Peter Thorogood

Transient expression of collagen type II at epitheliomesenchymal interfaces during morphogenesis of the cartilaginous neurocranium

In the avian embryo a matrix-mediated tissue interaction between retinal pigmented epithelium and neural crest-derived periocular mesenchyme leads to the differentiation of (scleral) cartilage. The composition of the extracellular matrix at the interface between these two tissues has been examined immunohistochemically, both during and after the interaction has taken place. Of the matrix components studied (fibronectin, laminin, and collagen types I, II, IV, and V) only collagen type II displayed a dramatic change in distribution between the two stages. During the interaction, at stage 15, type II was present in the extracellular compartment basal to the epithelium. After completion of the interaction, collagen type II was no longer detectable at the interface even though it was readily detectable in the vitreous humor, cornea, and perinotochordal sheath, and subsequently will be expressed by the chondrogenic tissue itself as overt differentiation commences. These results suggest that collagen type II might be causally involved in this particular epitheliomesenchymal interaction. Examination of the spatial and temporal patterns of collagen type II expression elsewhere in the developing craniofacial complex revealed a hitherto unreported pattern of distribution. In addition to its predictable locations (i.e., cornea, vitreous, and perinotochordal sheath) it was found to be present at certain other sites, for example, at the basal surfaces of some neuroepithelia. These additional locations are all known to be sites of chondrogenesis-promoting tissue interactions which result in the formation of the elements of the cartilaginous neurocranium (e.g., otic vesicle). Furthermore this spatial distribution exhibits a changing temporal pattern in that it is detectable at the time that the interactions are known to be taking place, but subsequently is no longer detectable by the immunohistochemical means employed. This definable pattern of transient collagen type II expression, occurring at very early stages of craniofacial development, is interpreted as reflecting one level of morphogenetic specification of chondrocranial/skull form in the developing vertebrate head.

KAL, a gene mutated in Kallmann's syndrome, is expressed in the first trimester of human development

Kallmanns syndrome (KS) is characterised by the association of anosmia and isolated hypogonadotrophic hypogonadism (IHH). Mutations of the KAL gene which is located at Xp22.3 cause X-linked KS (XKS). In this study we used the reverse transcriptase polymerase chain reaction and in situ hybridisation to examine the developmental expression of KAL in the first trimester of pregnancy, the earliest stage of human gestation examined thus far. At 45 days after fertilisation KAL mRNA was detected in the spinal cord, the mesonephros and metanephros but not in the brain. Later in gestation, at 11 weeks, the gene was expressed in the developing olfactory bulb, retina and kidney. This expression pattern correlates with the clinical findings in XKS since olfactory bulb dysgenesis with subsequent defective neural migration causes anosmia and IHH. Additionally, renal agenesis occurs in 40% of patients. Therefore this study provides strong evidence that KAL expression is required for the normal development of the olfactory bulb and kidney in the first trimester of human pregnancy.

Coordinated expression of 3' Hox genes during murine embryonal gut development: An enteric Hox code

BACKGROUND & AIMS Hox genes are highly conserved developmental control genes that may be organized and expressed in the form of a code required for correct morphogenesis. Little is known about their control of the embryonal gut. However, Hox paralogues 4 and 5, which are expressed at the sites of origin of vagal neural crest cells and splanchnic mesoderm, are likely to be important. We have studied the expression domains of these genes in the gut both spatially and temporally. METHODS CD1 mice embryos of embryonic days E8.5-E17.5 were studied. The spatial and temporal expression patterns of messenger RNA of Hoxa4, b4, c4, d4, a5, c5, and b5 homeoprotein were determined by in situ hybridization and immunohistochemistry in whole embryos, whole gastrointestinal tracts, and vibratome sections. RESULTS There were different spatial, temporal, and combinatorial expression patterns in different morphological regions: foregut, prececal gut, cecum, and postcecal gut. Two dynamic gradients, rostral and caudal, were coordinated with nested expression domains along the gut primordium. Region-specific domains were present in the stomach and cecum. CONCLUSIONS The expression patterns of genes in paralogous groups 4 and 5 suggest that they are organized to form a specific enteric Hox code required for correct enteric development.

Neural crest cells and skeletogenesis in vertebrate embryos.

ConclusionsEvidently it is the circumstances of tissue association which are important with regard to the differentiation of NC-derived cells into primary cartilage and membrane bone. Tissue interactions of this sort apparently do not play a role in the differentiation of secondary cartilage, where simply theposition of NC-derived cells and their progeny within the early membrane bone primordium determines whether or not those cells will subsequently express a secondary chondrogenic potential.Whether we are considering the type of tissue association generated or the ‘specification’ of cell positioning, both are controlled by the parameter of NC cell migration. Thus disturbances in the conditions of migration, for instance retarded migration or incorrect timing, will generate anomalies of cranio-facial morphogenesis and of skull development, (Johnstonet al., 1977; Morriss & Thorogood, 1978). Furthermore, as phylogenetic differences in (skull) form are generated by changes in developmental mechanisms, simple quantitative changes in such parameters as NC migration and proliferation will have profound evolutionary consequences (see, for example, Kollar & Fisher, 1980).This review started by asking the question ‘How, in a developmental sense, does one build a skull?’ That question has not been answered but a few suggestions have been provided as to the rules of the developmental programme whereby the various skeletal tissues are laid down in a skull-specific pattern. It seems that these rules can be defined in terms of timing, circumstances of tissue association and spatial positioning of cells. A comprehensive identification and fuller recognition of rules such as these is, I propose, a pre-requisite to understanding this particular developmental programme.

