Ghrelin receptors in human gastrointestinal tract during prenatal and early postnatal development

The aim of our study was to investigate the appearance, density and distribution of ghrelin cells and GHS-R1a and GHS-R1b in the human stomach and duodenum during prenatal and early postnatal development. We examined chromogranin-A and ghrelin cells in duodenum, and GHS-R1a and GHS-R1b expression in stomach and duodenum by immunohistochemistry in embryos, fetuses, and infants. Chromogranin-A and ghrelin cells were identified in the duodenum at weeks 10 and 11 of gestation. Ghrelin cells were detected individually or clustered within the base of duodenal crypts and villi during the first trimester, while they were presented separately within the basal and apical parts of crypts and villi during the second and third trimesters. Ghrelin cells were the most numerous during the first (∼11%) and third (∼10%) trimesters of gestation development. GHS-R1a and GHS-R1b were detected at 11 and 16 weeks of gestation, showed the highest level of expression in Brunner's gland and in lower parts of duodenal crypts and villi during the second trimester in antrum, and during the third trimester in corpus and duodenum. Our findings demonstrated for the first time abundant duodenal expression of ghrelin cells and ghrelin receptors during human prenatal development indicating a role of ghrelin in the regulation of growth and differentiation of human gastrointestinal tract.     

Constitutive Musashi1 expression impairs mouse postnatal development and intestinal homeostasis

Evolutionarily conserved RNA-binding protein Musashi1 (Msi1) can regulate developmentally relevant genes. Here we report the generation and characterization of a mouse model that allows inducible Msi1 overexpression in a temporal and tissue-specific manner. We show that ubiquitous Msi1 induction in ∼5-wk-old mice delays overall growth, alters organ-to-body proportions, and causes premature death. Msi1-overexpressing mice had shortened intestines, diminished intestinal epithelial cell (IEC) proliferation, and decreased growth of small intestine villi and colon crypts. Although Lgr5-positive intestinal stem cell numbers remained constant in Msi1-overexpressing tissue, an observed reduction in Cdc20 expression provided a potential mechanism underlying the intestinal growth defects. We further demonstrated that Msi1 overexpression affects IEC differentiation in a region-specific manner, with ileum tissue being influenced the most. Ilea of mutant mice displayed increased expression of enterocyte markers, but reduced expression of the goblet cell marker Mucin2 and fewer Paneth cells. A higher hairy and enhancer of split 1:mouse atonal homolog 1 ratio in ilea from Msi1-overexpressing mice implicated Notch signaling in inducing enterocyte differentiation. Together, this work implicates Msi1 in mouse postnatal development of multiple organs, with Notch signaling alterations contributing to intestinal defects. This new mouse model will be a useful tool to further elucidate the role of Msi1 in other tissue settings.     

Cytokeratin expression during mouse embryonic and early postnatal mammary gland development

Cytokeratins are intermediate filament proteins found in most epithelial cells including the mammary epithelium. Specific cytokeratin expression has been found to mark different epithelial cell lineages and also to associate with putative mammary stem/progenitor cells. However, a comparative analysis of the expression of cytokaratins during embryonic and postnatal mammary development is currently lacking. Moreover, it is not clear whether the different classes of putative mammary stem/progenitor cells exist during embryonic development. Here, we use double/triple-label immunofluorescence and immunohistochemistry to systematically compare the expression of cytokeratin 5 (K5), cytokeratin 6 (K6), cytokeratin 8 (K8), cytokeratin 14 (K14) and cytokeratin 19 (K19) in embryonic and early postnatal mouse mammary glands. We show that K6⁺ and K8⁺/K14⁺ putative mammary progenitor cells arise during embryogenesis with distinct temporal and spatial distributions. Moreover, we describe a transient disconnection of the expression of K5 and K14, two cytokeratins that are often co-expressed, during the first postnatal weeks of mammary development. Finally, we report that cytokeratin expression in cultured primary mammary epithelial cells mimics that during the early stages of postnatal mammary development. These studies demonstrate an embryonic origin of putative mammary stem/progenitor cells. Moreover, they provide additional insights into the use of specific cytokeratins as markers of mammary epithelial differentiation, or the use of their promoters to direct gene overexpression or ablation in genetic studies of mouse mammary development.     

