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At least 199 records · Page 11Linked to original sources
PubMed1996

A G/C-rich DNA-regulatory element controls positive expression of the sea urchin Lytechinus pictus aboral ectoderm-specific LpS1 gene.

The LpS1 beta gene of Lytechinus pictus is activated at the late cleavage stage about 12 hr after fertilization. LpS1 beta transcripts accumulate exclusively in aboral ectoderm lineages. LpS1 beta is thus a classic example of a gene whose expression is tightly controlled both temporally and spatially during early development. Previous studies on the LpS1 beta promoter identified two G-string DNA elements, one proximal and one distal to the LpS1 beta transcriptional start site, which bind to an ectoderm-enriched nuclear factor. In this report, we show that the ectoderm G-string factor binds to a G/C-rich region larger than the G-string itself and that the binding of the G-string factor requires sequences immediately downstream from the G-string. These downstream sequences are essential for full promoter activity. Two regions of 5'-flanking DNA are required for positive control of LpS1 beta, region I from base pairs -762 to -511, and region II, which includes the G/C-rich element, from base pairs -108 to -61. Region I also contains a mesenchyme cell repressor element. The results indicate that LpS1 beta expression is regulated positively in ectoderm cells and negatively in mesenchyme cells. Similar positive and negative control mechanisms regulate the expression of the related Spec genes of Strongylocentrotus purpuratus, but in this gene family the DNA elements are entirely different. We hypothesize that cis-regulatory elements are evolutionarily dynamic and that many different combinations of DNA elements are capable of given rise to aboral ectoderm-specific expression.

Animals↗
PubMed1996

Activation of different myogenic pathways: myf-5 is induced by the neural tube and MyoD by the dorsal ectoderm in mouse paraxial mesoderm.

Newly formed somites or unsegmented paraxial mesoderm (UPM) have been cultured either in isolation or with adjacent structures to investigate the influence of these tissues on myogenic differentiation in mammals. The extent of differentiation was easily and accurately quantified by counting the number of beta-galactosidase-positive cells, since mesodermal tissues had been isolated from transgenic mice that carry the n-lacZ gene under the transcriptional control of a myosin light chain promoter, restricting expression to striated muscle. The results obtained showed that axial structures are necessary to promote differentiation of paraxial mesoderm, in agreement with previous observations. However, it also appeared that the influence of axial structures could be replaced by dorsolateral tissues, adjacent to the paraxial mesoderm. To elucidate which of these tissues exerts this positive effect, we cultured the paraxial mesoderm with a variety of adjacent structures, either adherent to the mesoderm or recombined in vitro. The results of these experiments indicated that the dorsal ectoderm exerts a positive influence on myogenesis but only if left in physical proximity to it. In contrast, lateral mesoderm delays the positive effect of the ectoderm (and has no effect on its own) suggesting that this tissue produces an inhibitory signal. To investigate whether axial structures and dorsal ectoderm induce myogenesis through common or separate pathways, we dissected the medial half of the unsegmented paraxial mesoderm and cultured it with the adjacent neural tube. We also cultured the lateral half of the unsegmented paraxial mesoderm with adjacent ectoderm. The induction of the myogenic regulatory factors myf-5 and MyoD was monitored by double staining of cultured cells with antibodies against MyoD and beta-galactosidase since the tissues were isolated from mouse embryos that carry n-lacZ targeted to the myf-5 gene, so that myf-5 expressing cells could be easily identified by either histochemical or immunocytochemical staining for beta-galactosidase. After 1 day in culture myogenic cells from the medial half expressed myf-5 but not MyoD, while myogenic cells from the lateral half expressed MyoD but not myf-5. By the next day in vitro, however, most myogenic cells expressed both gene products. These data suggest that the neural tube activates myogenesis in the medial half of paraxial mesoderm through a myf-5-dependent pathway, while the dorsal ectoderm activates myogenesis through a MyoD-dependent pathway. The possible developmental significance of these observations is discussed and a model of myogenic determination in mammals is proposed.

Animals↗
PubMed2001

Two-step induction of primitive erythrocytes in Xenopus laevis embryos: signals from the vegetal endoderm and the overlying ectoderm.

