Lampbrush Chromosomes and Fragile X Mental Retardation Protein, FMRP

Fragile X Syndrome is the most common form of inherited mental retardation, occurring in 1/4000 males and 1/8000 females. This syndrome is caused by the lack of expression of the Fragile X mental retardation protein, or FMRP. FMRP is an RNA binding protein, involved in translational regulation of specific mRNA messages. However it is still relatively unknown where FMRP binds its mRNA cargo. Here we show endogenous FMRP associating with nascent transcripts along the actively transcribed loops of a Xenopus laevis oocyte chromosome. Nuclei were isolated from oocytes and prepared for fluorescence microscopy by fixing onto glass slides. Panels A and B show a phase contrast image of the chromosomes followed by fluorescent imaging where red is a DAPI stain for nucleic acid and green is FMRP. Panels C and D show a magnification of one especially large loop of single stranded DNA extending from the double stranded DNA axis. The scale bar represents 2 mm.