Role of thyroid hormones in tilapia larvae (Oreochromis mossambicus): II. Changes in the hormones and 5′-monodeiodinase activity during development

10.1007/BF02274229Fish Physiology and Biochemistry95-6487-496FPBI

Hepatic 5′-monodeiodinase activity in teleosts in vitro: A survey of thirty-three species

10.1007/BF00004426Fish Physiology and Biochemistry811-10FPBI

A qualitative account of discrete space

Abstract. Computations in geographic space are necessarily based on discrete versions of space, but much of the existing work on the foundations of GIS assumes a continuous infinitely divisible space. This is true both of quantitative approaches, using R n, and qualitative approaches using systems such as the Region-Connection Calculus (RCC). This paper shows how the RCC can be modified so as to permit discrete spaces by weakening Stell’s formulation of RCC as Boolean connection algebra to what we now call a connection algebra. We show how what was previously considered a problem—with atomic regions being parts of their complements—can be resolved, but there are still obstacles to the interplay between parthood and connection when there are finitely many regions. Connection algebras allow regions that are atomic and also regions that are boundaries of other regions. The modification of the definitions of the RCC5 and RCC8 relations needed in the context of a connection algebra are discussed. Concrete examples of connection algebras are provided by abstract cell complexes. In order to place our work in context we start with a survey of previous approaches to discrete space in GIS and related areas.

The Type 3 Deiodinase is a Critical Determinant of Appropriate Thyroid Hormone Action in the Developing Testis

Timely and appropriate levels of thyroid hormone (TH) signaling are necessary to ensure normal developmental outcomes in many tissues. Studies using pharmacological models of altered TH status have revealed an influence of these hormones on testis development and size, but little is known about the role of endogenous determinants of TH action in the developing male gonads. Using a genetic approach, we demonstrate that the type 3 deiodinase (D3), which inactivates TH and protects developing tissues from undue TH action, is a key factor. D3 is highly expressed in the developing testis, and D3-deficient (D3KO) mice exhibit thyrotoxicosis and cell proliferation arrest in the neonatal testis, resulting in an approximately 75% reduction in testis size. This is accompanied by larger seminiferous tubules, impaired spermatogenesis and a hormonal profile indicative of primary hypogonadism. A deficiency in the TH receptor alpha (TR1) fully normalizes testis size and adult testis gene expression in D3KO mice, indicating that the effects of D3 deficiency are mediated through this type of receptor. Similarly, genetic deficiencies in the type 2 deiodinase (D2) or in the monocarboxylate transporter 8 (MCT8) partially rescue the abnormalities in testis size and gonadal axis gene expression featured in the D3KO mice. Our study highlights the testis as an important tissue in which determinants of TH action coordinately converge to ensure normal development, and identifiesD3as a critical factor in testis development and in testicular protection from thyrotoxicosis