Embryonic and tissue-specific regulation of myostatin-1 and -2 gene expression in zebrafish

Deri Lila Icenoggle Helterline

Myostatin is a member of the TGF-[Beta] superfamily and a potent negative regulator of muscle growth and development in mammals, where its expression is limited primarily to skeletal muscle. Conversely, myostatin expression occurs in many different fish tissues suggesting alternative functional roles in these vertebrates, although quantitative measurements of the embryonic and tissue-specific expression profiles in fish are lacking. A recent phylogenetic analysis of all known myostatin genes led to the discovery of a novel paralogue in zebrafish, zfMSTN-2, and the reclassification of the entire subfamily to include MSTN-1 and -2 sister clades in the boney fishes. The differential expression of both genes was therefore determined using custom RNA panels generated from pooled (100-150/sampling) embryos at different stages of development and from individual adult tissues. High levels of both transcripts were present at the blastula stage, but quickly dropped to almost undetectable levels throughout gastrulation (7 hpf). Levels of zfMSTN-2 peaked with an initial 5-fold increase during early somitogenesis (11 hpf), returned to basal levels during late somitogenesis and did not begin to rise again until hatching (72 hpf). By contrast, zfMSTN-1 mRNA levels increased 30-fold during late somitogenesis (15.5-19 hpf) returned to baseline at 21.5 hpf and eventually rose 25-fold by 72 hpf. In adults, both transcripts were present in a wide variety of tissues. Although this distribution is similar to that previously described in zebrafish and other fish species, it includes additional tissues not previously known to express myostatin, including the spleen. Expression of zfMSTN-1 was highest in brain, muscle, heart and testes and was 1-3 log orders above that in other tissues. It was also greater than zfMSTN-2 expression in most tissues, nevertheless, levels of both transcripts increased 60-fold in spleens of fish subjected to stocking stress. These studies indicate that zfMSTN-1 and -2 gene expression is differentially regulated in developing embryos and in adult tissues. Their expression in spleens suggests the cytokines may additionally influence immune cell development. The increased expression of both genes in spleens from stressed fish is further supportive of an immunomodulatory role and may explain increased disease susceptibility associated with stocking stress.

Embryonic and tissue-specific regulation of myostatin-1 and -2 gene expression in zebrafish

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