RESUMEN
The gut mounts secretory immunoglobulin A (SIgA) responses to commensal bacteria through nonredundant T cell-dependent (TD) and T cell-independent (TI) pathways that promote the establishment of mutualistic host-microbiota interactions. SIgAs from the TD pathway target penetrant bacteria, and their induction requires engagement of CD40 on B cells by CD40 ligand on T follicular helper cells. In contrast, SIgAs from the TI pathway bind a larger spectrum of bacteria, but the mechanism underpinning their production remains elusive. Here, we show that the intestinal TI pathway required CD40-independent B cell-activating signals from TACI, a receptor for the innate CD40 ligand-like factors BAFF and APRIL. TACI-induced SIgA responses targeted a fraction of the gut microbiota without shaping its overall composition. Of note, TACI was dispensable for TD induction of IgA in gut-associated lymphoid organs. Thus, BAFF/APRIL signals acting on TACI orchestrate commensal bacteria-specific SIgA responses through an intestinal TI program.
Asunto(s)
Linfocitos B/inmunología , Microbioma Gastrointestinal , Tracto Gastrointestinal/inmunología , Tracto Gastrointestinal/microbiología , Inmunoglobulina A/inmunología , Proteína Activadora Transmembrana y Interactiva del CAML/inmunología , Animales , Bacterias/genética , Inmunidad Mucosa , Inmunoglobulina A/genética , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , ARN Ribosómico 16S/genética , Linfocitos TRESUMEN
Intestinal macrophages (mφ) form one of the largest populations of mφ in the body and are vital for the maintenance of gut homeostasis. They have several unique properties and are derived from local differentiation of classical Ly6Chi monocytes, but the factors driving this tissue-specific process are not understood. Here we have used global transcriptomic analysis to identify a unique homeostatic signature of mature colonic mφ that is acquired as they differentiate in the mucosa. By comparing the analogous monocyte differentiation process found in the dermis, we identify TGFß as an indispensable part of monocyte differentiation in the intestine and show that it enables mφ to adapt precisely to the requirements of their environment. Importantly, TGFßR signaling on mφ has a crucial role in regulating the accumulation of monocytes in the mucosa, via mechanisms that are distinct from those used by IL10.
Asunto(s)
Colon/inmunología , Macrófagos/inmunología , Monocitos/inmunología , Receptores de Factores de Crecimiento Transformadores beta/metabolismo , Factor de Crecimiento Transformador beta/metabolismo , Animales , Antígenos Ly/metabolismo , Diferenciación Celular , Células Cultivadas , Microambiente Celular , Femenino , Perfilación de la Expresión Génica , Homeostasis , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Especificidad de Órganos , Receptores de Factores de Crecimiento Transformadores beta/genética , Transducción de Señal , TranscriptomaRESUMEN
A microfluidic chip approach utilising integrated electrically connected stationary SERS targets based on inkjet-printed silver nanoparticles is presented. It enables multiple interference-free consecutive surface-enhanced Raman measurements inside chip channels by electrically assisted regeneration of the stationary SERS substrate. Thereby it circumvents common adsorption and memory effect problems associated with stationary SERS targets allowing multiple consecutive measurements in a continuous-flow system.
Asunto(s)
Electricidad , Técnicas Analíticas Microfluídicas , Espectrometría Raman , Nanopartículas del Metal/química , Técnicas Analíticas Microfluídicas/instrumentación , Impresión , Plata/química , Espectrometría Raman/instrumentación , Propiedades de SuperficieRESUMEN
Analysis of the intestinal B-cell system and properties of immunoglobulin A, the main antibody isotype produced in the gut, has dominated the rise of mucosal immunology as a discipline. Seminal work established concepts describing the induction, transport, and function of mucosal antibodies. Still, open questions remain and we lack a comprehensive view of how the various sites and pathways of immunoglobulin A induction are integrated to respond to gut antigens. Next-generation sequencing (NGS) offers a novel approach to study B-cell responses, which might substantially enhance our tool box to answer key questions in the field and to take the next steps toward therapeutic exploitation of the mucosal B-cell system. In this review we discuss the potential, challenges, and emerging solutions for gut B-cell repertoire analysis by NGS.