Primitive blood cells differentiate from the ventral mesoderm blood islands in Xenopus embryos. In order to determine the tissue interactions that propagate blood formation in early embryogenesis, we used embryos that had the ventral cytoplasm removed. These embryos gastrulated normally, formed a mesodermal layer and lacked axial structures, but displayed a marked enhancement of alpha-globin expression. Early ventral markers, such as msx-1, vent-1 and vent-2 were highly expressed at the gastrula stage, while a dorsal marker, goosecoid, was diminished. Several lines of experimental evidence demonstrate the critical role of animal pole-derived ectoderm in blood cell formation: 1) Mesoderm derived from dorsal blastomeres injected with beta-galactosidase mRNA (as a lineage tracer) expressed alpha-globin when interfaced with an animal pole-derived ectodermal layer; 2) Embryos in which the animal pole tissue had been removed by dissection at the blastula stage failed to express alpha-globin; 3) Exogastrulated embryos that lacked an interaction between the mesodermal and ectodermal layers failed to form blood cells, while muscle cells were observed in these embryos. Using dominant-negative forms of the BMP-4 and ALK-4 receptors, we showed that activin and BMP-4 signaling is necessary for blood cell differentiation in ventral marginal zone explants, while FGF signaling is not essential. In ventralized embryos, inactivation of the BMP-4 signal within a localized area of the ectoderm led to suppression of globin expression in the adjacent mesoderm layer, but inactivation of the activin signal did not have this effect. These observations suggest that mesodermal cells, derived from a default pathway that is induced by the activin signal, need an additional BMP-4-dependent factor from the overlying ectoderm for further differentiation into a blood cell lineage.

Activin Receptors, Type I↗
PubMed2006

Multiple agenesis and anhidrotic ectodermal dysplasia: a comparative longitudinal study of dental similarities and genetic differences in two groups of children.

AIM: Dental anomalies in shape and number may be present isolated or associated with other manifestations. In anhidrotic ectodermal dysplasia they occur more frequently and severely. The authors examined a group of children with similar dental anomalies but no other ectodermal or extra-ectodermal signs. METHODS: This study makes a comparative evaluation of similarities and differences of dental anomalies between two groups: A anhidrotic ectodermal dysplasia and B similar dental finding but without extra- dental anomalies. RESULTS: In group A, the average number of agenesis in primary teeth was 3.5 (upper) and 5.33 (lower); in permanent teeth it was 5.4 and 5.8, respectively. In group B, the average was 1.62 (upper) and 0.25 (lower) in primary teeth, and 4.0 and 4.25 in permanent teeth respectively, with no constant pattern of occurrence. The study of tooth morphology of both groups revealed numerous anomalies in both dentitions. No differences were found in the average number of agenesis and morphological anomalies in the permanent teeth between both groups, but in the primary dentition group B presented a lower degree of incidence. CONCLUSION: The presence of almost normal primary dentition (regarding to number), but with morphological anomalies, should lead to suspect their exacerbation in the permanent dentition.

Anodontia↗
PubMed1980

The ectodermal dysplasias. Problems of classification and some newer syndromes.

The ectodermal dysplasias are a heterogeneous group of disorders that, in the past, has included conditions best classified as progeroid disorders. The inaccuracy of the terminology has led to a proliferation of syndromes in which the patients are said to have poorly defined "ectodermal dysplasia," and a real need exists to define that appellation further. We suggest that the term "ectodermal dysplasia" be limited to those disorders that are congenital, are diffusely present, are not progressive, and do involve the epidermis and at least one of the appendages. We recognize that a heterogeneous group of disorders remains that generically have certain similarities. Not enough is known about the defects in each of the elements of the skin affected in these conditions to classify them more accurately. Several recently described disorders appear to have some degree of ectodermal dysplasia.

Abnormalities, Multiple↗
PubMed1981

Abnormal laryngeal vocal quality in ectodermal dysplasia.

Breathy vocal quality was verified in five of nine patients with the ectrodactyly--ectodermal dysplasia--cleft palate syndrome, nine of 15 patients with either suspected or confirmed anhidrotic ectodermal dysplasia (one case of partial expression), and one of two siblings with the Rapp-Hodgkin form of ectodermal dysplasia. Indirect laryngoscopy in eight of the breathy patients failed to show phonatory glottal chinks or any overt laryngeal pathologic conditions, but it did indicate absence of a normal mucosal covering of the folds. Limited spectrographic studies disclosed widely spaced voicing striations and also suggested prolonged voice onset times. Patients who exhibit breathy vocal quality in the presence of one of these ectodermal dysplasias should be counseled with regard to the advisability of longitudinal care and the avoidance of habitual use of increased vocal effort level.

