Lens regeneration in axolotl: new evidence of developmental plasticity

Background

Among vertebrates lens regeneration is most pronounced in newts, which have the ability to regenerate the entire lens throughout their lives. Regeneration occurs from the dorsal iris by transdifferentiation of the pigment epithelial cells. Interestingly, the ventral iris never contributes to regeneration. Frogs have limited lens regeneration capacity elicited from the cornea during pre-metamorphic stages. The axolotl is another salamander which, like the newt, regenerates its limbs or its tail with the spinal cord, but up until now all reports have shown that it does not regenerate the lens.

Results

Here we present a detailed analysis during different stages of axolotl development, and we show that despite previous beliefs the axolotl does regenerate the lens, however, only during a limited time after hatching. We have found that starting at stage 44 (forelimb bud stage) lens regeneration is possible for nearly two weeks. Regeneration occurs from the iris but, in contrast to the newt, regeneration can be elicited from either the dorsal or the ventral iris and, occasionally, even from both in the same eye. Similar studies in the zebra fish concluded that lens regeneration is not possible.

Conclusions

Regeneration of the lens is possible in the axolotl, but differs from both frogs and newts. Thus the axolotl iris provides a novel and more plastic strategy for lens regeneration.

     

Small intestine CD4+ T cells are profoundly depleted during acute simian-human immunodeficiency virus infection, regardless of viral pathogenicity

To analyze the relationship between acute virus-induced injury and the subsequent disease phenotype, we compared the virus replication and CD4(+) T-cell profiles for monkeys infected with isogenic highly pathogenic (KS661) and moderately pathogenic (#64) simian-human immunodeficiency viruses (SHIVs). Intrarectal infusion of SHIV-KS661 resulted in rapid, systemic, and massive virus replication, while SHIV-#64 replicated more slowly and reached lower titers. Whereas KS661 systemically depleted CD4(+) T cells, #64 caused significant CD4(+) T-cell depletion only in the small intestine. We conclude that SHIV, regardless of pathogenicity, can cause injury to the small intestine and leads to CD4(+) T-cell depletion in infected animals during acute infection.     

Mate preference in males of the cabbage butterfly, Pieris rapae crucivora, changes seasonally with the change in female UV color

We initially investigated whether females of the cabbage butterfly, Pieris rapae crucivora, exhibit a seasonal change in ultraviolet wing color, which is a key stimulus for mate recognition by conspecific males, and whether and how a seasonal change affects the mating behavior of the males. We found that female UV wing color changes seasonally, the color being more pronounced in summer than in spring or autumn. We also demonstrated that male mate preference changes seasonally, concomitantly with the change in female UV color. Specifically, males appearing in summer exhibit a mating preference for summer-form females over spring- or autumn-form females, while those appearing in spring or autumn exhibit no seasonal preference, thereby facilitating more effective mate location. Our results suggest that this field of study will require more strictly controlled experimental investigation in which the seasonal change in UV color is considered when UV-influenced mating behaviors such as mate choice are investigated.     

Dissecting beta-ring assembly pathway of the mammalian 20S proteasome

The 20S proteasome is the catalytic core of the 26S proteasome. It comprises four stacked rings of seven subunits each, alpha(1-7)beta(1-7)beta(1-7)alpha(1-7). Recent studies indicated that proteasome-specific chaperones and beta-subunit appendages assist in the formation of alpha-rings and dimerization of half-proteasomes, but the process involved in the assembly of beta-rings is poorly understood. Here, we clarify the mechanism of beta-ring formation on alpha-rings by characterizing assembly intermediates accumulated in cells depleted of each beta-subunit. Starting from beta2, incorporation of beta-subunits occurs in an orderly manner dependent on the propeptides of beta2 and beta5, and the C-terminal tail of beta2. Unexpectedly, hUmp1, a chaperone functioning at the final assembly step, is incorporated as early as beta2 and is required for the structural integrity of early assembly intermediates. We propose a model in which beta-ring formation is assisted by both intramolecular and extrinsic chaperones, whose roles are partially different between yeast and mammals.     

Muscle mechanoreflex augments arterial baroreflex-mediated dynamic sympathetic response to carotid sinus pressure

Although the muscle mechanoreflex is one of the pressor reflexes during exercise, its interaction with dynamic characteristics of the arterial baroreflex remains to be quantitatively analyzed. In anesthetized, vagotomized, and aortic-denervated rabbits (n = 7), we randomly perturbed isolated carotid sinus pressure (CSP) using binary white noise while recording renal sympathetic nerve activity (SNA) and arterial pressure (AP). We estimated the transfer functions of the baroreflex neural arc (CSP to SNA) and peripheral arc (SNA to AP) under conditions of control and muscle stretch of the hindlimb (5 kg of tension). The muscle stretch increased the dynamic gain of the neural arc while maintaining the derivative characteristics [gain at 0.01 Hz: 1.0 +/- 0.2 vs. 1.4 +/- 0.6 arbitrary units (au)/mmHg, gain at 1 Hz: 1.7 +/- 0.6 vs. 2.7 +/- 1.4 au/mmHg; P < 0.05, control vs. stretch]. In contrast, muscle stretch did not affect the peripheral arc. In the time domain, muscle stretch augmented the steady-state response at 50 s (-1.1 +/- 0.3 vs. -1.7 +/- 0.7 au; P < 0.05, control vs. stretch) and negative peak response (-2.1 +/- 0.5 vs. -3.1 +/- 1.5 au; P < 0.05, control vs. stretch) in the SNA step response. A simulation experiment using the results indicated that the muscle mechanoreflex would accelerate the closed-loop AP regulation via the arterial baroreflex.     

Conversion of AFLP markers to sequence-specific markers for closely related lines in rice by use of the rice genome sequence

DNA polymorphism between two major japonica rice cultivars, Nipponbare and Koshihikari, was identified by AFLP. Eighty-four polymorphic AFLP markers were obtained by analysis with 360 combinations of primer pairs. Nucleotide sequences of 73 markers, 29 from Nipponbare and 44 from Koshihikari, were determined, and 46 AFLP markers could be assigned to rice chromosomes based on sequence homology to the rice genome sequence. Specific primers were designed for amplification of the regions covering the AFLP markers and the flanking sequences. Out of the 46 primer pairs, 44 amplified single DNA fragments, six of which showed different sizes between Nipponbare and Koshihikari, yielding codominant SCAR markers. Eight primer pairs amplified only Nipponbare sequences, providing dominant SCAR markers. DNA fragments amplified by 13 primer pairs showed polymorphism by CAPS, and polymorphism of those amplified by 13 other primer pairs were detected by PCR-RF-SSCP (PRS). Nucleotide sequences of the other four DNA fragments were determined in Koshihikari, but no difference was found between Koshihikari and Nipponbare. In total, 40 sequence-specific markers for the combination of Nipponbare and Koshihikari were produced. All the SNPs identified by AFLP were detectable by CAPS and PRS. The same method was applicable to a combination of Kokoromachi and Tohoku 168, and 23 polymorphic markers were identified using these two rice cultivars. The procedure of conversion of AFLP-markers to the sequence-specific markers used in this study enables efficient sequence-specific marker production for closely related cultivars.