Louise Andersson

The developing mouse thyroid: embryonic vessel contacts and parenchymal growth pattern during specification, budding, migration, and lobulation.

Normal mouse thyroid development has been revised to identify critical morphogenetic events. The early thyroid primordium associates with the aortic sac endothelium at the time of specification and budding. The vascular contact is lost after the thyroid buds from the pharyngeal endoderm, but is resumed before the gland divides to form two lobes. Lateral expansion of parenchyma takes place along the course of the third pharyngeal arch arteries. Thyroid precursor cells expressing Titf1/Nkx2.1 do not proliferate until the migration stage, implicating that progenitors likely are recruited from outside the thyroid placode. Early lobulation involves engulfment of the entire ultimobranchial bodies by the growing midline thyroid. At the same time, proliferation of the ultimobranchial body epithelium is silenced preceding the differentiation of C cells. Before folliculogenesis, thyroid lobe enlargement is reminiscent of a budding‐branching‐like growth pattern. It is suggested that thyroid inductive signals arise from embryonic vessels, and that this provides ideas to conceptually new pathogenetic mechanisms of thyroid dysgenesis. Developmental Dynamics 235:444–455, 2006.

Revising the embryonic origin of thyroid C cells in mice and humans

Current understanding infers a neural crest origin of thyroid C cells, the major source of calcitonin in mammals and ancestors to neuroendocrine thyroid tumors. The concept is primarily based on investigations in quail–chick chimeras involving fate mapping of neural crest cells to the ultimobranchial glands that regulate Ca2+ homeostasis in birds, reptiles, amphibians and fishes, but whether mammalian C cell development involves a homologous ontogenetic trajectory has not been experimentally verified. With lineage tracing, we now provide direct evidence that Sox17+ anterior endoderm is the only source of differentiated C cells and their progenitors in mice. Like many gut endoderm derivatives, embryonic C cells were found to coexpress pioneer factors forkhead box (Fox) a1 and Foxa2 before neuroendocrine differentiation takes place. In the ultimobranchial body epithelium emerging from pharyngeal pouch endoderm in early organogenesis, differential Foxa1/Foxa2 expression distinguished two spatially separated pools of C cell precursors with different growth properties. A similar expression pattern was recapitulated in medullary thyroid carcinoma cells in vivo, consistent with a growth-promoting role of Foxa1. In contrast to embryonic precursor cells, C cell-derived tumor cells invading the stromal compartment downregulated Foxa2, foregoing epithelial-to-mesenchymal transition designated by loss of E-cadherin; both Foxa2 and E-cadherin were re-expressed at metastatic sites. These findings revise mammalian C cell ontogeny, expand the neuroendocrine repertoire of endoderm and redefine the boundaries of neural crest diversification. The data further underpin distinct functions of Foxa1 and Foxa2 in both embryonic and tumor development. Highlighted article: Mouse thyroid C cell precursors arise in foregut endoderm, and not the neural crest, disproving the current concept of a neural crest origin of thyroid neuroendocrine cells.

Expression of Islet1 in thyroid development related to budding, migration, and fusion of primordia

The LIM homeodomain transcription factor Isl1 was investigated in mouse thyroid organogenesis. All progenitor cells of the midline thyroid diverticulum and lateral primordia (ultimobranchial bodies) expressed Isl1. This pattern persisted until the growing anlagen fused at embryonic day (E) 13.5. In Isl1 null mutants thyroid progenitors expressing Nkx2.1 and Pax8 were readily specified in the anterior endoderm but the size of the thyroid rudiment was reduced. In late development, only immature C‐cells expressed Isl1. In the adult gland the number of Isl1+ cells was small compared with cells expressing calcitonin. Analysis of microarray profiles indicated a higher level of Isl1 expression in medullary thyroid carcinomas than in tumors derived from follicular cells. Together, these findings suggest that Isl1 may be a novel regulator of thyroid development before terminal differentiation of the endocrine cell types. Isl1 is an embryonic C‐cell precursor marker that may be relevant also in cancer developed from the mature C‐cell. Developmental Dynamics 237:3820–3829, 2008.

A maternal diet of fatty fish reduces body fat of offspring compared with a maternal diet of beef and a post-weaning diet of fish improves insulin sensitivity and lipid profile in adult C57BL/6 male mice.

The maternal diet during pregnancy and lactation may affect the long‐term health of the offspring. Our aim was to study how a fish or meat diet perinatal and after weaning affects body composition, insulin sensitivity and the profile of n‐3 and n‐6 polyunsaturated fatty acids (PUFAs) in breast milk, fat depots, skeletal muscle and liver in male adult mice offspring.

Lower vitamin D status in obese compared with normal-weight women despite higher vitamin D intake in early pregnancy

BACKGROUND Obesity is associated with lower vitamin D concentrations than normal-weight. Pregnancy may affect vitamin D status, especially in obese subjects. AIMS The purpose of this study was to compare vitamin D status and intake between obese and normal-weight women during pregnancy. METHODS Twenty-five obese and 80 normal-weight women were recruited in the Western Sweden region (latitude 57°N). Blood samples and information on diet and sun exposure were collected in each trimester during pregnancy. RESULTS During summer months, 12% of normal-weight and 50% of obese women in the first trimester had serum 25(OH)D concentrations <50 nmol/L (P < 0.01). Supplement use, body fat mass, season of blood sampling, and travelling to southern latitudes were the most important determinants of vitamin D status. Obese women had higher reported dietary vitamin D intake in early pregnancy compared with normal-weight women. Usage of supplements containing vitamin D was 61% in early pregnancy and declined thereafter. Nine percent of normal-weight and 33% of obese women (P < 0.01) reported a dietary vitamin D intake according to national recommendations in the beginning of pregnancy. CONCLUSIONS Half of the obese women had what could be considered as suboptimal vitamin D status in early pregnancy and lower vitamin D status compared with normal-weight women despite reporting a higher dietary vitamin D intake. A majority of the women did not reach intake of vitamin D according to dietary recommendations.