Child↗
PubMed1997

Family with "pure" hair-nail ectodermal dysplasia.

"Pure" ectodermal dysplasias are developmental disorders affecting only tissues of ectodermal origin. Two different pure ectodermal dysplasias involving only hair and nails have been described to date. Here we describe congenital nail dystrophy and hypotrichosis associated with folliculitis decalvans in a family suggesting autosomal-dominant transmission. This report documents peculiar clinical and ultrastructural hair findings that fit poorly into previously described conditions. Thus the reported patients could represent a new type of pure ectodermal dysplasia.

Adult↗
PubMed1997

Dynamic expression of chicken Sox2 and Sox3 genes in ectoderm induced to form neural tissue.

The chick genes, cSox2 and cSox3, are members of a large family of genes that encode transcription factors. Previous studies have shown that these genes are predominantly expressed in the central nervous system during embryonic development. We show that cSox3 is expressed throughout the ectoderm that is competent to form nervous tissue before neural induction. The expression of cSox3 is lost from cells as they undergo gastrulation to form nonectodermal tissues; the transcription factor, Brachyury, appears in cells about to undergo gastrulation a short time before cSox3 transcripts are lost. Therefore, Brachyury expression may act functionally upstream of cSox3 downregulation. cSox3 expression is also lost from non-neuronal ectoderm shortly after the neural plate becomes morphologically apparent. cSox2 expression increases dramatically in the central nervous system as neural ectoderm is established. The appearance of cSox2 in neural ectoderm represents one of the earliest molecular responses to neural induction documented thus far.

Animals↗
PubMed1992

The pattern of expression of the chicken homolog of HOX1I in the developing limb suggests a possible role in the ectodermal inhibition of chondrogenesis.

Homeobox-containing genes have been implicated in a variety of patterning events during vertebrate limb development. In an attempt to isolate cDNAs corresponding to 5' members of the chicken HOX 4 cluster of homeobox-containing genes, a cDNA library constructed from mRNAs expressed during early stages of chick limb development was screened with probes generated by the polymerase chain reaction (PCR) using oligonucleotide primers corresponding to sequences in the homeoboxes of the human HOX4C and HOX4F genes, the human homologs of Hox-4.4 and Hox-4.6. This screening resulted in the isolation of full length cDNAs for the chicken homolog of HOX4F (cognate of mouse Hox-4.6), which we have termed GHox-4.6, and the chicken homolog of human HOX1I, which we have named GHox-1i, a paralog of Hox-4.6 in the HOX 1 cluster. The homeodomains encoded by GHox-4.6 and GHox-1i differ by only three amino acids, and the two proteins show extensive similarity along their entire lengths. Despite their sequence similarity, in situ hybridization analysis has revealed that GHox-4.6 and GHox-1i exhibit strikingly different spatial patterns of expression during embryonic chick limb development. At early stages of limb development (stages 20-22), GHox-4.6 transcripts are present in high amounts throughout the posterior half of the limb mesoderm and are absent from the anterior half of the mesoderm, an expression pattern consistent with the possible involvement of GHox-4.6 in the specification of posterior positional identity. In contrast, GHox-1i exhibits no distinct anterior-posterior polarity of expression at stage 22, but rather is expressed in high amounts throughout the mesenchyme of the limb bud. At later stages of development (stage 25), GHox-1i continues to be expressed in high amounts throughout the undifferentiated mesenchyme subjacent to the apical ectodermal ridge, and, in addition, is expressed in the mesodermal cells in the proximal peripheral regions of the limb bud subjacent to the ectoderm which are differentiating into nonchondrogenic lineages. Conversely, little or no expression of GHox-1i is detectable in the proximal central core of the limb bud where chondrogenic differentiation is occurring. Thus, GHox-1i is expressed by the undifferentiated subridge mesenchymal cells and proximal peripheral mesenchymal cells of the limb bud that are being inhibited from undergoing chondrogenesis by the apical ectodermal ridge and nonridge ectoderm.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1994

Embryonic expression patterns of the Drosophila decapentaplegic gene: separate regulatory elements control blastoderm expression and lateral ectodermal expression.

