Revised genomic consensus for the hypermethylated CpG island region of the human L1 transposon and integration sites of full length L1 elements from recombinant clones made using methylation-tolerant host strains.

Efficient recovery of clones from the 5' end of the human L1 dispersed repetitive elements necessitates the use of deletion mcr- host strains since this region contains a CpG island which is hypermethylated in vivo. Clones recovered with conventional mcr+ hosts seem to have been derived preferentially from L1 members which have accumulated mutations that have removed sites of methylation. We present a revised consensus from the 5' presumptive control region of these elements. This revised consensus contains a consensus RNA polymerase III promoter which would permit the synthesis of transcripts from the 5' end of full length L1 elements. Such potential transcripts are likely to exhibit a high degree of secondary structure. In addition, we have determined the flanking sequences for 6 full length L1 elements. The majority of full length L1 clones show no convincing evidence for target site duplication in the insertion site as commonly observed with truncated L1 elements. These data would be consistent with two mechanisms of integration of transposing L1 elements with different mechanisms predominating for full length and truncated elements

Serotonin via 5-HT1B and 5-HT2B receptors stimulates anion secretion in the rat epididymal epithelium

The short-circuit current (Isc) technique was used to study the role of 5-hydroxytryptamine (5-HT) in the regulation of anion secretion in cultured rat cauda epididymal epithelia.5-HT, the 5-HT1B-selective agonist 5-nonyloxytryptamine (5-NOT) and the 5-HT2B-selective agonist α-methyl-5-hydroxytryptamine (α-methyl-5-HT) added basolaterally stimulated Isc in a dose-dependent manner with EC50 values of 0.4, 20 and 0.3 μm, respectively. No other agonists for 5-HT receptors had any effect.The pattern of responses to 5-HT was biphasic. Pretreating the tissues with the 5-HT1B-selective antagonist isamoltane (200 μm) and the 5-HT2B-selective antagonist rauwolscine (200 μm) inhibited the rapid transient phase by 55 and 45 %, whereas the sustained phase could only be blocked by rauwolscine.Removal of chloride or bicarbonate or both from the normal Krebs-Henseleit solution reduced the responses to 5-HT, 5-NOT and α-methyl-5-HT to varying degrees. The results suggest that 5-HT1B- and 5-HT2B-mediated responses were mainly due to chloride and bicarbonate secretion, respectively.Manipulation of the cAMP and Ca2+ signal transduction pathways with chemical agents provided evidence that the responses to 5-HT were mediated through cAMP.Piroxicam pretreatment abolished the Isc response to α-methyl-5-HT but not to 5-NOT, indicating that the 5-HT2B-mediated response, but not the 5-HT1B-mediated response, is dependent on prostaglandin synthesis.Immunohistochemical studies showed that 5-HT-like immunoreactivity was detected in nerve fibres and in small granular cells surrounding the epididymal tubules.It is suggested that the 5-HT released from serotonergic nerve endings and/or from mast cells regulates electrolyte and fluid secretion in the epididymis