Role of EphA4 Receptor Signaling in Thyroid Development: Regulation of Folliculogenesis and Propagation of the C-Cell Lineage

Transcriptome analysis revealed that the tyrosine kinase receptor EphA4 is enriched in the thyroid bud in mouse embryos. We used heterozygous EphA4-EGFP knock-in mice in which enhanced green fluorescent protein (EGFP) replaced the intracellular receptor domain (EphA4(+/EGFP)) to localize EphA4 protein in thyroid primordial tissues. This showed that thyroid progenitors originating in the pharyngeal floor express EphA4 at all embryonic stages and when follicles are formed in late development. Also, the ultimobranchial bodies developed from the pharyngeal pouch endoderm express EphA4, but the ultimobranchial epithelium loses the EGFP signal before it merges with the median thyroid primordium. Embryonic C cells invading the thyroid are exclusively EphA4-negative. EphA4 expression continues in the adult thyroid. EphA4 knock-out mice and EphA4-EGFP homozygous mutants are euthyroid and have a normal thyroid anatomy but display subtle histological alterations regarding number, size, and shape of follicles. Of particular interest, the pattern of follicular abnormality differs between EphA4(-/-) and EphA4(EGFP/EGFP) thyroids. In addition, the number of C cells is reduced by >50% exclusively in animals lacking EphA4 forward signaling (EphA4(EGFP/EGFP)). Heterozygous EphA4 mutants have no apparent thyroid phenotype. We conclude that EphA4 is a novel regulator of thyroid morphogenesis that impacts on postnatal development of the two endocrine cell lineages of the differentiating gland. In this process both EphA4 forward signaling (in the follicular epithelium) and reverse signaling mediated by its cognate ligand(s) (A- and/or B-ephrins expressed in follicular cells and C cells, respectively) are probably functionally important.

Misguided Migration of C Cell Precursors to Extra-Thyroidal LocationsRelated to Defective Pharyngeal Pouch Development in Shh DeficientMice

A possible role of sonic hedgehog (Shh) in recruitment of C cell precursors to the Ultimobranchial Body (UB) and embryonic thyroid was investigated in Shh-/- mice. Nkx2.1 and Foxa2 co-expression distinguished UB originating in the fourth pharyngeal pouch from other derivatives of pharyngeal endoderm. In mutants UB formed a single structure that failed to bud and instead of fusing with the midline thyroid primordium adhered to the thymic rudiments. Mature C cells appeared in the UB remnant and ectopically in the thymic parenchyma, foregut endoderm and trachea. Thyroid did not contain C cells except minute numbers close to the tracheal interface. Tracing progeny in Shh-CRE/Rosa26R mice showed the vast majority of both UB and thyroid progenitors derived from Shh negative endoderm, but Shh expressing cells appeared in both thyroid primordia before fusion of the two. The findings indicate that Shh determines the endoderm territory for C cell differentiation and guides the migration of C cell precursors into the thyroid, presumably by regulating the separation of glandular domains in the pharyngeal pouch endoderm. A cell-autonomous role of Shh in thyroid morphogenesis is suggested.

Cerebrospinal fluid levels of insulin, leptin, and agouti-related protein in relation to BMI in pregnant women.

During pregnancy, metabolic interactions must be adapted, though neuroendocrine mechanisms for increased food intake are poorly understood. The objective of this study was to characterize differences in insulin, leptin, and agouti‐related protein (AgRP) levels in serum and cerebrospinal fluid (CSF) in pregnant women with normal weight (NW) and pregnant women with overweight (OW) or obesity (OB). Placenta as a source for increased peripheral AgRP levels during pregnancy was also investigated.

Maternal beef and postweaning herring diets increase bone mineral density and strength in mouse offspring

The maternal diet during gestation and lactation affects the long-term health of the offspring. We sought to determine whether maternal and postweaning crossover isocaloric diets based on fish or meat affect the geometry, mineral density, and biomechanical properties of bone in mouse offspring in adulthood. During gestation and lactation, C57BL/6 dams were fed a herring- or beef-based diet. After weaning, half of the pups in each group were fed the same diet as their dams, and half were fed the other diet. Areal bone mineral density (aBMD) and bone mineral content (BMC) of the whole body and lumbar spine were measured in the offspring by dual X-ray absorptiometry at 9 and 21 weeks of age. At 22–26 weeks, tibia bone geometry (length, cortical volumetric (v) BMD, BMC, area and thickness) was analyzed by peripheral quantitative computed tomography, and the biomechanical properties of the tibia were analyzed by the three-point bending test. Plasma insulin-like growth factor-1 was analyzed at 12 weeks. In comparison to the maternal herring diet, the maternal beef diet increased aBMD and BMC in the whole body and lumbar spine of adult offspring, as well as cortical vBMD, BMC, bone area, and thickness at the mid-diaphyseal region of the tibia and the biomechanical properties of tibia strength. In contrast, a postweaning beef diet decreased aBMD in the lumbar spine and BMC in the whole body and lumbar spine compared with a postweaning herring diet, which instead increased plasma insulin-like growth factor-1 levels. The change from a maternal beef diet before weaning to a herring diet after weaning decreased body weight and increased the cortical area, vBMD, BMC, thickness, and strength of the tibia. These significant crossover effects indicate that a preweaning maternal beef diet and a postweaning herring diet are optimal for increasing BMC and bone strength in offspring in adulthood.