, it is shown that parietal endoderm cells synthesize these components and incorporate them into the matrix in organ cultures but do not degrade Reichert's membrane in the conditions used over a 6-day culture period. Evidence is presented that the high molecular weight collagenase-sensitive proteins (greater than 420,000) observed on polyacrylamide gel electrophoresis are due to lysyl oxidase-derived cross-links between Reichert's membrane components.

Hormonal induction of differentiation in teratocarcinoma stem cells: generation of parietal endoderm by retinoic acid and dibutyryl cAMP

It has previously been shown that retinoic acid induces multiple phenotypic changes in cultures of F9 teratocarcinoma stem cells. In this paper we demonstrate that these retinoid-generated cells can be converted to yet another cell type by compounds that elevate cAMP concentrations. The phenotype of the new cell type is characterized by the synthesis of plasminogen activator, laminin and type IV collagen, and by very low levels of alkaline phosphatase and lactate dehydrogenase. The secretion of plasminogen activator and type IV collagen, and low levels of alkaline phosphatase and lactate dehydrogenase, have been previously shown to be properties of parietal endoderm, an extraembryonic cell which is generated early in mouse embryonesis. We show here that parietal endoderm also synthesizes laminin. The cell type generated by retinoic acid and dibutyryl cAMP treatment is therefore indistinguishable from definitive parietal endoderm. Analysis of the final phenotype indicates that it is not dependent upon the continued presence of either compound, and that cAMP agents are active only on cells that have been treated with retinoic acid.