Patterns of decapentaplegic (dpp) transcripts derived from the intact gene were compared to the patterns of transcripts generated by partial dpp transgenes in Drosophila embryos. Sequences closest to the dpp coding regions, the dpp hin region, were sufficient to express lacZ-tagged mRNA in patterns indistinguishable from the patterns of endogenous dpp expression in the dorsal and terminal cells at the blastoderm stage, in the dorsal ectoderm during germ band elongation, and in narrow stripes of ectodermal cells along the dorsal edge of the ectoderm and at the boundary between the lateral and ventral neurogenic regions during germ band shortening. The latter pattern of expression responded to the segment polarity genes naked and wingless. However, these dpp sequences were not sufficient to drive lacZ-tagged mRNA expression in other cells normally expressing dpp, including cells in the gnathal segments, the clypeolabrum, the foregut, the midgut visceral mesoderm, and the hindgut. Two separate regulatory regions were found in the dpp hin region. A 479 bp region upstream of the promoter was necessary for the segmented pattern of expression in the lateral ectoderm and for expression in the midgut endoderm. Cis-acting elements in the 2 kbp second intron directed expression in the dorsal and terminal regions of the blastoderm, acted on a heterologous promoter, the P-element promoter, and responded to pattern information derived from the maternal effect dorsal/ventral patterning genes.

Animals↗
PubMed1994

Influence of digits, ectoderm, and retinoic acid on chondrogenesis by mouse interdigital mesoderm in culture.

We have cultured tissues isolated from the interdigital zones (IDZ) of the mouse footplate in the presence of the digits, ectoderm, and all-trans retinoic acid. The objective was to understand how these various factors influence the developmental fate of the interdigital tissues. Neutral red staining showed that these tissues normally differentiate by dying between day 12.5-14.5. However, if they were isolated from the footplate between day 12.5-13.5 (when cell death is not overtly obvious in the IDZ) and maintained in organ culture, these tissues would develop into cartilage and soft connective tissues. In culture, chondrogenesis is initiated very rapidly in the interdigital explants as revealed by in situ hybridization with riboprobes specific for type IIA and IIB procollagen mRNAs. The ability of interdigital tissues to form cartilage is not attributed to factors present in the serum of the culture medium as this phenomenon is also observed in serumless cultures. We have found that if all-trans retinoic acid, at concentrations of 10-50 ng/ml culture medium, were added to the explants it could inhibit chondrogenesis and promote cell death. Moreover, in some of the cultures, a single digit was left attached to the interdigital tissue. This also dramatically reduced the incidence of chondrogenesis. We have tried to determine whether the digits and ectoderm can produce a diffusible factor that can prevent cartilage from developing by culturing day 12.5 interdigital tissues in ectoderm and digit conditioned media. The ectoderm conditioned medium had no effects on interdigital growth or chondrogenesis. In contrast, the size of interdigital explants cultured in the presence of digit conditioned medium was shown to be significantly smaller than the control. These explants also produced a smaller quantity of cartilage as revealed by Alcian blue binding assay. In sum, our results showed that the fate of the interdigital tissues are not fully determined until after day 13.5. These tissues have the potentials to form cartilage and soft connective tissues. We tentatively propose that these interdigital tissues do not normally realize their histogenetic potentials because of the antichondrogenic influence of the digits and retinoic acid.

Animals↗
PubMed1992

Insulin improves survival but does not maintain function of cultured chick wing bud apical ectodermal ridge.

Previously we demonstrated that high levels of insulin (5 micrograms/ml) permit the survival of isolated chick apical ectodermal ridge in culture (Boutin and Fallon, Dev. Biol., 104:111-116, 1984). Here we address whether lower levels of insulin or insulin-like growth factors (IGFs) can also improve the survival of cultured apical ectodermal ridge and whether ridge function is maintained along with ridge survival. Neither IGF I nor IGF II (100 ng/ml) decreased ridge cell death; however, cell death was significantly decreased with 50 ng/ml insulin. No further improvement was obtained in the presence of both IGF I and insulin. These data suggest that insulin improved the survival of the isolated apical ectodermal ridge by binding its own receptor. To test for the maintenance of function, stage 20 ridges were cultured for 0, 6, 12, 18, or 24 hr with or without insulin (5 micrograms/ml or 5 ng/ml) and used to make recombinant limbs. Isolated ridges cultured for 12 hr or more produced fewer outgrowths and these were rarely distally complete. The medium in which the ridges had been cultured did not influence ridge activity, despite the major differences in cell survival. Recombinants made with ridges cultured with limb mesoderm for 18 hr did not yield outgrowths as often as those with freshly isolated ridges, but most of the limbs that did form were distally complete. These results suggest that the decline in function of cultured, isolated apical ectodermal ridge was not due merely to ridge cell death but rather, at least in part, to its separation from limb mesoderm.

