BOULE- Making its way into bilateral phyla back since the dawn of evolution
Boule is the one gene that is known to be responsible for sperm production in Homo sapiens and other species. The research work was carried out by Eugene Xu on a trout fish. He apparently went to a fish market and asked the fish-seller if he had trout fish. When the seller signalled the availability of the trout, to the fisherman's surprise, Xu told him that he needed its testicles only. As a matter of fact, he was trying to determine the presence of boule gene in trout fish. Later he focused his attention to another sea creature, sea anemone which is considered to be the most primitive organism that still exists on Earth.
Based on the conserved features of the consensus BOULE sequence, several lineages and species were taken under significant consideration and thorough experimentation and research work was done with them. It was then found that the boule homologs were absent in fungi and plants, thus restricting its presence to animals. Thus the research was then confined to basal metazoan animal species. Almost all major lineages were to be analysed for the gene's presence. The most primitive form of animals, for example, Trichoplax showed absolutely no presence of boule homologs in it. Nonetheless, as quoted earlier, its homolog was found to be present in sea anemone which belongs to Cnidaria phylum and is a primitive animal. It has two proteins exhibiting similarities to boule in terms of presence of RRM that is the RRM was found to be present. Although the second protein showed a wide divergence to boule so it is believed to be a more divergent version of boule gene, or to be clearer, a duplicate itself. While the 1st gene happen to encode a protein typically similar to the size of boule and possess a RRM sequence too, and so is considered to be a homolog of boule gene. The presence of boule homologs occurred to be a significant milestone in the studies. Further, most studies have shown that the nature of boule is male-biased i.e. it could be though present in females too in some species of the bilaterian phyla but its expression is limited to males only. It could probably those hormones possessed by male organisms that stimulate its functioning. Nonetheless the research work is in progress towards this aspect of the boule gene.
These findings placed the birth of boule prior to Cnidaria species but most likely after trichoplax. Both are branched from a common ancestor eumetazoans and thus suggest the existence of boule as the most primitive gene responsible for reproduction. DAZL arose due to the duplication of boule most likely after the splitting of protostomian and deuterostomian lineages. Homologs of boule have been found to be present in most of the vertebrate species but not yet in all the non-vertebrate species. Using BLAST analysis, genomes of species belonging to both vertebrates and non-vertebrates were analysed but no boule homologs were found to be present in non-vertebrates, thus limiting, or more precisely, restricting its presence to the vertebrates. Further, several species belonging to vertebrate species were taken under consideration to determine the presence of DAZL in vertebrate evolution viz. Petromyzon marinus but no DAZL homologs were found. Although a boule homolog was found in Callorhinchus milii but no signs of a DAZL homolog which suggested that DAZL likely appeared during the course of the ancient lineage of bony fish. This study including further phylogenetic analysis of metazoans, indicated the wide spread presence of boule homologs from sea anemone to fish while the DAZL and DAZ homologs were confined to a branch. This also pointed out the late arrival of DAZL and its reproductive functions in primate evolution. In other words it could be possible that the DAZL arrived into the gene family at a later point of time and that its presence of its reproductive functions in the evolution of bilateral primate evolution. Thus it can be concluded that boule and boule homologs are conserved in major animal species and they function almost for the same trait. It can be thus significantly pointed out that its role in reproduction is wide spread and conserved in all the lineages of the metazoans throughout the course of evolution.
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Researcher ID- J-4200-2012