New Genes Are Expressed in the Early Developing Human Brain
>Previous analyses of the molecular evolution of the human brain did not find consistent evidence of rapid evolution in the protein-coding genes expressed in the adult human brain [8]–[9]. Faster evolution in the human lineage was not observed at the gene expression level either [2].
>However, we noticed that all these analyses were based on the adult brain, just one stage of brain development. It is thus understandable that they were inconclusive as to the understanding of the genetic basis for the evolution of how the brain develops.
>Our analyses revealed an unexpected pattern: the expression patterns and protein sequences of new genes appear to contribute to the early (fetal and infant) brain development of humans.
>This pattern supports the argument that genes formed by duplication and by de novo origination could escape pleiotropic constraints [42]. On the other hand, the enrichment of transcription factors in human young genes also suggests the important role of regulation in the development of the human brain [1],[4]–[6].
>Our results show that regulatory evolution can occur in both cis [5] and trans, in the protein sequence of transcription factors [32],[43], and in the creation of new transcription factors through gene duplication. From this aspect, fine-tuning of gene regulation by human-specific genes [44] might underlie many human-specific characteristics and behaviors.
>However, we also observed that young genes were associated with diverse functions, ranging from nuclear pore proteins to ribosomal proteins (Table 1).
>In fact, the striking correspondence of the origination times of the neocortex and PFC with the ages of new genes suggests the functional association of these young genes with the development of these expanding brain structures. Specifically, new genes began to be recruited into neocortex or PFC after their morphological origination (Figure 5B, 5C).
>The recruitment of young genes into the early developmental stages of neocortex, regardless of the various processes which created these genes (Figures 3, S6), and their accelerated sequence evolution (Figures 4, S6; Tables 2, S8) suggest that the young genes may have evolved new functions as a consequence of positive selection for novel functions in the newly evolved brain structures.
>Compared to the early developing brain, the adult brain does not show an increased recruitment of young genes in the primate-specific lineage (Figure S2).
>Additional expressional data confirmed that young genes were less frequently upregulated in adult neocortex (Figure 2). This result is consistent with a previous study [3] arguing that novel aspects of the human brain are usually manifested in the early development.
>Thus, the expansion of DUF1220 family expressed in adult brain [20] might be an interesting exception, rather than a rule.
https://archive.is/zi8UA
Different humans = Different levels of these genes?