Biomedical subjects

Klaus B Rohr

Publications and source records attributed to Klaus B Rohr.

5 recordsLinked to original sources

PubMed2004

Anatomical and molecular reinvestigation of lamprey endostyle development provides new insight into thyroid gland evolution.

The thyroid gland of vertebrates is considered to be homologous to the endostyle of non-vertebrate chordates (cephalochordates, urochordates), a key character for understanding the origin and evolution of the chordate body plan. In lampreys, the larval endostyle transforms into an adult thyroid gland during metamorphosis, reflecting evolutionary changes that occurred in the vertebrate lineage. Focussing on thyroid-like cells in the endostyle, we here relate morphologically visible steps of lamprey (Lampetra fluviatilis) endostyle differentiation to embryonic stages and determine the onset of thyroid-like function. Analysing lamprey endostyle development using semi-thin histological sections, immunohistochemical detection of thyroid hormone, and the molecular marker thyroid transcription factor1 (Ttf1) refines our current view of the homology between endostyle and thyroid gland. In contrast to earlier literature, we find that a duct always persists to connect the endostyle lumen to the pharynx, a structure that resembles the thyroglossal duct in thyroid development and could further support the homology between endostyle and thyroid. Before the onset of thyroid-like function, Ttf1 expression becomes restricted to the ventral part of the endostyle, on the one hand showing that dorsal thyroid-like cells produce thyroid hormone in the absence of Ttf1, and on the other suggesting that Ttf1 was initially involved in specifying ventral fates in the endostyle.

Amino Acid Sequence↗

PubMed2003

Zebrafish hhex, nk2.1a, and pax2.1 regulate thyroid growth and differentiation downstream of Nodal-dependent transcription factors.

During zebrafish development, the thyroid primordium initiates expression of molecular markers such as hhex and nk2.1a in the endoderm prior to pharynx formation. As expected for an endodermally derived organ, initiation of thyroid development depends on Nodal signalling. We find that it also depends on three downstream effectors of Nodal activity, casanova (cas), bonnie and clyde (bon), and faust (fau)/gata5. Despite their early Nodal-dependent expression in the endoderm, both hhex and nk2.1a are only required relatively late during thyroid development. In hhex and nk2.1a loss-of-function phenotypes, thyroid development is initiated and arrests only after the primordium has evaginated from the pharyngeal epithelium. Thus, like pax2.1, both hhex and nk2.1a have similarly late roles in differentiation or growth of thyroid follicular cells, and here, we show that all three genes act in parallel rather than in a single pathway. Our functional analysis suggests that these genes have similar roles as in mammalian thyroid development, albeit in a different temporal mode of organogenesis.

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PubMed2003

Anterior and posterior waves of cyclic her1 gene expression are differentially regulated in the presomitic mesoderm of zebrafish.

Somite formation in vertebrates depends on a molecular oscillator in the presomitic mesoderm (PSM). In order to get a better insight into how oscillatory expression is achieved in the zebrafish Danio rerio, we have analysed the regulation of her1 and her7, two bHLH genes that are co-expressed in the PSM. Using specific morpholino oligonucleotide mediated inhibition and intron probe in situ hybridisation, we find that her7 is required for initiating the expression in the posterior PSM, while her1 is required to propagate the cyclic expression in the intermediate and anterior PSM. Reporter gene constructs with the her1 upstream sequence driving green fluorescent protein (GFP) expression show that separable regulatory regions can be identified that mediate expression in the posterior versus intermediate and anterior PSM. Our results indicate that the cyclic expression is generated at the transcriptional level and that the resulting mRNAs have a very short half-life. A specific degradation signal for her1 mRNA must be located in the 5'-UTR, as this region also destabilises the GFP mRNA such that it mimics the dynamic pattern of the endogenous her1 mRNA. In contrast to the mRNA, GFP protein is stable and we find that all somitic cells express the protein, proving that her1 mRNA is transiently expressed in all cells of the PSM.

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PubMed2002

Phenylthiourea disrupts thyroid function in developing zebrafish.

Thyroid hormone (T4) can be detected in thyroid follicles in wild-type zebrafish larvae from 3 days of development, when the thyroid has differentiated. In contrast, embryos or larvae treated with goitrogens (substances such as methimazole, potassium percholorate, and 6-n-propyl-2-thiouracil) are devoid of thyroid hormone immunoreactivity. Phenythiourea (PTurea; also commonly known as PTU) is widely used in zebrafish research to suppress pigmentation in developing embryos/fry. PTurea contains a thiocarbamide group that is responsible for goitrogenic activity in methimazole and 6-n-propyl-2-thiouracil. In the present study, we show that commonly used doses of 0.003% PTurea abolish T4 immunoreactivity of the thyroid follicles of zebrafish larvae. As development of the thyroid gland is not affected, these data suggest that PTurea blocks thyroid hormone production. Like other goitrogens, PTurea causes delayed hatching, retardation and malformation of embryos or larvae with increasing doses. At doses of 0.003% PTurea, however, toxic side effects seem to be at a minimum, and the maternal contribution of the hormone might compensate for compromised thyroid function during the first days of development.

Animals↗

PubMed2002

Pax2.1 is required for the development of thyroid follicles in zebrafish.

The thyroid gland is an organ primarily composed of endoderm-derived follicular cells. Although disturbed embryonic development of the thyroid gland leads to congenital hypothyroidism in humans and mammals, the underlying principles of thyroid organogenesis are largely unknown. In this study, we introduce zebrafish as a model to investigate the molecular and genetic mechanisms that control thyroid development. Marker gene expression suggests that the molecular pathways of early thyroid development are essentially conserved between fish and mammals. However during larval stages, we find both conserved and divergent features of development compared with mammals. A major difference is that in fish, we find evidence for hormone production not only in thyroid follicular cells, but also in an anterior non-follicular group of cells. We show that pax2.1 and pax8, members of the zebrafish pax2/5/8 paralogue group, are expressed in the thyroid primordium. Whereas in mice, only Pax8 has a function during thyroid development, analysis of the zebrafish pax2.1 mutant no isthmus (noi(-/-)) demonstrates that pax2.1 has a role comparable with mouse Pax8 in differentiation of the thyroid follicular cells. Early steps of thyroid development are normal in noi(-/-), but later expression of molecular markers is lost and the formation of follicles fails. Interestingly, the anterior non-follicular site of thyroid hormone production is not affected in noi(-/-). Thus, in zebrafish, some remaining thyroid hormone synthesis takes place independent of the pathway leading to thyroid follicle formation. We suggest that the noi(-/-) mutant serves as a new zebrafish model for hypothyroidism.

Animals↗