Integrin expression patterns during early limb muscle development in the mouse

Cell-extracellular matrix interactions play crucial roles in limb muscle development but practically nothing is known on what integrins are involved before the differentiation of muscle precursor cells (MPCs) in the limb muscle masses. In this study we determine the expression patterns of integrins during early forelimb muscle development in the mouse. alpha6beta1 integrin is downregulated in the lateral dermomyotome when delamination of MPCs occurs. In late E9.5 embryos, alpha1beta1 and alpha5beta1 are expressed in a pattern very similar to pax3, which marks MPCs migrating to the limb bud. After myf5 upregulation in the limb bud, alpha1beta1 and alpha5beta1 expression is maintained and the alpha4beta1 integrin starts being expressed.     

Integrin expression patterns during early limb muscle development in the mouse

Cell-extracellular matrix interactions play crucial roles in limb muscle development but practically nothing is known on what integrins are involved before the differentiation of muscle precursor cells (MPCs) in the limb muscle masses. In this study we determine the expression patterns of integrins during early forelimb muscle development in the mouse. alpha6beta1 integrin is downregulated in the lateral dermomyotome when delamination of MPCs occurs. In late E9.5 embryos, alpha1beta1 and alpha5beta1 are expressed in a pattern very similar to pax3, which marks MPCs migrating to the limb bud. After myf5 upregulation in the limb bud, alpha1beta1 and alpha5beta1 expression is maintained and the alpha4beta1 integrin starts being expressed.     

Ultrastructural localization of intestinal glucose-6-phosphatase activity during the postnatal development of the mouse

Summary The development of the endoplasmic reticulum (ER) and the ultrastructural localization of glucose-6-phosphatase activity have been studied in the proximal jejunum and distal ileum during the postnatal period. One day after birth, the amount and the repartition of ER in the jejunal enterocytes are similar to that observed in postweaning period. In the following days an extensive proliferation of SER is noted in the supranuclear zone of the absorbing cells. From day 7 till postweaning period a gradual decrease of the amount of SER is observed and after weaning, the ultrastructure of the enterocytes is similar to that in the adult mouse enterocytes. At all time, a positive reaction for G-6-Pase activity is observed in the cisternae of the endoplasmic reticulum and in the nuclear envelope. In the distal ileum, the SER is poorly developed one day after birth. During the first two weeks, the ER increases but no extensive proliferation of SER can be noted as in the jejunum. The G-6-Pase activity can be visualized in the rough and smooth endoplasmic reticulum as well as in the nuclear envelope. It appears that the proliferation of SER could be interpreted as the morphologic expression of an increased G-6-Pase activity.This work was supported by research grant from the Medical Research Council of CanadaD. Ménard, Ph. D. is «Chercheur-boursier du Conseil de la recherche en santé du Québec»     

Gene expression profiling of mouse postnatal cerebellar development using oligonucleotide microarrays designed to detect differences in glycoconjugate expression

Differences in gene expression patterns between adult and postnatal day 7 (P7) mouse cerebellum, at the peak of granule neuron migration, were analyzed by hybridization to the GLYCOv2 glycogene array. This custom designed oligonucleotide array focuses on glycosyl transferases, carbohydrate-binding proteins, proteoglycans and related genes, and 173 genes were identified as being differentially expressed with statistical confidence. Expression levels for 11 of these genes were compared by RT-PCR, and their differential expression between P7 and adult cerebellum confirmed. Within the group of genes showing differential expression, the sialyltransferases (SiaTs) and GalNAc-Ts that were elevated at P7 prefer glycoprotein substrates, whilst the SiaTs and GalNAc-Ts that were elevated in the adult preferentially modify glycolipids, consistent with a role for gangliosides in maintaining neuronal function in the adult. Also within this group, three proteoglycans--versican, bamacan and glypican-2--were elevated at P7, along with growth factor midkine, which is known to bind to multiple types of proteoglycans, and fibroblast growth factor receptor 1, whose activity is known to be influenced by heparan sulfate proteoglycans. Two sulfotransferases that can modify the extent of proteoglycan sulfation were also differentially regulated, and may modify the interaction of a subset of proteoglycans with their binding partners during cerebellar development. Bamacan, glypican-2 and midkine were shown to be expressed in different cell types, and their roles in cerebellar development during granule neuron migration and maturation are discussed.     

Comparative expression of the mRNA for three intestinal hydrolases during postnatal development in the rat

The distribution of the mRNA for intestinal aminopeptidase-N, lactase-phlorizin hydrolase and sucrase-isomaltase was compared during rat postnatal development as well as along the longitudinal axis of the intestinal tract including small-intestine and colon. We found out that each mRNA exhibited a specific pattern of accumulation, suggesting proper regulation steps for the expression of the corresponding digestive enzymes.     

