Climate change and seasonal reproduction in mammals

Seasonal reproduction is common among mammals at all latitudes, even in the deep tropics. This paper (i) discusses the neuroendocrine pathways via which foraging conditions and predictive cues such as photoperiod enforce seasonality, (ii) considers the kinds of seasonal challenges mammals actually face in natural habitats, and (iii) uses the information thus generated to suggest how seasonal reproduction might be influenced by global climate change. Food availability and ambient temperature determine energy balance, and variation in energy balance is the ultimate cause of seasonal breeding in all mammals and the proximate cause in many. Photoperiodic cueing is common among long-lived mammals from the highest latitudes down to the mid-tropics. It is much less common in shorter lived mammals at all latitudes. An unknown predictive cue triggers reproduction in some desert and dry grassland species when it rains. The available information suggests that as our climate changes the small rodents of the world may adapt rather easily but the longer lived mammals whose reproduction is regulated by photoperiod may not do so well. A major gap in our knowledge concerns the tropics; that is where most species live and where we have the least understanding of how reproduction is regulated by environmental factors.     

Root system architecture and gravitropism in the oil palm.

The oil palm (Elaeis guineensis Jacq.) has a root system consisting of primary (or order 1) roots, which are either orthogravitropic (R1 VD, with positive gravitropism) or diagravitropic (R1 H). Their statenchyma have very similar characteristics (mainly vacuolated, large cells). However, their statoliths sediment along the longitudinal wall in R1 H and along the distal wall in R1 VD (furthest cell wall from the apical meristem, opposite the proximal wall). Order 2 roots may have vertical upward (R2 VU) or downward growth (R2 VD) or even horizontal growth (R2 H). In all cases, the statoliths are located near the lower wall of the statocyte (distal in R2 VD, proximal in R2 VU and longitudinal in R2 H). Order 3 roots are usually agravitropic. When they grow upwards, R3 VU, their amyloplasts are located near the proximal wall. Likewise, the growth direction of R4 varies, but they have little or no statolith sedimentation. Roots with marked gravitropism (positive or negative) have amyloplasts that can sediment along different walls. But, irrespective of amyloplast position in the statocytes, the direction of root growth may be stable. The relation between the different reactions of roots and different sensitivity to auxin or to a curvature-halting signal is discussed.     

Actin participates in the structure of liver intermediate filaments

A dominating protein fraction (p45) having molecular weight of 45000 and pI 5.45 was found in the intermediate filaments pellet obtained from rat liver besides the present cytokeratins. Peptide mapping and radioimmunological assays with antibodies against this protein and muscle actin proved that the p45 protein belongs to the actin group. Immunoelectron microscopy revealed that this protein is located on the liver intermediate filaments. By melting of the cytokeratin complexes in urea it was established that p45 protein is complexed with the low molecular weight cytokeratin.     

Catalytic function of a tyrosyl residue in tryptophanase

Tryptophanase has an essential tyrosyl residue/active site which can be modified by tetranitromethane. Pyridoxal 5'-phosphate can prevent this modification efficiently, whereas pyridoxal 5'-phosphate N-oxide cannot, indicating that the free pyridinium N is required for the interaction of the coenzyme with the tyrosyl residue, probably via a hydrogen bond. The weakened binding of the coenzyme to the modified enzyme was confirmed on gel filtration, the modified enzyme being dissociated from the coenzyme seven-fold faster than the native enzyme. Furthermore, absorption spectral analyses demonstrated that the modified enzyme can catalyze the transaldimination step, but fails to abstract the alpha-H of substrates. The tyrosyl residue, therefore, not only participates in coenzyme binding, but also contributes to alpha-H labilization.     

Phosphoproteins in dictyostelium discoideum

The phosphoproteins of Dictyostelium discoideum were compared at different stages of development by polyacrylamide gel electrophoresis. Certain phosphoproteins of vegetative amoebae were conserved while others appeared and disappeared during development. Four major phosphoproteins with apparent subunit molecular weights of 50,000, 47,000, 38,000, and 34,000 disappeared precociously in response to exogenous cAMP. Two membranal phosphoproteins, with apparent subunit molecular weights of 80,000 and 81,000, appeared precociously in response to added cAMP. One of these phosphoproteins, molecular weight of 80,000, has been identified tentatively as the “contact site A” glycoprotein. Another membranal protein, with apparent subunit molecular weight of 42,000, unaffected in its appearance by cAMP, has been identified tentatively as phosphoactin.     

Synthesis of intrathecal interferon in systemic lupus erythematosus with neurological complications.

Intrathecal synthesis of interferon in the absence of viral or bacterial infection was detected during the occurrence of neurological complications in two patients with systemic lupus erythematosus. The interferons displayed characteristics similar to those observed in the sera of patients with the disease. No interferon inducing activity was detected in the cerebrospinal fluid or serum of the two patients. These observations support the hypothesis of a localised mechanism of interferon induction in systemic lupus erythematosus which includes the interaction of lymphocytes with damaged tissues.