Asunto(s)
Linfocitos B/inmunología , Secuenciación de Nucleótidos de Alto Rendimiento/métodos , Inmunoglobulina A/inmunología , Intestinos/inmunología , Receptores de Antígenos de Linfocitos B/genética , Animales , Humanos , Inmunidad Mucosa , Inmunoglobulina A/genéticaRESUMEN
Lymphoid organ hypertrophy is a hallmark of localized infection. During the inflammatory response, massive changes in lymphocyte recirculation and turnover boost lymphoid organ cellularity. Intriguingly, the exact nature of these changes remains undefined to date. Here, we report that hypertrophy of Salmonella-infected Peyer's patches (PPs) ensues from a global "shutdown" of lymphocyte egress, which traps recirculating lymphocytes in PPs. Surprisingly, infection-induced lymphocyte sequestration did not require previously proposed mediators of lymphoid organ shutdown including type I interferon receptor and CD69. In contrast, following T-cell receptor-mediated priming, CD69 was essential to selectively block CD4(+) effector T-cell egress. Our findings segregate two distinct lymphocyte sequestration mechanisms, which differentially rely on intrinsic modulation of lymphocyte egress capacity and inflammation-induced changes in the lymphoid organ environment.
Asunto(s)
Antígenos CD/metabolismo , Antígenos de Diferenciación de Linfocitos T/metabolismo , Lectinas Tipo C/metabolismo , Linfocitos/metabolismo , Ganglios Linfáticos Agregados/inmunología , Ganglios Linfáticos Agregados/patología , Receptores de Interferón/metabolismo , Animales , Hipertrofia , Ligandos , Recuento de Linfocitos , Linfocitos/inmunología , Ratones , Ratones Noqueados , Ratones Transgénicos , Ganglios Linfáticos Agregados/microbiología , Salmonella/inmunología , Infecciones por Salmonella/inmunología , Infecciones por Salmonella/metabolismo , Receptores Toll-Like/metabolismoRESUMEN
De novo induction of Foxp3⺠regulatory T cells (Tregs) is particularly efficient in gut-draining mesenteric and celiac lymph nodes (mLN and celLN). Here we used LN transplantations to dissect the contribution of stromal cells and environmental factors to the high Treg-inducing capacity of these LN. After transplantation into the popliteal fossa, mLN and celLN retained their high Treg-inducing capacity, whereas transplantation of skin-draining LN into the gut mesenteries did not enable efficient Treg induction. However, de novo Treg induction was abolished in the absence of dendritic cells (DC), indicating that this process depends on synergistic contributions of stromal and DC. Stromal cells themselves were influenced by environmental signals as mLN grafts taken from germ-free donors and celLN grafts taken from vitamin A-deficient donors did not show any superior Treg-inducing capacity. Collectively, our observations reveal a hitherto unrecognized role of LN stromal cells for the de novo induction of Foxp3⺠Tregs.
Asunto(s)
Microambiente Celular/inmunología , Intestinos/citología , Intestinos/inmunología , Ganglios Linfáticos/inmunología , Células del Estroma/fisiología , Linfocitos T Reguladores/inmunología , Animales , Comunicación Celular , Células Dendríticas/inmunología , Células Dendríticas/metabolismo , Factores de Transcripción Forkhead/metabolismo , Tolerancia Inmunológica , Interleucina-6/genética , Interleucina-6/metabolismo , Mucosa Intestinal/citología , Mucosa Intestinal/inmunología , Mucosa Intestinal/metabolismo , Mucosa Intestinal/microbiología , Intestinos/microbiología , Ratones , Ratones Noqueados , Microbiota , Retinal-Deshidrogenasa/genética , Retinal-Deshidrogenasa/metabolismo , Linfocitos T Reguladores/metabolismo , Vitamina A/metabolismoRESUMEN
Oral tolerance is the state of local and systemic immune unresponsiveness that is induced by oral administration of innocuous antigen such as food proteins. An analogous but more local process also regulates responses to commensal bacteria in the large intestine and, together, mucosally induced tolerance appears to prevent intestinal disorders such as food allergy, celiac disease, and inflammatory bowel diseases. Here we discuss the anatomical basis of antigen uptake and recognition in oral tolerance and highlight possible mechanisms underlying the immunosuppression. We propose a model of stepwise induction of oral tolerance in which specialized populations of mucosal dendritic cells and the unique microenvironment of draining mesenteric lymph nodes combine to generate regulatory T cells that undergo subsequent expansion in the small intestinal lamina propria. The local and systemic effects of these regulatory T cells prevent potentially dangerous hypersensitivity reactions to harmless antigens derived from the intestine and hence are crucial players in immune homeostasis.
