@article{THESIS,
      recid = {1771},
      author = {Albertin, Caroline Beth},
      title = {The Molecular Embryology of a Cephalopod Mollusc, Octopus  bimaculoides},
      publisher = {University of Chicago},
      school = {Ph.D.},
      address = {2016-08},
      number = {THESIS},
      pages = {218},
      abstract = {Cephalopods have a highly derived body plan and a suite of  innovations with no obvious correlates in other animals.  One of the most striking novelties in cephalopods is their  embryogenesis, which lacks any trace of the spiral cleavage  pattern found in non-cephalopod molluscs and other  spiralians. Instead, cephalopod embryos undergo bilateral,  meroblastic cleavage on top of a large yolk, greatly  resembling early embryogenesis in fish and constituting a  striking convergence between these two distantly related  groups. In this thesis, I explore cephalopod development  from a molecular perspective, leveraging genomics,  transcriptomics, and gene expression studies to shed light  on the development of these remarkable animals.

     To  identify the gene networks important in this highly derived  developmental program, we analyzed the genome and  transcriptomes of the California two-spot octopus, Octopus  bimaculoides. The core developmental gene repertoire of the  octopus is broadly similar to that found in typical  invertebrate bilaterians, except for massive expansions in  the protocadherins and the C2H2 zinc finger transcription  factor gene families. I identified hundreds of  cephalopod-specific genes, many of which showed elevated  expression levels in such specialized cephalopod structures  as the skin, the suckers, and the nervous system.  Comparative genome structure analysis suggests that  substantial expansion of a handful of gene families, along  with extensive remodeling of genome linkages, drove the  evolution of cephalopod morphological novelties.

     A  prominent cephalopod innovation is their large, complex  nervous system. The morphological structure of the  cephalopod embryonic brain was studied with molecular  markers of neuronal development. Expression of pan-neuronal  genes indicated that early neurogenic territories in  octopus are arranged as concentric cords rather than pairs  of ganglia, an arrangement hypothesized to be  characteristic of the ancestral molluscan nervous system.  The expression of a highly conserved developmental  transcription factor cassette that is characteristic of the  vertebrate midbrain-hindbrain boundary identified the major  division in the cephalopod brain, that between the  supraesophageal and subesophageal masses. Similar to the  vertebrate midbrain-hindbrain boundary, this territory is a  signaling center, although the signaling ligands detected  in octopus are greatly expanded from those described in  other animals. Gene expression study later in development  indicated a shared transcription factor “fingerprint”  between cephalopods and other animals of neurosecretory and  higher motor centers. In contrast, the cephalopod  frontal-vertical system, which is a higher integrative  center implicated in learning, memory and decision-making,  proved to have a different molecular signature from that of  the analogous structures in vertebrates and annelids.

      Finally, I examined the deployment of highly conserved  developmental toolkit genes using both bioinformatics and  gene expression. Analysis of Hox gene expression indicated  that, despite the absence of a Hox genomic cluster, these  genes are expressed in a canonical pattern of  anterior-posterior nested domains, one modified to reflect  the radial morphology of the cephalopod embryo.  Bioinformatic analyses detected the Hox genes and other  highly conserved developmental toolkit genes primarily  during stages that coincide with the emergence of the body  plan, but not before. Notably, many of the genes  differentially expressed in the early transcriptomes are  taxonomically restricted. Our results support a  mid-developmental period of highly conserved toolkit gene  expression preceded by the deployment of taxonomically  restricted genes. These results suggest the surprising  conclusion that it is cephalopod-specific genes that  underlie the “fish-like” embryogenesis of cephalopods.},
      url = {http://knowledge.uchicago.edu/record/1771},
      doi = {https://doi.org/10.6082/uchicago.1771},
}