Genetic Background of Prop1df Mutants Provides Remarkable Protection Against Hypothyroidism-Induced Hearing Impairment

Hypothyroidism is a cause of genetic and environmentally induced deafness. The sensitivity of cochlear development and function to thyroid hormone (TH) mandates understanding TH action in this sensory organ. Prop1df and Pou1f1dw mutant mice carry mutations in different pituitary transcription factors, each resulting in pituitary thyrotropin deficiency. Despite the same lack of detectable serum TH, these mutants have very different hearing abilities: Prop1df mutants are mildly affected, while Pou1f1dw mutants are completely deaf. Genetic studies show that this difference is attributable to the genetic backgrounds. Using embryo transfer, we discovered that factors intrinsic to the fetus are the major contributor to this difference, not maternal effects. We analyzed Prop1df mutants to identify processes in cochlear development that are disrupted in other hypothyroid animal models but protected in Prop1df mutants by the genetic background. The development of outer hair cell (OHC) function is delayed, but Prestin and KCNQ4 immunostaining appear normal in mature Prop1df mutants. The endocochlear potential and KCNJ10 immunostaining in the stria vascularis are indistinguishable from wild type, and no differences in neurofilament or synaptophysin staining are evident in Prop1df mutants. The synaptic vesicle protein otoferlin normally shifts expression from OHC to IHC as temporary afferent fibers beneath the OHC regress postnatally. Prop1df mutants exhibit persistent, abnormal expression of otoferlin in apical OHC, suggesting delayed maturation of synaptic function. Thus, the genetic background of Prop1df mutants is remarkably protective for most functions affected in other hypothyroid mice. The Prop1df mutant is an attractive model for identifying the genes that protect against deafness

Dispersal and colonization success of monoraphid vs. biraphid diatoms (Bacillariophyta).

Monoraphid diatoms (Bacillariophyta) evolved more recently than biraphid diatoms. Monoraphids initially support two raphes, but seal the second raphe during the valve construction process. I studied the change in relative abundance sizes of biraphid and monoraphid diatoms colonizing artificial substrates to determine if the monoraphid condition was advantageous to early colonists. Three monoraphid species (Cocconeis placentula, Achnanthidium minutissimum, and Eucocconeis flexella) and three biraphid species (Mastogloia smithii, Navicula cryptotenella, and Sellaphora pupula) were examined. Original diatom collections were made from artificial substrates in three northern Michigan lakes over the course of 21 days in 1975. Monoraphid and biraphid relative abundances were counted on days 1, 3, 6, 15, and 21. The hypothesis that monoraphids would initially out-compete biraphids as pioneer colonists had mixed support. Because both groups' relative abundances tended to increase over time and the site of collection had no effect on relative abundance, results suggest that both monoraphid and biraphid diatoms were colonizing the artificial substrate. There was no difference in relative abundance size across all lakes and all days. However, the monoraphid relative abundance increased faster than the biraphid relative abundance. Further research is necessary to determine why monoraphids have higher relative abundance growth rates.http://deepblue.lib.umich.edu/bitstream/2027.42/55057/1/3502.pdfDescription of 3502.pdf : Access restricted to on-site users at the U-M Biological Station

Early colonization patterns of diatoms across time and among three freshwater lakes.

Diatoms (Bacillariophyta) form stable colonies on artificial substrates in less than 21 days (Cairns et al., 1983), but the factors that affect such colonization have not been rigorously studied. In our study we explored different factors of diatom colonization in three different-sized freshwater lakes--Douglas (large), Munro (medium), and Lancaster (small). We used the MacArthur-Wilson equilibrium theory of island biogeography (1963) to explain our findings. This theory predicts that species should increase in number and diversity over time until an equilibrium is reached between colonization and extinction rates of species. This theory also predicts that larger islands should be more diverse and rich than smaller islands. In all three lakes, we found that species diversity and richness tended to increase on day 6, peak on day 15, and remain stable through day 21. Doulgas also generally had higher species richness and diversity than Munro and Lancaster. These results support predictions made by island theory. With regard to species in relative high abundance (>5%), Douglas and Munro showed a trend of succession from planktonic to 'attaching' and motile diatoms. In contrast, euplankton remained abundant across the 21-day period in Lancaster, and periphyton species colonized sooner than in the other two lakes. Lancaster's distinct littoral zone and smaler species pool may account for these differences. In looking at number of species from 1975 to 2005, Douglas had more types of genera and species than Munro and Lancaster. This result further supports island theory since species richness increased relative to island size. Finally, Lancaster was less similar over the 30-year period than Douglas and Munro, supporting the idea that smaller islands tend to change more than larger lakes.http://deepblue.lib.umich.edu/bitstream/2027.42/55042/1/3486.pdfDescription of 3486.pdf : Access restricted to on-site users at the U-M Biological Station