Mechanisms of Morphogenetic Specification in Skull Development

The nature of the developmental transition from the linear complexity of the genotype, encoded in the sequence of nucleotides along the DNA molecule, to the three-dimensional complexity of the phenotype remains a fundamental challenge to contemporary developmental biologists. In this paper, I wish to consider one particular three-dimensional pattern or form - that of the vertebrate skull, and to address the question of how the embryo constructs such a form. In other words, what are the ‘assembly rules’ underlying the formation of the skull during development? Answering this question is clearly an awesome task if one tries to analyse development in terms of the finished structure. Instead, of course, we can rationalise the form into its component, blastemal parts as seen in the embryo. Thus, the developing skull can be rationalised into ‘neurocranium’ and ‘viscerocranium’ which fulfill, respectively, the traditionally observed functions of protection (of the brain and sense organs) and ingestion/respiration. Both components contain cartilaginous and ‘membranous’ (membrane bone) elements and it is the formation of the cartilaginous neurocranium which I wish to discuss. This structure has a basic pattern which is common to all vertebrates from living agnathans to Man. There are two paired elements - the trabeculae and the parachordals - which fuse together to form the embryonic cranial floor, and three pairs of capsular cartilages - olfactory, optic and otic - which surround and support the organs of smell, sight and hearing/balace respectively (de Beer, 1937).

Using HyperCard and Interactive Video in Education: An Application in Cell Biology

Interactive video seems to have much potential in education, particularly in areas where the use of visual material is essential to the understanding of the subject Finding effective ways of incorporating videodisc material into educational courses is not easy. Producing courseware for interactive video to intergrate with existing courses can be very expensive, particularly in terms of staff time This paper suggests an alternative model for the development of interactive video material for education using existing videodiscs and Apples HyperCard

Contact behaviour exhibited by migrating neural crest cells in confrontation culture with somitic cells.

SummaryWhen grown in confrontation culture on a planar substratum, avian neural crest cells and somite cells display both homotypic and heterotypic contact inhibition of movement as judged by analysis of time-lapse video recordings of locomotory and contact behaviour, and by use of a nuclear overlap assay. It is therefore unlikely that migration of neural crest cells within the embryo, and within embryonic tissues, can be explained on the basis of a lack of contact inhibition. The results are discussed in the general context of cell invasiveness.

Differential expression of RAR-ß and RXR-γ transcripts in cultured cranial neural crest cells

In situ hybridization reveals that RAR-β and RXR-γ genes in mesencephalic neural crest cultures are independently regulated. RAR-β transcripts are found in all cells, with a slight increase in signal/cell with time in culture. In contrast, the distribution of RXR-γ transcript is initially uniform but becomes increasingly heterogeneous, so that after 72 h in culture, a significant proportion of cells lack transcripts while a small subpopulation contains very high levels of message. These differences in the behaviour of the RARβ and RXRγ genes in vitro can be related to differences in their expression patterns in vivo.

Interactive Learning and Biology: A Hypermedia Approach

The terms hypertext and hypermedia are becoming very well-known in computing literature. More and more software packages that have the look and feel of hypermedia systems are coming into the market and their use is set to increase rapidly. But there has been very little work done on the effectiveness of such interfaces in teaching and learning. This paper reports on a project being undertaken at t h e University of Southampton to evaluate a hypermedia system that has been developed for use in education. The project concentrates particularly on the integration of graphics and video information into the system, and has been applied to an area of biology education.

Keratan sulfate expression during avian craniofacial morphogenesis

SummaryUsing the monoclonal antibody MZ15 in immunocytochemical and ultrastructural studies we have been able to determine the spatiotemporal pattern of keratan sulfate (KS) distribution during quail craniofacial morphogenesis. KS-containing proteoglycans are found associated with invaginating placodes (olfactory, lens and otic), in developing pronephric tubules, notochord, pharynx and endocardium, and display developmental regulation. The appearance of such proteoglycans (PGs) during placode morphogenesis is particularly striking and we suggest that they may be an important component of the extracellular matrix which has been previously implicated in mediating the morphogenetic interactions and cell movements occurring at these sites. The otic vesicle during stage 18–22 displays a notable asymmetric distribution of KS-containing PGs. The role that these molecules may play and the reasons for this regionalization are, as yet, unclear but it is conceivable that the distribution of proteoglycans at this stage reflects subsequent differentiative events during otocyst development. Furthermore, our ultrastructural observations indicate that over the developmental period studied (H & H stages 8–22) keratan sulfate exists in at least two proteoglycan forms. Some spatiotemporal correlation has been found to exist between the distributions of KS-containing PGs and type II collagen as previously reported by Thorogood et al. (1986). We suggest that the proteoglycan detected at such sites is cartilage-specific proteoglycan and that it plays an important role, together with type II collagen, in the “signalling” mechanism which specifies the subsequent pattern of the chondrocranium. It is proposed that this interaction at epithelio-mesenchymal interfaces in the developing head parallels the matrix-mediated tissue interaction between notochord and somites which results in the formation of the cartilaginous primordia of the vertebrae from the sclerotomes as reported by Lash and Vasan (1978).