Chronic administration of estradiol produces a triphasic effect on serum concentrations of gonadotropins and messenger ribonucleic acid for gonadotropin subunits, but not on pituitary content of gonadotropins, in ovariectomized ewes

To determine the acute and chronic effects of estradiol on synthesis and secretion of LH and FSH, ovariectomized ewes were administered estradiol via silastic capsules for 0 h, 12 h, 1 day, 2 days, 4 days, 8 days, 16 days, or 32 days (n = 5/group). Concentrations of GnRH in the median eminence began to decrease within 12 h and were lower (p less than 0.05) than in control ewes from 1 to 4 days after estradiol administration was begun. Serum concentrations of LH were decreased relative to pretreatment control levels from 1 to 10 h, elevated during a preovulatory-like surge from 11 to 22 h, and then decreased and remained below 1 ng/ml for the duration of the experiment. Serum concentrations of FSH followed a pattern similar to those for LH except that the magnitude of change was smaller. Treatment with estradiol initially (12 h) reduced (p less than 0.05) quantities of mRNA for alpha-, LH beta-, and FSH beta-subunits, after which the quantities of mRNA for the subunits returned to near or above control levels by Day 2. After 8 days of treatment the amounts of mRNAs for gonadotropin subunits were again less (p less than 0.05) than those of controls, and they remained suppressed through Day 32. Pituitary concentrations of LH and FSH decreased (p less than 0.05) during the first day of treatment and remained suppressed for the duration of the experiment. Thus, estradiol had a triphasic effect on secretion of gonadotropins and steady-state levels of mRNA for the gonadotropin subunits, but not on pituitary content of gonadotropins.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional analysis of Asb-1 using genetic modification in mice

The Asbs are a family of ankyrin repeat proteins that, along with four other protein families, contain a C-terminal SOCS box motif, which was first identified in the suppressor of cytokine signaling (SOCS) proteins. While it is clear that the SOCS proteins are involved in the negative regulation of cytokine signaling, the biological roles of the other SOCS box-containing families are unknown. We have investigated Asb-1 function by generating mice that lack this protein, as well as mice that overexpress full-length or truncated Asb-1 in a wide range of tissues. Although Asb-1 is expressed in multiple organs, including the hematopoietic compartment in wild-type mice, Asb-1(-/-) mice develop normally and exhibit no anomalies of mature blood cells or their progenitors. While most organs in these mice appear normal, the testes of Asb-1(-/-) mice display a diminution of spermatogenesis with less complete filling of seminiferous tubules. In contrast, the widespread overexpression of Asb-1 in the mouse has no apparent deleterious effects.     

Agm1/Pgm3-mediated sugar nucleotide synthesis is essential for hematopoiesis and development

Carbohydrate modification of proteins includes N-linked and O-linked glycosylation, proteoglycan formation, glycosylphosphatidylinositol anchor synthesis, and O-GlcNAc modification. Each of these modifications requires the sugar nucleotide UDP-GlcNAc, which is produced via the hexosamine biosynthesis pathway. A key step in this pathway is the interconversion of GlcNAc-6-phosphate (GlcNAc-6-P) and GlcNAc-1-P, catalyzed by phosphoglucomutase 3 (Pgm3). In this paper, we describe two hypomorphic alleles of mouse Pgm3 and show there are specific physiological consequences of a graded reduction in Pgm3 activity and global UDP-GlcNAc levels. Whereas mice lacking Pgm3 die prior to implantation, animals with less severe reductions in enzyme activity are sterile, exhibit changes in pancreatic architecture, and are anemic, leukopenic, and thrombocytopenic. These phenotypes are accompanied by specific rather than wholesale changes in protein glycosylation, suggesting that while universally required, the functions of certain proteins and, as a consequence, certain cell types are especially sensitive to reductions in Pgm3 activity.     

A new mouse model of Canavan leukodystrophy displays hearing impairment due to central nervous system dysmyelination

Canavan disease is a leukodystrophy caused by mutations in the ASPA gene. This gene encodes the enzyme that converts N-acetylaspartate into acetate and aspartic acid. In Canavan disease, spongiform encephalopathy of the brain causes progressive mental retardation, motor deficit and death. We have isolated a mouse with a novel ethylnitrosourea-induced mutation in Aspa. This mutant, named deaf14, carries a c.516T>A mutation that is predicted to cause a p.Y172X protein truncation. No full-length ASPA protein is produced in deaf14 brain and there is extensive spongy degeneration. Interestingly, we found that deaf14 mice have an attenuated startle in response to loud noise. The first auditory brainstem response peak has normal latency and amplitude but peaks II, III, IV and V have increased latency and decreased amplitude in deaf14 mice. Our work reveals a hitherto unappreciated pathology in a mouse model of Canavan disease, implying that auditory brainstem response testing could be used in diagnosis and to monitor the progression of this disease.KEY WORDS: Canavan disease, Aspa, Aspartoacylase, Leukodystrophy, ENU mutagenesis, Myelin     

Glycogen utilization in rat respiratory muscles during intense running

Glycogen concentration in the adult rat diaphragm and intercostal muscles has been examined following heavy treadmill exercise to determine the recruitment strategy and the significance of glycogen as a substrate to satisfy the elevated energy requirements accompanying hyperpnea. Short-term continuous running at 60 m/min and a 12 degree grade resulted in a reduction (p less than 0.05) in the concentration of glycogen (39%) in the costal region of the rat diaphragm. Similarly, glycogen concentration was significantly reduced (p less than 0.05) with this exercise protocol in all respiratory muscles studied, with the exception of the sternal region of the diaphragm. With the less intense running protocols, glycogen degradation continued to be pronounced (p less than 0.05) in the majority of the respiratory muscles sampled. The significance of muscle glycogen as a substrate for energy metabolism in the respiratory muscles was not affected by the procedure used to prepare the animal for tissue sampling (Somnitol, diethyl ether, decapitation). Examination of selected locomotor muscles revealed extensive glycogen loss in muscles composed of essentially slow oxidative fibres (soleus), fast oxidative glycolytic fibres (vastus lateralis red), and fast glycolytic fibres (vastus lateralis white). It is concluded that during heavy exercise in the rat, recruitment of motor units occurs in all regions of the diaphragm and in the intercostal muscles. At least for the costal region of the diaphragm and as evidenced by the modest (two- to four-fold) but significant (p less than 0.05) increases in lactate concentration, the increased ATP requirements in these muscles are met to a large degree by increases in aerobic metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)