No abstract

SUMMARYCarbonic anhydrase (CA) is critical for CO 2 excretion in adult fish, but little is known of the expression or function of CA during early development. The present study examined the hypothesis that, as rates of CO 2 production increased during early development in zebrafish (Danio rerio), CA would become necessary for effective CO 2 excretion, and that the pattern of CA expression during early development would reflect this transition. Real-time RT-PCR was used to examine the mRNA expression of the two main intracellular CA isoforms over a time course of early development ranging from 0 to 120h post fertilization (h.p.f.). The mRNA expression of zCAb was generally higher than that of zCAc, particularly during the earliest stages of development. Rates of CO 2 excretion increased approximately 15-fold from 24 to 48h.p.f. whereas rates of O 2 uptake increased only 6.7-fold over the same period, indicating a relative stimulation of CO 2 excretion over O 2 uptake. Treatment of 48h.p.f. larvae with the CA inhibitor acetazolamide resulted in CO 2 excretion rates that were 52% of the value in control larvae, a significant difference that occurred in the absence of any effect on O 2 uptake. Antisense morpholino oligonucleotides were used to selectively knock down one or both of the main intracellular CA isoforms. Subsequent measurement of gas transfer rates at 48h.p.f. indicated that CA knockdown caused a significant relative inhibition of CO 2 excretion over O 2 uptake, regardless of which cytosolic CA isoform was targeted for knockdown. These results suggest that between 24h.p.f. and 48h.p.f., developing zebrafish begin to rely on CA to meet requirements for increased CO 2 excretion.

Data about the compositional diversity of Canadian medical schools are limited. However, the few studies available report a common observation: Black medical students are disproportionately underrepresented compared with other minority groups. 1,2 In 2018, Khan and colleagues surveyed medical students at 14 English-speaking Canadian medical schools. 1 Among the 1388 students who responded (response rate of 16.6%), only 1.7% selfidentified as Black in contrast to 6.4% of the Canadian Census population. 2,3 In their qualitative study on underrepresented Black, Hispanic and Native American residents from 21 residency programs, Osseo-Asare and colleagues describe that minority trainees face pervasive discrimination, experience feelings of "otherness" and lack in mentors. 4 Participants also describe being burdened with promoting diversity in their institutions, often at the expense of traditional scholarly work more highly esteemed in academia -a phenomenon coined the "minority tax" in prior literature. 5,6 In 1 longitudinal study on discrimination set in an undisclosed Canadian medical faculty, Black and other ethnic minority medical students facing daily microaggressions from peers often did not report instances of discrimination owing to fears of having their claims dismissed or lacking access to appropriate institutional support. 7 The limited data on Black students' experiences do not mean that disparities, discrimination and systemic exclusion are absent from Canadian medical faculties. 8,9 Henry and colleagues' landmark study on the experiences of racialized faculty in Canadian academia highlighted that universities reproduce