Cytophotometric evidence for cell ‘transdifferentiation’ in planarian regeneration

Summary The role and fate of male germ cells in planarian regeneration was studied in a population ofDugesia lugubris s.1. which provided a suitable karyological marker to distinguish diploid male germ cells from triploid embryonic and somatic cells. The nuclear Feulgen-DNA content in non-replicating triploid muscle cells of the pharynx and in non-replicating male gonia of testes from intact animals were measured by the cytophotometric technique. The pharynx was then removed by transection and each anterior regenerant was allowed to completely regenerate this organ. Measurements of the Feulgen-DNA content in muscle cells of the regenerated pharynx showed that most of these cells (95%) have a DNA content typical of triploid cells; however, some muscle cells (5%) with a nuclear DNA content typical of male gonia alone were observed.These results were interpreted in the following way. After transection, young male germ cells move from the testes to the wound where they participate in blastema formation along with reserve and/or somatic dedifferentiated cells. During regeneration some of these cells of male origin differentiate into pharyngeal muscle cells. Our findings are discussed in relation to the occurrence of mataplasia in planarians.     

Renal volume and human somatic type

The abdominal C. T. of 128 patients (45 women and 83 men) aged more than 25, without any history of renal disease, have been analyzed by an evaluation computer. By the measure of the areas of kidney in each C. T. scan, the volume of the whole organ has been calculated. In men the volume resulted to be cm3 167 +/- 84,6 (M. +/- S.D.) for the right kidney and cm3 170 +/- 58 for the left one. In women it was cm3 142 +/- 54,9 for the right kidney and cm3 156 +/- 54,5 for the left one. The volumes of the organs collected into 3 classes according to their dimension, have been compared to the 3 somatic types of the subjects (Mega, Medium, Micro) obtained following the Brian & coll. method. Using a test for a monotonic trend for two ordered variables, no significant association has been demonstrated between the volume of the kidney and the human somatic type.     

Djeyes absent (Djeya) controls prototypic planarian eye regeneration by cooperating with the transcription factor Djsix-1

A conserved network of nuclear proteins is crucial to eye formation in both vertebrates and invertebrates. The finding that freshwater planarians can regenerate eyes without the contribution of Pax6 suggests that alternative combinations of regulatory elements may control the morphogenesis of the prototypic planarian eye. To further dissect the molecular events controlling eye regeneration in planarians, we investigated the role of eyes absent (Djeya) and six-1 (Djsix-1) genes in Dugesia japonica. These genes are expressed in both regenerating eyes and in differentiated photoreceptors of intact adults. Through RNAi studies, we show that Djsix-1 and Djeya are both critical for the regeneration of normal eyes in planarians and genetically cooperate in vivo to establish correct eye cell differentiation. We further demonstrate that the genetic interaction is mediated by physical interaction between the evolutionarily conserved domains of these two proteins. These data indicate that planarians use cooperatively Djsix-1 and Djeya for the proper specification of photoreceptors, implicating that the mechanism involving their evolutionarily conserved domains can be very ancient. Finally, both Djsix-1 and Djeya double-stranded RNA are substantially more effective at producing no-eye phenotypes in the second round of regeneration. This is probably due to the significant plasticity of the planarian model system, based on the presence of a stable population of totipotent stem cells, which ensure the rapid cell turnover of all differentiated cell types.     

Ultrastructural study of oogenesis in Monocelis lineata (Turbellaria,Proseriata)

Summary

Oogenesis in the marine turbellarian proseriat Monocelis lineata was investigated at the ultrastructural level. Oocyte differentiation is not synchronous so that successive stages of germ cell maturation were simultaneously detected in each of the two ovaries. Each developing oocyte is enveloped by follicle cell projections which are presumably involved in a morphologically undetectable support of vitellogenesis. The main features evidenced during oocyte differentiation are: (1) The synthesis of cortical granules by the rough endoplasmic reticulum and Golgi complex, occurring in the earlier stages of oogenesis; (2) The synthesis of yolk globules by the rough endoplasmic reticulum (RER) and Golgi complex, occurring in the later stages of oogenesis, namely late meiotic prophase I. Neither morphologically visible endocytotic activity, nor the presence of intercellular bridges, nor even the development of microvilli were observed at the oolemma or cortical ooplasm, so that the sole mechanism of vitellogenesis appears to be autosynthetic. The significance of these findings is discussed in relation to the taxonomic position of M. lineata and more generally in relation to the phylogenetic history of the class Turbellaria.     

An olfactory receptor pseudogene whose function emerged in humans: a case study in the evolution of structure–function in GPCRs

Human olfactory receptor, hOR17-210, is identified as a pseudogene in the human genome. Experimental data has shown however, that the gene product of frame-shifted, cloned hOR17-210 cDNA was able to bind an odorant-binding protein and is narrowly tuned for excitation by cyclic ketones. Supported by experimental results, we used the bioinformatics methods of sequence analysis (genome-wide and pair-wise), computational protein modeling and docking, to show that functionality in this receptor is retained due to sequence-structure features not previously observed in mammalian ORs. This receptor does not possess the first two transmembrane helical domains (of seven typically seen in GPCRs). It however, possesses an additional TM that has not been observed in other human olfactory receptors. By incorporating these novel structural features, we created two putative models for this receptor. We also docked odor ligands that were experimentally shown to bind hOR17-210. We show how and why structural modifications of OR17-210 do not hinder this receptor's functionality. Our studies reveal that novel gene rearrangements that result in sequence and structural diversity may have a bearing on OR and GPCR function and evolution.