Asunto(s)
Células Dendríticas/inmunología , Proteínas en la Dieta/inmunología , Hipersensibilidad a los Alimentos/inmunología , Enfermedades Inflamatorias del Intestino/inmunología , Subgrupos de Linfocitos T/inmunología , Linfocitos T Reguladores/inmunología , Administración Oral , Animales , Presentación de Antígeno , Homeostasis , Humanos , Tolerancia Inmunológica , Inmunidad Mucosa , Mucosa Intestinal/inmunologíaRESUMEN
BACKGROUND: Enterochromaffin cells and enteric neurons synthesize and release serotonin (5-HT). Reuptake, mediated by a plasmalemmal transporter (SERT) terminates the action of released 5-HT. Serotonin secretion and serotonin reuptake transporter (SERT) expression have been reported to be decreased in TNBS-induced experimental colitis and in patients with ulcerative colitis. The present study was designed to utilize the transgenic deletion of SERT as a gain-of-function model to test the hypothesis that 5-HT is a pro-inflammatory mediator in experimental colitis. METHODS: Colitis was compared in animals with IL10(+/+)SERT(+/+) (wild-type), IL10(-/-)SERT(+/+), IL10(-/-)SERT(+/-), and IL10(-/-)/SERT(-/-) (double knockout) genotypes. Macroscopic and histological damage scores were evaluated after a time period of up to 15 weeks. KEY RESULTS: Serotonin reuptake transporter expression was significantly increased in the inflamed colons of IL-10(-/-) mice, which displayed intestinal damage and a minor decrement in general health. General health was significantly worse and intestinal inflammation was more severe in IL-10(-/-)SERT(+/-), and IL-10(-/-)SERT(-/-) mice than in IL-10(-/-)SERT(+/+) or wild-type animals. Regardless of the associated SERT genotype, the number of 5-HT-immunoreactive cells was decreased by approximately 55-65% in all mice lacking IL-10. CONCLUSIONS & INFERENCES: Our observations indicate that colitis associated with IL-10 deficient mice is enhanced when the IL-10 deficiency is combined with a SERT deficiency. The data support the concept that 5-HT is a pro-inflammatory mediator in the gut.
Asunto(s)
Inflamación/genética , Interleucina-10/genética , Enfermedades Intestinales/genética , Proteínas de Transporte de Serotonina en la Membrana Plasmática/genética , Animales , Colitis/genética , Colitis/patología , Femenino , Inmunohistoquímica , Inflamación/patología , Interleucina-10/fisiología , Enfermedades Intestinales/patología , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Proteínas de Transporte de Serotonina en la Membrana Plasmática/fisiologíaRESUMEN
INTRODUCTION: The clinical application of small bowel transplantation (SBTx) is hampered by its pronounced immunogenicity. In this study we examined the effects of the novel immunosuppressant FTY720 and costimulation blockade by an anti-CD40L mAb (MR-1) in a stringent mouse model of SBTx. METHODS: SBTx was performed in mice with a full MHC mismatch (donors: C3H=H-2(k); recipients: C57BL/6=H-2(b)). Recipients were divided into four groups: 1, untreated group; 2, MR1 monotherapy (500 microg IV on days 0, 2, 4, and 7); 3, FTY720 monotherapy (1 mg/kg body weight PO for 14 consecutive days after transplantation); 4, FTY720 plus MR1-treated group. Graft rejection grades were assessed by H&E staining. Graft mesenteric lymph nodes (MLNs), Peyer's patches (PPs), as well as intraepithelial lymphocytes (IELs) and lamina propria lymphocytes (LPLs) were analyzed by flow cytometry and three-color immunofluorescence staining. RESULTS: Neither FTY720 nor MR1 monotherapy was efficient in preventing the rejection of mouse intestinal allografts, whereas FTY720 plus MR1 profoundly inhibited the rejection response at the 14th posttransplant day. The infiltration of host lymphocytes was reduced in graft MLNs, PPs, IELs, and LPLs by FTY720 therapy. FTY720 plus MR1 inhibited host CD8(+) T-cell infiltration in graft LPLs when compared with grafts treated with FTY720 only. Additionally, two subpopulations, CD11b(+high) Gr1(-) and CD11b(+intermediate) Gr1(+) cells, were decreased in FTY720-treated grafts. CONCLUSIONS: FTY720 plus MR1 efficiently delayed intestinal allograft rejection in a mouse model by preventing the infiltration of host lymphocytes, particularly of CD8(+) cells.
