The role of Nodal-dependent transcription factors and blood vessels in the development of the zebrafish thyroid gland

Abstract The thyroid gland is an endocrine organ primarily composed of endoderm-derived cells. During embryonic development, the thyroid primordium evaginates from its site of induction in the pharyngeal endoderm, relocating to a final position deep in the hypopharyngeal mesoderm. In this study, I investigate molecular and genetic mechanisms that control thyroid development. My work can be separated into two parts, the first one dealing with the requirement of thyroid-autonomously acting transcription factors for differentiation, the second one giving first insights into a role of blood vessels in thyroid morphogenesis. As expected for an endoderm-derived organ, initiation of thyroid development depends on Nodal signaling, which is a key component in endoderm formation. More specifically, I find that this initiation depends on three endoderm-specific downstream effectors of Nodal activity, casanova (cas), bonnie and clyde (bon), and faust (fau)/gata5. In thyroid progenitor cells initiate expression of the genes encoding thyroid-specific transcription factors such as Hhex and Nk2.1a starts already in the endoderm prior to pharynx formation. However, despite their early Nodal-dependent expression in the endoderm, both hhex and nk2.1a are required only relatively late during thyroid differentiation. Although abnormal positioning of the developing thyroid gland is a well known, frequently occurring cause of reduced thyroid function in newborn humans, the molecular mechanisms that are responsible for proper thyroid positioning remain largely unknown. In the second part of my thesis, I investigate zebrafish mutants with defects in blood vessel development. I find that vessel and thyroid development is linked via several molecular pathways such as Hedgehog and Vegf signalling, showing for the first time an influence of vessels on thyroid morphology

Maternal thyroid hormones are essential for neural development in Zebrafish

Teleost eggs contain an abundant store of maternal thyroid hormones (THs), and early in zebrafish embryonic development, all the genes necessary for TH signaling are expressed. Nonetheless the function of THs in embryonic development remains elusive. To test the hypothesis that THs are fundamental for zebrafish embryonic development, an monocarboxilic transporter 8 (Mct8) knockdown strategy was deployed to prevent maternal TH uptake. Absence of maternal THs did not affect early specification of the neural epithelia but profoundly modified later dorsal specification of the brain and spinal cord as well as specific neuron differentiation. Maternal THs acted upstream of pax2a, pax7, and pax8 genes but downstream of shha and fgf8a signaling. The lack of inhibitory spinal cord interneurons and increased motoneurons in the mct8 morphants is consistent with their stiff axial body and impaired mobility. The mct8 mutations are associated with X-linked mental retardation in humans, and the cellular and molecular consequences of MCT8 knockdown during embryonic development in zebrafish provides new insight into the potential role of THs in this condition.Portuguese Science Foundation (FCT) [PTDC/MAR/115005/2009]; FCT [SFRH/BPD/66808/2009, SFRH/BPD/67008/2009, Pest-OE/EQB/LA0023/2013]info:eu-repo/semantics/publishedVersio

Phenothiourea Sensitizes Zebrafish Cranial Neural Crest and Extraocular Muscle Development to Changes in Retinoic Acid and IGF Signaling

1-phenyl 2-thiourea (PTU) is a tyrosinase inhibitor commonly used to block pigmentation and aid visualization of zebrafish development. At the standard concentration of 0.003% (200 µM), PTU inhibits melanogenesis and reportedly has minimal other effects on zebrafish embryogenesis. We found that 0.003% PTU altered retinoic acid and insulin-like growth factor (IGF) regulation of neural crest and mesodermal components of craniofacial development. Reduction of retinoic acid synthesis by the pan-aldehyde dehydrogenase inhibitor diethylbenzaldehyde, only when combined with 0.003% PTU, resulted in extraocular muscle disorganization. PTU also decreased retinoic acid-induced teratogenic effects on pharyngeal arch and jaw cartilage despite morphologically normal appearing PTU-treated controls. Furthermore, 0.003% PTU in combination with inhibition of IGF signaling through either morpholino knockdown or pharmacologic inhibition of tyrosine kinase receptor phosphorylation, disrupted jaw development and extraocular muscle organization. PTU in and of itself inhibited neural crest development at higher concentrations (0.03%) and had the greatest inhibitory effect when added prior to 22 hours post fertilization (hpf). Addition of 0.003% PTU between 4 and 20 hpf decreased thyroxine (T4) in thyroid follicles in the nasopharynx of 96 hpf embryos. Treatment with exogenous triiodothyronine (T3) and T4 improved, but did not completely rescue, PTU-induced neural crest defects. Thus, PTU should be used with caution when studying zebrafish embryogenesis as it alters the threshold of different signaling pathways important during craniofacial development. The effects of PTU on neural crest development are partially caused by thyroid hormone signaling

