6 research outputs found
Activins and activin receptors in the rat testis
Inhibin and activin are gonadal protein hormones, which were originally
defined by their negative and positive feedback action on the release of follicle
stimulating hormone (FSH) from the pituitary gland. However, recent studies
revealed that inhibin and activin do not only control FSH release but can also affect
the functions of a large number of other cell types, as will be discussed in section
1.7. This section is preceded by short descriptions of the testicular cell types
(section 1.2), the structures of inhibins, activins and other members of the TGF·-B
family of growth and differentiation factors (sections 1.3 and 1.4), and of receptors
and non-receptor binding proteins for inhibin and activin (sections 1.6 and 1.7).
Finally, events occurring after binding of activin to its receptor are discussed in
section 1.8.
The aim of the experiments described in this thesis was the elucidation of
intratesticular effects of activin. The expression of activin receptors, the secretion of
activins and the effects of activins in the rat testis have been investigated
Activin is produced by rat Sertoli cells in vitro and can act as an autocrine regulator of Sertoli cell function
Regulation of androgen receptor (AR) mRNA expression was studied in
Sertoli cells and peritubular myoid cells isolated from immature rat
testis, and in the lymph node carcinoma cell line derived from a human
prostate (LNCaP). Addition of dibutyryl-cyclic AMP (dbcAMP) to Sertoli
cell cultures resulted in a rapid transient decrease in AR mRNA expression
(5 h), which was followed by a gradual increase in AR mRNA expression
(24-72 h). This effect of dbcAMP mimicked follicle-stimulating hormone
(FSH) action. In peritubular myoid cells, there was only a moderate but
prolonged decrease during incubation in the presence of dbcAMP, and in
LNCaP cells no effect of dbcAMP on AR mRNA expression was observed. When
Sertoli cells or peritubular myoid cells were cultured in the presence of
androgens, AR mRNA expression in these cell types did not change. This is
in contrast to LNCaP cells, that showed a marked reduction of AR mRNA
expression during androgen treatment. In the present experiments,
transcriptional regulation of AR gene expression in Sertoli cells and
LNCaP cells was also examined. Freshly isolated Sertoli cell clusters were
transfected with a series of luciferase reporter gene constructs, driven
by the AR promoter. It was found that addition of dbcAMP to the
transfected Sertoli cells resulted in a small but consistent increase in
reporter gene expression (which was interpreted as resulting from AR
promoter activity); a construct that only contained the AR 5' untranslated
region of the cDNA sequence did not show such a regulation. The same
constructs, transfected into LNCaP cells, did not show any transcriptional
down-regulation when the synthetic androgen R1881 was added to the cell
cultures. A nuclear transcription elongation experiment (run-on), however,
demonstrated that androgen-induced AR mRNA down-regulation in LNCaP cells
resulted from an inhibition of AR gene transcription. The present results
indicate that in Sertoli cells and LNCaP cells, hormonal effects on AR
gene transcription play a role in regulation of AR expression. However, AR
gene transcription in these cells is differentially regulated
Inhibin interferes with activin signaling at the level of the activin receptor complex in Chinese hamster ovary cells
To gain more insight in the mechanism of action of inhibin, we studied the
effect of inhibin on activin signaling in Chinese hamster ovary cells.
Inhibin specifically counteracted activin-induced expression of a
plasminogen activator inhibitor 1 promoter element (3TP) and of the junB
gene, but was ineffective when the responses were induced by transforming
growth factor-beta. This indicates that inhibin acts only on the
activin-specific part of these signaling cascades. Using a constitutively
active activin type IB receptor we determined whether inhibin acted at the
level of the activin-receptor complex or downstream of it. The mutant
activin receptor stimulated the expression of the 3TP promoter in the
absence of activin. This stimulation was insensitive to inhibin
A novel member of the transmembrane serine/threonine kinase receptor family is specifically expressed in the gonads and in mesenchymal cells adjacent to the mullerian duct
The activin and TGF-beta type II receptors are members of a separate
subfamily of transmembrane receptors with intrinsic protein kinase
activity, wh
Dysfunctional sarcomere contractility contributes to muscle weakness in ACTA1-related nemaline myopathy (NEM3)
Objective: Nemaline myopathy (NM) is one of the most common congenital nondystrophic myopathies and is characterized by muscle weakness, often from birth. Mutations in ACTA1 are a frequent cause of NM (ie, NEM3). ACTA1 encodes alpha-actin 1, the main constituent of the sarcomeric thin filament. The mechanisms by which mutations in ACTA1 contribute to muscle weakness in NEM3 are incompletely understood. We hypothesized that sarcomeric dysfunction contributes to muscle weakness in NEM3 patients. Methods: To test this hypothesis, we performed contractility measurements in individual muscle fibers and myofibrils obtained from muscle biopsies of 14 NEM3 patients with different ACTA1 mutations. To identify the structural basis for impaired contractility, low angle X-ray diffraction and stimulated emission-depletion microscopy were applied. Results: Our findings reveal that muscle fibers of NEM3 patients display a reduced maximal force-generating capacity, which is caused by dysfunctional sarcomere contractility in the majority of patients, as revealed by contractility measurements in myofibrils. Low angle X-ray diffraction and stimulated emission-depletion microscopy indicate that dysfunctional sarcomere contractility in NEM3 patients involves a lower number of myosin heads binding to actin during muscle activation. This lower number is not the result of reduced thin filament length. Interestingly, the calcium sensitivity of force is unaffected in some patients, but decreased in others. Interpretation: Dysfunctional sarcomere contractility is an important contributor to muscle weakness in the majority of NEM3 patients. This information is crucial for patient stratification in future clinical trials. Ann Neurol 2018;83:269–282