Asunto(s)
Rechazo de Injerto/prevención & control , Supervivencia de Injerto/inmunología , Intestino Delgado/trasplante , Glicoles de Propileno/uso terapéutico , Trasplante Homólogo/inmunología , Animales , Anticuerpos Monoclonales/uso terapéutico , Ligando de CD40/inmunología , Clorhidrato de Fingolimod , Supervivencia de Injerto/efectos de los fármacos , Prueba de Histocompatibilidad , Inmunosupresores/uso terapéutico , Intestino Delgado/efectos de los fármacos , Intestino Delgado/inmunología , Intestino Delgado/patología , Complejo Mayor de Histocompatibilidad , Ratones , Ratones Endogámicos C3H , Ratones Endogámicos C57BL , Esfingosina/análogos & derivadosRESUMEN
Targeted disruption of the transcription factor NKX2.3 gene in mice results in anatomical defects of intestine and secondary lymphoid organs. Here, we report that spleen and Peyer's patches of NKX2. 3-deficient mice are considerably reduced in size and lack the ordered tissue architecture. T and B cells are misplaced within the spleen and mesenteric lymph nodes and fail to segregate into the appropriate T and B cell areas. Furthermore, splenic marginal zones, characterized by specific B cells and various types of macrophage-derived cells around the marginal sinus, are absent in mutants. Homozygous NKX2.3 mutants lack the mucosal addressin cell adhesion molecule-1 (MAdCAM-1) that is normally expressed in mucosa-associated lymphoid tissue (MALT) and spleen. We provide evidence that NKX2.3 can activate MAdCAM-1 transcription directly, suggesting that MAdCAM-1 is at least partly responsible for the migration and homing defects of lymphocytes and macrophages in mutants. Therefore, expression of MAdCAM-1 seems to be required for building functional structures in spleen and MALT, a prerequisite for unimpaired migration and segregation of B and T cells to and within these organs.
Asunto(s)
Regulación de la Expresión Génica , Proteínas de Homeodominio/fisiología , Inmunoglobulinas/genética , Linfocitos/inmunología , Mucoproteínas/genética , Ganglios Linfáticos Agregados/inmunología , Bazo/inmunología , Proteínas de Pez Cebra , Animales , Moléculas de Adhesión Celular , Movimiento Celular , Células Cultivadas , Citometría de Flujo , Genes Reporteros/genética , Proteínas de Homeodominio/genética , Inmunohistoquímica , Ganglios Linfáticos/anomalías , Ganglios Linfáticos/citología , Ganglios Linfáticos/inmunología , Linfocitos/citología , Macrófagos/citología , Macrófagos/inmunología , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos , Ratones Noqueados , Microscopía Electrónica , Ganglios Linfáticos Agregados/anomalías , Ganglios Linfáticos Agregados/citología , Regiones Promotoras Genéticas/genética , ARN Mensajero/genética , ARN Mensajero/metabolismo , Eliminación de Secuencia/genética , Bazo/anomalías , Bazo/citología , Bazo/ultraestructura , Activación TranscripcionalRESUMEN
NKX2 genes in vertebrates encode a sub- family of homeodomain-containing transcription factors which regulate morphogenetic events and cell differentiation during embryogenesis. In mouse embryos several NKX2 genes are expressed in the ventral midline domains of the neuroectoderm, while other NKX2 genes are primarily expressed in the mesendoderm and mesendodermally derived organs, such as heart and gut. Within several patterning centers for tissue organization sonic hedgehog (Shh) is an important signal in the formation of ventral midline structures in vertebrate embryos. Here, we investigated the role of Shh in the embryonic expression of six different but closely related NKX2 genes in Shh null mutant mice. We found that expression of NKX2.1, NKX2.2, and NKX2.9 in neural domains requires Shh signaling, whereas NKX2.3, NKX2.5 and NKX2.6 expression in endoderm and mesoderm is independent of Shh.