Phenylthiourea Specifically Reduces Zebrafish Eye Size

Phenylthiourea (PTU) is commonly used for inhibiting melanization of zebrafish embryos. In this study, the standard treatment with 0.2 mM PTU was demonstrated to specifically reduce eye size in larval fish starting at three days post-fertilization. This effect is likely the result of a reduction in retinal and lens size of PTU-treated eyes and is not related to melanization inhibition. This is because the eye size of tyr, a genetic mutant of tyrosinase whose activity is inhibited in PTU treatment, was not reduced. As PTU contains a thiocarbamide group which is presented in many goitrogens, suppressing thyroid hormone production is a possible mechanism by which PTU treatment may reduce eye size. Despite the fact that thyroxine level was found to be reduced in PTU-treated larvae, thyroid hormone supplements did not rescue the eye size reduction. Instead, treating embryos with six goitrogens, including inhibitors of thyroid peroxidase (TPO) and sodium-iodide symporter (NIS), suggested an alternative possibility. Specifically, three TPO inhibitors, including those that do not possess thiocarbamide, specifically reduced eye size; whereas none of the NIS inhibitors could elicit this effect. These observations indicate that TPO inhibition rather than a general suppression of thyroid hormone synthesis is likely the underlying cause of PTU-induced eye size reduction. Furthermore, the tissue-specific effect of PTU treatment might be mediated by an eye-specific TPO expression. Compared with treatment with other tyrosinase inhibitors or bleaching to remove melanization, PTU treatment remains the most effective approach. Thus, one should use caution when interpreting results that are obtained from PTU-treated embryos

Pengaruh Kepemilikan Manajerial, Kebijakan Deviden, Profitabilitas, dan Struktur Aset Terhadap Kebijakan Hutang (Studi Kasus pada Perusahaan Manufaktur yang Terdaftar di Bursa Efek Indonesia Tahun 2013-2015)

The purpose of this study was to investigate the managerial ownership,dividend policy, profitability, Assetes Structure to corporate debt policy. This study focused on manufacturing companies listed in Bursa Efek Indonesia for period 2013-2015. This study design is associative causal method.Popolasi research include a manufacturing company that has been and is still listed in the period 2013-2015. This study used purposive sampling method in order to collect the sample. Based on certain criteria, number of manufacturing companies sample is 31 companies with observations for 3 years the total sample was 141 financial statement . The statistical method used in this study was multiple regression. The result of this study showed that managerial ownership has the positive (0,254) and un-significant (0,056) effect to corporate debt policy. Dividend policy has the negative (-0,041) and and un-significant (0,383) effect to corporate debt policy. Profitability has the negative (-1,147) and significant (0,009) effect to corporate debt policy. Assets Structure has the positive (0,032) and un-significant (0,857) effect to corporate debt policy The simultaneous testing showed that managerial ownership,dividend policy, profitability, Assetes Structure were influenced to corporate debt policy with count F value (3,005) and significant (0,022). The formula of the multiple regression was : Y = 0,568 + 0,254MOWN – 0,041DPR – 1,147ROA+ 0,032AS+ePenelitian ini bertujuan untuk membuktikan pengaruh Kepemilikan Manajerial, Kebijakan Dividen, Profitabilitas, dan Struktur Aset secara parsial maupun simultan terhadap Kebijakan Utang pada perusahaan manufaktur yang terdaftar di Bursa Efek Indonesia. Periode yang digunakan dalam penelitian ini adalah 3 (tiga) tahun, mulai dari tahun 2013 -2015. Desain penelitian ini adalah penelitian asosiatif kausal. Populasi penelitian meliputi perusahaan manufaktur yang sudah dan masih terdaftar di Bursa Efek Indonesia periode 2013-2015. Teknik pengambilan sampel yang digunakan adalah purposive sampling, dan berdasarkan criteria yang ada, diperoleh sebanyak 31 unit observasi dari 141 perusahaan sampel. Metode analisis data yang digunakan adalah regresi linier berganda. Berdasarkan hasil analisis data, Kepemilikan Manajerial tidak berpengaruh terhadap Kebijakan Utang perusahaan dibuktikan dengan nilai beta coefficient sebesar 0,254 pada nilai signifikansi 0,056. Kebijakan Dividen tidak berpengaruh terhadap Kebijakan Utang perusahaan dibuktikan dengan nilai beta coefficient sebesar -0,041 pada nilai signifikansi 0,383. Profitabilitas berpengaruh negatif dan signifikan terhadap Kebijakan Utang perusahaan dibuktikan dengan nilai beta coefficient sebesar -1,147 pada nilai signifikansi 0,009. Struktur Aset tidak berpengaruh terhadap Kebijakan Utang perusahaan dibuktikan dengan nilai beta coefficient sebesar 0,032 pada nilai signifikansi 0,857. Secara simultan Kepemilikan Manajerial, Kebijakan Dividen, Profitabilitas, dan Struktur Aset berpengaruh terhadap Kebijakan Utang, hal ini dibuktikan dengan nilai F hitung sebesar 3,005 pada nilai signifikansi sebesar 0,022. Persamaan regresi linier berganda pada penelitian ini dirumuskan menjadi : Y = 0,568 + 0,254MOWN – 0,041DPR – 1,147ROA+ 0,032AS+e93 HalamanSkripsi Sarjan

A record of bluespotted cornetfish, Fistularia commersonii (Actinopterygii: Syngnathiformes: Fistulariidae), off the coast of Benghazi, Libya (southern Mediterranean)

The first record of bluespotted cornetfish Fistularia commersonii Rüppell, 1835, (Fistulariidae) from the depth of 30 m, caught off the coast of Benghazi, Libya (Southern Mediterranean), is reported herewith

A record of bluespotted cornetfish, Fistularia commersonii (Actinopterygii: Syngnathiformes: Fistulariidae), off the coast of Benghazi, Libya (southern Mediterranean)

The first record of bluespotted cornetfish Fistularia commersonii Rüppell, 1835, (Fistulariidae) from the depth of 30 m, caught off the coast of Benghazi, Libya (Southern Mediterranean), is reported herewith