Northern blot of long transcripts

[Daigoro]

Hi everyone!
Technically is there any problem with Northern blot for long transcripts, let say over 7 kp? Do we have to do some sort of treatment like when we do Southern for large DNA fragments (HCl treatment)?
We have cloned full sequences of 4 genes and now we wanna study their expression. But we have failed to obtain any signal from all of these genes by Northern blot. Their sizes are around 7 to 10 kb and their mRNA sizes are approx. 6 to 9 kb.
Thanks!

[Rainbird]

I haven't done Northerns of long transcripts before, but I'm curious, have you confirmed their expression by qPCR?

EDIT:
Also, a quick check on Ji, et. al., (2003) showed that they were able to detect MALAT-1 (~8kb) on a northern, and don't seem to use anything special.
"..10 mg of (total RNA) was subjected to electrophoresis and Northern blotting. MALAT-1 was hybridized with a digoxygenin-labeled RNA probe of 800 nt cloned from the RACE reaction for MALAT-1.."

You could try remaking your probes to have multiple concatenated target binding sites? (source: hearsay, it apparently improved signal multi-fold)

[mchlbrmn]

I don't remember details, but you might check whether a lower % gel might transfer better.