Biomedical subjects
Publications and source records attributed to K J Peterson.
The adult body plan of bilaterians is achieved by imposing regional specifications on pluripotential cells. The establishment of spatial domains is governed in part by regulating expression of transcription factors. The key to understanding bilaterian evolution is contingent on our understanding of how the regulation of these transcription factors influenced bilaterian stem-group evolution.
Putative fossil embryos and larvae from the Precambrian phosphorite rocks of the Doushantuo Formation in Southwest China have been examined in thin section by bright field and polarized light microscopy. Although we cannot completely exclude a nonbiological or nonmetazoan origin, we identified what appear to be modern cnidarian developmental stages, including both anthozoan planula larvae and hydrozoan embryos. Most importantly, the sections contain a variety of small (</=200 microm) structures that greatly resemble gastrula stage embryos of modern bilaterian forms.
A prediction from the set-aside theory of bilaterian origins is that pattern formation processes such as those controlled by the Hox cluster genes are required specifically for adult body plan formation. This prediction can be tested in animals that use maximal indirect development, in which the embryonic formation of the larva and the postembryonic formation of the adult body plan are temporally and spatially distinct. To this end, we quantitatively measured the amount of transcripts for five Hox genes in embryos of a lophotrochozoan, the polychaete annelid Chaetopterus sp. The polychaete Hox complex is shown not to be expressed during embryogenesis, but transcripts of all measured Hox complex genes are detected at significant levels during the initial stages of adult body plan formation. Temporal colinearity in the sequence of their activation is observed, so that activation follows the 3'-5' arrangement of the genes. Moreover, Hox gene expression is spatially localized to the region of teloblastic set-aside cells of the later-stage embryos. This study shows that an indirectly developing lophotrochozoan shares with an indirectly developing deuterostome, the sea urchin, a common mode of Hox complex utilization: construction of the larva, whether a trochophore or dipleurula, does not involve Hox cluster expression, but in both forms the complex is expressed in the set-aside cells from which the adult body plan derives.
Several recent laboratory observations that bear on the origin of the Bilateria are reviewed and interpreted in light of our set-aside cell theory for bilaterian origins. We first discuss new data concerning the phylogeny of bilaterian phyla. Next, we use systematic, molecular, and paleontological lines of evidence to argue that the latest common ancestor of echinoderms plus hemichordates used a maximal indirect mode of development. Furthermore, the latest common ancestor of molluscs and annelids was also indirectly developing. Finally, we discuss new data on Hox gene expression patterns which suggest that both sea urchins and polychaete annelids use Hox genes in a very similar fashion. Neither utilizes the complete Hox complex in the development of the larva per se, while the Hox complex is expressed in the set-aside cells from which the adult body plan is formed. Our current views on the ancestry of the bilaterians are summarized in phylogenetic terms, incorporating the characters discussed in this paper.
A new genus and species of freshwater sponge, Clypeatula cooperensis, collected from three lakes in the Northern Rocky Mountains of Montana, USA, are described. The sponge grows as a hard, disc-shaped encrustation on the undersides of rocks and logs. It lacks microscleres and has amphioxeal megascleres that often show a slight midregion bulb and are usually covered with short, conical spines except at their tips. The sponge is also non-gemmulating, overwintering in a regressed state in which choanocyte chambers are reduced in number. Phylogenetic analyses of complete 18S rDNA sequences of C. cooperensis, Ephydatia muelleri, Spongilla lacustris and Eunapius fragilis suggest that C. cooperensis is more closely related to Ephydatia muelleri than to Spongilla lacustris or Eunapius fragilis. Our data, nonetheless, do not rule out the possibility that C. cooperensis is more closely related to the non-gemmulating sponges of Lake Baikal (Russia) than it is to Ephydatia muelleri. These phylogenetic analyses support the erection of a new genus, the monophyly of freshwater sponges belonging to the families Spongillidae and Lubomirskiidae, and the monophyly of demosponges.
