Us dudes are always accused of thinking with our dicks. Perhaps it's because the genes expressed in our brains are similar to those expressed in our 'nads:
Among the 17 tissues, the highest similarity in gene expression patterns was between human brain and testis, based on DDD and clustering analysis. Genes contributing to the similarity include ribosomal protein (RP) genes as well as genes involved in transcription, translation and cell division.
The authors of the paper allege that their result has something to do with speciation. They even claim, "Brain is the most important tissue in human speciation." Given their data, it may be balls, not brains.
J. Guo, P. Zhu, C. Wu, L. Yu, S. Zhao, X. Gu. 2003. In silico analysis indicates a similar gene expression pattern between human brain and testis. Cytogenet Genome Res 103: 58-62 doi:10.1159/000076290
Objectives: Previous data has reported similarity between human brain and testis gene expression patterns. Brain is the most important tissue in human speciation. Hence, it means that human testis could also play a crucial role in human speciation if these two tissues exhibit similar gene expression patterns. However, previous reports were based on only limited and scattered data. Determining the large scale anatomy of gene expression patterns of various human tissues could draw a more convincing conclusion, and better our understanding of the correlation/inter-correlation among different tissues. Furthermore, it could also provide a clue for evolutionary study. Methods: To obtain gene expression information for large-scale data analysis, expression data of 760 Unigenes in seventeen human tissues (liver, lung, testis, brain, ovary, uterus, colon, stomach, heart, eye, kidney, spleen, gall bladder, breast, thymus, prostate and pancreas) were retrieved by DDD (differential digital display) analysis, and this expression data was subjected to clustering analysis. These Unigenes represent a wide range of genes classified according to their characterization and function. Results: Among the 17 tissues, the highest similarity in gene expression patterns was between human brain and testis, based on DDD and clustering analysis. Genes contributing to the similarity include ribosomal protein (RP) genes as well as genes involved in transcription, translation and cell division. Conclusions: Present results provide evidence to support the proposal that human testis and brain share the highest similarity of gene expression patterns. The implications of the similarity regarding that both brain and testis contributed to human speciation are discussed.
Well, did they do the comparable study in females? Or is this yet another example of male biased research? And what age group did they look at? I would look at the paper but, oh wait, I cannot access it.
Its a well known fact for us gene cloners that RNA from testes contains the highest number of different transcripts. A decade or so previously one would generally use fetal brain mRNA (no, we buy it from a company, we don't make our own!) as it was thought to be the closest to a 'normalized' expression pattern every gene being expressed.
As for why testes expresses so many genes, it is a mystery but it may be to do with secondary effects such as generating piwi transcripts that may inhibit active transposition in the germ line.
Some Highly Accelerated Regions are expressed primarily in brain and testis tissue, e.g. HAR1.
I wonder whether mechanisms are in place to ensure high expression of genes in order to prevent epigenetic silencing of genes in gametes that are otherwise inactivated in other tissues.