The genome of the diploid anuran Xenopus tropicalis contains a novel array of sarcoplasmic myosin heavy chain genes expressed in larval muscle and larynx

Abstract

The sarcomeric myosin heavy chain (MyHC) proteins are a family of molecular motors responsible for the transduction of chemical energy into mechanical work in striated muscle. The vertebrate genome contains multiple copies of the MyHC gene, and expression of different isoforms correlates with differences in the physiological properties of muscle fibers. Most MyHC isoforms are found in two arrays, one containing the "fast-twitch" skeletal muscle isoforms and the other the "slow-twitch" or cardiac isoforms. To extend our understanding of MyHC evolution, we have examined the genome of the anuran Xenopus tropicalis. The X. tropicalis genome includes15 full-length MyHC genes organized in seven genomic locations. One unique array of MyHC genes is similar to the mammalian fast-skeletal array, but is not found in amniotes. The isoforms in this array are expressed during larval stages and in muscles of the adult larynx. Duplication of the fast-skeletal MyHC array appears to have led to expression divergence of muscle proteins in the larval and adult stages of the anuran life cycle. A striking similarity of gene order between regions flanking X. tropicalis MyHC arrays and human arrays was evident; genomic organization of MyHC isoforms may thus be highly conserved across tetrapods.

Sexually differentiated, androgen-regulated, larynx-specific myosin heavy-chain isoforms in Xenopus tropicalis; comparison to Xenopus laevis

“…The reaction yielded a 1,300-bp PCR product from the reverse-transcribed cDNA sample, which, when digested with the restriction enzyme MseI, yields a specific pattern of subfragments ( Fig. 2a) for each of the 16 identified xtMyHC genes (Nasipak and Kelley 2008). The PCR was performed using Ready Taq DNA polymerase (Sigma) in 20-μL reactions with 500 nM primer concentrations (1 min at 95°C, 2 min at 52°C, 1 min at 72°C [eight times]; 1 min at 95°C, 1 min at 60°C, 1 min at 72°C [20 times]).…”

“…Real-time PCR reactions were performed using SYBR green (Invitrogen) in 20-μl reactions with 0.33 μl of cDNA and a 300-nM concentration of primers against the X. tropicalis MyHC genes (primer sequences in Nasipak and Kelley 2008). Samples were run in an ABI 7700 thermal light cycler under the following conditions: 15 min at 94°C (1×), 1 min at 94°C, 1 min at 52°C, and 1 min at 72°C (40×).…”

“…The 16 MyHC sequences from X. tropicalis (Nasipak and Kelley 2008) were analyzed using the sequence of the masticatory myosin from dog (cfMyHC16) to root the final tree. Sequences were aligned using Clustal, and poorly aligned regions were removed.…”

“…Although the entire set of X tropicalis MyHC sequences was analyzed, only the branch containing the four xtMyHC-101a-dand xlMyHC-LM is shown. The remainder of the tree is the same as that previously obtained from a similar analysis (Nasipak and Kelley 2008).…”

“…The inspection of the X. tropicalis genome reveals three MyHC arrays, two of which show the conservation of synteny with MyHC arrays in the human genome (Nasipak and Kelley 2008). A third X. tropicalis MyHC array has no human homolog and differs from the other arrays in that it contains two types of the MyHC gene: three isoforms expressed during embryonic and larval stages and one expressed only in the laryngeal muscle (Nasipak and Kelley 2008).…”