A gonadotropin releasing hormone analog induces spermiation in intact and hypophysectomized frogs, Rana esculenta

The sperm-releasing activity of a gonadotropin releasing hormone (GnRH) agonist, Buserelin (GnRH) and hypophysis homogenate (PD) preparations was studied in intact and hypophysectomized (PDX) frogs, Rana esculenta. In addition, human chorion gonadotropin (hCG) was tested in PDX animals, and GnRH antagonist (GnRHA) treatments were carried out in intact and PDX animals, in combination with the hormonal injections. GnRH or PD treatments were able to elicit spermiation in intact and PDX animals. While GnRH, injected 24 h later, was again effective in inducing spermiation in intact animals, this was not the case in PDX frogs. GnRHA counteracted GnRH effects in intact frogs. Moreover, in PDX animals GnRHA injections counteracted the sperm-releasing activity induced by hCG or GnRH, but failed to inhibit sperm-releasing activity induced by PD homogenate.     

The control of the frog (Rana esculenta) thumb pad

Summary Extirpation of the pars distalis of the pituitary or castration in any period of the year cause thumb pad regression. Thumb pad development is regulated by an interaction of both temperature and androgenic hormones.Work done under the C.N.R.-finalized project Biologia della Riproduzione.     

Low density lipoprotein receptor-related protein 1 couples β1 integrin activation to degradation

Low density lipoprotein receptor-related protein (LRP) 1 modulates cell adhesion and motility under normal and pathological conditions. Previous studies documented that LRP1 binds several integrin receptors and mediates their trafficking to the cell surface and endocytosis. However, the mechanism by which LRP1 may regulate integrin activation remains unknown. Here we report that LRP1 promotes the activation and subsequent degradation of β1 integrin and thus supports cell adhesion, spreading, migration and integrin signaling on fibronectin. LRP1 interacts with surface β1 integrin, binds the integrin activator kindlin2 and stimulates β1 integrin–kindlin2 complex formation. Specifically, serine 76 in the LRP1 cytoplasmic tail is crucial for the interaction with kindlin2, β1 integrin activation and cell adhesion. Interestingly, a loss of LRP1 induces the accumulation of several integrin receptors on the cell surface. Following internalization, intracellular trafficking of integrins is driven by LRP1 in a protein kinase C- and class II myosin-dependent manner. Ultimately, LRP1 dictates the fate of endocytosed β1 integrin by directing it down the pathway of lysosomal and proteasomal degradation. We propose that LRP1 mediates cell adhesion by orchestrating a multi-protein pathway to activate, traffic and degrade integrins. Thus, LRP1 may serve as a focal point in the integrin quality control system to ensure a firm connection to the extracellular matrix.     

Influence of photoperiodism on high temperature-induced testicular recrudescence in the green frog

Summary In connection with the circannual testicular rhythmRana esculenta does not seem to be a strictly photoperiodic species. In fact testicular growth can be induced (at a favourable temperature) with a daily 2-h light pulse as well as with a daily 12-h light pulse.Work done under the CNR-finalized project Biologia della Riproduzione.     

HDACs link the DNA damage response, processing of double-strand breaks and autophagy

Protein acetylation is mediated by histone acetyltransferases (HATs) and deacetylases (HDACs), which influence chromatin dynamics, protein turnover and the DNA damage response. ATM and ATR mediate DNA damage checkpoints by sensing double-strand breaks and single-strand-DNA-RFA nucleofilaments, respectively. However, it is unclear how acetylation modulates the DNA damage response. Here we show that HDAC inhibition/ablation specifically counteracts yeast Mec1 (orthologue of human ATR) activation, double-strand-break processing and single-strand-DNA-RFA nucleofilament formation. Moreover, the recombination protein Sae2 (human CtIP) is acetylated and degraded after HDAC inhibition. Two HDACs, Hda1 and Rpd3, and one HAT, Gcn5, have key roles in these processes. We also find that HDAC inhibition triggers Sae2 degradation by promoting autophagy that affects the DNA damage sensitivity of hda1 and rpd3 mutants. Rapamycin, which stimulates autophagy by inhibiting Tor, also causes Sae2 degradation. We propose that Rpd3, Hda1 and Gcn5 control chromosome stability by coordinating the ATR checkpoint and double-strand-break processing with autophagy.     

Dopamine regulation of testicular activity in intact and hypophysectomized frogs,Rana esculenta

In intact frogs, both GnRHA and L-dopa were able to increase testicular and plasma androgen levels and to induce spermiation. The dopamine antagonist pimozide inhibited both the effects of L-dopa but not those of GnRHa. Hypophysectomy reduced androgen levels, but spermiation was still induced by both GnRHa and L-dopa, suggesting that these agents can directly influence the testis through a route not involving the pars distalis. Again, pimozide antagonised spermiation induced by L-dopa but not that induced by GnRHa.This work was supported (40% and 60%) by the Italian Ministry of Education and the C.N.R. Special Project.