Asunto(s)
Desarrollo Embrionario y Fetal/genética , Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/genética , Proteínas/genética , Transactivadores , Factores de Transcripción/genética , Animales , Ectodermo , Inducción Embrionaria , Proteínas Hedgehog , Proteína Homeobox Nkx-2.2 , Mesodermo , RatonesRESUMEN
The homeodomain transcription factor Nkx2-3 is expressed in gut mesenchyme and spleen of embryonic and adult mice. Targeted inactivation of the Nkx2-3 gene results in severe morphological alterations of both organs and early postnatal lethality in the majority of homozygous mutants. Villus formation in the small intestine appears considerably delayed in Nkx2-3(-)/- foetuses due to reduced proliferation of the epithelium, while massively increased growth of crypt cells ensues in surviving adult mutants. Interestingly, differentiated cell types of the intestinal epithelium are present in homozygous mutants, suggesting that Nkx2-3 is not required for their cell lineage allocation or migration-dependent differentiation. Hyperproliferation of the gut epithelium in adult mutants is associated with markedly reduced expression of BMP-2 and BMP-4, suggesting that these signalling molecules may be involved in mediating non-cell-autonomous control of intestinal cell growth. Spleens of Nkx2-3 mutants are generally smaller and contain drastically reduced numbers of lymphatic cells. The white pulp appears anatomically disorganized, possibly owing to a homing defect in the spleen parenchyme. Moreover, some of the Nkx2-3 mutants exhibit asplenia. Taken together these observations indicate that Nkx2-3 is essential for normal development and functions of the small intestine and spleen.
Asunto(s)
Proteínas Aviares , Proteínas de Homeodominio/fisiología , Intestino Delgado/embriología , Bazo/embriología , Factores de Transcripción/fisiología , Factor de Crecimiento Transformador beta , Animales , Animales Recién Nacidos , Proteína Morfogenética Ósea 2 , Proteína Morfogenética Ósea 4 , Proteínas Morfogenéticas Óseas/genética , División Celular , Movimiento Celular , Regulación de la Expresión Génica , Marcación de Gen , Proteínas de Homeodominio/genética , Mucosa Intestinal , Intestino Delgado/citología , Intestino Delgado/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Mutagénesis , Fenotipo , Factores de Transcripción/genéticaRESUMEN
Nkx homeobox transcription factors are expressed in diverse embryonic cells and presumably control cell-type specification and morphogenetic events. Nkx2-9 is a novel family member of NK2 genes which lacks the conserved TN-domain found in all hitherto known murine Nkx2 genes. The prominent expression of Nkx2-9 in ventral brain and neural tube structures defines a subset of neuronal cells along the entire neuraxis. During embryonic development, Nkx2-9-expressing cells shift from the presumptive floor plate into a more dorsolateral position of the neuroectoderm and later become limited to the ventricular zone. Nkx2-9 expression overlaps with that of Nkx2-2 but is generally broader. While initially Nkx2-9 is expressed in close proximity to sonic hedgehog, its expression domain clearly segregates from sonic hedgehog at later developmental stages. The dynamic expression pattern of Nkx2-9 in ventral domains of the CNS is consistent with a possible role in the specification of a distinct subset of neurons.