Animals↗
PubMed2005

Lens and retina formation require expression of Pitx3 in Xenopus pre-lens ectoderm.

Pitx3 is expressed in tissues fated to contribute to eye development, namely, neurula stage ectoderm and pre-chordal mesoderm, then presumptive lens ectoderm, placode, and finally lens. Pitx3 overexpression alters lens, optic cup, optic nerve, and diencephalon development. Many of the induced anomalies are attributable to midline deficits; however, as assessed by molecular markers, ectopic Pitx3 appears to temporarily enlarge the lens field. These changes are usually insufficient to generate either ectopic lenses to enlarge the eye that eventually differentiates. Conversely, use of a repressor chimera or of antisense morpholinos alters early expression of marker genes, and later inhibits lens development, thereby abrogating retinal induction. Reciprocal grafting experiments using wild-type and morpholino-treated tissues demonstrate that Pitx3 expression in the presumptive lens ectoderm is required for lens formation. Contradictory to recent assertions that retina can form in the absence of a lens, the expression of Pitx3 in the presumptive lens ectoderm is critical for retina development.

Animals↗
PubMed1990

Behavior of rabbit dental tissues in heterospecific association with embryonic quail ectoderm.

The behavior of dental tissues from the rabbit, Oryctolagus cuniculus, in association with epithelium from the quail, Coturnix coturnix japonica, has been examined. Adult and embryo rabbits were employed in this study. Dental papillae from teeth at the cap stage from rabbit embryos and dental pulp from adult rabbits were isolated surgically and recombined with skin ectoderm from 72-hour-old quail embryos. The recombined tissues were cultured for 48 hours on semi-solid medium and subsequently removed and placed on chorio-allantoic membranes of 7-day-old chick embryos. Control cultures (dental pulp, dental papillae, and quail ectoderm) showed regression, atrophy, or differentiation according to the phenotype of the tissue. After 8 days in explant culture, heterologous recombinants composed of dental papillae and flank skin ectoderm from quail embryos developed differentiated chimeric tooth structures. It was unclear whether or not enamel was being secreted. The fact that the interactions between the enamel epithelium and the dental papillae are reciprocal is well known. The differentiation of odontoblasts can only occur in the presence of an enamel organ. Thus, the quail epithelium must have been induced to become an enamel organ, the lack of enamel proteins notwithstanding. Apical pulp and root pulp from adult rabbits plus quail ectoderm showed a high degree of regression and atrophy. At around 15 days of gestation, the rabbit dental papillae at the cap stage have already acquired odontogenic potential. By contrast, under the same experimental conditions, the dental pulp from continuous-growth teeth from adult rabbits did not show odontogenic potential.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Gravitational effects on apoptosis of presumptive ectodermal cells of amphibian embryo.

The effects of simulated microgravity (clinostat rotation at 6 rpm) on the presumptive ectodermal cells of amphibian embryos were examined. When morulae of Cynops pyrrhogaster developed under the influence of simulated microgravity, the thickness of the presumptive ectoderm was greater significantly. Embryonic cells isolated from the presumptive ectoderm of morulae were cultured for one day under the influence of simulated microgravity. The number of cells was greater after such clinostat rotation than in the control culture. TUNEL staining and electron microscopy revealed apoptotic cells both in embryos and among cultured cells, but the number of apoptotic cells was smaller in clinostat-treated embryos and cultured cells than in their controls. These results suggest that simulated microgravity suppresses apoptosis in the amphibian embryo, and as a result, affects the thickness of the presumptive ectoderm.

Animals↗
PubMed2006

Larval ectoderm, organizational homology, and the origins of evolutionary novelty.