Ultrastructural localization of intestinal glucose-6-phosphatase activity during the postnatal development of the mouse

The development of the endoplasmic reticulum (ER) and the ultrastructural localization of glucose-6-phosphatase activity have been studied in the proximal jejunum and distal ileum during the postnatal period. One day after birth, the amount and the repartition of ER in the jejunal enterocytes are similar to that observed in postweaning period. In the following days an extensive proliferation of SER is noted in the supranuclear zone of the absorbing cells. From day 7 till postweaning period a gradual decrease of the amount of SER is observed and after weaning, the ultrastructure of the enterocytes is similar to that in the adult mouse enterocytes. At all time, a positive reaction for G-6-Pase activity is observed in the cisternae of the endoplasmic reticulum and in the nuclear envelope. In the distal ileum, the SER is poorly developed one day after birth. During the first two weeks, the ER increases but no extensive proliferation of SER can be noted as in the jejunum. The G-6-Pase activity can be visualized in the rough and smooth endoplasmic reticulum as well as in the nuclear envelope. It appears that the proliferation of SER could be interpreted as the morphologic expression of an increased G-6-Pase activity.     

Abnormal cardiac inflow patterns during postnatal development in a mouse model of Holt-Oram syndrome

Tbx5(del/+) mice provide a model of human Holt-Oram syndrome. In this study, the cardiac functional phenotypes of this mouse model were investigated with 30-MHz ultrasound by comparing 12 Tbx5(del/+) mice with 12 wild-type littermates at 1, 2, 4, and 8 wk of age. Cardiac dimensions were measured with two-dimensional and M-mode imaging. The flow patterns in the left and right ventricular inflow channels were evaluated with Doppler flow sampling. Compared with wild-type littermates, Tbx5(del/+) mice showed significant changes in the mitral flow pattern, including decreased peak velocity of the left ventricular (LV) early filling wave (E wave), increased peak velocity of the late filling wave (A wave), and decreased or even reversed peak E-to-A ratio. The prolongation of LV isovolumic relaxation time was detected in Tbx5(del/+) neonates as early as 1 wk of age. In Tbx5(del/+) mice, LV wall thickness appeared normal but LV chamber dimension was significantly reduced. LV systolic function did not differ from that in wild-type littermates. In contrast, the Doppler flow spectrum in the enlarged tricuspid orifice of Tbx5(del/+) mice demonstrated increased peak velocities of both E and A waves and increased total time-velocity integral but unchanged peak E/A. In another 13 mice (7 Tbx5(del/+), 6 wild-type) at 2 wk of age, significant correlation was found between Tbx5 gene expression level in ventricular myocardium and LV filling parameters. In conclusion, the LV diastolic function of Tbx5(del/+) mice is significantly deteriorated, whereas the systolic function remains normal.     

Gene expression profiling reveals the mechanism and pathophysiology of mouse liver regeneration

Comprehensive analysis of the changes in gene expression during liver regeneration was carried out by using an in-house microarray composed of 2,304 distinct mouse liver cDNA clones. Mice were subjected to partial two-thirds hepatectomy, and changes in mRNA levels were monitored up to 48 h. Of the 2,304 genes analyzed, 496 genes showed expression levels measurable at all time points after the partial hepatectomy. 317 genes were up- or down-regulated 2-fold or more at least at one time point during liver regeneration and were classified into eight clusters based on their expression patterns. With a more stringent cut-off value of +/-2 S.D., 68 genes were listed and were classified into five clusters. In these two analyses with different clustering criteria, functionally categorized genes showed similar cluster distributions. Genes involved in protein synthesis and posttranslational processing were significantly enriched in the cluster characterized by rapid gene activation and subsequent persistence. This suggests the importance of modulating the efficiency of protein supply and/or altering the composition of protein population from the early phase of hepatocyte proliferation. Genes for two major liver functions, i.e. plasma protein secretion and intermediate metabolism were enriched in distinct clusters exhibiting the features of gradual gene activation and sustained repression, respectively. Therefore, these genes are differentially regulated during the regeneration, possibly leading to changes in the flow of amino acids and energy from enzyme proteins to plasma proteins in their synthesis. Thus, clustering analysis of expression patterns of functionally classified genes gave insights into mechanism and pathophysiology of liver regeneration.