Asunto(s)
Sistema Nervioso Central/embriología , Proteínas de Homeodominio/genética , Transactivadores , Factores de Transcripción/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Encéfalo/embriología , Encéfalo/metabolismo , Sistema Nervioso Central/metabolismo , Endodermo/metabolismo , Genes Sobrepuestos , Proteínas Hedgehog , Proteína Homeobox Nkx-2.2 , Proteínas de Homeodominio/biosíntesis , Ratones , Datos de Secuencia Molecular , Cresta Neural/metabolismo , Biosíntesis de Proteínas , Alineación de Secuencia , Factores de Transcripción/biosíntesis , Proteínas de Pez CebraRESUMEN
The cDNA cFKH-1 encodes a chicken winged helix/forkhead domain transcription factor that presents a dynamic expression pattern during chicken embryogenesis. Transcripts accumulate predominantly in early paraxial mesoderm, developing somites, and within mesenchymal precursors of skeletal structures. cFKH-1 RNA is first detected in the developing mesoderm of HH stage 6 embryos. During subsequent development cFKH-1 RNA accumulates in a dorsal domain of the anterior presomitic mesoderm and later in all cells of the epithelial somites before it becomes limited to the sclerotome when somites compartmentalise. cFKH-1 expression persists in the sclerotome, forming the vertebrae and in mesenchymal condensations in limb buds that will give rise later to the appendicular bones. In differentiated chondrocytes and definitive bone structures, however, cFKH-1 expression is down-regulated. Additional expression domains are found in mesenchyme of branchial arches and the head, in the dorsal aorta, and weakly in the endocardium. Based on its expression pattern and the structure of the forkhead DNA-binding domain cFKH-1 constitutes a chicken relative to the murine family of fkh-1/MF1 and MFH-1 factors. The embryonic expression of the cFKH-1 gene defines distinct mesodermal domains and suggests that it may regulate gene expression in mesenchymal cell lineages that will form cartilage in trunk and limb buds.
Asunto(s)
Proteínas Aviares , Tipificación del Cuerpo , Desarrollo Óseo/fisiología , Proteínas de Unión al ADN/fisiología , Factores de Transcripción/fisiología , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico , Embrión de Pollo , ADN Complementario , Proteínas de Unión al ADN/biosíntesis , Proteínas de Unión al ADN/genética , Secuencias Hélice-Asa-Hélice , Humanos , Mesodermo , Datos de Secuencia Molecular , ARN , Homología de Secuencia de Aminoácido , Factores de Transcripción/biosíntesis , Factores de Transcripción/genéticaRESUMEN
The Nkx homeodomain proteins are members of a growing family of known vertebrate transcription factors that are believed to play a role in cell type specification and/or maintenance of the differentiated phenotype. In this article we report on the identification and developmental expression pattern of the mouse Nkx2-3 gene. The gene is expressed primarily in gut mesoderm, dinstinct regions of the branchial arches, the tongue epithelium, and limited domains in the developing jaws, possibly including tooth anlagen. In contrast to the chicken and Xenopus genes, Nkx2-3 expression in the mouse was not observed in the developing heart or neural tube. Thus, although structurally related to chicken and Xenopus Nkx2-3, the mouse gene exhibits an overlapping but distinct expression pattern that may suggest the existence of additional family members, as yet unidentified, in vertebrate organisms.
Asunto(s)
Proteínas Aviares , Sistema Digestivo/embriología , Desarrollo Embrionario y Fetal/genética , Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/genética , Factores de Transcripción/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Femenino , Mesodermo , Ratones , Datos de Secuencia Molecular , EmbarazoRESUMEN
NKx homeodomain proteins are members of a growing family of vertebrate transcription factors with strong homology to the NK genes in Drosophila. Here, we describe the cloning of cNKx-2.3 and cNKx-2.5 cDNAs and their expression during chick development. Both genes are expressed in the developing heart with distinct but overlapping spatio-temporal patterns. While cNKx-2.5 is activated in early precardiac mesoderm and continues to be uniformly expressed throughout the mature heart, expression of NKx-2.3 starts later in differentiated myocardial cells with regional differences compared to NKx-2.5. Additionally, both genes are expressed in adjacent domains of the developing mid- and hindgut mesoderm as well as in branchial arches. The highly conserved structure of cNKx-2.5 and its similar expression to mouse and Xenopus NKx-2.5 genes and to the Drosophila gene tinman argue that it constitutes the chick homologue of these genes. Different temporal and spatial activity of cNKx-2.3 in heart and gut as well as in a regionally restricted expression domain in the neural tube suggest that cNKx-2.3 is a member of the NK-2 gene family which may be involved in specifying mesodermally and ectodermally derived cell types in the embryo.