This work concerns the expression of two transcription factors during the development of the sea urchin Strongylocentrotus purpuratus: SpNot, the orthologue of the vertebrate Not gene, and SpBra, the orthologue of the vertebrate Brachyury gene. SpNot transcripts are detected by in situ hybridization in the vegetal plate at the mesenchyme-blastula stage. Later the gene is expressed in the secondary mesenchyme, but expression is no longer detectable after gastrulation. SpNot is upregulated during larval development, in the invaginating vestibule of the adult rudiment. Transcripts are also found in several larva-specific tissues, including the epaulets, blastocoelar cells, and pigment cells. SpBra also displays a discontinuous pattern of expression. Much like SpNot, this gene is expressed during embryogenesis in the embryonic vegetal plate and secondary mesenchyme founder cells, and expression is then extinguished. The gene is upregulated over a week later in the feeding larva, in the vestibule of the adult rudiment. In contrast to SpNot, SpBra is also expressed in the mesoderm of both left and right hydrocoels, and it is not expressed in any larva-specific tissues. We compare the spatial expression profile determined in this study with that of the orthologous Brachyury gene in an indirectly developing enteropneust hemichordate, a representative of the sister group to the echinoderms within the deuterostomes. These observations illuminate the genetic basis underlying the process of maximal indirect development in basal deuterostomes. Finally, Brachyury appears to be an excellent marker for the progeny of the set-aside cells of the sea urchin embryo.
TGF-beta ligands are probably pan-bilaterian in phylogenetic distribution. The family appears to have diversified greatly with the evolution of the vertebrates, but only a few invertebrate deuterostome TGF-beta molecules have so far been isolated. A search for members of this family expressed in sea urchin embryos, using canonical PCR primers, revealed a single-copy gene encoding a new TGF-beta protein. The sequence which it encodes is closely related to those of vertebrate bone morphogenetic proteins (BMPs) 5-7. No additional TGF-beta family members were uncovered other than univin, which had previously been reported.
This work concerns the formation of mesoderm in the development of an enteropneust hemichordate, Ptychodera flava, and the expression of the Brachyury gene during this process. Brachyury expression occurs in two distinct phases. In the embryo, Brachyury is transcribed during gastrulation in the future oral and anal regions of the gut, but transcripts are no longer detected by 2 weeks of development. Brachyury expression is not detected during the 5 months of larval planktonic existence. During this time, the adult coeloms begin to develop, originating as coalescences of cells that appear to delaminate from the wall of the gut. Brachyury expression cannot be detected again until metamorphosis, when transcripts appear in the mesoderm of the adult proboscis, collar and the very posterior region of the trunk. It is also expressed in the posterior end of the gut. At no time is Brachyury expressed in the stomochord, the putative homologue of the chordate notochord. These observations illuminate the process of maximal indirect development in Ptychodera and, by comparison with patterns of Brachyury expression in the indirect development of echinoderms, their sister group, they reveal the evolutionary history of Brachyury utilization in deuterostomes.
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In the maximal form of indirect development found in many taxa of marine invertebrates, embryonic cell lineages of fixed fate and limited division capacity give rise to the larval structures. The adult arises from set-aside cells in the larva that are held out from the early embryonic specification processes, and that retain extensive proliferative capacity. We review the locations and fates of set-aside cells in two protostomes, a lophophorate and a deuterostome. The distinct adult body plans of many phyla develop from homologous set-aside cells within homologous larvae. We argue that the stocks from which these phyla arose utilized these respective larvae, and the diversity of their adult body plans reflects diverse pattern formation processes executed in their set-aside cell populations. Chordates and arthropods develop directly, but share adult characters with indirectly developing phyla. Thus the deuterostome and protostome stocks that were ancestral to chordates and arthropods, respectively, also utilized maximal indirect development.
