Melav2, an elav-like gene, is essential for spermatid differentiation in the flatworm Macrostomum lignano.
BACKGROUND
Failure of sperm differentiation is one of the major causes of male sterility. During spermiogenesis, spermatids undergo a complex metamorphosis, including chromatin condensation and cell elongation. Although the resulting sperm morphology and property can vary depending on the species, these processes are fundamental in many organisms. Studying genes involved in such processes can thus provide important information for a better understanding of spermatogenesis, which might be universally applied to many other organisms.


RESULTS
In a screen for genes that have gonad-specific expression we isolated an elav-like gene, melav2, from Macrostomum lignano, containing the three RNA recognition motifs characteristic of elav-like genes. We found that melav2 mRNA was expressed exclusively in the testis, as opposed to the known elav genes, which are expressed in the nervous system. The RNAi phenotype of melav2 was characterized by an aberrant spermatid morphology, where sperm elongation often failed, and an empty seminal vesicle. Melav2 RNAi treated worms were thus male-sterile. Further analysis revealed that in melav2 RNAi treated worms precocious chromatin condensation occurred during spermatid differentiation, resulting in an abnormally tightly condensed chromatin and large vacuoles in round spermatids. In addition, immunostaining using an early-spermatid specific antibody revealed that melav2 RNAi treated worms had a larger amount of signal positive cells, suggesting that many cells failed the transition from early spermatid stage.


CONCLUSIONS
We characterize a new function for elav-like genes, showing that melav2 plays a crucial role during spermatid differentiation, especially in the regulation of chromatin condensation and/or cell elongation.
Sekii
Kiyono
K
Department of Evolutionary Biology, Zoological Institute, University of Basel, Basel, Switzerland. kiyono.sekii@unibas.ch
Salvenmoser
Willi
W
De Mulder
Katrien
K
Scharer
Lukas
L
Ladurner
Peter
P
D000595:Amino Acid Sequence; D000818:Animals; D000954:Antigens, Surface / Q000235:genetics / Q000378:metabolism*; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; D008297:Male; D008969:Molecular Sequence Data; D010986:Platyhelminths / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D013091:Spermatogenesis; D013737:Testis / Q000166:cytology / Q000378:metabolism
D000954:Antigens, Surface; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; C098770:ELAVL1 protein, human; D012333:RNA, Messenger; D016601:RNA-Binding Proteins