Comprehending the origin of marine invertebrate larvae remains a key domain of research for evolutionary biologists, including the repeated origin of direct developmental modes in echinoids. In order to address the latter question, we surveyed existing evidence on relationships of homology between the ectoderm territories of two closely related sea urchin species in the genus Heliocidaris that differ in their developmental mode. Additionally, we explored a recently articulated idea about homology called 'organizational homology' (Müller 2003. In: Müller GB, Newman SA, editors. Origination of organismal form: beyond the gene in developmental and evolutionary biology. Cambridge, MA: A Bradford Book, The MIT Press. p 51-69. ) in the context of this specific empirical case study. Applying the perspective of organizational homology to our experimental system of congeneric echinoids has led us to a new hypothesis concerning the ectoderm evolution in these species. The extravestibular ectoderm of the direct developer Heliocidaris erythrogramma is a novel developmental territory that arose as a fusion of the oral and aboral ectoderm territories found in indirect developing echinoids such as Heliocidaris tuberculata. This hypothesis instantiates a theoretical principle concerning the origin of developmental modules, 'integration', which has been neglected because the opposite theoretical principle, 'parcellation', is more readily observable in events such as gene duplication and divergence (Wagner 1996. Am Zool 36:36-43).

Animals↗
PubMed2005

Mouse epiblasts change responsiveness to BMP4 signal required for PGC formation through functions of extraembryonic ectoderm.

Mouse primordial germ cells (PGCs) are initially identified as a cluster of alkaline phosphatase (AP)-positive cells within the extraembryonic mesoderm near the posterior part of the primitive streak at embryonic day (E) 7.25. Clonal analysis of epiblast cells has revealed that the putative precursors of PGCs are localized in the proximal epiblast, and we demonstrated that the conditions required for PGC formation are induced in the proximal region of epiblasts by extraembryonic ectoderm. Bone morphogenetic protein (BMP) 4 and BMP8b, which belong to the transforming growth factor-beta (TGF-beta) superfamily, might generate induction signals from extraembryonic ectoderm. Smad1 and Smad5, which are intracellular signaling molecules for BMP4, might also play a critical role in stimulating epiblasts to form PGC. However, how pluripotential epiblasts temporally and spatially respond to BMP signals to form PGCs remains unclear. The present study examines changes of responsiveness to BMP4 for PGC formation in epiblasts and their molecular mechanisms. We initially examined the effect of recombinant human (rh) BMP4 upon cultured epiblasts at different developmental stages, and found that they acquire the ability to respond to BMP4 signals for PGC formation between E5.25 and E5.5. In addition, such competence was conferred upon epiblasts by the extraembryonic ectoderm. We also showed that the increased expression of Smad1 and the onset of Smad5 expression induced by extraembryonic ectoderm might be responsible for quick acquisition of this competence. Furthermore, we show that only proximal epiblast cells maintain responsiveness to BMP4 for PGC formation at E6.0, and that this is associated with the proximal epiblast-specific expression of Smad5. These results explain why only the proximal region of epiblasts can sustain the ability to form PGCs.

Animals↗
PubMed1994

Thymic hypoplasia and T-cell deficiency in ectodermal dysplasia: case report and review of the literature.

Ectodermal dysplasia is a heterogeneous disorder that includes a constellation of congenital malformations occasionally associated with mild to moderate immune dysfunction. In this report, we describe a female infant with ectodermal dysplasia who was found to have thymic hypoplasia but no other phenotypic features of the DiGeorge anomalad. She experienced Candida parapsilosis sepsis at 1 week of age and a skin infection with Mycobacterium chelonii at 6 months. The numbers of blood B cells were normal and serum immunoglobulins normal to slightly reduced, but serum antibody responses of all immunoglobulin isotypes to protein immunogens were absent. Blood T cells were profoundly reduced and proliferative responses of T cells to mitogens were blunted. In contrast, there was an increased number of natural killer (NK) cells and increased NK activity in the blood. Over the first year of life, some of the immunodeficiencies resolved. Although the numbers of blood T cells (17% of total lymphocytes) remained low, proliferative responses to mitogens normalized and specific antibody responses improved. It seems likely that the thymic hypoplasia in this case was due to a paucity of ectodermal elements in the developing thymus, and that the immune defects were largely secondary to that event. In that respect, this human model of ectodermal dysplasia and thymic hypoplasia resembled the ectodermal/thymic defects found in the nude mouse.

Cell Line↗