Endosperm development in the Araceae (Alismatales) and evolution of developmental modes in monocots

The Araceae, a basal-most family of Alismatales that basally diverged subsequent to Acorales in monocot phylogeny, are known to have diverse modes of endosperm development: nuclear, helobial, and cellular. However, the occurrence of nuclear and helobial endosperm development has long been debated. Here, we report a (re-)investigation of endosperm development in Lysichiton, Orontium, and Symplocarpus of the Orontioideae (a basal Araceae), in which nuclear endosperm development was recorded more than 100 years ago. The results show that all three genera exhibit a cellular, rather than nuclear, endosperm development and suggest that the helobial endosperm development reported as an “unmistakable record” from Ariopsis is likely cellular. Thus the Araceae are very likely characterized by cellular endosperm development alone. An extensive comparison with other monocots in light of phylogenetic relationships demonstrates that a plesiomorphic cellular endosperm development is restricted to the three basal monocot orders Acorales, Alismatales, and Petrosaviales, in which evolutionary changes from cellular to nuclear endosperm development occurred twice as major events, once within Alismatales and once as a synapomorphy of the eight remaining monocot orders, including Dioscoreales, Liliales, Asparagales, and Poales, and that helobial endosperm development, which is known for many monocot families, evolved as homoplasy throughout the monocots.     

NudC is required for interkinetic nuclear migration and neuronal migration during neocortical development

NudC is a highly conserved protein necessary for cytoplasmic dynein-mediated nuclear migration in Aspergillus nidulans. NudC interacts genetically with Aspergillus NudF and physically with its mammalian orthologue Lis1, which is crucial for nuclear and neuronal migration during brain development. To test for related roles for NudC, we performed in utero electroporation into embryonic rat brain of cDNAs encoding shRNAs as well as wild-type and mutant forms of NudC. We show here that NudC, like Lis1, is required for neuronal migration during neocorticogenesis and we identify a specific role in apical nuclear migration in radial glial progenitor cells. These results identify a novel neuronal migration gene with a specific role in interkinetic nuclear migration, consistent with cytoplasmic dynein regulation.     

MITOCHONDRIAL GENOTYPES HAVE NO DETECTABLE EFFECTS ON MERISTIC TRAITS IN CUTTHROAT TROUT HYBRID SWARMS

Efforts to detect effects of cytoplasmic genes are confounded by the problem of partitioning nuclear and cytoplasmic effects. In this study we test for effects of mtDNA haplotype on development in hybrid populations of cutthroat trout (Oncorhynchus clarki) with randomly associated nuclear and mtDNA genotypes. We have previously described several intraspecific hybrid swarms formed by interbreeding of westslope cutthroat trout (O. c. lewisi) and Yellowstone cutthroat trout (O. c. bouvieri). Genetic distance between these subspecies is high (Nei's D = 0.30; mtDNA P = 0.02), and diagnostic alleles at multiple nuclear loci and two distinct mtDNA haplotypes are present in the hybrids. Historical associations between alleles at nuclear loci and between cytotypes and nuclear alleles have largely decayed. We test for differences in meristic characters between fish with alternate mtDNA haplotypes. Counts and fluctuating bilateral asymmetry for these characters have been previously shown to be sensitive indicators of genetic differences that affect development. No differences were found between mtDNA types in meristic counts or fluctuating asymmetry. Therefore, the alternate mtDNA haplotypes had no detectable effect on development as measured by meristic counts in these hybrid populations. However, diagnostic alleles at one nuclear allozyme locus (CK-CI) were associated with several fin ray counts.     

A freeze-fracture study of the nuclear envelope during spermiogenesis inMarsilea. Formation of a pore-free zone associated with the microtubule ribbon

Summary The nuclear envelope was freeze-fractured at different stages during spermiogenesis inMarsilea. Nuclear pores were seen at all stages of development, but were excluded from a specialized region of the nuclear envelope that is in contact with the microtubule ribbon. The microtubule ribbon is associated with one edge of the nuclear envelope throughout nuclear shaping and chromatin condensation and the pore-free zone may be a region of the nuclear envelope that is important in these processes.