Echinoderms are the sister group of the chordates and hemichordates within the deuterostomes. They lack a notochord or any structures obviously homologous with it. To gain insight into developmental mechanisms important in the origin and early evolution of chordates, we investigated sea urchin homologues of chordate genes that are implicated in notochord formation, viz. Brachyury and HNF-3 beta. Here we report the pattern of expression of a sea urchin orthologue of forkhead, Hphnf3 which is present as a single copy per haploid genome. An Hphnf3 transcript of 3.0 kb was first detected at the swimming blastula stage, accumulated maximally at the gastrula and prism-embryo stages, and decreased at the pluteus-larva stage. In situ hybridization signals were found in cells of the vegetal plate of the swimming blastula. During gastrulation, intense staining was evident in the cells surrounding the blastopore, whereas weak staining was detected in the invaginating archenteron. At the prism-embryo stage, the entire archenteron stained intensely; then, at pluteus stage, the larva staining decreased in intensity. The forkhead and Brachyury genes begin to be expressed almost simultaneously in sea urchin embryos, in the vegetal plate at the late blastula stage. After the onset of gastrulation, however, Hphnf3 is expressed in the posterior part of the archenteron, whereas the Brachyury orthologue, HpTa, is expressed in the secondary mesenchyme founder cells, which occupy the anterior tip of archenteron. Hphnf3 may contribute to specification of embryonic cells as archenteron, and the role of HpTa may be directed towards specification of mesodermal founder cells. Except for the basal character of expression in endoderm and endomesoderm, these transcription factors are clearly utilized differently in chordates.
An argument is proposed to explain the origin of large metazoans, based on the regulatory processes that underlie the morphogenetic organization of pattern in modern animals. Genetic regulatory systems similar to those used in modern, indirectly developing marine invertebrates are considered to indicate the Precambrian regulatory platform on which were erected innovations that underlie the development of macroscopic body plans. Those systems are genetic regulatory programs that produce groups of unspecified "set-aside cells" and hierarchical regulatory programs that initially define regions of morphogenetic space in terms of domains of transcription factor expression. These ideas affect interpretation of the development of arthropods and chordates as well as interpretation of the role of the genes of the homeotic complex in embryogenesis.
Hypertrophic cardiomyopathy (HCM) has been intriguing health care professionals for years. It is a disease of the cardiac muscle characterized by hypertrophy with or without left ventricular outflow tract obstruction. It affects people of all ages and is commonly associated with sudden death. The clinical presentation and treatment of HCM varies widely with the individual and therefore offers the cardiovascular nurse a unique challenge. This article assists the nurse in providing care to these patients by reviewing the cause and prognosis, pathophysiology, clinical manifestations, surgical and medical therapy, and the nursing care following surgical intervention for HCM.
Family-centered perinatal education is a health education service focused on the family unit during the childbirth period and is supportive to all family members as the family moves from one stage of development to the next. It is distinct from traditional childbirth education and family-centered maternity care by being a single educational intervention that addresses the needs of the entire family during the prenatal and postpartum periods. The advantages of family-centered perinatal education are discussed from the consumer's and educator's perspectives. Such education emphasizes extending social support into the postpartum period as a buffer against the effects of stress on new parents. Teaching and learning occur in a more timely manner. Family members learn what is most needed when it is most needed and avoid the feeling of being "cut loose" from the health care system right after the birth. Family-centered perinatal education is likely to become an increasingly popular consumer option as hospitals compete to provide the best obstetric/neonatal care.
This study assessed social workers' differential knowledge about human immunodeficiency virus (HIV) infection. A questionnaire was mailed to a random sample of 500 members of the National Association of Social Workers in July 1988. Results show that social workers have the most information regarding transmission of HIV infection and the least information about the effects of HIV on specific subpopulations. Of particular concern was that respondents who stated they had either a personal or professional reason for being knowledgeable about acquired immune deficiency syndrome were no more informed about minority issues than those who did not think they had a personal or professional reason for being knowledgeable.
A study was conducted to assess social workers' knowledge about human immunodeficiency virus (HIV) infection. A questionnaire was mailed to a random sample of 500 members of the National Association of Social Workers in July 1988. Three hundred seventy-nine (75.8 percent) members responded, and limited demographic comparisons indicated that the sample was representative of the association's membership. Results showed that social workers have much to learn about acquired immune deficiency syndrome (AIDS); less than half the questions were answered correctly. Respondents had the most information about transmission of the virus and the least information about the impact of the epidemic on specific populations. Of particular concern was the small number of respondents who reported that they had professional reasons for being knowledgeable about AIDS, given the pervasive nature of the AIDS epidemic and every social worker's professional responsibility to be knowledgeable about HIV infection.
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